Structural features of the coatings of the Ni-Al system obtained by air-plasma spraying

This article deals with the structural features of nickel aluminides coatings obtained by air-plasma spraying with the unit of annular injection of powder. The subsonic (plasma velocity is 1200 m/s) and supersonic (plasma velocity is 1900 m/s) regimes were used for coatings deposition. Ni3Al powder (Ni is base; 13-15 wt. % Al) was applied to the pipes of low-carbon steel 20 (0.2 % C). The structure and phase composition of the coatings were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray phase analysis. It is established that the porosity of the coatings obtained at supersonic regimes is reduced by a factor of 2. Ni3Al and Ni5Al3 are shown to be the main phases of coatings. Ni5Al3 phase volume fraction of the coatings obtained at supersonic regimes is revealed to be lower which reduces the microhardness of these coatings. It is shown that Ni3Al phase has subgrain structure and Ni5Al3 phase has lamellar structure.