Availableonlineatwww.sciencedirect.com Science Direct E噩≈RS ELSEVIER Joumal of the European Ceramic Society 28(2008)1097-1104 www.elsevier.comlocate/jeurceramsoc Automotive and industrial applications of structural ceramics in Japan Akira okada Nissan Research Center, Nissan Motor Co, Ltd, Yokosuka 237-8523, Japan Available online 17 October 2007 Abstract This paper reviews the status of structural ceramics in Japan. Until around 1980, successful applications of these materials were limited to wear resistant parts and structural components working under very low stresses. Considerable work has been done over the years on applying ceramics to mechanical parts used under higher stresses. This led to some successful applications of silicon nitride to automotive components, including arbocharger rotors and glow plugs. However, the recent market for silicon nitride automotive components has not been as large as was expecte Cordierite honeycombs for catalysts and diesel particulate filters made of silicon carbide are becoming more important applications in Japan. It is noteworthy that the Japanese market for structural ceramics has been steadily increasing since 1985, with the leading applications being apparatus for purifying the exhaust gas of automotive engines and parts for semiconductor manufacturing equipment. Alumina, for example, is widely used for vacuum process chambers. High-purity alumina is also used for the components of liquid crystal device manufacturing equipment and various mechanical parts. The recent applications of structural ceramics in Japan summarized in this review include vacuum process chambers for manufacturing semiconductor and liquid crystal devices, wear- resistant ceramics used for steel-making, optical lens forming and cutting tools refractory tubes for casting aluminum alloys, and automotive applications o 2007 Elsevier Ltd. All rights reserved. Keywords: Structural applications; Wear parts; Engine components: Al2O3: Si3N4 Introduction motive components, including turbocharger rotors and glow plugs. These applications actually resulted from various tech The general advantages of structural ceramics, such as alu- nical advances achieved through research and development mina, silicon nitride, silicon carbide and zirconia, in comparison work done on ceramic gas turbines. Such advances included with steel are light weight, chemical and thermal stabilities at (i) enhancement of the fracture toughness of ceramics, (ii) elevated temperatures and excellent wear resistance. In addi- development of process technologies for suppressing the gener tion, the high yield stress of ceramics enables the production of ations of flaws responsible for brittle failure, (iii) development precisely machined parts that maintain their accurate dimen- of techniques for designing ceramic components with reduced sions over long periods of use. This is due to the strong maximum stresses, and (iv) progress in assuring the strength chemical bonds formed in ceramics, although it also leads to of components and in inspection techniques for detecting unreliable mechanical properties responsible for brittle fail- flaws. These advances were based on the application of frac re. The brittle behavior of ceramics has generally restricted ture mechanics as well as the findings of intensive studies of eir applications to structural components. Successful applica- ceramic gas turbines. Applications of silicon nitride to automo- ions until around 1980 were typically wear-resistant parts like tive engines, however, gradually decreased in the 1990s. Instead, thread guides and ceramic cutting tools, and structural compo- the application of high-purity alumina was gradually expanded nents used under very low stresses such as ceramic pumps and to the parts of equipment for producing semiconductor devices and liquid crystal displays Considerable work has been done on applying ceramics to This paper reviews recent advances in applications of struc- mechanical parts working under relatively high stresses In the tural ceramics in Japan 980s, silicon nitride was successfully applied to some auto- 2. Market for structural ceramics in Japan Correspondence address: 1, Natsushima-cho, Yokosuka, Kanagawa 237- 8523, Japan.Tel:+81468675196;fax:+8l468655796 The beginning of the Japanese market for structural ceramics E-mail address: okada-a@mail. nissan co jp dates to around 1980, and the market has expanded steadily 0955-2219/S-see front matter o 2007 Elsevier Ltd. All rights reserved. doi: 10.1016/j-jeurceramsoc 2007.09.016
Available online at www.sciencedirect.com Journal of the European Ceramic Society 28 (2008) 1097–1104 Automotive and industrial applications of structural ceramics in Japan Akira Okada ∗ Nissan Research Center, Nissan Motor Co., Ltd., Yokosuka 237-8523, Japan Available online 17 October 2007 Abstract This paper reviews the status of structural ceramics in Japan. Until around 1980, successful applications of these materials were limited to wearresistant parts and structural components working under very low stresses. Considerable work has been done over the years on applying ceramics to mechanical parts used under higher stresses. This led to some successful applications of silicon nitride to automotive components, including turbocharger rotors and glow plugs. However, the recent market for silicon nitride automotive components has not been as large as was expected. Cordierite honeycombs for catalysts and diesel particulate filters made of silicon carbide are becoming more important applications in Japan. It is noteworthy that the Japanese market for structural ceramics has been steadily increasing since 1985, with the leading applications being apparatus for purifying the exhaust gas of automotive engines and parts for semiconductor manufacturing equipment. Alumina, for example, is widely used for vacuum process chambers. High-purity alumina is also used for the components of liquid crystal device manufacturing equipment and various mechanical parts. The recent applications of structural ceramics in Japan summarized in this review include vacuum process chambers for manufacturing semiconductor and liquid crystal devices, wear-resistant ceramics used for steel-making, optical lens forming and cutting tools, refractory tubes for casting aluminum alloys, and automotive applications. © 2007 Elsevier Ltd. All rights reserved. Keywords: Structural applications; Wear parts; Engine components; Al2O3; Si3N4 1. Introduction The general advantages of structural ceramics, such as alumina, silicon nitride, silicon carbide and zirconia, in comparison with steel are light weight, chemical and thermal stabilities at elevated temperatures and excellent wear resistance. In addition, the high yield stress of ceramics enables the production of precisely machined parts that maintain their accurate dimensions over long periods of use. This is due to the strong chemical bonds formed in ceramics, although it also leads to unreliable mechanical properties responsible for brittle failure. The brittle behavior of ceramics has generally restricted their applications to structural components. Successful applications until around 1980 were typically wear-resistant parts like thread guides and ceramic cutting tools, and structural components used under very low stresses such as ceramic pumps and blowers. Considerable work has been done on applying ceramics to mechanical parts working under relatively high stresses. In the 1980s, silicon nitride was successfully applied to some auto- ∗ Correspondence address: 1, Natsushima-cho, Yokosuka, Kanagawa 237- 8523, Japan. Tel.: +81 468 67 5196; fax: +81 468 65 5796. E-mail address: okada-a@mail.nissan.co.jp. motive components, including turbocharger rotors and glow plugs.1,2 These applications actually resulted from various technical advances achieved through research and development work done on ceramic gas turbines. Such advances included (i) enhancement of the fracture toughness of ceramics, (ii) development of process technologies for suppressing the generations of flaws responsible for brittle failure, (iii) development of techniques for designing ceramic components with reduced maximum stresses, and (iv) progress in assuring the strength of components and in inspection techniques for detecting flaws. These advances were based on the application of fracture mechanics as well as the findings of intensive studies of ceramic gas turbines. Applications of silicon nitride to automotive engines, however, gradually decreased in the 1990s. Instead, the application of high-purity alumina was gradually expanded to the parts of equipment for producing semiconductor devices and liquid crystal displays. This paper reviews recent advances in applications of structural ceramics in Japan. 