Ceramics international 21(1995)317-323 Performance of laminated ceramic Composite Cutting Tools Maurice F Amateau, Bruce Stutzman, Joseph C. Conway Joseph Halloran The Pennsylvania State University, P O. Box 30, State College, PA 16804, USA Greenleaf Corporation, Seagertown, PA 16433, USA ( Received 31 October 1994: accepted 1 December 1994) Abstract Laminated ceramic composite cutting tools have been developed which demonstrate improvements in strength, toughness, and thermal shock resistance compared to the conventional non-laminated ceramic composites. Silicon carbide whisker and titanium carbide particulate reinforced ceramic matrix composites have been designed as multilayer structures and fabricated into cutting tool inserts for evaluation in machining tests. Laminated ceramic composite designs exhibited significantly better wear resistances, as well as improved mechanical strength and toughness. Successful designs were achieved by minimizing residual core tensile stress and interlaminar stress while maximizing the compressive residual stress on the contact surfaces. These designs minimized flank wear and chipping 1 INTRODUCTION The main limitations of ceramics for cutting tools is their low tensile strength, fracture toughness, Cutting tool materials must have high hardness impact resistance and thermal shock resistance and stiffness to resist deformation under the high These property limitations make ceramic cutting cutting forces exerted in machining operations. tools prone to premature failure by chipping, crack They must also possess high wear resistance to ing or edge failure. Various methods may be maintain sharp cutting edges and permit high employed to increase the impact resistance and frac machining accuracy over extended periods of ture toughness of ceramics; however, whisker tough- time. Long cutting tool life also requires high ten- ening is particularly effective. 2 The low toughness sile and compressive strength, fatigue resistance, and the thermal shock resistance of monolithie high temperature strength, chemical inertness, ceramics can be significantly improved by the incor high fracture toughness, impact resistance and poration of discontinuous reinforcements such as high thermal shock resistance silicon carbide whiskers. Whiskers improve the Ceramics possess many, but not all, of the desir- toughness and strength of the ceramics through ablc propcrtics rcquircd for cutting tools and have crack bridging, whisker pullout, crack deflection, some of the characteristics necessary to counteract microcracking and transformation toughening he principal wear mechanisIms. The principal The toughness and strength can also b dvantages of ceramic cutting tools are hardness, improved through the use of thermoelastically stiffness, high temperature strength, and chemical tailored surface residual compressive stresses tability at elevated temperatures. Chemical stabil- Surface residual compressive stresses can be incor ity is particularly important in minimizing rake porated into ceramic laminates upon cooling by face crater wear. Minimizing reactive type wear introducing low coefficient of thermal expansion permits higher cutting speeds, which lowers cut- layers to the surface of the material. The residual ting forces thus minimizing work piece distortion surface compressive stresses resist surface tensile High temperature strength of ceramics also retains stresses typically generated through bending. The tool hardness and minimizes abrasive wear during compressive stresses can also serve to effectively extended cutting operations blunt or close cracks in the material. 5, Ceramics international Printed in Great Britain 0272-8842/95/$9.50 @1995 Elsevier Science Limited, England and Techna S r I
Ceramics International 21 (1995) 3 1 l-323 Performance of Laminated Ceramic Composite Cutting Tools Maurice F. Amateau,B Bruce Stutzman,B Joseph C. Conwaya & Joseph Halloran” ’ The Pennsylvania State University, P.O. Box 30, State College, PA 16804, USA b Greenleaf Corporation, Seagertown, PA 16433, USA (Received 31 October 1994; accepted 1 December 1994) Abstract Laminated ceramic composite cutting tools have been developed which demonstrate improvements in strength, toughness, and thermal shock resistance compared to the conventional non-laminated ceramic composites. Silicon carbide whisker and titanium carbide particulate reinforced ceramic matrix composites have been designed as multilayer structures and fabricated into cutting tool inserts for evaluation in machining tests. Laminated ceramic composite designs exhibited significantly better wear resistances, as well as improved mechanical strength and toughness. Successful designs were achieved by minimizing residual core tensile stress and interlaminar stress while maximizing the compressive residual stress on the contact surfaces. These designs minimized flank wear and chipping. 