Availableonlineatwww.sciencedirect.com DIRECT E噩≈3S SEVIER Journal of the European Ceramic Society 25(2005)605-611 www.elsevier.com/locate/jeurceramsoc Preparation and performance of an advanced multiphase composite ceramic material Chonghai xux Department of Mechanical and Electronic Engineering, Shandong Institute of Light Industry, Jinan, 250100, PR China Received 9 October 2003; received in revised form 30 March 2004, accepted 10 April 2004 Available online 15 June 2004 Abstract According to the optimum composition achieved from the material design, an advanced 15 vol. SiC and 15 vol. Ti(C, N)containing alumina-based multiphase ceramic material with good comprehensive mechanical properties has been fabricated with hot pressing technique Only under suitable hot pressing conditions and material compositions can better microstructures and mechanical properties be achieved Sic/Ti(c duration equals to 60 min and the pressure remains 35 MPa. The content of each dispersed SiC and Ti(C, N) phase has significant effects not only on the mechanical properties but on the engineering performances of the ceramic materials. Good wear resistance is found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel, Failure mechanisms are mainly the abrasive wear and the adhesive wear. The developed SiC/Ti(C, N)Al2O3 multiphase ceramic material will be well used as the structural parts with the nt of high wear resistance such as cutting tools Keywords: Microstructure; Mechanical properties; Cutting tools; Wear resistance, SIC/TI(C, N)Al20 1. Introduction Till now, ceramic composites have been used widely in cutting tools drawing or extrusion, seal rings valve seats Multiphase composite is one of the important developing bearing parts, and a variety of high temperature engine parts, trends of the advanced structural ceramic materials in the etc. because of their higher wear resistance, higher thermal 21st century. .2 The trend of ceramic material researches and chemical stability. Varieties of researches have been car- from monolithic phase to multiphase will provide wider ried out focusing on the cutting performance, friction and space for the consideration of the ceramic material de- wear and fracture mechanisms of ceramics when used as the sign. Considerable improvement in mechanical properties tool materials in machining different work materials. - >It of the single phase ceramic materials has been achieved is concluded that wear of ceramic tools is resulted from the by incorporating one or more other components into com binative function of both mechanical and chemical wear base material to form ceramic matrix composites(CMCs). Wear mechanisms include the abrasive wear, adhesive wear The reinforcing component is often in the form of particles chemical wear, diffusion wear and oxidation wear, etc. Wear or whiskers, such as TiC, TIN, TiB2, SiC particulate, Sic is not the intrinsic feature of the ceramic tool materials. It is whisker, B4C, ZrO, wC,(W,Ti)C, Ti(C, N), Cr3 C2, NbC, closely related with the cutting conditions. If the tool mate- te. -7 Ceramic composites are of increasing interest with rial is different, or the cutting condition or the work material oxide matrices, particularly alumina being dominant. How- is different, the dominant wear mechanism may vary ever, the corresponding material compositions, the process In the present study, according to the results of the mate- ing techniques, the reinforcing and toughening mechanisms, rial design in the former reports, 4. 5 an advanced Sic and the properties and their application still need further study. Ti(C, N) containing alumina-based multiphase ceramic ma- terial with good comprehensive mechanical properties has been manufactured using the hot pressing technique. The *Tel:+8653186198588556865;fax:+865318968495 microstructure and the engineering performance of the ma E-mailaddress:xch@.edu.cn(C.Xu) terial are also studied in detail 0955-2219/s-see front matter O 2004 Elsevier Ltd. All rights reserved doi: 10. 1016/j jeurceramsoc 2004 04.002
Journal of the European Ceramic Society 25 (2005) 605–611 Preparation and performance of an advanced multiphase composite ceramic material Chonghai Xu∗ Department of Mechanical and Electronic Engineering, Shandong Institute of Light Industry, Jinan, 250100, PR China Received 9 October 2003; received in revised form 30 March 2004; accepted 10 April 2004 Available online 15 June 2004 Abstract According to the optimum composition achieved from the material design, an advanced 15 vol.% SiC and 15 vol.% Ti(C,N) containing alumina-based multiphase ceramic material with good comprehensive mechanical properties has been fabricated with hot pressing technique. Only under suitable hot pressing conditions and material compositions can better microstructures and mechanical properties be achieved. The optimum hot pressing parameters for the SiC/Ti(C,N)/Al2O3 material are as follows: the hot pressing temperature is 1780 ◦C, the time duration equals to 60 min and the pressure remains 35 MPa. The content of each dispersed SiC and Ti(C,N) phase has significant effects not only on the mechanical properties but on the engineering performances of the ceramic materials. Good wear resistance is found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel. Failure mechanisms are mainly the abrasive wear and the adhesive wear. The developed SiC/Ti(C,N)/Al2O3 multiphase ceramic material will be well used as the structural parts with the requirement of high wear resistance such as cutting tools. © 2004 Elsevier Ltd. All rights reserved. Keywords: Microstructure; Mechanical properties; Cutting tools; Wear resistance; SiC/Ti(C,N)/Al2O3 1. Introduction Multiphase composite is one of the