2. Market for structural ceramics in Japan The beginning of the Japanese market for structural ceramics dates to around 1980, and the market has expanded steadily 0955-2219/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2007.09.016
A Okada/Journal of the European Ceramic Society 28(2008)1097-1104 Table I for producing semiconductors and liquid crystal display pan- Shipments of structural ceramics in the Japanese market els, where the parts are exposed to plasma and reactive gases Fiscal year High-purity alumina is commonly used for insulators and elec- 1985 1990 1995 2003 trostatic wafer chucks in these devices, as is aluminum nitride, and silicon carbide is also used for other components of the heat Alumina treatment equipment for Si wafers. Automotive applications also ilicon nitrid contribute to the overall ceramics market Cordierite ceramics Silicon carbide 49 for catalyst honeycombs account for the major portion of auto- Aluminum nitride 40 motive applications, with a relatively small contribution made Others 135 by silicon nitride used for engine parts. The market for general Total 715 mechanical parts is the third largest and includes wear-resistant Millions of euros; I euro=163 yen. parts such as thread guides and mechanical seals. Magnetic head sliders for hard discs and optical connectors are included in the category of communication and electric products. Al2O3-TiC since then except for several years in the early 1990s. Table 1 composites are used for magnetic head sliders, and ZrO2 is summarizes the market trends for individual ceramic materials used for ferrule connectors for optical fibers. The category of in terms of the value of shipments from 1985 to 2003. High- precision mechanical parts includes both the mechanical parts purity alumina accounts for the largest portion of the structural of precision machines like ceramic bearings and production ceramics market, exceeding the total for zirconia, silicon nitride machinery parts such as ceramic surface plates for producing and silicon carbide combined. The recent increase in shipments precision machines. The category of non-ferrous alloy making of high-purity alumina is due to its application to equipment for includes thermocouple protection uae -ferrous alloy making manufacturing semiconductor devices and liquid crystal display panels. High-strength zirconia ceramics, typically made with 3. Application to the components of industrial the addition of yttria, are used for wear-resistant parts, cutting production equipment blades and ferrule connectors for optical fibers The market for silicon nitride expanded in the 1980s with 3. 1. Semiconductor production its application to automotive engine parts, though the market recently has been relatively smaller than what was originally In the semiconductor production process, high-purity sili- expected. The market for silicon carbide has recently expanded, con carbide is used for the parts of diffusion furnaces, where mainly as a result of its application to diesel particulate filters. silicon wafers are heat-treated. High purity is required to sup- Although the major application of aluminum nitride has been as press the migration of impurities. 6. This property is particularly a functional c c applied to the heat sink of semiconductors, important for silicon carbide wafer boats and for the liner tubes s use as a structural ceramic began from around 1996 when it that shut out diffusive impurities. The high thermal conductivity was first applied to semiconductor production equipment. The of silicon carbide is advantageous for homogenizing the local major application under the"Others"category in Table I is for temperature gradient. The general procedure for producing high cordierite ceramics applied to catalyst honeycombs, which sup- purity silicon carbide is as follows. High-purity reaction-sintered port fine particles of precious metal catalysts for purifying the silicon carbide is produced from compacts of high-purity sili- exhaust gas of gasoline engines. Annual sales of this material con carbide powder, and high-purity liquid silicon is infused into have reached around 20 billion yen(approximately 120 million the compacts at elevated temperatures. Finally, the surfaces are euros)recently coated with chemically vapor deposited(CVD)SiC. Table 2 shows the value of shipments of structural ceramics Fig. I shows typical silicon carbide boats used in the heat for various products in the Japanese market in fiscal 2004 and treatment process for Si wafers. Fig. 2 shows a scanning electron 2005. Many ceramic parts are used in severe environments micrograph of the cross-section of a wafer boat, which indicates hat the boat material consists of reaction-sintered silicon car- bide covered with dense CVd Sic on the surface. 7 While fused Shipments of recent structural ceramic products in Japan silica has been extensively used for diffusion furnaces, the major Product FY 2004 FY 2005 advantages of using SiC for wafer boats are its thermal stability at elevated temperatures and a coefficient of thermal expansion closer to silicon than that of fused silica. During heat cycles, Liquid crystal display production equipment the latter property suppresses the generation of debris, which might otherwise result from sliding movement due to a thermal coefficient mismatch Non-ferrous alloy making equipment High-purity alumina is used for the parts that support silicon Automobile parts wafers in the vacuum chamber where the etching of semiconduc tors is done. 8 This is due to the materials excellent performance Total 76 in corrosive and plasma environments. The requirements for Millions of euros; I euro=163 yen such materials are (i)to have excellent resistance to halogen