1 INTRODUCTION Cutting tool materials must have high hardness and stiffness to resist deformation under the high cutting forces exerted in machining operations. They must also possess high wear resistance to maintain sharp cutting edges and permit high machining accuracy over extended periods of time. Long cutting tool life also requires high tensile and compressive strength, fatigue resistance, high temperature strength, chemical inertness, high fracture toughness, impact resistance and high thermal shock resistance. Ceramics possess many, but not all, of the desirable properties required for cutting tools and have some of the characteristics necessary to counteract the principal wear mechanisms. The principal advantages of ceramic cutting tools are hardness, stiffness, high temperature strength, and chemical stability at elevated temperatures. Chemical stability is particularly important in minimizing rake face crater wear. Minimizing reactive type wear permits higher cutting speeds, which lowers cutting forces, thus minimizing work piece distortion. High temperature strength of ceramics also retains tool hardness and minimizes abrasive wear during extended cutting operations. The main limitations of ceramics for cutting tools is their low tensile strength, fracture toughness, impact resistance and thermal shock resistance. These property limitations make ceramic cutting tools prone to premature failure by chipping, cracking or edge failure. Various methods may be employed to increase the impact resistance and fracture toughness of ceramics; however, whisker toughening is particularly effective.‘,2 The low toughness and the thermal shock resistance of monolithic ceramics can be significantly improved by the incorporation of discontinuous reinforcements such as silicon carbide whiskers. Whiskers improve the toughness and strength of the ceramics through crack bridging,3 whisker pullout, crack deflection, microcracking and transformation toughening.4 The toughness and strength can also be improved through the use of thermoelastically tailored surface residual compressive stresses. Surface residual compressive stresses can be incorporated into ceramic laminates upon cooling by introducing low coefficient of thermal expansion layers to the surface of the material. The residual surface compressive stresses resist surface tensile stresses typically generated through bending. The compressive stresses can also serve to effectively blunt or close cracks in the material.5,6 317 Ceramics International Printed in Great Britain 0272-8842/95/$9.50 01995 Elsevier Science Limited, England and Techna S.r.1
318 M. F. Amateau, B. Stutzman, J. C. Conway, J. Halloran Whisker-reinforced ceramics also exhibit Malakoff Industries Inc. The Sic whiskers were improved wear resistance compared to unrein- obtained from Advanced Composite Materials forced ceramics. The tribological characteristics of Corporation, Greenville Sc monolithic ceramics can be improved through the addition of wear resistant surface layers such as 3 LAMINATE DESIGN SiN. sialON, or TiC. In the current art of man facturing whisker-reinforced ceramic cutting Modified classical plate laminate theory was used tools, the matrix ceramic and the whiskers are to thermoelastically tailor the laminate design to pre-blended and hot pressed to form the densified optimize the residual stresses, toughness and the tool insert body. This method provides very little tribological performance. Thermoelastic properties control over the distribution and orientation of of lamina materials used for laminate properties the whisker reinforcements in the final tool body. calculations were obtained from manufacturer Another significant limitation to the current supplied data when available. For composites method of manufacturing of whisker-reinforced where such data were not available the lamina ceramic cutting tools is the cost of the silicon car- properties were calculated from constituent data bide whiskers. Whiskers cost 10 times that of the using the Halpin-Tsai method. 8.9 A summary of common matrix materials; hence, material designs lamina properties is given in Table 2 and manufacturing methods suitable for cost The designs used in this study are considered ffective cutting tools, are required. Manufactur- hybrid composites by conventional laminate ter ing method and material designs for ceramic cut- minology since they use multiple compositions ting tools, that make efficient use of the minimum within a single laminate. Some of the designs used amount of reinforcing whiskers to minimize cost, pure alumina surface layers to provide chemically are the ultimate goals of this research inert material on the rake face, while other designs used titanium carbide and silicon carbide rein 2 MATERIALS forcement alumina on this surface. The individual layers in all designs were arranged symmetrically Composites were fabricated using either Al2O, or with respect to the mid-plane to eliminate in-plane Si3N4 as the matrix with TiC particulate, TiN par- and out-of-plane coupling of stresses and deflec ticulate, or SiC whisker reinforcements. A list of tions. Laminate designs have been selected to these materials and their designation is given in avoid large tensile stresses within the lamina and Table 1. The osition amounts given in this large differences in stresses between lamina to table are in percent. The alumina powers, minimize delamination. All designs except GX-06 grade RC-HPBM containing 0-05% MgO, with a and GX-08 use compressive stresses on the outer article size of 34 um were obtained from surfaces Table 1. Materials used in this program Composition Designation Source 30SiCw-70 Al2O3 NG-300 Grccnlcaf Corporation 26TiCp-79Al2O HC-2 NTK Corporation 17TiNp-83S RD3905 Greenleaf Corporation 17TiNp-83Si3N NTK Corporation TiCp-Al203 5 layer laminate #1 Gx-06 Penn State University TiCp-Al2O3 5 layer laminate #2 GX-08 Penn State University TiCp-Al2O3 3 layer laminate GX-20 Penn State University SiCw-AL2O3 7 layer laminate Penn State University SiCw-AL2O3 5 layer laminate DX-13 Penn State University Table 2. Lamina properties used to calculate laminate properties Material Elastic modulus Poisson's ratio Shear modulus Coefficient of thermal (GPa) expansion(10/C) 159 792 5SiCw/95Alumina 160 10SiCw/90Alumina 772 20SiCw/80Alumin 165 26TiC/74Alumina 022
