Comparative Study on the Annealing of Cold-Sprayed Boron Nitride Nanosheet/Copper Coating Using Spark Plasma Sintering and Atmosphere Furnace

Cold spray is an emerging additive manufacturing technique, as it provides an avenue for oxide-free and non-phase-transformation deposition. Pores within the cold-sprayed coatings generally adversely affect the mechanical performances of the coatings. In this work, a comparative study on the annealing of cold-sprayed boron nitride nanosheets (BNNSs)/copper (Cu) composite coating using spark plasma sintering (SPS) and the atmosphere furnace (AF) was performed at various temperatures. SPS exhibited a much higher efficiency in reducing the coating porosity: the porosity reduced from 1.31 % to 0.65 % after merely 5 min of annealing by SPS, while the value was 1.1 % after one-hour annealing at 600 °C in the AF. The bending test showed that the SPS-treated coatings had higher ductility than AF-treated ones due to their better interfacial bonding. The possible mechanisms are proposed as follows: the higher interfacial healing efficiency may arise from multiple physical fields of SPS, which promotes the destruction of the oxide layer, the cleaning of the particle surface, and the atomic diffusion. Thus, BNNSs prevent crack propagation during fracture, thereby improving the coating ductility.