Ultrafast thermomechanical effects in aerosol deposition of hydroxyapatite nanoparticles on a titanium substrate

Abstract

Hydroxyapatite [Ca10 (PO4)6 (OH)2] is the main mineral component of bone and teeth and is widely used for implant coatings due to its desirable osteoconductive and bioactive properties which are necessary for early bone formation. Aerosol deposition (AD), a novel coating method using a cold vacuum spray, offers the opportunity to produce robust, dense and pore-free coating by nanoceramic particles such as hydroxyapatite (HA). However, the high-velocity impact of HA particles with underlying substrates such as titanium is poorly understood. Here we use large-scale molecular dynamics simulations that reveal the mechanical deformation, stress and temperature during the fast impact of a 3 nm HA particle on a titanium surface. The effect of deposition velocity on deformation and the development of mechanical stresses and temperature of particle and substrate are discussed. We show that during an ultrahigh strain rate (>1010 s−1) deformation process, the temperatures of particle and substrate rise within a few picoseconds to ~1100–1253 K depending on the velocity. However, the particle and substrate temperatures remain lower than their melting temperatures. The simulations capture the initial elastic deformation and subsequent yield and plastic deformation of the particle. The dependence of particle penetration depth and structural transformation of the top layers of titanium on particle velocity is studied, revealing ultrafast mechanisms of particle–substrate bonding.