important developing trends of the advanced structural ceramic materials in the 21st century.1,2 The trend of ceramic material researches from monolithic phase to multiphase will provide wider space for the consideration of the ceramic material design. Considerable improvement in mechanical properties of the single phase ceramic materials has been achieved by incorporating one or more other components into the base material to form ceramic matrix composites (CMCs). The reinforcing component is often in the form of particles or whiskers, such as TiC, TiN, TiB2, SiC particulate, SiC whisker, B4C, ZrO2, WC, (W,Ti)C, Ti(C,N), Cr3C2, NbC, etc.3–7 Ceramic composites are of increasing interest with oxide matrices, particularly alumina being dominant. However, the corresponding material compositions, the processing techniques, the reinforcing and toughening mechanisms, the properties and their application still need further study. ∗ Tel: +86 531 8619858/8556865; fax: +86 531 8968495. E-mail address: xch@sdili.edu.cn (C. Xu). Till now, ceramic composites have been used widely in cutting tools, drawing or extrusion, seal rings, valve seats, bearing parts, and a variety of high temperature engine parts, etc. because of their higher wear resistance, higher thermal and chemical stability. Varieties of researches have been carried out focusing on the cutting performance, friction and wear and fracture mechanisms of ceramics when used as the tool materials in machining different work materials.8–13 It is concluded that wear of ceramic tools is resulted from the combinative function of both mechanical and chemical wear. Wear mechanisms include the abrasive wear, adhesive wear, chemical wear, diffusion wear and oxidation wear, etc. Wear is not the intrinsic feature of the ceramic tool materials. It is closely related with the cutting conditions. If the tool material is different, or the cutting condition or the work material is different, the dominant wear mechanism may vary. In the present study, according to the results of the material design in the former reports,14,15 an advanced SiC and Ti(C,N) containing alumina-based multiphase ceramic material with good comprehensive mechanical properties has been manufactured using the hot pressing technique. The microstructure and the engineering performance of the material are also studied in detail. 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.04.002
C. Xu/Journal of the European Ceramic Sociery 25 (2005)605-611 2. Experimental procedures Table 1 Machining parameters used in the cutting tests High purity Al2O3, B-SiC and Ti(C, N)powders were Cutting speed used as the starting materials with sizes of 0.8, 1.0 and number w(m/min) (mm/rev) ap(mm) 1.0 um, respectively. Before mixing, all the powders had to I be cleaned with the hot diluted HNO3 and NaOH solution 2 in order to reduce the effect of the impurities. Then, Al203 3 was blended with SiC and TI(C, N)and doped with different amounts of sintering additives The mixtures were subse quently homogenized with absolute alcohol media in a ball analysis of the sintered samples with the scanning speed of mill for 80h. After milling, the slurry was screened in ni- 4/min, the working voltage of 44 kv and the electric cur- trogen and dried in vacuum. Samples were then formed by rent of 150 mA hot pressing(HP)technique in N2 atmosphere in a graphite The developed ceramic material was then utilized as a mould. Sintered bodies were then cut with a diamond wheel tool material, and cutting tests were done according to the pecimens and inserts following cutting conditions. Continuous turning experi- Relative density of the sample was measured by ments were carried out on a lathe( model CA6 140)equipped Archimedes'technique. The three point bending method with a 450 lead angle, 5 negative inclination, 50 negative was used to measure the flexural strength with a span of rake tool holder, 5%clearance and dry cut. The geometry of 20 mm and a cross head speed of 0.5 mm/min. The test bars the tool inserts is SNGN160603 with an edge chamfer of were carefully ground and polished into the size of 3 mm 0.2 mm at 200. The work material is a 0. 45%C mild carbon thick, 4 mm wide and 30 mm long with the surface rough- steel (#45 steel) with a hardness of 40-42 HRC in the form ness less than 0.1 um. The edges of the tensile surface were of round bars. Machining parameters are given in Table I chamfered. The fracture toughness was determined on bars Here AST is used to indicate the SiC/Ti(C, N)/Al2O3 se- of 3 mm(thickness)x 4mm(width)x 40 mm (length) ries ceramic materials. AS15T15, ASIOT10 and AS10T30 by a four point SENB(single edge notched beam)method indicates the SiC/Ti(C, N)/Al2O3 ceramic material with with a 10 mm inner span and a 20 mm outer span at a cross 15 vol. SiC and 15 vol. TI(C, N), 10 vol. SiC and head speed of 0. I mm/min. A straight notch with a ratio 10 vol %Ti(C N), 10 vol. SiC and 30 vol. Ti(C, N),re- to thickness of about 0.5 mm was introduced at the center spectively. Ao indicates the pure alumina ceramic. In order part of the test bar using a 0.2 mm wide diamond blade and for the comparison, Al2O3/30 vol %(W,Ti)c ceramic com- depth of notch was about 1.5 mm. To reduce the effect of a posite was also fabricated with the same technique, which finite notch tip radius on the initial crack propagation, the is marked as Aw30 bottom portion of the saw notch was sharpened by using a sharp razor blade that had been sprinkled with 1 um dia- mond paste. This double notch procedure allowed the notch 3. Results and analyses radius to be reduced up to 10.8 92-10.1