318 M, F. Amateau, B. Stutzman, J. C. Conway, J. Halloran Whisker-reinforced ceramics also exhibit improved wear resistance compared to unreinforced ceramics. The tribological characteristics of monolithic ceramics can be improved through the addition of wear resistant surface layers such as S&N,, SiAlON, or TiC.7 In the current art of manufacturing whisker-reinforced ceramic cutting tools, the matrix ceramic and the whiskers are pre-blended and hot pressed to form the densified tool insert body. This method provides very little control over the distribution and orientation of the whisker reinforcements in the final tool body. Another significant limitation to the current method of manufacturing of whisker-reinforced ceramic cutting tools is the cost of the silicon carbide whiskers. Whiskers cost 10 times that of the common matrix materials; hence, material designs and manufacturing methods suitable for cost effective cutting tools, are required. Manufacturing method and material designs for ceramic cutting tools, that make efficient use of the minimum amount of reinforcing whiskers to minimize cost, are the ultimate goals of this research. Malakoff Industries Inc. The SIC whiskers were obtained from Advanced Composite Materials Corporation, Greenville S.C. 3 LAMINATE DESIGN Modified classical plate laminate theory was used to thermoelastically tailor the laminate design to optimize the residual stresses, toughness and the tribological performance. Thermoelastic properties of lamina materials used for laminate properties calculations were obtained from manufacturer supplied data when available. For composites where such data were not available the lamina properties were calculated from constituent data using the Halpin-Tsai method.8,9 A summary of lamina properties is given in Table 2. 2 MATERIALS Composites were fabricated using either Al,O, or S&N, as the matrix with TiC particulate, TIN particulate, or SIC whisker reinforcements. A list of these materials and their designation is given in Table 1. The composition amounts given in this table are in volume percent. The alumina powers, grade RC-HPBM containing 0.05% MgO, with a particle size of 34 pm were obtained from The designs used in this study are considered hybrid composites by conventional laminate terminology since they use multiple compositions within a single laminate. Some of the designs used pure alumina surface layers to provide chemically inert material on the rake face, while other designs used titanium carbide and silicon carbide reinforcement alumina on this surface. The individual layers in all designs were arranged symmetrically with respect to the mid-plane to eliminate in-plane and out-of-plane coupling of stresses and deflections. Laminate designs have been selected to avoid large tensile stresses within the lamina and large differences in stresses between lamina to minimize delamination. All designs except GX-06 and GX-08 use compressive stresses on the outer surfaces. Table 1. Materials used in this program Composition ~OSICW-70 AI,O, 26TiCp79Al,03 17TiNp-83Si3N, 17TiNp-83Si,N, TiCp-Al,O, 5 layer laminate #I TiCp-A&O, 5 layer laminate #2 TiCp-Al,O, 3 layer laminate SiCw-Al,O, 7 layer laminate SiCw-Al,O, 5 layer laminate Designation WG-300 HC-2 RD-3905 sx-5 GX-06 GX-08 GX-20 DX-14 DX-13 Source Greenleaf Corporation NTK Corporation Greenleaf Corporation NTK Corporation Penn State University Penn State University Penn State University Penn State University Penn State University Table 2. Lamina properties used to calculate laminate properties Material Alumina 5SiCw/95Alumina lOSiCw/90Alumina 20SiCw/80Alumina 26Ti074Alumina Elastic modulus (GPaI 390 392 395 400 395 Poisson’s ratio 0.23 0.23 0.22 0.22 0.22 Shear modulus Coefficient of thermal (GPaI expansion (lO?C) 159 7.92 160 7.72 161 7.54 165 7.16 162 8.10
Ceramic composite cutting tools Table 3. Residual stresses in hybrid laminate designs Table 4. Slurry formulations for tape cast surface layers Design Composition Thickness Stress x Stress y Composition Toluene (mm (MPa) (MPa) olume fraction fraction fraction GX-06 AlO 306 306 6TiCp-Al2O3 3.49 A 0220 0.171 064 30630 5SIC/ALO 10Sc/Al2O30211 Gx-08 Al2O 0.25 03 0·20 0.246 TICp-A 425 30SiC/A 20 0.171 0307 0.25 365 26TiC/ALO 0.210 0619 0.171 GX-20 26TICp-Al20 025 425 26TiCp-AI2O 025 365 prised of ceramic powder, organic polymer, and DX-13 10SiCw-AL,O 005 135 solvent. The composition of the slurry provided 20SiCw-Al2O3 0-30 -335 the required rheological pre 5SiCw-AI2O3 20SiCw-Al2O3 0.30 335 well as flexibility for handling and shaping of the 10SICW-Al2O3 0.05 dried tape. As much as 20 vol% of the unfired laminate was composed of organic additives that Dx-1410scwA2O30.13 20SiCW-ALO 019 262 must be removed by thermal decomposition or 10scW-Al2O30.19 oxidation prior to high temperature densification 5SICW-Al2O3 3 The high temperature densification step was per 10SiCw-Al2O formed by hot pressing at 1750C 20SiCw-AlzO -262 267 10ScW-A2O30.13 The processing techniques normally use producing multilayer laminated ceramic compos ites were modified in these studies to simplify manufacturing and decrease production time. The The laminate configurations and their residual previous techniques used tape cast materials to stress distributions are given in table 3. The form the entire specimen. This procedure was time designs were restricted to odd-number plies consuming due to the time needed for tape cast- between three and seven. The center ply consti- ing, cutting and laminating many plies. Long peri tuted 60-90% of the total thickness. Designs des- ods