Engineering the resistance to sliding-contact damage through controlled gradients in elastic properties at contact surfaces

Experimental and computational results are presented to demonstrate that controlled gradients in elastic modulus alone can result in a pronounced enhancement in the resistance of a surface to frictional sliding contact. The model material chosen for the demonstration of this new concept is polycrystalline alumina infiltrated with aluminosilicate glass. In this system, the elastic modulus increased continuously by 50% from the contact surface to a depth of about 2 mm beneath the surface, with essentially no long-range residual stresses. The strength and local fracture toughness of the contact surface markedly deteriorates as a result of elastic modulus gradation. However, the gradation in elastic modulus alone reduces the principal tensile stresses introduced by frictional sliding contact to such an extent that the glass-infiltrated alumina is far more resistant to contact damage than either monolithic alumina or glass or alumina-glass composite of uniform composition which is equal to the composition of the contact surface. A wide variety of mechanics and materials issues pertaining to sliding contact resistance of homogeneous and graded materials are also addressed. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.