Effects of substrate heat accumulation on the cold sprayed Ni coating quality: Microstructure evolution and tribological performance

The residual stress and distortion caused by non-uniform temperature distribution has limited the application of cold spray (CS) technique as an effective additive manufacturing and damage repair method for large-scale components. In order to investigate the influence of heat accumulation on coating quality, two types of CS Ni coatings with different building dimensions were deposited onto substrates. The type II Ni coatings with smaller fabrication size possess a fully dense microstructure without cracks, while the type I coatings with larger size show a significantly higher porosity value. The type II coatings show relatively higher microhardness. The tribological tests show that the type II Ni coatings present a better wear resistance with lower coefficient of friction and lower wear rate. The distinct worn morphologies show that the lower microhardness and porous microstructure of type I coatings lead to numerous delamination and exposure of interior coating. According to the temperature history recorded by infrared imaging camera, higher average temperature was found at the type II coatings due to enhanced heat accumulation of coating/substrate system at the short nozzle movement. The increased particle plastic deformation can further promote the coating densification rate and further ameliorate the coating quality. It can be summarized that the nozzle trajectory and deposition strategy can affect the temperature distribution and determine the coating qualities. This work provides a potential guidance for the optimization of coating quality by cold spraying additive manufacturing.