were also required to burn out the organic ignated GX-06, GX-08 and GX-20 contain Tic matter prior to hot pressing. Tape casting is still particulate-reinforced alumina (Greenleaf Corp. used to form the thin outer layers; however, direct grade GEM 2), while designs designated DX-13 dry powder filling was used to form the thick core and DX-14 contain SiC whisker-reinforced alu- This processing change reduced the number of mina. Designs GX-06 and gX-08 have pure tape cast layers that needed to be cut and lam alumina outer surfaces to minimize erosion by nated from eighty to twenty. This also allowed the eliminating carbides from the rake face contact intermediate binder burnout step to be eliminated surface. This design, however, results in a residual since the small amount of binder contained in the tensile stress in the outer alumina layer. Design outer layers can be burned out during the hot GX-20 produces compressive stresses in the outer pressing cycle. This process was used to produce layer but exposes the carbide containing material nine ceramic tiles 50.8 mm X 50.8 mm X 4. 76 to erosion wear. Designs DX-13 and DX-14 were mm, designated as DX-13, DX-14, GX-06, GX- selected to minimize the carbide content of the 08. and CX-20. with a maximum thickness varia outer surface while still resulting in surface com- tion of 0. 254 mm pressive residual stresses Tape casting slurry mixtures for AlO3, SICwAl2O3 nd TiC/AlO3 were optimized to provide the 4 SPECIMEN FABRICATION proper rheological properties necessary for tape casting while producing a high quality, easily The outer surface layers of the laminated ceramic handled tape 0. 127 mm thick with excellent uni structures were fabricated by tape casting. Individ formity. Slurry formulations are given in Table 4 ual tapes of 0.102-0. 152 mm thick and up to 76 mm wide were deposited continuously onto a car- 5 TESTING AND CHARACTERIZATION rier tape under a spreading blade(Doctor Blade) from which they were separated after drying. The In order to verify the residual stress calculations tapes were cast from a formulated slurry com- and the processing techniques, one of the spe
Ceramic composite cutting tools 319 Table 3. Residual stresses in hybrid laminate designs Table 4. Slurry formulations for tape cast surface layers Design Composition Thickness Stress x Stress y (mm) (MPa) (MPa) GX-06 AI,O, 26TiCp-A120, A1203 GX-08 AI,O, 26TiCp-A120, AI203 0.64 306 306 3.49 -110 -110 0.64 306 306 0.25 365 365 4.25 -44 -44 0.25 365 365 GX-20 26TiCp-AI,O, AI203 26TiCp-AI,O, 0.25 -365 -365 4.25 44 44 0.25 -365 -365 DX-13 IOSiCw-Al,O, 0.05 -135 -81 20SiCw-A1203 0.30 -364 -335 5SiCw-AI,O, 4.03 54 48 2OSiCw-A120, 0.30 -364 -335 IOSiCw-Al,O, 0.05 -135 -81 DX-14 1 OSiCw-Al,O, 0.13 -34 -12 ~OSICW-A1203 0.19 -262 -267 IOSICW-A&O3 0.19 -34 -12 5SiCw-A120, 3.75 127 117 IOSiCw-A120, 0.19 -34 -12 20SiCw-A1203 0.19 -262 -267 IOSICW-AI~O~ 0.13 -34 -12 The laminate configurations and their residual stress distributions are given in Table 3. The designs were restricted to odd-number plies between three and seven. The center ply constituted 60-90% of the total thickness. Designs designated GX-06, GX-08 and GX-20 contain TIC particulate-reinforced alumina (Greenleaf Corp. grade GEM 2), while designs designated DX-13 and DX-14 contain Sic whisker-reinforced alumina. Designs GX-06 and GX-08 have pure alumina outer surfaces to minimize erosion by eliminating carbides from the rake face contact surface. This design, however, results in a residual tensile stress in the outer alumina layer. Design GX-20 produces compressive stresses in the outer layer but exposes the carbide containing material to erosion wear. Designs DX-13 and DX- 14 were selected to minimize the carbide content of the outer surface while still resulting in surface compressive residual stresses. 4 SPECIMEN FABRICATION The outer surface layers of the laminated ceramic structures were fabricated by tape casting. Individual tapes of 0.102-O. 152 mm thick and up to 76 mm wide were deposited continuously onto a carrier tape under a spreading blade (Doctor Blade) from which they were separated after drying. The tapes were cast from a formulated slurry comComposition A1203 5SiC/A1203 10SiC/A1203 20SiC/A1203 30SiC/A1203 26TiC/A1203 Solid Binder Toluene volume volume volume fraction fraction fraction 0.220 0.609 0.171 0.219 0.594 0.187 0.211 0.583 0.206 0.200 0.554 0.246 0.171 0.521 0.307 0.210 0.619 0.171 prised of ceramic powder, organic polymer,” and solvent. The composition of the slurry provided the required rheological properties for casting, as well as flexibility for handling and shaping of the dried tape. As much as 20 ~01% of the unfired laminate was composed of organic additives that must be removed by thermal decomposition or oxidation prior to high temperature densification. The high temperature densification step was performed by hot pressing at 1750°C. The processing techniques normally used for producing multilayer laminated ceramic composites were modified in these studies to simplify manufacturing and decrease production time. The previous techniques used tape cast materials to form the entire specimen. This procedure was time consuming due to the time needed for tape casting, cutting and laminating many plies. Long periods were also required to burn out the organic matter prior to hot pressing. Tape casting is still used to form the thin outer layers; however, direct dry powder filling was used to form the thick core. This processing change reduced the number of tape cast layers that needed to be cut and laminated from eighty to twenty. This also allowed the intermediate binder burnout step to be eliminated, since the small amount of binder contained in the outer layers can be burned out during the hot pressing cycle. This process was used to produce nine ceramic tiles 50.8 mm X 50.8 mm X 4.76 mm, designated as DX-13, DX-14, GX-06, GX- 08, and CX-20, with a maximum thickness variation of 0.254 mm. Tape casting slurry mixtures for Al,03, SiC,JA&O,, and TiC/Al,O, were optimized to provide the proper rheological properties necessary for tape casting while producing a high quality, easily handled tape 0.127 mm thick with excellent uniformity. Slurry formulations are given in Table 4. 5 TESTING AND CHARACTERIZATION In order to verify the residual stress calculations and the processing techniques, one of the speci-
