Examination on Substrate Preheating Process in Cold Gas Dynamic Spraying

Substrate preheating always takes an important role in particle bonding and formation of the first layer coating in cold gas dynamic spraying (CGDS). In this study, a systemic investigation on substrate preheating process is conducted with Cu, Al, Steel, and Ti substrate by both numerical and experimental methods. The computational fluid dynamic (CFD) approach is adopted to simulate the heat exchange process between gas and solid substrate. The numerical results show that substrate can be significantly preheated by the high-temperature gas, especially by the gas at the near-wall zone behind the bow shock where the temperature is extremely high. Moreover, the comparison between different substrates implies that substrates with smaller thermal conductivity can achieve higher surface temperature and larger temperature gradient which may greatly contribute to the generation of residual stress, such as Ti substrate in this study. For the heat flux, Cu substrate obtains the largest value at the center zone of the substrate surface, followed by Al, Steel, and Ti substrate, but at the outer zone, the heat flux through the Cu substrate surface is smaller than the other three types of substrates. Besides, based on the experimental results, it is found that the substrate surface temperature amounts to the peak value only when the preheating time is sufficiently long.