606 C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 2. Experimental procedures High purity Al2O3, -SiC and Ti(C,N) powders were used as the starting materials with sizes of 0.8, 1.0 and 1.0m, respectively. Before mixing, all the powders had to be cleaned with the hot diluted HNO3 and NaOH solution in order to reduce the effect of the impurities. Then, Al2O3 was blended with SiC and Ti(C,N) and doped with different amounts of sintering additives. The mixtures were subsequently homogenized with absolute alcohol media in a ball mill for 80 h. After milling, the slurry was screened in nitrogen and dried in vacuum. Samples were then formed by hot pressing (HP) technique in N2 atmosphere in a graphite mould. Sintered bodies were then cut with a diamond wheel into specimens and inserts. Relative density of the sample was measured by Archimedes’ technique. The three point bending method was used to measure the flexural strength with a span of 20 mm and a cross head speed of 0.5 mm/min. The test bars were carefully ground and polished into the size of 3 mm thick, 4 mm wide and 30 mm long with the surface roughness less than 0.1 m. The edges of the tensile surface were chamfered. The fracture toughness was determined on bars of 3 mm (thickness) × 4 mm (width) × 40 mm (length) by a four point SENB (single edge notched beam) method with a 10 mm inner span and a 20 mm outer span at a cross head speed of 0.1 mm/min. A straight notch with a ratio to thickness of about 0.5 mm was introduced at the center part of the test bar using a 0.2 mm wide diamond blade and depth of notch was about 1.5 mm. To reduce the effect of a finite notch tip radius on the initial crack propagation, the bottom portion of the saw notch was sharpened by using a sharp razor blade that had been sprinkled with 1 m diamond paste. This double notch procedure allowed the notch radius to be reduced up to 10.8 9.2–10.1 – – – <0.3 <0.2 – – <0.7 Table 1 Machining parameters used in the cutting tests Group number Cutting speed, v (m/min) Feed rate, f (mm/rev) Depth of cut, ap (mm) 1 90 0.2 1.0 2 150 0.2 1.0 3 220 0.15 0.6 analysis of the sintered samples with the scanning speed of 4◦/min, the working voltage of 44 kV and the electric current of 150 mA. The developed ceramic material was then utilized as a tool material, and cutting tests were done according to the following cutting conditions. Continuous turning experiments were carried out on a lathe (model CA6140) equipped with a 45◦ lead angle, 5◦ negative inclination, 5◦ negative rake tool holder, 5◦clearance and dry cut. The geometry of the tool inserts is SNGN160603 with an edge chamfer of 0.2 mm at 20◦. The work material is a 0.45% C mild carbon steel (#45 steel) with a hardness of 40–42 HRC in the form of round bars. Machining parameters are given in Table 1. Here AST is used to indicate the SiC/Ti(C,N)/Al2O3 series ceramic materials. AS15T15, AS10T10 and AS10T30 indicates the SiC/Ti(C,N)/Al2O3 ceramic material with 15 vol.% SiC and 15 vol.% Ti(C,N), 10 vol.% SiC and 10 vol.% Ti(C,N), 10 vol.% SiC and 30 vol.% Ti(C,N), respectively. A0 indicates the pure alumina ceramic. In order for the comparison, Al2O3/30 vol.% (W,Ti)C ceramic composite was also fabricated with the same technique, which is marked as AW30. 3. Results and analyses 3.1. Processing technology The results of the chemical analysis of the used powders are shown in Table 2. Since small quantities of impurities like Fe, Fe2O3, etc. resulted from the incomplete chemical reaction and other production stages of the raw materials, have been mixed into these ceramic powders, all the powders have to be washed before use with the hot diluted HNO3 and NaOH solution in order to reduce the impurities. Although results of the technological design of the ceramic material suggest that the pressure should be the higher the better,15 the pressure used in the present study is 35 MPa limited by the strength of the graphite mould at elevated
C. Xu/ Journal of the European Ceramic Society 25(2005)605-61 16501700175018001850 Hot pressing temperature T/C Fig. 1. Variation of the relative density of As15T15 ceramic material Fig 3. XRD analysis of the sintered As15T15 ceramic material. with the hot pressing parameters. ture, the time duration and the pressure is 1780C, 60 min and 35 MPa, respectively. The flexural strength, the fracture temperature. Figs. I and 2 indicates the effect of hot press press- toughness and the hardness of AS15T15 ceramic material is ing temperature and time duration on the relative density measured to be 721 MPa, 5.4 MPam/2 and 18.97 GPa, re- and the fracture toughness of AS15T15 ceramic material, spectively, which is 43.9, 42. 1 and 4.6%, respectively, higher ture is 1780oC and the time duration equals to 60 min, the than that of the pure alumina ceramic. Mechanical properties relative density of the material can reach about 98%and the The hot pressing parameters have significant effect fracture toughness is higher than 5.2 MPam/. With these the microstructure and the mechanical property of the ce- processing parameters, the other mechanical properties such ramic materials Under the condition of 1700 C X 30 min as the flexural strength and the hardness are all relatively the fracture surface of the sample is relatively smooth high. The experimental results coincide well with that of which corresponds to the flexural strength of 561 MPa and the technological design. 