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 speCeramic 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 consti￾tuted 60-90% of the total thickness. Designs des￾ignated 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 alu￾mina. 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 com￾pressive residual stresses. 4 SPECIMEN FABRICATION The outer surface layers of the laminated ceramic structures were fabricated by tape casting. Individ￾ual tapes of 0.102-O. 152 mm thick and up to 76 mm wide were deposited continuously onto a car￾rier tape under a spreading blade (Doctor Blade) from which they were separated after drying. The tapes were cast from a formulated slurry com￾Composition 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 per￾formed by hot pressing at 1750°C. The processing techniques normally used for producing multilayer laminated ceramic compos￾ites 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 cast￾ing, cutting and laminating many plies. Long peri￾ods 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 lami￾nated 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 varia￾tion 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 uni￾formity. 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-