320 M. F. Amateau, B. Stutzman ,J. C. Conway, halloran mens, designated as DX- 14, was machined into 4 the most aggressive of all cutting configurations test bars 4.76 mm x 6-35 mm x 50-8 mm for The performance of the laminated ceramics was material property characterization. The four test compared to the performance of other typic ound and the edges chamfered te ceramic cutting tools. The testing parameters. 0.762 mm. The corners were finished to 0-0635 the standard tool life tests are given in table 5 mm radius to minimize the stress concentrations The remaining plate was machined into cutting 6. 1 Cutting tests against 718 superalloy tool specimens 12.7 mm x 12 7 mm X 4. 76 mm The density of the DX-14 specimens was mea- Four cutting tool materials were evaluated against sured using Archimedes' principle with water as 718 nickel based superalloy: two grades of TiN the liquid medium. The measured value of 3 88 reinforced Si,N4(SX-5 and RD-3905), one grade g/cc was within 2% of the expected density for of conventional Sic whisker-reinforced alu fully solid material. A four-point bend test with a mina(wG300)and one grade of laminated Sic major span of 31.7 mm, minor span of 15 875 whisker reinforced alumina(DX-14). Four sepa mm,and loading rate of 0.51 in/min was used to rate cutting operations were performed on a 718 measure the modulus of rupture(MOR) of the superalloy billet. The first operation removed DX-14 material. The elastic modulus of this mate- approximately 4 mm of material from a 159 mm rial was measured using a dynamic resonance diameter billet. The second cutting operation technique. The clastic moduli and MOR values removed 2.0 mm of material from the remaining for an average of four tests were 380 GPa and 577 152 mm diameter billet using unused tools of the MPa, respectively same composition as in the first cutting operation The elastic modulus results are within 2% of the The third cutting operation removed 6 mm from rule-of-mixtures(ROM)calculations. The strength the 141 mm diameter billet with a new WG-300 of the DX- 14 laminate is about 8% greater than cutting tool. The last cutting operation removed would be expected for monolithic silicon carbide 2.0 mm from a 133 mm diameter billet using new whisker-reinforced alumina Density measurements SX-5, DX-14 and rD-3905 cutting tools. Flank on the DX-14 material indicate at least 98% of wear in the nose region and in the depth-of-cut theoretical density was obtained during fabrica- region were measured and are referred to as nose tion of this specimen. This indicates that the hot and notch wear, respectively. The average wear pressing parameters are sufficient for complete rates measured after the first cutting operation are densification The agreement between elastic modu- given in Table 6 lus measurements and ROM predictions indicates that good bonding between fiber reinforcement Table 6. Wear rates for cutting tool materials against and matrix was achieved 718 nickel based su Average wear rate for Average wear rate fo 6 WEAR PERFORMANCE TESTS material nose wear(mm/min) notch wear(mm/min) RDC-3905 0.178 0.051 The ceramic tiles were cut into cutting tool specimens sx-5 0.117 0.127 127mm×127mm×476 mm and tested for DX-14 0.053 0127 cutting performance by measuring nose and either WG-300 0.046 0300 notch or flank wear rate versus cutting time. The insert style of the cutting tools used was Greenleaf Corporation Style SNGN-433. The cutting tool specimens were tested against either Inconel 718 superalloy or 4340 steel in lathing operation using 0.75 a negative rake angle configuration. The negative rake angle configuration was chosen because it is 0.50 Table 5. Testing parameters for the standard tool life tests 025 Material Allvac 718 superalloy AlsI 4340 steel Hardness(Rc) 45678 015 213 Depth of cut (mm) 19 Fig. 1. Nose wear of ceramic composite cutting tools against 718 nickel based superalloy
320 AI. F. Amateau, B. Stutzman, J. C. Conway, J. Halloran mens, designated as DX-14, was machined into 4 test bars 4.76 mm X 6.35 mm X 50.8 mm for material property characterization. The four test bars were ground and the edges chamfered to 0.762 mm. The corners were finished to 0.0635 mm radius to minimize the stress concentrations. The remaining plate was machined into cutting tool specimens 12.7 mm X 12.7 mm X 4.76 mm. The density of the DX- 14 specimens was measured using Archimedes’ principle with water as the liquid medium. The measured value of 3.88 g/cc was within 2% of the expected density for fully solid material. A four-point bend test with a major span of 31.7 mm, minor span of 15.875 mm, and loading rate of 0.51 in/min was used to measure the modulus of rupture (MOR) of the DX-14 material. The elastic modulus of this material was measured using a dynamic resonance technique. The elastic moduli and MOR values for an average of four tests were 380 GPa and 577 MPa, respectively. the most aggressive of all cutting configurations. The performance of the laminated ceramics was compared to the performance of other typical ceramic cutting tools. The testing parameters for the standard tool life tests are given in Table 5. 