5 However, both the hot pressing the fracture toughness of 3.9 MPam/ 2. But when the hot temperature and the time duration that are needed to reach pressing temperature is 1780C and the time duration is the same density of the SiC containing Alumina ceramic 60 min, the fracture surface of the sample is noticeably acci- of th material without SiC addition. The main reason consists in reached 721 MPa and the fracture toughness 5.4 MPam/2 that the covalent bond compound SiC is more difficult The first reason is the increase of the relative density which be sintered than other ionic and metallic bond compounds is increased from approximately 93% at conditions of such as TiC and ZrO2, etc. Analysis with XRd denotes that 1700.C x 30 min to 98% at 1780.C x 60 min. The second the material after sintering keeps the same composition wit reason is that affected by the internal residual thermal stres that before sintering and no new phases are found to exist field, the dispersed SiC and ti(C N) grains interact with the inside the As15T15 material(Fig 3) propagating cracks which results in the crack deflection, crack bridging or grain pulling-out(Fig. 4b and c). Thus 3.2. Microstructure and mechanical property the crack path is extended and the flexural strength and the fracture toughness are then increased. Furthermore, differ- According to the former study, comprehensive mechan- ent extent of brittle cleavage may happen in the fracture ical properties will be achieved for the SiC/i(C, NyAl2O3 process in some alumina grains resulted from the complex ceramic material when the volume fraction of both Sic and residual thermal stresses around the grains. The complex i(C, N)is nearly 15% and when the hot pressing tempera- cleavage surface is then formed with obvious features of the pulling-out effect of grains(Fig. 4d). As a result, the energy of fracture is increased and both fracture tor and flexural strength are subsequently enhanced Table 3 Mechanical properties of the selected ceramic materials at hot pressing conditions of 1780C x 60min x 35 MPa Material Flexural Fracture strength toughness, K hardness Tf(MPa (MPam/ Hy(GPa) ASI5T15 1650170017508001850 ASIOTIO 18.79 ASIOT30 18.82 Fig. 2. Variation of the fracture toughness of AS15T15 with the hot pressing parameters(unit of fracture toughness is MPam 2) AW30 1892
C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 607 Fig. 1. Variation of the relative density of AS15T15 ceramic material with the hot pressing parameters. temperature. Figs. 1 and 2 indicates the effect of hot pressing temperature and time duration on the relative density and the fracture toughness of AS15T15 ceramic material, respectively. It seems that when the hot pressing temperature is 1780 ◦C and the time duration equals to 60 min, the relative density of the material can reach about 98% and the fracture toughness is higher than 5.2 MPa m1/2. With these processing parameters, the other mechanical properties such as the flexural strength and the hardness are all relatively high. The experimental results coincide well with that of the technological design.15 However, both the hot pressing temperature and the time duration that are needed to reach the same density of the SiC containing Alumina ceramic is higher and longer than that of the corresponding ceramic material without SiC addition. The main reason consists in that the covalent bond compound SiC is more difficult to be sintered than other ionic and metallic bond compounds such as TiC and ZrO2, etc. Analysis with XRD denotes that the material after sintering keeps the same composition with that before sintering and no new phases are found to exist inside the AS15T15 material (Fig. 3). 3.2. Microstructure and mechanical property According to the former study,14 comprehensive mechanical properties will be achieved for the SiC/Ti(C,N)/Al2O3 ceramic material when the volume fraction of both SiC and Ti(C,N) is nearly 15% and when the hot pressing temperaFig. 2. Variation of the fracture toughness of AS15T15 ceramic material with the hot pressing parameters (unit of fracture toughness is MPa m1/2). Fig. 3. XRD analysis of the sintered AS15T15 ceramic material. ture, the time duration and the pressure is 1780 ◦C, 60 min and 35 MPa, respectively. The flexural strength, the fracture toughness and the hardness of AS15T15 ceramic material is measured to be 721 MPa, 5.4 MPa m1/2 and 18.97 GPa, respectively, which is 43.9, 42.1 and 4.6%, respectively, higher than that of the pure alumina ceramic. Mechanical properties of all the selected ceramic materials are listed in Table 3. The hot pressing parameters have significant effect on the microstructure and the mechanical property of the ceramic materials. Under the condition of 1700 ◦C × 30 min, the fracture surface of the sample is relatively smooth which corresponds to the flexural strength of 561 MPa and the fracture toughness of 3.9 MPa m1/2. But when the hot pressing temperature is 1780 ◦C and the time duration is 60 min, the fracture surface of the sample is noticeably accidented (Fig. 4a). The flexural strength has correspondingly reached 721 MPa and the fracture toughness 5.4 MPa m1/2. The first reason is the increase of the relative density which is increased from approximately 93% at conditions of 1700 ◦C × 30 min to 98% at 1780 ◦C × 60 min. The second reason is that affected by the internal residual thermal stress field, the dispersed SiC and Ti(C,N) grains interact with the propagating cracks which results in the crack deflection, crack bridging or grain pulling-out (Fig. 4b and c). Thus, the crack path is extended and the flexural strength and the fracture toughness are then increased. Furthermore, different extent of brittle cleavage may happen in the fracture process in some alumina grains resulted from the complex residual thermal stresses around the grains. The complex cleavage surface is then formed with obvious features of the pulling-out effect of grains (Fig. 4d). As a result, the energy of fracture is increased and both fracture toughness and flexural strength are subsequently enhanced. Table 3 Mechanical properties of the selected ceramic materials at hot pressing conditions of 1780 ◦C × 60 min × 35 MPa Material Flexural strength, σf (MPa) Fracture toughness, KIC (MPa m1/2) Vickers hardness, HV (GPa) AS15T15 721 5.4 18.97 AS10T10 697 5.2 18.79 AS10T30 660 5.0 18.82 A0 501 3.8 18.1 AW30 765 5.1 18.92