1098 A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 Table 1 Shipments of structural ceramics in the Japanese market3 Fiscal year 1985 1990 1995 2003 Alumina 105 172 203 372 Zirconia 12 53 82 73 Silicon nitride 13 45 43 45 Silicon carbide 10 28 23 49 Aluminum nitride – – – 40 Others 20 88 117 135 Total 160 387 468 715 Millions of euros; 1 euro = 163 yen. since then except for several years in the early 1990s.3 Table 1 summarizes the market trends for individual ceramic materials in terms of the value of shipments from 1985 to 2003. Highpurity alumina accounts for the largest portion of the structural ceramics market, exceeding the total for zirconia, silicon nitride and silicon carbide combined. The recent increase in shipments of high-purity alumina is due to its application to equipment for manufacturing semiconductor devices and liquid crystal display panels. High-strength zirconia ceramics, typically made with the addition of yittria, are used for wear-resistant parts, cutting blades and ferrule connectors for optical fibers. The market for silicon nitride expanded in the 1980s with its application to automotive engine parts, though the market recently has been relatively smaller than what was originally expected. The market for silicon carbide has recently expanded, mainly as a result of its application to diesel particulate filters. Although the major application of aluminum nitride has been as a functional ceramic applied to the heat sink of semiconductors, its use as a structural ceramic began from around 1996 when it was first applied to semiconductor production equipment. The major application under the “Others” category in Table 1 is for cordierite ceramics applied to catalyst honeycombs, which support fine particles of precious metal catalysts for purifying the exhaust gas of gasoline engines. Annual sales of this material have reached around 20 billion yen (approximately 120 million euros) recently. Table 2 shows the value of shipments of structural ceramics for various products in the Japanese market in fiscal 2004 and 2005.4,5 Many ceramic parts are used in severe environments Table 2 Shipments of recent structural ceramic products in Japan4,5 Product FY 2004 FY 2005 Communication and electric products 67 85 Semiconductor production equipment 182 207 Liquid crystal display production equipment 73 74 Precision mechanical parts 11 12 General mechanical parts 101 104 Non-ferrous alloy making equipment 12 14 Automobile parts 168 184 Others 84 82 Total 699 761 Millions of euros; 1 euro = 163 yen for producing semiconductors and liquid crystal display panels, where the parts are exposed to plasma and reactive gases. High-purity alumina is commonly used for insulators and electrostatic wafer chucks in these devices, as is aluminum nitride, and silicon carbide is also used for other components of the heattreatment equipment for Si wafers. Automotive applications also contribute to the overall ceramics market. Cordierite ceramics for catalyst honeycombs account for the major portion of automotive applications, with a relatively small contribution made by silicon nitride used for engine parts. The market for general mechanical parts is the third largest and includes wear-resistant parts such as thread guides and mechanical seals. Magnetic head sliders for hard discs and optical connectors are included in the category of communication and electric products. Al2O3–TiC composites are used for magnetic head sliders, and ZrO2 is used for ferrule connectors for optical fibers. The category of precision mechanical parts includes both the mechanical parts of precision machines like ceramic bearings and production machinery parts such as ceramic surface plates for producing precision machines. The category of non-ferrous alloy making includes thermocouple protection tubes. 3. Application to the components of industrial production equipment 3.1. Semiconductor production In the semiconductor production process, high-purity silicon carbide is used for the parts of diffusion furnaces, where silicon wafers are heat-treated. High purity is required to suppress the migration of impurities.6,7 This property is particularly important for silicon carbide wafer boats and for the liner tubes that shut out diffusive impurities. The high thermal conductivity of silicon carbide is advantageous for homogenizing the local temperature gradient. The general procedure for producing highpurity silicon carbide is as follows. High-purity reaction-sintered silicon carbide is produced from compacts of high-purity silicon carbide powder, and high-purity liquid silicon is infused into the compacts at elevated temperatures. Finally, the surfaces are coated with chemically vapor deposited (CVD) SiC. Fig. 1 shows typical silicon carbide boats used in the heattreatment process for Si wafers. Fig. 2 shows a scanning electron micrograph of the cross-section of a wafer boat, which indicates that the boat material consists of reaction-sintered silicon carbide covered with dense CVD SiC on the surface.7 While fused silica has been extensively used for diffusion furnaces, the major advantages of using SiC for wafer boats are its thermal stability at elevated temperatures and a coefficient of thermal expansion closer to silicon than that of fused silica. During heat cycles, the latter property suppresses the generation of debris, which might otherwise result from sliding movement due to a thermal coefficient mismatch.7 High-purity alumina is used for the parts that support silicon wafers in the vacuum chamber where the etching of semiconductors is done.8 This is due to the material’s excellent performance in corrosive and plasma environments. The requirements for such materials are (i) to have excellent resistance to halogen
A Okada/Joumal of the European Ceramic Sociery 28(2008)1097-1104 (a) Fig. 1. Typical silicon carbide wafer boats for heat treatment of Si wafers. '(a) A view of the boats with Si wafers and(b)a magnified view of a wafer supp gases in the plasma environment, (ii)to be free of hazardous con, frictional movement between the wafers and susceptors hat degrade the performance of semiconductors, reduced (ii) not to release any evaporating gases that obstruct the vacu- Ceramics with zero or a low thermal expansion coefficient are uming procedure. Fig 3 shows examples of the dense ceramic used for the parts that support silicon wafers in steppers. Such components of the manufacturing equipment for semiconductor ceramics are suitable for this application because steppers must devices and liquid crystal display panels. 8 maintain the right position of the silicon wafers independent of Applications of aluminum nitrides are expanding and include temperature changes. Furthermore, the materials for support electrostatic wafer chucks, susceptors and substrate heaters for ing silicon wafers in steppers must be lightweight and have A pporting silicon wafers in the CVD, PVD, stepper and etch- high rigidity, and electric conductance is desirable in order to ng processes. 6, 9 In comparison with alumina, the advantages eliminate static electricity of using aluminum nitride for supporting silicon wafers are, Fused silica is also used for the crucibles employed in the firstly, its high thermal conductivity that helps to homoge- Czochralski process of producing single-crystal semiconductors nize the temperature gradient, and secondly, a reduction of and for the supports used in the heat treatment and dry etching the particle generation rate owing to less frictional movement processes of semiconductors. Graphite materials are used for between the silicon wafers and AIN susceptors during repeated heating elements and the parts of ion implantation devices. 7 heating and cooling processes. Because the thermal expansion coefficient of aluminum nitride is very close to that of sili- CVD-SiC 9 Dark: SiC particle Light: Si on micrograph of the cross-section of the SiC materiaL. The material is reaction-sintered silicon carbide covered with dense CVD Sic Fig 3. Examples of dense ceramic components of manufacturing equipment for on the surface semiconductor devices and liquid crystal display panels