6.1 Cutting tests against 718 superalloy The elastic modulus results are within 2% of the rule-of-mixtures (ROM) calculations. The strength of the DX-14 laminate is about 8% greater than would be expected for monolithic silicon carbide whisker-reinforced alumina. Density measurements on the DX-14 material indicate at least 98% of theoretical density was obtained during fabrication of this specimen. This indicates that the hot pressing parameters are sufficient for complete densification The agreement between elastic modulus measurements and ROM predictions indicates that good bonding between fiber reinforcement and matrix was achieved. Four cutting tool materials were evaluated against 718 nickel based superalloy: two grades of TiN reinforced S&N, (SX-5 and RD-3905), one grade of conventional SiC whisker-reinforced alumina (WG300) and one grade of laminated Sic whisker reinforced alumina (DX-14). Four separate cutting operations were performed on a 718 superalloy billet. The first operation removed approximately 4 mm of material from a 159 mm diameter billet. The second cutting operation removed 2.0 mm of material from the remaining 152 mm diameter billet using unused tools of the same composition as in the first cutting operation. The third cutting operation removed 6 mm from the 141 mm diameter billet with a new WG-300 cutting tool. The last cutting operation removed 2.0 mm from a 133 mm diameter billet using new SX-5, DX-14 and RD-3905 cutting tools. Flank wear in the nose region and in the depth-of-cut region were measured and are referred to as nose and notch wear, respectively. The average wear rates measured after the first cutting operation are given in Table 6. Table 6. Wear rates for cutting tool materials against 718 nickel based superalloy 6 WEAR PERFORMANCE TESTS The ceramic tiles were cut into cutting tool specimens 12.7 mm X 12.7 mm i< 4.76 mm and tested for cutting performance by measuring nose and either notch or flank wear rate versus cutting time. The insert style of the cutting tools used was Greenleaf Corporation Style SNGN-433. The cutting tool specimens were tested against either Inconel 718 superalloy or 4340 steel in lathing operation using a negative rake angle configuration. The negative rake angle configuration was chosen because it is Tool Average wear rate for Average wear rate for material nose wear (mm/min) notch wear (mm/min) RDC-3905 0.178 0.051 sx-5 0.117 0.127 DX-14 0.053 0.127 WG-300 0.046 0.300 1.00 l WG-300 Table 5. Testing parameters for the standard tool life tests Material Allvac 718 superalloy AISI 4340 steel Hardness (Rc) Coolant Feed (mm/rev.) Speed (m/min) Depth of cut (mm) 42 28132 Yes No 0.15 0.25 213 457 I.0 1.9 I 012345678 Cutting Time, min. Fig. 1. Nose wear of ceramic composite cutting tools against 718 nickel based superalloy
Ceramic composite cutting tools 321 also be seen in this figure. The nose wear for the Sic whisker composites WG-300 and DX-14 are all low compared to the tin reinforced Si,N4 1,25 materials(SX-5 and RD3905) for all subsequent cutting operations 6. 2 Cutting tests against 4340 steel 是a° One commercially available conventional Tic-alt mina cutting tool and various TiC-alumina lami 2345678 nated designs and one Sic whisker/alumina design Cutting Time, min were tested against 4340 steel. In these tests, each Fig. 2. Notch wear of ceramic composite cutting tools against of the eight corners of the cutting tool were sub- 718 nickel based superalloy jected to increasing cutting times. Figure 4 shows a comparison of nose wear for the conventional and laminated TiC/alumina composite and a lami Figures 1 and 2 compare the nosc and notch nated Sic whisker/alumina cutting tool material wear,respectively, for monolithic materials, wG. The nose wear data for these tests appear to fall 300, SX-5 and RD-3905, with the laminated into three groups. The TiC/alumina composite ceramic design DX-14 during the first cuttin laminate designs GX-06 and GX-08 have the operation. Both tin reinforced Si3N4 composi- highest wear rates, while the design GX-20 has the tions, SX-5 and RD3905, exhibited significantly lowest wear rate. The former two designs use alu greater wear than either the monolithic SiC mina on the outer surface which results in a resid- whisker-reinforced alumina, WG-300, or the lami- ual tensile stress in that layer. The latter nated SiC whisker/alumina hybrid design, DX-14, uses TiCp-alumina as the outer layer and for up to 5.7 minutes of cutting. The DX-14 speci- in a substantial residual compressive stress. The men experienced chipping at 6.7 minutes of cut- conventional TiCp-alumina cutting tool material ting. The notched wear of these materials during has a wear rate between these two design this operation (Fig. 2) did not follow the same The results of these tests indicate that the cut order of wear resistance as did the nosc wcar. In ting performance of ceramic cutting tools is infl- this case, the SX-5 material had the best wear uenced by the state of residual stress in the performance while the wG-300 had the poorest. material. a typical wear surface is shown for lami Both WG-300 and DX-14 chipped after 4.7 min- nate design GX-20 in Fig. 5. Both the wear land utes of cutting in the nose area and in the fank area are similar The chipping in the depth-of-cut notch region is Er rrosive wear is seen to extend from the depth-of clearly seen in Fig 3. The chipping on the rake cut notch to the nose area on the rake face.A face near the nose region of the cutting tool can laminated Sic-alumina design(DX-13)cutting tool was also tested against 4340 steel. The wear surface for this cutting tool is shown in Fig.6 The low flank and nose wear for this tool design is EEz 00LLLL 01234567 Fig. 3. SEM photograph of laminated SiC/alumina(DX-14) Fig. 4. Nose wear of various laminated ceramic composites cutting tool showing large chip near the depth-of-cut region against 4340 steel
