Abstract:
Cold spray technology, commonly employed for depositing ductile metal particles on metal substrates, traditionally avoids coating ceramic particles due to their lack of ductility. Recent breakthroughs have, however, demonstrated successful ceramic coating on metal substrates. However, understanding the initial bonding mechanisms between the ceramic particles and the metal substrate is crucial for optimizing coating performance. In this study, we investigated the impact behavior of single TiO2 particles on AlMg3 (soft) and 304 SS (hard) substrates using arbitrary Lagrangian Eulerian (ALE) with smoothed particle hydrodynamics (SPH) numerical methods. Our results revealed that upon impact, both substrates underwent significant plastic deformation due to a temperature rise exceeding 60-70% of the melting point (MP), suggesting conditions for adiabatic shear instability (ASI). However, the ceramic (TiO2) particles, limited in their deformability, fragmented and became trapped within the softened substrate due to ASI in 304 SS. At higher impact velocities on soft AlMg3, the particles exhibited reduced adherence, possibly due to excessive substrate heating (beyond MP). Interestingly, the fragmented particles formed cap-shaped splats at velocities below a threshold velocity (Vth) and ring-shaped splats above Vth. This transition is attributed to the intensity of the spring-back force, favoring a ring shape at higher impact forces. The morphology changes were evident from numerical simulations analyzing critical stress, equivalent plastic strain and temperature near the particle-substrate interface. These findings, supported by potential experimental observations, provide valuable insights into the initial stages of ceramic deposition, particularly the first layer formation, which is crucial for developing metal-ceramic coatings through cold spray.