C. Xu/Journal of the European Ceramic Sociery 25 (2005)605-611 咄画 1.7m I.n (d) Fig. 4. Fracture morphology of As15T15 ceramic material at 1780.C x 60 min(a)accidented fracture surface; (b)crack bridging, (c)grain pulling-out; (d) brittle cleavage Microstructural morphology of the material under TEM of the material but also to the increase in the fracture tough- is shown in Fig. 5. Both the two dispersed phases SiC and ness of the material which is similar, to a certain extent, to Ti(C, N), distributed uniformly in the matrix, bond well with the toughening mechanism found in the whisker toughened Al2O3 at the interface with fine grain size. SiC particles ceramic material. I8 are usually dispersed uniformly in the matrix, but few of Dislocations have also been observed in the SiC/TI(C, N)/ them with the sub-micron meter grain size, nearly less than Al2O3 ceramic material. Typical morphology is given in 200 nm, can be observed to exist inside the alumina grains Fig 5c. Most of the dislocations originate from the interface (Fig. 5a). These existing sub-micron meter sized Sic par- under the action of the residual thermal stresses and then ticles inside the alumina grains can improve the flexural propagate into the grains On the one side, the elastic strain strength and the fracture toughness of the material with the energy can be deposited in the dislocations On the other similar toughening mechanism of intergranular fracture hap. side. when the crack reaches. the dislocations can absorb pened frequently in ceramic nanocomposites. 16. 7 On the parts of the energy of fracture through their own deforma- other hand, the twin sub-structure can be observed clearly tion. The propagating crack will be pinned and the fracture no matter inside large or small SiC grains among which the toughness is resultedly increased. At a matter of fact, the twin sub-structure with the orientation angle of 60o is dis- dislocation toughening, which is similar to the microcrack covered(Fig 5b). The formation of twins will absorb the toughening, can cause the regional blunting effect in the tip energy of fracture at the interface of Al2 O3/SiC so that the area of the extending crack and it will have the KR-curve addition of Sic can contribute not only to the reinforcement behavior. 9.20 The interlaced dislocation lines are seemed
608 C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 Fig. 4. Fracture morphology of AS15T15 ceramic material at 1780 ◦C × 60 min (a) accidented fracture surface; (b) crack bridging; (c) grain pulling-out; (d) brittle cleavage . Microstructural morphology of the material under TEM is shown in Fig. 5. Both the two dispersed phases SiC and Ti(C,N), distributed uniformly in the matrix, bond well with Al2O3 at the interface with fine grain size. SiC particles are usually dispersed uniformly in the matrix, but few of them with the sub-micron meter grain size, nearly less than 200 nm, can be observed to exist inside the alumina grains (Fig. 5a). These existing sub-micron meter sized SiC particles inside the alumina grains can improve the flexural strength and the fracture toughness of the material with the similar toughening mechanism of intergranular fracture happened frequently in ceramic nanocomposites.16,17 On the other hand, the twin sub-structure can be observed clearly no matter inside large or small SiC grains among which the twin sub-structure with the orientation angle of 60◦ is discovered (Fig. 5b). The formation of twins will absorb the energy of fracture at the interface of Al2O3/SiC so that the addition of SiC can contribute not only to the reinforcement of the material but also to the increase in the fracture toughness of the material which is similar, to a certain extent, to the toughening mechanism found in the whisker toughened ceramic material.18 Dislocations have also been observed in the SiC/Ti(C,N)/ Al2O3 ceramic material. Typical morphology is given in Fig. 5c. Most of the dislocations originate from the interface under the action of the residual thermal stresses and then propagate into the grains. On the one side, the elastic strain energy can be deposited in the dislocations. On the other side, when the crack reaches, the dislocations can absorb parts of the energy of fracture through their own deformation. The propagating crack will be pinned and the fracture toughness is resultedly increased. At a matter of fact, the dislocation toughening, which is similar to the microcrack toughening, can cause the regional blunting effect in the tip area of the extending crack and it will have the KR-curve behavior.19,20 The interlaced dislocation lines are seemed