A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 1099 Fig. 1. Typical silicon carbide wafer boats for heat treatment of Si wafers.7 (a) A view of the boats with Si wafers and (b) a magnified view of a wafer support. gases in the plasma environment, (ii) to be free of hazardous elements that degrade the performance of semiconductors, and (iii) not to release any evaporating gases that obstruct the vacuuming procedure. Fig. 3 shows examples of the dense ceramic components of the manufacturing equipment for semiconductor devices and liquid crystal display panels.8 Applications of aluminum nitrides are expanding and include electrostatic wafer chucks, susceptors and substrate heaters for supporting silicon wafers in the CVD, PVD, stepper and etching processes.6,9 In comparison with alumina, the advantages of using aluminum nitride for supporting silicon wafers are, firstly, its high thermal conductivity that helps to homogenize the temperature gradient, and secondly, a reduction of the particle generation rate owing to less frictional movement between the silicon wafers and AlN susceptors during repeated heating and cooling processes. Because the thermal expansion coefficient of aluminum nitride is very close to that of siliFig. 2. A scanning electron micrograph of the cross-section of the SiC material. The material is reaction-sintered silicon carbide covered with dense CVD SiC on the surface.7 con, frictional movement between the wafers and susceptors is reduced. Ceramics with zero or a low thermal expansion coefficient are used for the parts that support silicon wafers in steppers.8 Such ceramics are suitable for this application because steppers must maintain the right position of the silicon wafers independent of temperature changes. Furthermore, the materials for supporting silicon wafers in steppers must be lightweight and have high rigidity, and electric conductance is desirable in order to eliminate static electricity. Fused silica is also used for the crucibles employed in the Czochralski process of producing single-crystal semiconductors and for the supports used in the heat treatment and dry etching processes of semiconductors. Graphite materials are used for heating elements and the parts of ion implantation devices.7 Fig. 3. Examples of dense ceramic components of manufacturing equipment for semiconductor devices and liquid crystal display panels.8
A Okada/Journal of the European Ceramic Society 28(2008)1097-1104 3.2. Steel making and aluminum casting The basic process for making steel is as follows. First, coal is carbonized in a coke oven to produce coke. Powdered ferrous ore mixed with limestone is then sintered in a sintering machine to produce lumps with suitable dimensions. The ferrous ore is then reduced with coke in a blast furnace to produce a melt of cast iron. The cast iron is then converted to molten steel in a steel converter or in the Linz-Donawitz process of a basic oxy gen furnace by introducing oxygen into the cast iron melt. The molten steel is cast to produce steel slabs that then are hot-and cold-rolled to form steel sheets. The surfaces are occasionally covered with a zinc plating for protection against corrosion The tubes used for transferring powders such as ferrous ore and coal are lined with a ceramic material for protection against erosive wear. The blowers used for transferring and collecting the powders also require ceramic liners to protect the blades from wear. Alumina is widely used for such parts, though silicon nitride is applied in particularly severe environments. 0 Fig.4 shows typical ceramic-lined tubes used for transferring powder materials in the steel-making process. Ceramic plates are bonded on the inner surfaces of steel tubes to improve wear resistance. I0 Silicon nitride rollers are used for transferring steel sheets on rolling lines. Roller bearings are used in the zinc plating Fig 4. Ceramic-lined tubes used for transferring powdery materials in the steel- bath in which cold-rolled steel coils are immersed at 500C in making process. Ceramic plates are bonded on the inner surfaces of steel tubes the process of making zinc-coated steel. Stainless steel roller bearings coated with cemented carbide had been widely used previously, but SiaION has been applied recently to improve productivity on plating lines. Sleeves made of hot-rolled die steel for aluminum die cast- Siaion is also used for the stalks and sleeves that transfer ing require a large amount of lubricant between the sleeve casting processes. 2 Cast iron had been used previously for the Steel sleeves have recently been changed to ceramic-lined stalks in low-pressure casting, but suffered a short lifetime due to ones, in which a ceramic tube is inserted inside the metal iron immigration into the melt. This problem has been improved tube. Consequently, the amount of lubricant is considerably e use of sialon sleeves. Fig. 5 shows sialon stalks for redu it is also effective in eliminating casting defects the low-pressure casting process of molten aluminum. The stalks Fig. 6 shows a typical Siaion sleeve used in aluminum die are supported vertically in the aluminum melt. I casting. II Fig. 5. SiAlON stalks for the low-pressure casting process of molten aluminum. (a)Schematic diagram of the low-pressure casting furnace with the stalk located the center of the furnace and (b) sialon stalks
1100 A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 3.2. Steel making and aluminum casting The basic process for making steel is as follows. First, coal is carbonized in a coke oven to produce coke. Powdered ferrous ore mixed with limestone is then sintered in a sintering machine to produce lumps with suitable dimensions. The ferrous ore is then reduced with coke in a blast furnace to produce a melt of cast iron. The cast iron is then converted to molten steel in a steel converter or in the Linz-Donawitz process of a basic oxygen furnace by introducing oxygen into the cast iron melt. The molten steel is cast to produce steel slabs that then are hot- and cold-rolled to form steel sheets. The surfaces are occasionally covered with a zinc plating for protection against corrosion. The tubes used for transferring powders such as ferrous ore and coal are lined with a ceramic material for protection against erosive wear. The blowers used for transferring and collecting the powders also require ceramic liners to protect the blades from wear. Alumina is widely used for such parts, though silicon nitride is applied in particularly severe environments.10 Fig. 4 shows typical ceramic-lined tubes used for transferring powdery materials in the steel-making process. Ceramic plates are bonded on the inner surfaces of steel tubes to improve wear resistance.10 Silicon nitride rollers are used for transferring steel sheets on rolling lines.11 Roller bearings are used in the zinc plating bath in which cold-rolled steel coils are immersed at 500 ◦C in the process of making zinc-coated steel. Stainless steel roller bearings coated with cemented carbide had been widely used previously, but SiAlON has been applied recently to improve productivity on plating lines.12 SiAlON is also used for the stalks and sleeves that transfer molten aluminum to the dies in low-pressure casting and diecasting processes.12 Cast iron had been used previously for the stalks in low-pressure casting, but suffered a short lifetime due to iron immigration into the melt. This problem has been improved by the use of SiAlON sleeves. Fig. 5 shows SiAlON stalks for the low-pressure casting process of molten aluminum. The stalks are supported vertically in the aluminum melt.11 Fig. 4. Ceramic-lined tubes used for transferring powdery materials in the steelmaking process.10 Ceramic plates are bonded on the inner surfaces of steel tubes to improve wear resistance. Sleeves made of hot-rolled die steel for aluminum die casting require a large amount of lubricant between the sleeve and plunger to push the melt out during the casting process. Steel sleeves have recently been changed to ceramic-lined ones, in which a ceramic tube is inserted inside the metal tube. Consequently, the amount of lubricant is considerably reduced, and it is also effective in eliminating casting defects. Fig. 6 shows a typical SiAlON sleeve used in aluminum die casting.11 Fig. 5. SiAlON stalks for the low-pressure casting process of molten aluminum.11 (a) Schematic diagram of the low-pressure casting furnace with the stalk located at the center of the furnace and (b) SiAlON stalks
