Scratch Testing of Hard Ceramics: Manifestation of Viscoelasticity

Viscoelasticity is studied extensively in polymers and polymer-based composites-but hardly in ceramics. We have studied viscoelastic behavior of three ceramics as manifested in scratching tests: 98 weight % B4C + 2% hexagonal boron nitride (h-BN), 92% B4C and 8% h-BN, 91% B4C + 5% CrSi2 + 2% h-BN. Clear viscoelastic recovery (the groove depth becoming shallower within 2 minutes) is seen in all three materials, the recovery in each case of at least 90%. Taking into account viscoelasticity and introducing appropriate additives, one could significantly improve the scratch resistance of the boron carbides, and possibly of other hard ceramics as well.