Experimental Study of the Porosity of Ni + Zn + Al₂O₃ Coatings Deposited by Low-Pressure Cold Spraying

The goal of the article is to understand the effect of temperature and air pressure at the inlet to the supersonic nozzle, as well as the distance from the nozzle to the substrate (stand-off distance), on the microstructure and porosity of coatings obtained from Ni + Zn + Al₂O₃ powder mixture during low-pressure cold spraying. In the study, a nickel-based powder mixture was used as a powder material, in which the proportion of Al₂O₃ is approximately 30% mass. VT9 titanium alloy plates were used as the substrate material. Based on the multi-factor planning of the experiment, the influence of complex parameters of the low-pressure cold spraying on the porosity of coatings was studied. Porosity estimation was performed on prepared microsamples using electron microscopy. The scientific novelty is the following: the dependences of the influence of complex parameters of the spraying process on the porosity of Ni + Zn + Al₂O₃ coatings are constructed from the analysis of the obtained statistical data. The results show that the air temperature has the greatest influence on the studied parameter, and by changing the spraying modes it is possible to control the porosity values in a rather wide range, which ranged from 2.7% to 6.6% in this study. The practical value is that obtained results can be used for development of technological recommendations for cold spraying of nickel-based coatings with minimum porosity for surface protection and repairing.