D.-S. Lim et al./Wear251(2001)l452-1458 Table I orma Starting ceramic powder compositions of samples(vol % tape casting direction Component Parallel with 995 79.5 AKP-30, Sumitomo Chemical, Osaka, Japan. bEP, Junsei Chemical, Tokyo, Japan. SCW#1, Tateho Chemical Industries, Hyogo, Japan. Normal with 2. Experimenta Fig. 2. Schematic repr ion of the sliding direction with to the tape casting and lamination direction. whiskers are well Table I shows the compositions of samples used for according to these directions this study. For sample A, the two ceramic powders were mixed by planetary ball milling for 8h. Ethanol, alumina lel, normal with tape casting direction, and normal with the balls 5mm in diameter(SSA999, Nikkato Corp, Tokyo, lamination direction). Fig. 2 shows a schematic illustration Japan) and a plastic jar were used for mixing. The mixed of the sliding directions with respect to whisker orientation powder was hot pressed at 1823K for I h under 30 MPa. The wear volume of the flat sample was obtained by wear For samples T10 and T20, a modified tape casting method track length multiplied cross-sectional worn area that was was employed for aligning the whiskers. The diameters measured from the center portion of the groove by a surface and lengths of the Sic whiskers used in this study were profilometer after cleaning in a ultrasonic bath. Each wear 1-1. 4 and 10-20 um, respectively, according to information test was repeated three times and the average values of the supplied from the manufacturer. Details of the processing measurements were expressed in the results. The wear scar Tape cast products were cut and laminated at 353 K under with an energy dispersive X-ray analyzer: Scope equipped conditions and modification are described elsewhere [6, 8] was examined by a scanning electron micre 50 MPa for 0.5h. Binder burn-out was performed at 823 K for 10 h in open air, and then the sample was hot pressed at 2123K under 30 MPa for 1 h 3. Results Tribological behavior was studied by using the ball-on- reciprocating flat geometry. Fig. I shows a schematic dia- iding on sample A was carried out on the surface in a gram of the high temperature wear tester. A silicon nitride normal direction with hot pressing direction, Different slid- ball(NDB200, Norton Co., Northboro, MA, USA) of ing directions with respect to the whisker orientation are 35 mm in diameter was used against a flat alumina-Sic shown in Fig. 2. Fig. 3 shows the values of the average whisker composite sample surface which was polished with friction coefficient and standard deviations measured dur- um diamond slurry. The normal load was 40N and the sliding parallel with tape casting direction for the test average speed was 10 mm/s. The reciprocating stroke was materials at different temperatures. The friction coefficient 5.64 mm and the duration was I h. Wear tests were per- formed at a range of temperature between 403 and 873K. 0.7- In order to examine the effect of whisker orientation on wear rate, tests were carried out on three directions(paral 0.5 Load cell heater c0.3 Ball DC Moto Computer Indicator Whisker content(vol % Fig. 3. Friction coefficients between the alumina-SiC whisker composite Fig. 1. Schematic diagram of the high temperature tester. and silicon nitride ball as a function of whisker content.D.-S. Lim et al. / Wear 251 (2001) 1452–1458 1453 Table 1 Starting ceramic powder compositions of samples (vol.%) Component Sample A T10 T20 Al2O3 a 99.5 89.5 79.5 MgOb (wt.%) 0.5 0.5 0.5 SiC whiskerc – 10 20 a AKP-30, Sumitomo Chemical, Osaka, Japan. b EP, Junsei Chemical, Tokyo, Japan. c SCW#1, Tateho Chemical Industries, Hyogo, Japan. 2. Experimental Table 1 shows the compositions of samples used for this study. For sample A, the two ceramic powders were mixed by planetary ball milling for 8 h. Ethanol, alumina balls 5 mm in diameter (SSA999, Nikkato Corp., Tokyo, Japan) and a plastic jar were used for mixing. The mixed powder was hot pressed at 1823 K for 1 h under 30 MPa. For samples T10 and T20, a modified tape casting method was employed for aligning the whiskers. The diameters and lengths of the SiC whiskers used in this study were 1–1.4 and 10–20
m, respectively, according to information supplied from the manufacturer. Details of the processing conditions and modification are described elsewhere [6,8]. Tape cast products were cut and laminated at 353 K under 50 MPa for 0.5 h. Binder burn-out was performed at 823 K for 10 h in open air, and then the sample was hot pressed at 2123 K under 30 MPa for 1 h. Tribological behavior was studied by using the ball-on￾reciprocating flat geometry. Fig. 1 shows a schematic dia￾gram of the high temperature wear tester. A silicon nitride ball (NDB200, Norton Co., Northboro, MA, USA) of 6.35 mm in diameter was used against a flat alumina–SiC whisker composite sample surface which was polished with 1
m diamond slurry. The normal load was 40 N and the average speed was 10 mm/s. The reciprocating stroke was 5.64 mm and the duration was 1 h. Wear tests were per￾formed at a range of temperature between 403 and 873 K. In order to examine the effect of whisker orientation on wear rate, tests were carried out on three directions (paral￾Fig. 1. Schematic diagram of the high temperature tester. Fig. 2. Schematic representation of the sliding direction with respect to the tape casting and lamination direction. Whiskers are well aligned according to these directions. lel, normal with tape casting direction, and normal with the lamination direction). Fig. 2 shows a schematic illustration of the sliding directions with respect to whisker orientation. The wear volume of the flat sample was obtained by wear track length multiplied cross-sectional worn area that was measured from the center portion of the groove by a surface profilometer after cleaning in a ultrasonic bath. Each wear test was repeated three times and the average values of the measurements were expressed in the results. The wear scar was examined by a scanning electron microscope equipped with an energy dispersive X-ray analyzer. 3. Results Sliding on sample A was carried out on the surface in a normal direction with hot pressing direction. Different slid￾ing directions with respect to the whisker orientation are shown in Fig. 2. Fig. 3 shows the values of the average friction coefficient and standard deviations measured dur￾ing sliding parallel with tape casting direction for the test materials at different temperatures. The friction coefficient Fig. 3. Friction coefficients between the alumina–SiC whisker composite and silicon nitride ball as a function of whisker content