C. Xu /Journal of the European Ceramic Sociery 25 (2005)605-61 10.25um(c) 0.2um Fig. 5. TEM morphology of As15T15 ceramic material:(a) sub-micron meter sized SiC grain; (b) twin formed in SiC grain;(c)dislocation. to be equivalent to the second fining of the matrix grains. of wear resistance is AW30 N AS15T15> ASIOT10> Since its size has reached the nano-meter degree, the effect AS1oT30> A0 which is nearly the same with that of the of reinforcement on the ceramic material is self-evident comprehensive mechanical properties(Table 3). After & min of machining, the flank wear resistance of As15T15 ce- 3.3. Cutting performance ramic is 21.4, 35.7 and 71.5% higher than that of AS1OT10 ASIOT30 and the pure Al2 O3 ceramic material, respectively The flank wear curves of the selected ceramic materials Wear modes of the developed SiC/Ti(C N)/Al2O3 series when machining the hardened #45 carbon steel are given in ceramic materials are primarily the same, i.e., mainly the v=220 m/min, the feed rate f=0. 15 mm/rev and the depth of cut wear. SEM morphologies of the crater wear depth of cut ap =0.6 mm. It seems that wear curves of all and the fank wear of as15T15 ceramic material are shown the ceramic materials obey the wear law well. But wear as an example in Fig. 7. Under the experimental condi- resistance of different ceramic materials vary with each tions, the adhesion between the tool material and the work other. Under the present experimental conditions, wear material happens in some areas in the rake face of the tool resistance of AS15T15 ceramic is higher than the other where clumps of the adhered materials can notably be ob- SIC/Ti(C N)Al2O3 series ceramic materials, while is nearly served(Fig. 7a). The case is ceaselessly intensified with the same with that of Aw30 ceramic material. With the the increase in the cutting speed resulted from the high cut- prolonging of the cutting time, the gap in the wear resis- ting temperature. In the flank wear area, main wear mode tance between several ceramics is enlarged. The sequence is changed from the abrasive wear at lower speed to the adhesive wear at higher speed where the plowing grooves 0.5 are relatively short and shallow(Fig. 7b). Occasionally, few ceramic grains have ever been observed to break off in the flank wear area in as10T30 ceramic material In fact, when machining hardened steel with SiC contain- ment in the work material at high cutting temperature. a ing ceramic tool material. Sic will react with the iron ele The following reaction is the most possible one that happens 4Fe+SiC= FeSi+ Fe3C Thermal dynamic calculation indicates that when the cutting temperature reaches 425K, the free energy is -O 112 kJ/mol <0, which suggests that the reaction might Fig. 6. Variation of the flank wear of the selected ceramic materials with the cutting time when machining the hardened #45 carbon steel with the happen. The reaction will be intensified with the increase in cutting speed 220 m/min, the feed rate 0.15 mm/rev and the depth of the cutting temperature which is resulted from the increase in the cutting speed. The reaction will then lower the hardness
C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 609 Fig. 5. TEM morphology of AS15T15 ceramic material: (a) sub-micron meter sized SiC grain; (b) twin formed in SiC grain; (c) dislocation. to be equivalent to the second fining of the matrix grains. Since its size has reached the nano-meter degree, the effect of reinforcement on the ceramic material is self-evident. 3.3. Cutting performance The flank wear curves of the selected ceramic materials when machining the hardened #45 carbon steel are given in Fig. 6 where the cutting conditions are: the cutting speed v = 220 m/min, the feed rate f = 0.15 mm/rev and the depth of cut ap = 0.6 mm. It seems that wear curves of all the ceramic materials obey the wear law well. But wear resistance of different ceramic materials vary with each other. Under the present experimental conditions, wear resistance of AS15T15 ceramic is higher than the other SiC/Ti(C,N)/Al2O3 series ceramic materials, while is nearly the same with that of AW30 ceramic material. With the prolonging of the cutting time, the gap in the wear resistance between several ceramics is enlarged. The sequence Fig. 6. Variation of the flank wear of the selected ceramic materials with the cutting time when machining the hardened #45 carbon steel with the cutting speed 220 m/min, the feed rate 0.15 mm/rev and the depth of cut 0.6 mm. of wear resistance is AW30 ≈ AS15T15 > AS10T10 > AS10T30 > A0 which is nearly the same with that of the comprehensive mechanical properties (Table 3). After 8 min of machining, the flank wear resistance of AS15T15 ceramic is 21.4, 35.7 and 71.5% higher than that of AS10T10, AS10T30 and the pure Al2O3 ceramic material, respectively. Wear modes of the developed SiC/Ti(C,N)/Al2O3 series ceramic materials are primarily the same, i.e., mainly the flank wear and the crater wear accompanied with slight depth of cut wear. SEM morphologies of the crater wear and the flank wear of AS15T15 ceramic material are shown as an example in Fig. 7. Under the experimental conditions, the adhesion between the tool material and the work material happens in some areas in the rake face of the tool where clumps of the adhered materials can notably be observed (Fig. 7a). The case is ceaselessly intensified with the increase in the cutting speed resulted from the high cutting temperature. In the flank wear area, main wear mode is changed from the abrasive wear at lower speed to the adhesive wear at higher speed where the plowing grooves are relatively short and shallow (Fig. 7b). Occasionally, few ceramic grains have ever been observed to break off in the flank wear area in AS10T30 ceramic material. In fact, when machining hardened steel with SiC containing ceramic tool material, SiC will react with the iron element in the work material at high cutting temperature.10,11 The following reaction is the most possible one that happens. 4Fe + SiC = FeSi + Fe3C (1) Thermal dynamic calculation indicates that when the cutting temperature reaches 425 K, the free energy is −0.112 kJ/mol < 0, which suggests that the reaction might happen. The reaction will be intensified with the increase in the cutting temperature which is resulted from the increase in the cutting speed. The reaction will then lower the hardness
