Strain rate sensitivity of hydroxyapatite coatings

The strain-rate sensitivity of strength is a significant factor to evaluate the deformation mode of crystalline materials. The strain rate sensitivity of hardness is experimentally investigated here for hydroxyapatite coatings that are sputter deposited onto titanium-coated silicon wafers. These biocompatible HA coatings can provide a strong, dense interface between metal alloy implants and porous hydroxyapatite that can help in-growth of tissue. The interface to the metal alloy implant is important to transfer stress during loading. So, it is very important to know the behavior of the coating under different conditions of loading. Our dynamic test procedure now takes advantage of nanoscratch testing to measure the change in scratch hardness of the coating over a strain rate range that may well simulate the mechanical loading conditions found at the interface between implants and hydroxyapatite coatings.