A Okada/Joumal of the European Ceramic Sociery 28(2008)1097-1104 Metal Mold Ladle Molten aluminum Sleeve Fig. 6. Die-casting and SiAION sleeve.(a) Schematic diagram of the die-casting structure and(b)Siaion sleeve where a SiAIOn tube is inserted into the metal 33. Ceramic molds carbide(wC) particles are particularly advantageous because their electric conductivity facilitates a wire electrical discharge Optical lenses have generally been produced by cutting and machining(EDM) process. 3 grinding glass. However, non-spherical lenses have recently begun to be used for information and electronic devices. These 3.4. Cutting tools/ lenses are produced under pressure in a mold at temperatures over 300C. The molds used at such high temperatures are Materials used for cutting tools require properties such as: (1) usually made of hard materials such as steels, cemented car- hardness greater than that of the materials to be machined, (ii) bides, and ceramics. Among these materials, silicon carbides an absence of chemical reactions with machined materials, (ii) coated with CVD SiC are used in particular for high-temperature durability at elevated temperatures resulting from high-speed molding. 3Fig. 7 shows a schematic diagram of the lens mold- cutting, and (iv) an absence of brittle failure during machining ing process and the appearance of a lens mold made of precision Ceramics are usually superior with respect to the characteristics in(i)to(iii), and the improvement of their resistance to brittle Press-formed copper alloys are used for the connecters in failure is thought to make them advantageous as tool materials llular phones and automobiles. The connector dies were pre However. the market share of ramic tools remains at only viously made primarily of steel and cemented carbides, but eral percent, accounted for largely by cemented carbide followed zirconia ceramics with high fracture toughness have been used by TiC cermets. This low level is clearly due to the brittleness of since around 2000. ZrO2 ceramics dispersed with tungsten ceramics that causes the tool edges to chip easily. The share of coated tips, consisting of cemented carbide coated with ceramic (a) Preform in the mold Hot pressing Produced lens materials such as alumina and titanium carbide, is increasing This is due to improvements in material combinations that take advantage of the characteristics of ceramics in(i)to(iii) for the tool surface, while the inside is made of tough cemented carbide that has good resistance to brittle failure Nowadays, major applications of ceramic tools are for high- speed machining of cast iron due to the high temperature resistance of ceramic materials. This category includes(i) high purity alumina, nina composites with TiC, ZrO2, or Si whiskers, and (iii) silicon nitrides. Among them, silicon nitride is used for rough machining of cast iron and wet machining This is because silicon nitride has relatively high toughness for a ceramic material, which enables a rather large cutting depth. 4. Automotive applications 4.1. Catalyst honeycomb A three-way catalyst system utilizing a precious-metal-based catalytic converter is generally used today to control the exhaust Punch of the mold Die of the mold emissions of automotive gasoline engines. To support the proper Fig. 7. Precision ceramics for lens molding. (a) Schematic diagram of lens me operation of the catalysts, the air-fuel ratio is controlled within ing process and (b)the appearance of the lens mold and die made of precision an appropriate range by an electronic system using oxygen sen- sors. The oxygen sensors have a solid-state electrode made of
A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 1101 Fig. 6. Die-casting and SiAlON sleeve.11 (a) Schematic diagram of the die-casting structure and (b) SiAlON sleeve where a SiAlON tube is inserted into the metal sleeve. 3.3. Ceramic molds Optical lenses have generally been produced by cutting and grinding glass. However, non-spherical lenses have recently begun to be used for information and electronic devices. These lenses are produced under pressure in a mold at temperatures over 300 ◦C. The molds used at such high temperatures are usually made of hard materials such as steels, cemented carbides, and ceramics. Among these materials, silicon carbides coated with CVD SiC are used in particular for high-temperature molding.13 Fig. 7 shows a schematic diagram of the lens molding process and the appearance of a lens mold made of precision ceramics.13 Press-formed copper alloys are used for the connecters in cellular phones and automobiles. The connector dies were previously made primarily of steel and cemented carbides, but zirconia ceramics with high fracture toughness have been used since around 2000. ZrO2 ceramics dispersed with tungsten Fig. 7. Precision ceramics for lens molding. (a) Schematic diagram of lens molding process and (b) the appearance of the lens mold and die made of precision ceramics.13 carbide (WC) particles are particularly advantageous because their electric conductivity facilitates a wire electrical discharge machining (EDM) process.13 3.4. Cutting tools1 Materials used for cutting tools require properties such as: (i) hardness greater than that of the materials to be machined, (ii) an absence of chemical reactions with machined materials, (iii) durability at elevated temperatures resulting from high-speed cutting, and (iv) an absence of brittle failure during machining. Ceramics are usually superior with respect to the characteristics in (i) to (iii), and the improvement of their resistance to brittle failure is thought to make them advantageous as tool materials. However, the market share of ceramic tools remains at only several percent, accounted for largely by cemented carbide followed by TiC cermets. This low level is clearly due to the brittleness of ceramics that causes the tool edges to chip easily. The share of coated tips, consisting of cemented carbide coated with ceramic materials such as alumina and titanium carbide, is increasing. This is due to improvements in material combinations that take advantage of the characteristics of ceramics in (i) to (iii) for the tool surface, while the inside is made of tough cemented carbide that has good resistance to brittle failure. Nowadays, major applications of ceramic tools are for highspeed machining of cast iron due to the high temperature resistance of ceramic materials. This category includes (i) highpurity alumina, (ii) alumina composites with TiC, ZrO2, or SiC whiskers, and (iii) silicon nitrides. Among them, silicon nitride is used for rough machining of cast iron and wet machining. This is because silicon nitride has relatively high toughness for a ceramic material, which enables a rather large cutting depth. 4. Automotive applications 4.1. Catalyst honeycomb2 A three-way catalyst system utilizing a precious-metal-based catalytic converter is generally used today to control the exhaust emissions of automotive gasoline engines. To support the proper operation of the catalysts, the air-fuel ratio is controlled within an appropriate range by an electronic system using oxygen sensors. The oxygen sensors have a solid-state electrode made of
