D.-H. Kuo, W.M. Kriven/ Materials Science and Engineering A210(1996)123-1.34 Powder+dispersant annealed at 1500C for 6 h and on LP/A laminates (ball mill for 48 hrs) Shurry compositions: annealed at 1250C for 6 h Lower annealing tempera- tures than used for hot pressing were employed to compensate for the oxygen deficiency found in oxide ene gycol/docta phthalate ceramics after hot pressing. Four-point flexural tests (ball mil for 24 hrs) were performed with the tensile surface parallel to the laminate, at room temperature, using a screw-driven machine (model 4502, Instron Corp, Canton, MA) pe casting rate: 1 cm/sec ctor blade opening: 25 with a crosshead speed of 0.05 mm min Three bend bars with ground surfaces were tested for flexural strength. Two or three bend bars with indented surfaces and two or three bars with notches were also tested in essive lamination: flexure. Five indents parallel to the width direction and laminator der an uniaxial compression the center of the tensile surface were produced under a 3 kg indentation load. Radial cracks were generated under a 5 kg indentation load in order to study crack propagation profiles and interaction with the mi- Binder removal crostructure. The notched specimens were cut with a 160 um thick diamond-edged blade CIP condition 2.5. Pushout tests of fiber model systems Cold isostatic pressing 170 MPa for 10 min 2.5. 1. Sample prepard Since the available amount of single-crystal YAG fibers was limited, fiber model systems wer Hot pressing to obtain the interfacial shear strengths. To the densification problem without using hot or hot isostatic pressing techniques, a high surface area Fig. 1. Tape casting procedures for making laminated composites. (75-90 m2g ')Al2 O, powder(Praxair Surface Tech nologies, Inc, Indianapolis, IN) was mixed with A16- laminates, and at 1300C for 3 h in the case of LP a SG Al,O3 powder (60 vol %) to form the powder laminates. Single phase LP, YAG and Lau were also for the matrix. The mixture of powders was intended hot pressed at 1600C for comparison. The holding to lower the sintering temperature and to control time at this temperature was 3 h shrinkage a slurry was prepared by ball milling a mixture 2. 4. Mechanical evaluation of laminated composites of lp powder(approximately 70 wt. ) ethanol(ap proximately 27 wt %)and polyvinyl butyral (approxi The hot pressed slabs were cut into bars with dimen mately 3 wt %) AL,O fibers (diameter, 140 um) sions of 25 mm x 2 mm x 2 mm. Mechanical testing and YAG fibers(diameter, 160 um) were subsequently was conducted on LP/YAG and LP/LA, laminates dip coated with the LP slurry. Next, the dip-coated fibers and a marker (SCS-8 SiC fiber, Textron Specialty Materials, Lowell, MA) were embedded in the matrix The marker fiber Slurry formulation for tape casting of different materials dded to facilitate the fiber alignment and positioning before sintering, as well Constituent Amount (g) Function as the cutting of thin slices for pushout testing. After embedding, the fiber-containing pellets were dry pressed Ceramic powder at approximately 1 MPa, isostatically cold pressed at about 70 MPa and sintered in air at 1550oC for 3 h YAlsO, rather than at 1600oC for 3 h as when Al6-SG Al, O, Dispersant powders were used alone. The 50C difference in sintering temperature had a large effect on the Al,O3 Solvent fibers. Damage was observed on the Al2O3 fibers after Polyvinyl butyral Plasticizer sintering at 1600C, but they stayed intact at 1550oC Dioctyl phthalate Plasticizer This damage, which was observable by SEM, was also reported for Al,O, fibers under high temperature load Emphos PS-21A (Witco Chemicals. Houston. TX) ng[24]D.