The microstructure and deposition behavior of the NiCr alloy coating using laminar plasma Spray

A new method of spraying is developed to produce both a ceramic and a metal coating in an atmospheric environment. As opposed to a traditional turbulent plasma jet, a plasma in a laminar flow state shows a much greater jet length with less ambient air engulfment. In the experiment, the total length of the plasma jet exceeded 600 mm, which agreed with the simulation results. NiCr alloy was picked as the coating material. The spray distance ranged from 250 mm to 500 mm. All the samples were observed through SEM. Coatings deposited under different stand-off distances showed different structures, which indicated that a specific structure could be realized at a certain distance. Structure with higher porosity were generated at relatively short distance and dense structure were obtained at a distance where the feedstock is fully molten. The XRD patterns indicated that the spraying process did not change the chemical composition of the material. Besides, the linear EDS scan results indicated that chemical and metallurgical bonding were realized. The Vickers hardness of the alloy coating showed a relatively high value, 8 GPa. Thus, the coatings performed well and the method of laminar plasma spray is promising to generate special functional and structural coatings.