Ceramic composite cutting tools 321 c A E 1.25 DX-14 v RD-3905 i I 012345678 Cutting Time, min. Fig. 2. Notch wear of ceramic composite cutting tools against 71X nickel based superalloy. Figures 1 and 2 compare the nose and notch wear, respectively, for monolithic materials, WG- 300, SX-5 and RD-3905, with the laminated ceramic design DX-14 during the first cutting operation. Both TIN reinforced S&N, compositions, SX-5 and RD3905, exhibited significantly greater wear than either the monolithic Sic whisker-reinforced alumina, WG-300, or the laminated SIC whisker/alumina hybrid design, DX-14, for up to 5.7 minutes of cutting. The DX-14 specimen experienced chipping at 6.7 minutes of cutting. The notched wear of these materials during this operation (Fig. 2) did not follow the same order of wear resistance as did the nose wear. In this case, the SX-5 material had the best wear performance while the WG-300 had the poorest. Both WG-300 and DX-14 chipped after 4.7 minutes of cutting. The chipping in the depth-of-cut notch region is clearly seen in Fig. 3. The chipping on the rake face near the nose region of the cutting tool can Fig. 3. SEM photograph of laminated SKYalumina (DX-14) cutting tool showing large chip near the depth-of-cut region. also be seen in this figure. The nose wear for the Sic whisker composites WG-300 and DX-14 are all low compared to the TiN reinforced S&N, materials (SX-5 and RD3905) for all subsequent cutting operations. 6.2 Cutting tests against 4340 steel One commercially available conventional TiC-alumina cutting tool and various Tic-alumina laminated designs and one SIC whisker/alumina design were tested against 4340 steel. In these tests, each of the eight corners of the cutting tool were subjected to increasing cutting times. Figure 4 shows a comparison of nose wear for the conventional and laminated Tic/alumina composite and a laminated Sic whisker/alumina cutting tool material. The nose wear data for these tests appear to fall into three groups. The Tic/alumina composite laminate designs GX-06 and GX-08 have the highest wear rates, while the design GX-20 has the lowest wear rate. The former two designs use alumina on the outer surface which results in a residual tensile stress in that layer. The latter design uses TiCp-alumina as the outer layer and results in a substantial residual compressive stress. The conventional TiCp-alumina cutting tool material has a wear rate between these two designs. The results of these tests indicate that the cutting performance of ceramic cutting tools is influenced by the state of residual stress in the material. A typical wear surface is shown for laminate design GX-20 in Fig. 5. Both the wear land in the nose area and in the flank area are similar. Errosive wear is seen to extend from the depth-ofcut notch to the nose area on the rake face. A laminated Sic-alumina design (DX-13) cutting tool was also tested against 4340 steel. The wear surface for this cutting tool is shown in Fig. 6. The low flank and nose wear for this tool design is 2 0.2 2 . HC-2 : 0.1 :;I;; v GX-06 + DX-13 0.0 - 01234567 Cutting Time, min. Fig. 4. Nose wear of various laminated ceramic composites against 4340 steel
M. F. Amateau, B. Stutzman, J C. Conway, J. Halloran performed in this work provide a reasonable indi cation of the effect of laminate tailoring The design concept is to avoid large differences in residual stress between layers while still provid ing reasonable compressive stresses in the outer layer (i.e. the rake fac large number of different layer composite demonstrated in the design Dx-14. The residual stress criteria, however, may be in confict with the need to minimize wear and erosion resistance hence, some designs that contained tensile stresses in their outer layer were evaluated (e.g. GX-06 and GX-08) The results of this study showed that both com- position and residual stress patterns affected the ig. 5. Wear surface of laminated TiCp-alumina cutting tool cutting tool performance. The SiCw-alumina cut GX-20) ng tool compositio to nose wear than TiCp-alumina compositions for cutting nickel based superalloy 718. The conven tional SiCw-alumina composition, however, is not as resistant to notch wear as the TiNp- Si3N4 tool materials. Low notch wear was however retained for the laminated version of the sicw-alumina cutting tool. The lamination process which produces surface compressive stresses results in ceramic cutting tool materials with improved wear performance compared to laminated designs which produce surface tensile stresses. The laminated design with surface compositions similar to the howed supers compared to the conventional tool material design REFERENCES Fig. 6. Wear surface of laminated SiCw-alumina cutting tool (DX-13) 1. beCheR, P, f. WEl G. c Sic-whisker-reinforced alumina Toughening raisin ite obvio this figure. However, there 2. WEL,G. C.