Characterization and fatigue damage of plasma sprayed HAp top coat with Ti and HAp/Ti bond coat layers on commercially pure titanium substrate

The surface of commercially pure Ti (cp-Ti) substrate was grit-blasted with Al2O3 powders and then wet-blasted with HAp/Ti mixed powders at room temperature. Then plasma spraying with Ti powders or HAp/Ti mixed powders on the blasted surface was carried out to form a bond coat layer, denoted as T50 and T100 bond coat for the former and HT100 bond coat for the later. The HAp top coat was subsequently sprayed with 100 μm thickness. The XRD patterns showed that the as-sprayed HT100 bond coat layer was mainly composed of HAp with minor components of Ti and TiO2. EDS analysis also showed there co-existed HAp and Ti without reaction in the HT100 bond coat layer. Some cracks were observed in the bond coat and the top coat layers after compression–compression and tension–tension fatigue tests. The HT100 bond coat specimen produced less AE signal and a small amount of debonding and cracking in compression–compression fatigue test. The HT100 specimen could survive up to 10 million cycles at stress amplitude of 200 MPa, which is high enough compared to the maximum stress in bones: the order of 100 MPa. The degree of damage (debonding and cracking) in tension–tension fatigue test was more severe than that in compression–compression fatigue testing.