A Okada/Journal of the European Ceramic Society 28(2008)1097-1104 Table 3 Developments in processing cordierite honeycomb at NGK Insulators Ltd 2 Cell structure 6/400 4/400 3/400 3/600 2/900 Wall thickness(um) umber of cells per unit cross-sectional area(cell number/cm-) Apparent density (g/cm) 0.25 Surface area per unit volume(cm2/cm3) Year of production start 1996 1999 a Wall thickness in mils(1/1000 in )and number of cells/in. 2 zirconia ceramics, and the catalysts are supported on a cordierite with air Particulate matter is thought to be related to the causes of honeycomb produced by extrusion forming. The cell surface of cancer and bronchial asthma, and regulatory standards forengine the honeycomb is covered with fine alumina particles coated emissions are becoming more stringent. Since particulate mat with fine particles of precious metal catalysts on the surface. ter must be removed from exhaust gas, diesel particulate filters Since exhaust gas catalysts only work at elevated temper- of the wall flow type are generally installed on diesel vehicles. atures, the catalyst temperature must be raised rapidly to the The wall flow type filter is made of a porous ceramic honey ght-off level after the engine is started. To accomplish that, the comb with square cell holes, and either the inlet or outlet end is system was improved by reducing the thickness of the honey- filled alternatively. As the exhaust gas passes through the porous comb walls, in addition to modifying the chemical composition inlet walls, particulate matter condenses on the outer and inner of the catalysts and reducing the dimensions of the catalyst par- surfaces of the walls. The major materials of diesel particulate ticles. The development history shown in Table 3 indicates that filters are silicon carbide and cordierite the wall thickness of NGK honeycombs was 300 um in 1976, which was reduced to just 50 um in 1999. Fig. 8 shows catalyst 43. Automotive part honeycombs with different cell densities Table 4 shows typical applications of silicon nitride to auto- 4.2. Diesel particulate filter motive engine parts. It is clear that such applications were actively promoted in the early and mid-1980s. Examples include The advantages of diesel engines in comparison with their glow plugs for starting dieselengines more quickly, turbocharger gasoline counterparts include low fuel consumption and resul- rotors(Fig. 9) for enabling quick acceleration response by tant low emissions of carbon dioxide, a greenhouse gas employing lightweight ceramics, and wear parts for cam fol- responsible for global warming. This performance is due to lowers such as rocker arm pads and tappets(Fig. 10). These diesel engine characteristics such as (i) explosive burning at applications were promoted by an extraordinarily strong inter higher pressure, (ii) basically lean-burn combustion, and (ii) est in ceramics in Japan at that time, referred to as the"ceramic an absence of pumping(throttle)loss. However, the explosive fever. "Some ceramic parts were subsequently removed from burning process of diesel engines, which results from injecting the next generation of automobile models because the improved fuel into compressed air, gives rise to a problem of particulate performance did not justify the higher production cost matter formation due to incomplete combustion when the explo- Lightweight exhaust valves would sion occurs before the fuel is completely evaporated and mixed dynamic parts because of their lower inertial mass at high engine (b)smil/400cpsi mil/400cpsi ig. 8. Catalyst honeycombs with different cell densities(courtesy of NGK Insulators Ltd ).(a) Typical catalyst honeycomb and (b) four honeycombs with differen cell structures(see also Table 3)
1102 A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 Table 3 Developments in processing cordierite honeycomb at NGK Insulators Ltd.2 Cell structurea 12/300 6/400 4/400 4/600 3/400 3/600 2/900 Wall thickness (m) 300 150 100 100 75 75 50 Number of cells per unit cross-sectional area (cell number/cm2) 47 62 62 93 62 93 140 Apparent density (g/cm3) 0.6 0.4 0.25 0.3 0.2 0.25 0.2 Surface area per unit volume (cm2/cm3) 20 30 30 35 30 35 45 Year of production start 1976 1979 1995 1996 1999 1999 1999 a Wall thickness in mils (1/1000 in.) and number of cells/in.2. zirconia ceramics, and the catalysts are supported on a cordierite honeycomb produced by extrusion forming. The cell surface of the honeycomb is covered with fine alumina particles coated with fine particles of precious metal catalysts on the surface. Since exhaust gas catalysts only work at elevated temperatures, the catalyst temperature must be raised rapidly to the light-off level after the engine is started. To accomplish that, the system was improved by reducing the thickness of the honeycomb walls, in addition to modifying the chemical composition of the catalysts and reducing the dimensions of the catalyst particles. The development history shown in Table 3 indicates that the wall thickness of NGK honeycombs was 300 m in 1976, which was reduced to just 50m in 1999. Fig. 8 shows catalyst honeycombs with different cell densities. 4.2. Diesel particulate filter2 The advantages of diesel engines in comparison with their gasoline counterparts include low fuel consumption and resultant low emissions of carbon dioxide, a greenhouse gas responsible for global warming. This performance is due to diesel engine characteristics such as (i) explosive burning at higher pressure, (ii) basically lean-burn combustion, and (iii) an absence of pumping (throttle) loss. However, the explosive burning process of diesel engines, which results from injecting fuel into compressed air, gives rise to a problem of particulate matter formation due to incomplete combustion when the explosion occurs before the fuel is completely evaporated and mixed with air. Particulate matter is thought to be related to the causes of cancer and bronchial asthma, and regulatory standards for engine emissions are becoming more stringent. Since particulate matter must be removed from exhaust gas, diesel particulate filters of the wall flow type are generally installed on diesel vehicles. The wall flow type filter is made of a porous ceramic honeycomb with square cell holes, and either the inlet or outlet end is filled alternatively. As the exhaust gas passes through the porous inlet walls, particulate matter condenses on the outer and inner surfaces of the walls. The major materials of diesel particulate filters are silicon carbide and cordierite. 4.3. Automotive parts1 Table 4 shows typical applications of silicon nitride to automotive engine parts. It is clear that such applications were actively promoted in the early and mid-1980s. Examples include glow plugs for starting diesel engines more quickly, turbocharger rotors (Fig. 9) for enabling quick acceleration response by employing lightweight ceramics, and wear parts for cam followers such as rocker arm pads and tappets (Fig. 10). These applications were promoted by an extraordinarily strong interest in ceramics in Japan at that time, referred to as the “ceramic fever.” Some ceramic parts were subsequently removed from the next generation of automobile models because the improved performance did not justify the higher production cost. Lightweight exhaust valves would be advantageous as dynamic parts because of their lower inertial mass at high engine Fig. 8. Catalyst honeycombs with different cell densities (courtesy of NGK Insulators Ltd.). (a) Typical catalyst honeycomb and (b) four honeycombs with different cell structures (see also Table 3).
