Scratch Damage in Zirconia Ceramics

Scratch damage modes in zirconia‐based ceramics—Mg‐PSZ, Y‐TZP, and Ce‐TZP—are investigated. Precursor indentation tests with a tungsten carbide sphere foreshadow the nature of damage: in Mg‐PSZ, extensive (quasi‐)plastic deformation in the region outside and beneath the contact; in Y‐TZP, less plastic deformation beneath the contact but incipient cone cracking in the region of tension outside the contact; in Ce‐TZP, intermediate behavior. Scratch testing is conducted using a conical diamond indenter. In all materials the damage mode changes from smooth plastic deformation to limited cracking with increasing scratch load: in Mg‐PSZ, plastic deformation is predominant at lower loads, with microcracking at higher loads; in Y‐TZP, plastic deformation is predominant over the range of the test loads—macrocracks initiate only at relatively high loads, but penetrate to a relatively large depth; again, Ce‐TZP shows intermediate behavior, but with cracking patterns closer to that of Mg‐PSZ. Bending tests on specimens subjected to scratch damage indicate a relatively high damage tolerance in the Mg‐PSZ and Ce‐TZP; Y‐TZP shows the highest initial strength, but suffers relatively large strength loss above the critical load for macrocracking. Implications concerning relative merits of each zirconia type for wear properties, contact fatigue, and machining damage are briefly discussed.