Research On Deformation, Deposition Behaviors Of Particles And Microstructures, Mechanical Properties Of Coatings In Cold Spray

The effects of gas temperature, substrate hardness on the deformation and deposition behaviors of the cold-sprayed Ni, Cu alloy particles were investigated by observing their impacted morphologies. With the aid of OM, SEM, TEM, EPMA, micro-hardness and tensile tester, etc., the effects of annealing treatment, micro-forging on the microstructures and mechanical properties of the cold-sprayed Ni coating were also studied. Two mechanisms were proposed to clarify the microstructural evolution in the cold-sprayed Ni coating. The bonding mechanism of the cold-sprayed metallic coatings was also discussed.Experimental results show that the particle flattening ratio increases with the increase of the gas temperature, but the increment rate decreases at higher gas temperature. Moreover, the bonding ratio increases due to the increment of material jet area at the interface. With the increase of substrate hardness, the particle flattening ratio increases, and the main bonding mechanism between particle and substrate transits from mechanical interlocking to metallic bonding. When substrate hardness is much higher, however, only particles are heavily deformed, and therefore they cannot be effectively deposited onto the substrate.A typical impacted Ni particle consists of shear instability thin layer, severe plastic deformation region and low plastic deformation region. The quality of particle/substrate bonding is mainly governed by the shear instability thin layer, while the shape of the deposited particle is mainly governed by the plastic deformation regions.The local microstructures of cold-sprayed Ni coating reveal a quite nonuniform appearance. The grain refinement near the particle-particle interface is more pronounced than the periphery of the interface, and the typical microstructures at the interface are elongated grains and equiaxed grains. The main mechanisms for microstructural evolution at, and near the interface are the dynamic recrystallization under high-strain-rate deformation and the plastic strain-induced grain refinement due to dislocation movement, respectively.Micro-forging influences significantly the properties of cold-sprayed coating, but it works only in the scope of 1~3 particles because of its short-range effect.As annealing temperature increases, the micro-hardness and the elongation after...