-H. Kuo, W.M. Kriven /Materials Science and Engineering A210 (1996) 123-134 125 Powder + dispersant +solvent (ball mill for 48 hrs) Slurry compositions: Ceramic powders ~r Dispersant: phosphate ester Slovents: trichioroathylene / ethanol I Binder: polyvinyl butyral Add: ptasticizers Plasticizers: polyethylene glycol / dioctyt phthalate + binder (ball mill for 24 hrs) Tape casting rate: 1 cm / sec Tape casting Doctor blade opening: 250 - 350 p,m and drying Drying under solvent - saturated atmosphere I I Condition of thermocompressive lamination: Cutting, stacking 50 - 80°C for 1 hr and lamination under an uniaxial compression , of t0 MPa l Binder removal cycles: Binder removal R.T. - 150°C at 60"C / hr 150 - 500°C at 3°C / hr I 1 CIP condition: Cold isostaticpressing -170 MPa for 10 min (CIP) I HP conditions Hot pressing 1300"C &1600"C for 3 hr (HP) at a pressure of 28 MPa Fig. 1. Tape casting procedures for making laminated composites. laminates, and at 1300 °C for 3 h in the case of LP/A laminates. Single phase LP, YAG and LA~ were also hot pressed at 1600 °C for comparison. The holding time at this temperature was 3 h. 2.4. Mechanical evaluation of laminated composites The hot pressed slabs were cut into bars with dimen￾sions of 25 mm × 2 mm × 2 mm. Mechanical testing was conducted on LP/YAG and LP/LA~I laminates Table 1 Slurry formulation for tape casting of different materials Constituent Amount (g) Function A1203 100 Ceramic powder LaPO 4 128 Y3AIsOI2 105 or LaAlllOi8 100 Phosphate ester" 1.8 Dispersant Trichlorethylene 62 --75 Solvent Ethanol 24 35 Solvent Polyvinyl butyral 8.4 Binder Polyethylene glycol 5.9 Plasticizer Dioctyl phthalate 5.9 Plasticizer "Emphos PS-21A (Witco Chemicals, Houston, TX). annealed at 1500 °C for 6 h and on LP/A laminates annealed at 1250 °C for 6 h. Lower annealing tempera￾tures than used for hot pressing were employed to compensate for the oxygen deficiency found in oxide ceramics after hot pressing. Four-point flexural tests were performed with the tensile surface parallel to the laminate, at room temperature, using a screw-driven machine (model 4502, Instron Corp., Canton, MA) with a crosshead speed of 0.05 mm min ~. Three bend bars with ground surfaces were tested for flexural strength. Two or three bend bars with indented surfaces and two or three bars with notches were also tested in flexure. Five indents parallel to the width direction in the center of the tensile surface were produced under a 3 kg indentation load. Radial cracks were generated under a 5 kg indentation load in order to study crack propagation profiles and interaction with the mi￾crostructure. The notched specimens were cut with a 160/lm thick diamond-edged blade. 2.5. Pushout tests of fiber model systems 2.5.1. Sample preparation Since the available amount of single-crystal YAG fibers was limited, fiber model systems were studied to obtain the interfacial shear strengths. To overcome the densification problem without using hot pressing or hot isostatic pressing techniques, a high surface area (75 90 m 2 g 1) A12Os powder (Praxair Surface Tech￾nologies, Inc., Indianapolis, IN) was mixed with A16- SG AI203 powder (60 vol.%) to form the powder for the matrix. The mixture of powders was intended to lower the sintering temperature and to control shrinkage. A slurry was prepared by ball milling a mixture of LP powder (approximately 70 wt.%), ethanol (ap￾proximately 27 wt.%) and polyvinyl butyral (approxi￾mately 3 wtY,,). A1203 fibers (diameter, 140 /zm) and YAG fibers (diameter, 160/~m) were subsequently dip coated with the LP slurry. Next, the dip-coated fibers and a marker (SCS-8 SiC fiber, Textron Specialty Materials, Lowell, MA) were embedded in the matrix. The marker fiber was added to facilitate the fiber alignment and positioning before sintering, as well as the cutting of thin slices for pushout testing. After embedding, the fiber-containing pellets were dry pressed at approximately 1 MPa, isostatically cold pressed at about 70 MPa and sintered in air at 1550 °C for 3 h rather than at 1600 °C for 3 h as when A16-SG AI20~ powders were used alone. The 50 °C difference in sintering temperature had a large effect on the A1203 fibers. Damage was observed on the A1203 fibers after sintering at 1600 °C, but they stayed intact at 1550 °C. This damage, which was observable by SEM, was also reported for A1203 fibers under high temperature load￾ing [24]