& BECHER, P. F,, Development of Sic- whisker reinforced ceramics. Amer. Ceram. Soc. BulL. 64 appears to be cracking in the bottom of the crater (2)(1985)298-304 wear scar on the rake face These cracks are con 3. BECHER, P. F, HSUEH, C. H. anGelini, P. fined to the surface layer and are terminated before TIEGS, T.N., Theoretical and experimental analysis of the toughening behavior of whisker reinforcemen they reach the region of residual tensile tress ceramic matrix compo Mater. Sci. Eng, 107(1989) 257-59 7 DISCUSSION AND CONCLUSIONS RICE, R. W, Toughening in ceramic l1(7-8) The objective of these experiments was to deter- 5. AMATEAU, M. F, Propertie mine if thermoelastic and wear properties could be Conf. Proc., ed. D. J. Viechnicki. Materials Tecl optimized by laminate design to improve cutting Laboratory, Watertown, MA, October 1990, pp tool performance. The tool wear in actual cutting 6. AMATEAU, M. F.& MESSIl operations plex phenomenon, whi Ceramic. In International Encyclopedia of Composites, among other things, depends upon the homogeneity vol3, ed S M. Lee vCH, New York, 1990, pp 11-16 7. KASUMURA, Y, FUKATSU, t.& KOBAYASHI of the metal being cut and the distribution of flaws A, Effects of TiC content and grain size on cutting in the cutting tool. For these reasons, standard formance of AlOx-TiC ceramic tools. Trib. Trans., 36 cutting tool tests normally produce large amounts 8. HALPIN.J. C. KARDoS.J. L. The Halpin-tsai of scatter. Nevertheless, the results of the tests equations: A Review. Polymer Eng. Sci, 16(1976)344-52
322 Fig. 5. Wear surface of laminated TiCpalumina cutting tool (GX-20). M. F. Amateau, B. Stutzman, J. C. Conway, J. Halloran performed in this work provide a reasonable indication of the effect of laminate tailoring. The design concept is to avoid large differences in residual stress between layers while still providing reasonable compressive stresses in the outer layer (i.e. the rake face surface). This may require a large number of different layer compositions as demonstrated in the design DX-14. The residual stress criteria, however, may be in conflict with the need to minimize wear and erosion resistance; hence, some designs that contained tensile stresses in their outer layer were evaluated (e.g. GX-06 and GX-08). The results of this study showed that both composition and residual stress patterns affected the cutting tool performance. The SiCw-alumina cutting tool compositions exhibited greater resistance to nose wear than TiCp-alumina compositions for cutting nickel based superalloy 718. The conventional SiCw-alumina composition, however, is not as resistant to notch wear as the TiNp-S&N, tool materials. Low notch wear was, however, retained for the laminated version of the SiCw-alumina cutting tool. The lamination process which produces surface compressive stresses results in ceramic cutting tool materials with improved wear performance compared to laminated designs which produce surface tensile stresses. The laminated design with surface compositions similar to the composition showed superior wear performance compared to the conventional tool material design. REFERENCES Fig. 6. Wear surface of laminated SiCw-alumina cutting tool (DX-13). quite obvious in this figure. However, there appears to be cracking in the bottom of the crater wear scar on the rake face. These cracks are confined to the surface layer and are terminated before they reach the region of residual tensile tress. 7 DISCUSSION AND CONCLUSIONS The objective of these experiments was to determine if thermoelastic and wear properties could be optimized by laminate design to improve cutting tool performance. The tool wear in actual cutting operations is a complex phenomenon, which, among other things, depends upon the homogeneity of the metal being cut and the distribution of flaws in the cutting tool. For these reasons, standard cutting tool tests normally produce large amounts of scatter. Nevertheless, the results of the tests 1. 2. 3. 4. 5. 6. 7. 8. BECHER, P. F. & WEI, G. C., Toughening behavior in Sic-whisker-reinforced alumina. J. Amer. Ceram. Sot., 67 (12) (1984) C276-C269. WEI, G. C. & BECHER, P. F., Development of SiCwhisker reinforced ceramics. Amer. Ceram. Sot. Bull., 64 (2) (1985) 298-304. BECHER, P. F., HSUEH, C. H., ANGELINI, P. & TIEGS, T. N., Theoretical and experimental analysis of the toughening behavior of whisker reinforcement in ceramic matrix composites. Mater. Sci. Eng., 107 (1989) 257-59. RICE, R. W., Toughening in ceramic particulate and whisker composites. Ceram. Eng. Sci. Proc., 11 (7-8) (1990) 667-94. AMATEAU, M. F., Properties of laminated ceramic composites. 37th Sagmore Army Materials Research Conf Proc., ed. D. J. Viechnicki. Materials Technology Laboratory, Watertown, MA, October 1990, pp. 317-38. AMATEAU, M. F. & MESSING, G. L., Laminates, Ceramic. In International Encyclopedia of Composites, Vol. 3., ed. S. M. Lee. VCH, New York, 1990, pp. 11-16. KASUMURA, Y., FUKATSU, T. & KOBAYASHI, M., Effects of TIC content and grain size on cutting performance of Al,O,-TiC ceramic tools. Trib. Trans., 36 (1) (1993) 43-8. HALPIN, J. C. & KARDOS, J. L., The Halpin-Tsai equations: A Review. Polymer Eng. Sci., 16 (1976) 344-52
Ceramic composite cutting tools 323 hALPIN. J C. tSAl s w. Environmental factors in 10. WALKER, w.J.& REED, J, Polyethylene glycol composite materials. Laboratory Report, AFML-TRG7 binders for advanced ceramics Ceram. Engng 14(11-12)(1993)5879
Ceramic composite cutting tools 323 9. HALPIN, J. C. & TSAI, S. W., Environmental factors in composite materials. Laboratory Report, AFML-TRG7- 473, June 1969. 10. WALKER, W. J. & REED, J., Polyethylene glycol binders for advanced ceramics. Ceram. Engng. Sci. Proc., 14 (11-12) (1993) 58-79