A Okada/Joumal of the European Ceramic Sociery 28(2008)1097-1104 Table 4 Ceramic parts used on commercial vehicles in Japan Ceramic parts Materials Advantages of using ceramics First application Silicon nitride Quicker engine start 981 Hot plugs for diesel engine swirl chamber Silicon nitride Reduction of noise and unburned fuel in exhaust gas Silicon nitride Silicon nitride Improvement in acceleration response Tappets for diesel engines(cam followers) Silicon nitride Improvement in wear resistance Exhaust control valves of twin turbochargers Silicon nitride Improvement in transient characteristics by minimizing gas leakage 1993 diamond-like-carbon coating has been applied to valve lifters for that purpos 4.4. Uses in manufacturing processes for automobile Ceramics are used in the welding and heat treatment pro- cesses in the manufacture of steel parts for automobiles. Alumina tageous in plasma welding where the welding nozzle tip reaches high temperatures around 600.C. The advantages of using sili- con nitride nozzles include less adhesion to the metal sputtered from welding materials as well as excellent durability at high s temperatures. Silicon nitrides are applied to the squeezing rolls for manufacturing electric-resistance-welded tubes due to their excellent thermal shock resistance high strength and wear resis- Fig. 9. Ceramic turbocharger rotors. tance. Work supports used in the induction hardening process for steel parts, such as gears, require excellent wear resistance speeds. There have been strong expectations for the application to ensure a long lifetime, and silicon nitride has been applied of ceramics to exhaust valves in view of their light weight an requirement. high-temperature durability. Intensive R&D work has been done, require materials with high strength and wear resistance, and and ceramic valves were used on Formula One race cars in the zirconia ceramics have been applied here late 1980s which confirmed the lightweight benefits of ceramic valves. Moreover, Daimler-Benz conducted successful road tests 5. Concluding remarks of vehicles with ceramic valves in the 1990s however. ceramic exhaust valves have yet to be used on production automobiles The market for structural ceramics has been steadily increas- Recent requirements for wear parts include not only wear ing, while research activities for these materials have declined in resistance but also low friction. Creating a low-friction surface comparison with the very active period of the 1980s, character is effective in improving efficiency by reducing friction loss. a ized by the"ceramic fever"in Japan. High-purity alumina for the components of the equipment used in producing semiconductor devices and liquid crystal display panels has contributed sub- stantially to the recent market for structural ceramics. Cordierite honeycombs and diesel particulate filters are also important examples of automotive applications. While structural ceram cs are used in these applications, the stress levels are relatively low in comparison with gas turbine and turbocharger rotors that were the original uses targeted for these materials Extensive research on silicon nitride has led to new areas of application such as ceramic bearings and ceramic springs Hot-pressed silicon nitride bearings applied to the major shaft of lathe turning machines have contributed to improved preci sion in these machine tools. In addition, silicon nitride springs capable of withstanding temperatures up to 1000C have been developed and applied to the fixtures used in the brazing pro- cess, resulting in higher productivity. Alumina has been applied Fig. 10. Tappets as wear parts used for cam followers to the single lever mixing valves of cold and hot water supply
A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 1103 Table 4 Ceramic parts used on commercial vehicles in Japan1 Ceramic parts Materials Advantages of using ceramics First application Diesel engine glow plugs Silicon nitride Quicker engine start 1981 Hot plugs for diesel engine swirl chamber Silicon nitride Reduction of noise and unburned fuel in exhaust gas 1983 Rocker arm pads (cam followers) Silicon nitride Improvement in wear resistance 1984 Turbocharger rotors Silicon nitride Improvement in acceleration response 1985 Tappets for diesel engines (cam followers) Silicon nitride Improvement in wear resistance 1993 Exhaust control valves of twin turbochargers Silicon nitride Improvement in transient characteristics by minimizing gas leakage 1993 Fig. 9. Ceramic turbocharger rotors. speeds. There have been strong expectations for the application of ceramics to exhaust valves in view of their light weight and high-temperature durability. Intensive R&D work has been done, and ceramic valves were used on Formula One race cars in the late 1980s, which confirmed the lightweight benefits of ceramic valves. Moreover, Daimler-Benz conducted successful road tests of vehicles with ceramic valves in the 1990s. However, ceramic exhaust valves have yet to be used on production automobiles. Recent requirements for wear parts include not only wear resistance but also low friction. Creating a low-friction surface is effective in improving efficiency by reducing friction loss. A Fig. 10. Tappets as wear parts used for cam followers.1 diamond-like-carbon coating has been applied to valve lifters for that purpose.14 4.4. Uses in manufacturing processes for automobile parts15 Ceramics are used in the welding and heat treatment processes in the manufacture of steel parts for automobiles. Alumina welding nozzles have high temperature resistance and are advantageous in plasma welding where the welding nozzle tip reaches high temperatures around 600 ◦C. The advantages of using silicon nitride nozzles include less adhesion to the metal sputtered from welding materials as well as excellent durability at high temperatures. Silicon nitrides are applied to the squeezing rolls for manufacturing electric-resistance-welded tubes due to their excellent thermal shock resistance, high strength and wear resistance. Work supports used in the induction hardening process for steel parts, such as gears, require excellent wear resistance to ensure a long lifetime, and silicon nitride has been applied to meet that requirement. Bending rolls for metal spinning also require materials with high strength and wear resistance, and zirconia ceramics have been applied here. 5. Concluding remarks The market for structural