Cold spray deposition of hydroxyapatite powder onto magnesium substrates for biomaterial applications

Abstract

A simple, modified, cold spray process was developed in which hydroxyapatite powder was coated onto pure magnesium substrates preheated to 350 or 550°C and ground to either 240 or 2000 grit surface roughness, with stand-off distances of 20 or 40 mm. The procedure was repeated five and 10 times. The hydroxyapatite coatings did not show any phase changes. Atomic force microscopy revealed a uniform coating topography, and scanning electron microscopy revealed good bonding between the coated layers and the substrates. As the p values were < 0·05, all factors except the number of sprays were considered to be significant. The response optimiser indicated that a 22·7 mm stand-off distance, a 649·2 grit surface roughness and a 496°C substrate heating temperature produced good hydroxyapatite coatings of 46·3 μm thickness, 436·5 MPa nanohardness and 43·9 GPa elastic modulus. The modified cold spray technique with substrate heating showed promising results in terms of product coating thickness and mechanical properties.