C. Xu/Journal of the European Ceramic Sociery 25 (2005)605-611 km回 Fig. 7. Wear morphologies of As15T15 ceramic material when machining the hardened #45 carbon steel with the cutting speed 220 m/min, the feed rate 0. 15 mm/rev and the depth of cut 0.6 mm: (a)crater wear in the rake face and(b)fank wear and the the material, which can undoubtedly contribute to the tough strength between SiC and the alumina matrix. As a result, ening and strengthening of the ceramic material. when the Sic particulates will break off easily under the action of the developed material is used as a tool material in the machin scratching of the hard particles in the work material and the ing of the hardened #45 carbon steel, its wear resistance is cutting performance of the ceramic tool will be lowered 71.5% higher than that of the pure alumina ceramics Additionally, the dissolution wear happened at elevated temperature is one of the factors that will influence the utting performance of Sic containing ceramics. Brandt cknowledgements ointed out that the solubility of iron in SiC at elevated tem- perature is two orders of magnitude higher than that in TiC The Foundation for University Key Teacher by the Min- The increase of the content of iron element in the ceramic istry of Education, China, the Research Fund for the Excel tool material will intensify the adhesion between the tool lent Young& Middle-aged Scientists, Shandong Province, and the work material, which will lead to the lower cutting the Natural Science Fund, Shandong Province, are all greatl appreciated for supporting this project But on the other hand, since the free energy of formation of Ti(C wer than other hard carbides such as tic and WC, it has higher chemical stability and is difficult to References react with the work material. Ti(C, N)is known as possess ing higher crater wear resistance and higher adhesion wear 1. Guo. J. K. The frontiers of research on ceramic science. J. Solid resistance through the effective prevention of the diffusion State chen1992,69,108-112. ween the tool and work material. 22,23 As an integrated re- 2. Evans, A. G. Perspective on the development of high toughness ceramics. J. Am. Ceram. Soc. 1990. 73. 187-19 sult, SiC/Ti(C, N)/Al2O3 ceramic material still reveals good 3. Fu,Y, Gu, Y. w and Du, H, SiC whisker toughened Al2O3-Ti, W)C cutting performance eramic matrix composites. Scripta Materialia 2001, 44, 111 4. Gong, J, Miao, H. and Zhao, Z, The influence of TiC-particle-size 4. Conclusions on the fracture toughness of Al2O3-30 wt. TiC composites. J. Eur. Ceram.Soc.2001,21,2377-2381 An advanced SiC/Ti(C, N)AlO3 multiphase ceramic 5. Peillon, F. C. and Thevenot, F, Microstructural designing of silicon material has been developed by means of the hot pressing 6. Acchar, W Greil, P, Martinelli, A.E. et al, Effect of Y2 03 addition technique with the flexural strength, the fracture toughness on the densification and mechanical properties of alumina-niobium and the hardness of 721 MPa, 5.4 MPam/ and 18.97 GPa, Ceram.lm.2001,27,225-230 respectively. The optimum processing parameters for the 7. Rak, Z. S. and Czechowski, J, Manufacture and properties of material are that the hot pressing temperature is 1780C Al2O3-hin particulate composites. J. Eur: Ceram. Soc. 1998, 18 373-380. the time duration is 60 min and the pressure is 35 MPa. 8.Xu, C, Ai, X. and Huang, C, Fabrication and performance of an Quantities of twins and dislocations are observed to exist in advanced ceramic tool material. Wear 2001. 249. 503-508
610 C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 Fig. 7. Wear morphologies of AS15T15 ceramic material when machining the hardened #45 carbon steel with the cutting speed 220 m/min, the feed rate 0.15 mm/rev and the depth of cut 0.6 mm: (a) crater wear in the rake face and (b) flank wear. and the wear resistance of SiC and weaken the bonding strength between SiC and the alumina matrix. As a result, SiC particulates will break off easily under the action of the scratching of the hard particles in the work material and the cutting performance of the ceramic tool will be lowered. Additionally, the dissolution wear happened at elevated temperature is one of the factors that will influence the cutting performance of SiC containing ceramics. Brandt21 pointed out that the solubility of iron in SiC at elevated temperature is two orders of magnitude higher than that in TiC. The increase of the content of iron element in the ceramic tool material will intensify the adhesion between the tool and the work material, which will lead to the lower cutting performance. But on the other hand, since the free energy of formation of Ti(C,N) is lower than other hard carbides such as TiC and WC, it has higher chemical stability and is difficult to react with the work material. Ti(C,N) is known as possessing higher crater wear resistance and higher adhesion wear resistance through the effective prevention of the diffusion between the tool and work material.22,23 As an integrated result, SiC/Ti(C,N)/Al2O3 ceramic material still reveals good cutting performance. 4. Conclusions An advanced SiC/Ti(C,N)/Al2O3 multiphase ceramic material has been developed by means of the hot pressing technique with the flexural strength, the fracture toughness and the hardness of 721 MPa, 5.4 MPa m1/2 and 18.97 GPa, respectively. The optimum processing parameters for the material are that the hot pressing temperature is 1780 ◦C, the time duration is 60 min and the pressure is 35 MPa. Quantities of twins and dislocations are observed to exist in the material, which can undoubtedly contribute to the toughening and strengthening of the ceramic material. When the developed material is used as a tool material in the machining of the hardened #45 carbon steel, its wear resistance is 71.5% higher than that of the pure alumina ceramics. Acknowledgements The Foundation for University Key Teacher by the Ministry of Education, China, the Research Fund for the Excellent Young & Middle-aged Scientists, Shandong Province, the Natural Science Fund, Shandong Province, are all greatly appreciated for supporting this project. References 1. Guo, J. K., The frontiers of research on ceramic science. J. Solid State Chem. 1992, 69, 108–112. 