ceramics has been steadily increasing, while research activities for these materials have declined in comparison with the very active period of the 1980s, characterized by the “ceramic fever” in Japan. High-purity alumina for the components of the equipment used in producing semiconductor devices and liquid crystal display panels has contributed substantially to the recent market for structural ceramics. Cordierite honeycombs and diesel particulate filters are also important examples of automotive applications. While structural ceramics are used in these applications, the stress levels are relatively low in comparison with gas turbine and turbocharger rotors that were the original uses targeted for these materials. Extensive research on silicon nitride has led to new areas of application such as ceramic bearings and ceramic springs. Hot-pressed silicon nitride bearings applied to the major shaft of lathe turning machines have contributed to improved precision in these machine tools.1 In addition, silicon nitride springs capable of withstanding temperatures up to 1000 ◦C have been developed and applied to the fixtures used in the brazing process, resulting in higher productivity.1 Alumina has been applied to the single lever mixing valves of cold and hot water supply
A Okada/Journal of the European Ceramic Society 28(2008)1097-1104 systems, precision guides such as air slides, and surface plates. 5. Sugimoto, T, 2005 activity of ceramic industries in Japan. Bull. CeramSoc. ilicon carbide has been applied to fishing guides. While earl Jpn., 2006, 41, 703-744 [in Japanese]. applications of zirconia were to knives and scissors, the scope 6. Urashima, K and Kuramoto, N, Handbook of Ceramics(2nd ed. ). Ceramic of application has recently been expanded to the ferrule con- 7. Sotoya, E, Fine ceramics for semiconductor manufacturing process. Bull nectors of optical fibers and impellers of slug pumps. Alumina Ceram. Soc. Jpn., 2005, 40, 438-442 [in Japanese]. with dispersed TiC particles has been applied to the magnetic 8.Sakamaki, M, Kishi, Y and Iniguchi, M, High density ceramics for semi- conductor manufacturing devices. Bull. Ceram Soc. Jpn., 2003, 38, 287-290 Recent successful applications of structural ceramics have been limited to low levels of stress in severe environments The K, Application of aluminum cation apparatus. Bull. Ceram. Soc. 叫,21sb next step for the application of ceramics is thought to be uses in severe environments under higher stresses. 10. Takahashi, T, Fine ceramic parts used for iron and steel-making process Bull. Ceram. Soc. Jpn., 2005, 40, 423-429 [in Japanese References 11. Kato, K, Large silicon nitride rollers for steel rolling. FC Repor 1999 17(8), 194-195 [in Japanese]- 1.Okada,A, Challenges of ceramics for structural application. Bull. Ceram. 12. Hamayoshi, S, Application of ceramics in aluminum casting and iron-steel Soc. Jpn., 2005, 40, 259-275 [in Japanese making. Bull. Ceram. Soc. Jpn., 2005, 40, 430-433 in Japanese 2. Okada, A Current status of structural ceramics--application to engines and 13. Nagano, M Precision ceramic die materials for recent industrial applica automobiles. Eng Mater(Kogyo Zairyo), 2005, 53(8), 23-27 [in Japanese]. tions. Bull. Ceram. Soc. Jpn., 2005, 40, 443-448 [ in Japanese]. 3. Sugimoto, T, 2003 activity of ceramic industries in Japan. Bull. Ceram. Soc 14. Kanamori, T, DLC and Me-DLC coating technologies for automobile parts. Jpn., 2004, 39, 700-740 [in Japanese]- Kikai Gigyutsl, 2006, 59(12), 20-27 [i 4. Sugimoto, T, 2004 activity of ceramic industries in Japan. Bull. Ceram. Se 15. Ukai, E, Ceramic application for producing automobile parts. JFA (Bull. Jpn., 2005, 40, 703-741 [in Japanese]- Japan Forging As 2007, 18, 51-56 [in Japanese]
1104 A. Okada / Journal of the European Ceramic Society 28 (2008) 1097–1104 systems, precision guides such as air slides, and surface plates. Silicon carbide has been applied to fishing guides. While early applications of zirconia were to knives and scissors, the scope of application has recently been expanded to the ferrule connectors of optical fibers and impellers of slug pumps.1 Alumina with dispersed TiC particles has been applied to the magnetic head slider of hard discs. Recent successful applications of structural ceramics have been limited to low levels of stress in severe environments. The next step for the application of ceramics is thought to be uses in severe environments under higher stresses. References 1. Okada, A., Challenges of ceramics for structural application. Bull. Ceram. Soc. Jpn., 2005, 40, 259–275 [in Japanese]. 2. Okada, A., Current status of structural ceramics—application to engines and automobiles. Eng. Mater. (Kogyo Zairyo), 2005, 53(8), 23–27 [in Japanese]. 3. Sugimoto, T., 2003 activity of ceramic industries in Japan. Bull. Ceram. Soc. Jpn., 2004, 39, 700–740 [in Japanese]. 4. Sugimoto, T., 2004 activity of ceramic industries in Japan. Bull. Ceram. Soc. Jpn., 2005, 40, 703–741 [in Japanese]. 5. Sugimoto, T., 2005 activity of ceramic industries in Japan. Bull. Ceram. Soc. Jpn., 2006, 41, 703–744 [in Japanese]. 6. Urashima, K. and Kuramoto, N., Handbook of Ceramics (2nd ed.). Ceramic Society of Japan, Gihodo, Tokyo, 2002, pp. 1250–1256 [in Japanese]. 7. Sotoya, E., Fine ceramics for semiconductor manufacturing process. Bull. Ceram. Soc. Jpn., 2005, 40, 438–442 [in Japanese]. 8. Sakamaki, M., Kishi, Y. and Iniguchi, M., High density ceramics for semiconductor manufacturing devices.Bull. Ceram. Soc. Jpn., 2003, 38, 287–290 [in Japanese]. 9. Kawasaki, K., Application of aluminum ceramics for semiconductor fabrication apparatus. Bull. Ceram. Soc. Jpn., 2004, 39, 688–691 [in Japanese]. 10. Takahashi, T., Fine ceramic parts used for iron and steel-making process. Bull. Ceram. Soc. Jpn., 2005, 40, 423–429 [in Japanese]. 11. Kato, K., Large silicon nitride rollers for steel rolling. FC Report, 1999, 17(8), 194–195 [in Japanese]. 12. Hamayoshi, S., Application of ceramics in aluminum casting and iron-steel making. Bull. Ceram. Soc. Jpn., 2005, 40, 430–433 [in Japanese]. 13. Nagano, M., Precision ceramic die materials for recent industrial applications. Bull. Ceram. Soc. Jpn., 2005, 40, 443–448 [in Japanese]. 14. Kanamori, T., DLC and Me-DLC coating technologies for automobile parts. Kikai Gigyutsu, 2006, 59(12), 20–27 [in Japanese]. 15. Ukai, E., Ceramic application for producing automobile parts. JFA (Bull. Japan Forging Assoc.), 2007, 18, 51–56 [in Japanese]
