Mechanical performance of apatite/TiO2 composite coatings formed on Ti and NiTi shape memory alloy

To make metals bioactive for orthopaedic applications, apatite/TiO2 composite coatings were formed on Ti and NiTi shape memory alloy (SMA) using a H2O2-oxidation and hot water aging technique and the subsequent accelerated biomimetic process. In the current investigation, nanoindentation, scratch testing and frictional testing were employed to assess mechanical properties and the adhesion of apatite/TiO2 composite coatings formed on Ti and NiTi SMA. Nanoindentation testing conducted on cross-sections of composite coatings indicated that there was no significant difference in nanohardness and elastic modulus between apatite/TiO2 composite coatings formed on Ti and NiTi SMA samples. The enhancement of the adhesion between the apatite layer and the metal substrates arose from the TiO2 intermediate layer in the composite coating. The highest values of coating adhesion strength for Ti and NiTi SMA samples, as measured by scratch tests, were 22.58 N and 19.07 N, respectively. However, compared to corresponding Ti samples, NiTi SMA samples had better tribological properties.