Improving bond strength and deposition efficiency of ceramic coatings via low pressure cold spraying: A study on hydroxyapatite coatings with Cu-Zn blends

Abstract

This study presents Low Pressure Cold Spraying (LPCS) method for ceramic coatings, aimed at enhancing efficiency and elucidating bonding mechanisms. It focuses on the deposition of ceramic coatings using LPCS, with hydroxyapatite (HA) on 316L stainless steel (SS) as an illustrative example. Despite the advantages of LPCS, retaining HA particles has proven challenging, resulting in thin coatings (11.09 f 2.56 mu m) with low bonding strength (1.80 f 0.19 MPa). To address this issue, a composite coating strategy was developed by blending 20 wt % Cu and Zn powder with 80 wt% HA. This approach significantly improved coating properties, achieving enhanced bonding strength (33.70 f 1.13 MPa), deposition efficiency (27 %), and hardness (136.30 f 2.45 HV) compared to pure Cu-Zn coatings. Numerical simulations were conducted to interpret these experimental results, indicating that blending metal with HA improves deposition efficiency, bonding strength, and hardness. In HA coatings, particles fragment into submicron grains and embed into the substrate through mechanical interlocking (MI), with shockwave-induced bonding strengthening subsequent layers. For Cu-Zn coatings, bonding occurs through MI and adiabatic shear instability (ASI). In HA-Cu-Zn coatings, high-velocity HA particles and Zn particles enhance bonding further through in-situ tamping.