An evaluation of plasma-sprayed coatings based on Al2O3 and Al2O3–13 wt.% TiO2 with bond coat on pure titanium substrate

In this study, the effects of bond coat on the properties of Al2O3 and Al2O3–13 wt.% TiO2 coatings, which is plasma sprayed onto a commercial pure titanium substrate with and without Ni–5 wt.% Al (METCO 450 NS) as bond coating layer were investigated in terms of microhardness, bonding strength and surface roughness. Optical and scanning electron microscopy (SEM) examinations revealed that there is a uniform coating layer with no spalling and delamination. However, there is a little amount of porosity. The results indicated that the application of bond coat layer in the plasma spraying of Al2O3 and Al2O3–13 wt.% TiO2 on pure titanium substrate has increased the hardness and bonding strength of coatings. While the adhesive bonding is dominant without bond coat, the cohesive bonding is dominant with the application of the bond coating layer. It has been observed that percentage of cohesion strength was about three times higher than that of adhesion strength.