1552 Journal of the American Ceramic Sociery-Toschi et al Vol 86. No 9 a ransgrany Intergranular. p “5h Fig 9. Example of the fracture surface observed in the wear tracks of the A/AZ composite. Both intergranular and transgranular fractures are visible This behavior has been observed on all the materials studied (A/AZ). As a result there were fewer fractured grains available for erosive wear of the hybrid-laminated composite, resulting in a lower total specific wear of this material, even under these conditions. Figure 8 shows a typical plastically deformed surface of MA material tested at 150N and 0. 15 m/s. When the fracture occurred, it was both intergranular and transgranular, regardless of the materials(Fig. 9). It is also interesting to note that the wear of the alumina pin on the A/AZ composite was generally lower than that observed for the other pairings(particularly when compared with the MA pairing) In addition to high wear resistance, another important charac teristic useful when selecting materials for tribological use is their Fig. 7. Surface cracking showed by different materials for the same tion. This capability can be associated with the extreme conditions According to Adachi et al., the possibility of this transition occurring is lower when the tested material exhibits high tough 3 Under more severe experimental conditions (150 N and 0. 15 ness. In fact. the superior behavior of the laminated composite s),a pronounced plastic deformation and increase in the A/AZ can also be shown by considering the different wear regimes production of debris were observed. This debris, which acts as ar exhibited by the three materials studied under the various operat abrasive third body, stimulates an increase in wear rate. Under ing conditions. Although a sharp transition with a drastic change in such conditions, the effect of compressive stresses was less wear rate was not observed under the experimental conditions that pronounced and the specific wear increased significantly for all were used, according to the previously proposed limit, the three materials being tested. However, as the cracking of the transition from mild wear to severe wear occurs when the specifi surface(and consequent removal of grains) initially triggered this wear exceeds the values of 10mm(ml hich correspon avalanche-type mechanism. debris production was hindered from to about 4 x 10 g(km.N) in our case. This transition limit is the outset by high toughness in the case of stressed material evidenced as a solid line in Fig. 6. y analyzing the results, we can see (Fig. 6) that the laminate A/AZ still exhibits mild wear even when the applied load reaches 100 N (except with a sliding speed of 0. 15 m/s), while the transition from mild wear to severe wear occurs when the applied load exceeds 50 N in the case of the other two materials from opposites in the system Al,O /ZrO, were prepared by warm pressing and sintering. Using layers of pure alumina and alumina/ zirconia composites, symmetric hybrid laminates were produced Due to the different thermal expansion coefficients and shrinkage ible to stimulate residual stress on the surface by ordering the layers of different materials properly, Using indentation techniques, the value of the 50 surface residual stress was estimated at-141MPa The surface properties(physical, mechanical, and tribological) of the A/AZ laminated composite showed the superiority of the hybrid structure when compared with those of analogous but stress-free material Fig. 8. Plastically deformed debris spread over the surfaces of wear The hardness and toughness of the monophase laminate AA and tracks in the MA material tested at 150 N and 0.15 m/s monolithic MA are almost the same as that of a typical commercial