New Insights on Bonding Mechanism of High Entropy Alloy Microparticles upon Impact using Microparticle Adhesion and HR-TEM Analyses

Particle bonding remains an important area of study in cold spray. Most of the research in this field has focused on bonding mechanism analyses of pure elements and is often studied at the level of a full coating. High entropy alloys (HEA) are an emerging class of materials that have superior work-hardening ability and are usually resistant to softening, a behavior that makes their particle impact and bonding interesting. In this study, single particles of HEA powders are deposited using four spray parameters: low pressure and high-pressure cold spray system with and without particle preheating using nitrogen and helium as propellant gas. The impact temperatures and velocities of HEA particles were estimated using modelling. The adhesion strength of single particles was measured using the micromechanical splat adhesion test. The correlation of adhesion strength with HEA particle impact temperature and velocity is used to propose bonding mechanism of HEA particles that were subsequently explored using high resolution transmission electron microscopy.