Crack Propagation Resistance of alpha-Al2O3 Reinforced Pulsed Laser-Deposited Hydroxyapatite Coating on 316 Stainless Steel

Abstract

Hydroxyapatite (HA) is a widely used bioceramic known for its chemical similarity with that of bone and teeth (Ca/P ratio of 1.67). But, owing to its extreme brittleness, alpha-Al2O3 is reinforced with HA and processed as a coating via pulsed laser deposition (PLD). Reinforcement of alpha-Al2O3 (50 wt.%) in HA via PLD on 316L steel substrate has shown modulus increase by 4% and hardness increase by 78%, and an improved adhesion strength of 14.2 N (improvement by 118%). Micro-scratching has shown an increase in the coefficient-of-friction from 0.05 (pure HA) to 0.17 (with 50 wt.% Al2O3) with enhancement in the crack propagation resistance (CPR) up to 4.5 times. Strong adherence of PLD HA-Al2O3 coatings (similar to 4.5 times than that of HA coating) is attributed to efficient release of stored tensile strain energy (similar to 17 x 10(-3) J/m(2)) in HA-Al2O3 composites, making it a potential damage-tolerant bone-replacement surface coating.