2. Evans, A. G., Perspective on the development of high toughness ceramics. J. Am. Ceram. Soc. 1990, 73, 187–195. 3. Fu, Y., Gu, Y. W. and Du, H., SiC whisker toughened Al2O3–(Ti,W)C ceramic matrix composites. Scripta Materialia 2001, 44, 111– 116. 4. Gong, J., Miao, H. and Zhao, Z., The influence of TiC-particle-size on the fracture toughness of Al2O3–30 wt. TiC composites. J. Eur. Ceram. Soc. 2001, 21, 2377–2381. 5. Peillon, F. C. and Thevenot, F., Microstructural designing of silicon nitride related to toughness. J. Eur. Ceram. Soc. 2002, 22, 271–278. 6. Acchar, W., Greil, P., Martinelli, A. E. et al., Effect of Y2O3 addition on the densification and mechanical properties of alumina-niobium carbide composites. Ceram. Int. 2001, 27, 225–230. 7. Rak, Z. S. and Czechowski, J., Manufacture and properties of Al2O3–TiN particulate composites. J. Eur. Ceram. Soc. 1998, 18, 373–380. 8. Xu, C., Ai, X. and Huang, C., Fabrication and performance of an advanced ceramic tool material. Wear 2001, 249, 503–508
C. Xu /Journal of the European Ceramic Sociery 25(2005)605-61 611 9. Barry, J. and Byrne, G, Cutting tool wear in the machining of 16. Oh, Y.-S, Kim, C -S, Lim, D.S. et al., Fracture strengths and m hardened steels-Part I: alumina/TiC cutting tool wear. Wear 2001 restructures of Si3 Na/SiC nanocomposites fabricated by in-situ pro- 247,139-151. cess. Scripta Materialia 2001, 44, 2079-2081 10. Novak, S, Kalin, M. and Kosmac, T, Chemical aspects of wear of 17. Tan, H. L. and Yang, W, Toughening mechanisms of nano-composite alumina ceramics. Wear 2001. 250 318-321 ceramics. Mech. Mater: 1998.30.111-123 11. Lo Casto, S, Lo Valvo, E, Lucchini, E et al, Ceramic materials wear 18. Rachman, C, Mechanical properties and microstructure of whisker mechanisms when cutting nickel-based alloys. Wear 1999, 225-229, reinforced Al2O3 matrix composite .. Am. Ceram. Soc. 1989, 72, 27-233 1636-1640. 2. Lo Casto. S. Lo Valvo. E. Lucchini. E. et al. Wear rates and wear 19. Evans, A. G. and Faber, K. T, Crack growth resistance of microc- mechanisms of alumina-based tools cutting steel at a low cutting racking brittle materials. J. Am. Ceram. Soc. 1984. 67.255-258 speed.earl997,208,67-72. S and Kleebe, H J, Microcracking in B. C-TnB2 composites. 3. Zhao, X, Liu, J, Zhu, B. et al., Wear behavior of Si3N4 ceramic J.Am. Ceran.Soc.1995,78,2374-2380. utting tool material against stainless steel in dry and water-lubricated 21. Brandt, G, Flank and crater wear mechanisms of Al, O3 based cutting onditions. Ceram. Int. 1999. 25. 309-315 tools when machining steel. Wear 1989. 112, 39-43 4. Xu, C. and AL, x, Multiphase tailoring and design of an advanced 22. Ettmayer, P, Kolaska, H, Lengauer, w. et al, Ti(C, N)cermets ceramic material. Key Eng. Maters. 2004, 259-260, 112-116 metallurgy and properties. Int J. Refract. Metals Hard Mater. 1995 15. Xu, C and Ai, X, Computer simulation of the densification kinetics 13,343-351 in the fabrication of ceramic composites with hot pressing technique. 23. Porat, R, New cutting materials based on titanium carbonitride Mod. Model. Meas. Control A 2001. 74. 45-54 Dev. Powder Metallurg. 1988, 19, 345-365
C. Xu / Journal of the European Ceramic Society 25 (2005) 605–611 611 9. Barry, J. and Byrne, G., Cutting tool wear in the machining of hardened steels—Part I: alumina/TiC cutting tool wear. Wear 2001, 247, 139–151. 10. Novak, S., Kalin, M. and Kosmac, T., Chemical aspects of wear of alumina ceramics. Wear 2001, 250, 318–321. 11. Lo Casto, S., Lo Valvo, E., Lucchini, E. et al., Ceramic materials wear mechanisms when cutting nickel-based alloys. Wear 1999, 225–229, 227–233. 12. Lo Casto, S., Lo Valvo, E., Lucchini, E. et al., Wear rates and wear mechanisms of alumina-based tools cutting steel at a low cutting speed. Wear 1997, 208, 67–72. 13. Zhao, X., Liu, J., Zhu, B. et al., Wear behavior of Si3N4 ceramic cutting tool material against stainless steel in dry and water-lubricated conditions. Ceram. Int. 1999, 25, 309–315. 14. Xu, C. and Ai, X., Multiphase tailoring and design of an advanced ceramic material. Key Eng. Maters. 2004, 259–260, 112–116. 15. Xu, C. and Ai, X., Computer simulation of the densification kinetics in the fabrication of ceramic composites with hot pressing technique. Model. Meas. Control A 2001, 74, 45–54. 16. Oh, Y.-S., Kim, C.-S., Lim, D.-S. et al., Fracture strengths and microstructures of Si3N4/SiC nanocomposites fabricated by in-situ process. Scripta Materialia 2001, 44, 2079–2081. 17. Tan, H. L. and Yang, W., Toughening mechanisms of nano-composite ceramics. Mech. Mater. 1998, 30, 111–123. 18. Rachman, C., Mechanical properties and microstructure of whisker reinforced Al2O3 matrix composite. J. Am. Ceram. Soc. 1989, 72, 1636–1640. 19. Evans, A. G. and Faber, K. T., Crack growth resistance of microcracking brittle materials. J. Am. Ceram. Soc. 1984, 67, 255–258. 20. Sigl, L. S. and Kleebe, H. J., Microcracking in B4C-TiB2 composites. J. Am. Ceram. Soc. 1995, 78, 2374–2380. 21. Brandt, G., Flank and crater wear mechanisms of Al2O3 based cutting tools when machining steel. Wear 1989, 112, 39–43. 22. Ettmayer, P., Kolaska, H., Lengauer, W. et al., Ti(C,N) cermets: metallurgy and properties. Int. J. Refract. Metals Hard Mater. 1995, 13, 343–351. 23. Porat, R., New cutting materials based on titanium carbonitride. Mod. Dev. Powder Metallurg. 1988, 19, 345–365
