EROSION WEAR PROPERTIES OF TETRAGONAL ZRO2(Y2O3)-TOUGHENED AL2O3 COMPOSITES

Erosion wear properties of tetragonal zirconia (t-ZrO2 with 3 mol% Y2O3)/Al2O3 composites with different volume fractions of t-ZrO2 in the range of 0 to 100 vol% (including Al2O3 or t-ZrO2 ceramics), were measured by a collision test between Al2O3 or SiC particles accelerated in an air stream (240 m/s) and a stationary composite or ceramics target. In the case of Al2O3 erodent particles, the wear rate of composites decreased to one-tenth of the wear rate of Al2O3 or t-ZrO2 ceramics. The optimum volume fraction of the additive phase for increased wear resistance was in the range of 7 to 22 vol% of t-ZrO2. However, the wear resistance of all composites in collision with SiC particles deteriorated. The maximum wear rate appeared at about 40 vol% of t-ZrO2, and reached two times that of the Al2O3 or t-ZrO2 ceramics. The mean fracture load of the SiC erodent particle in a diametral compression test under quasi-static loading was 2.3 times the value of the Al2O2 particle, which broke after collision with the target. Therefore, the mean impact force produced by Al2O3 particles striking the target was much lower than that from SiC particles. Because the impact force acting from the Al2O3 particles did not reach the threshold force required for lateral crack propagation in the composites, the principal damage mechanism, the wear resistance of composites increased. However, the impact force from SiC particles was greater than the threshold force, and lateral or other damaging cracking was promoted at the wear surface of the composite materials. This discussion is in agreement with the analysis by the lateral crack model and the results for the median crack length of each ceramic measured by Vickers indentation tests with different loads. The slope of the logarithm of median crack length as a function of the logarithm of Vickers indent load was larger than the value of 2/3 obtained theoretically.