Effect of Graded Coating on the Nanoindentation Properties of HA/Ti Composite Coatings Synthesized by Mechanical Coating Technique on Ti-6Al-4V Substrate

One of the new methods for determining the mechanical properties of thin layers and coatings is nanoindentation, which is of interest to a number of researchers.  In this research, composite and graded coatings containing HA/Ti were deposited on Ti-6Al-4V substrate by mechanical coating technique and their cross-sectional structure was determined and compared using Scanning Electron Microscope (SEM). Their mechanical properties including elastic modulus and hardness were also studied through the nanoindentation method. The SEM results show that due to the presence of more hydroxyapatite particles on the top layer of the graded coating, its surface enjoys more smoothness and compactness and less porosity than the non-graded composite coating. According to the nanoindentation test results, the elastic modulus and hardness of the graded coating (modulus 36.6 ± 4.7 and hardness 0.94 GPa) is higher and more uniform than the composite coating (modulus 13.3 ± 8.5 and hardness 0.26 GPa). As illustrated in the SEM images of the cross-section of the coatings, this happens due to the greater porosity and roughness of the non-graded composite coating.