Analysis of Distinct Substrate Pre-treatment Effects on Flame-Sprayed Hydroxyapatite Coating

This paper experiments with stainless-steel AISI 316L substrate pre-treatment techniques in preparation for hydroxyapatite (HAp) flame spray coating. The mechanical, chemical, and combination pre-treatments were compared for the coating thickness and layer adhesion of the HAp to understand the influence of roughness on the layer adhesion of the flame-sprayed HAp layer on the flat substrate. The heat treatment at 800 °C for 1 h with 160 °C/h heating and cooling rate was conducted after spraying. Phase identification by XRD analysis shows that the substrates were partially coated with amorphous HAp. All pre-treated specimens have coating thickness that complies with medical requirements. Sandblasting creates the best hydroxyapatite layer coverage due to the highest surface roughness. On the other hand, the acidic immersion with sulfuric acid lowered the roughness value and caused the hydroxyapatite layer to have poor adhesion.