Atmospheric Plasma Spraying of Ni-Based Alloy Coating by Oxide-Free Droplets Based on De-Oxidizing Effect of Boron

Abstract

Plasma spraying is a flexible and versatile coating process capable to deposit metallic protective coatings. However, oxidation of molten metal droplets in open atmosphere makes the resultant coatings full of pores and oxides and hinders the wide applications of plasma sprayed metallic coatings. In this study, a novel approach to deposit dense Ni-based alloy coatings was proposed by introducing de-oxidizing effect of B via plasma spraying Ni20Cr4B powder. As compared with the reference coating sprayed with Ni20Cr powder (oxygen content of 2.8 wt.%), the Ni20Cr4B coatings show the low oxygen content less than 0.2 wt.% in a wide spray distance range from 60 mm up to 140 mm. The decreased B content of the particles during coating deposition indicates that the highly dense Ni-based coating (porosity of 0.15 ± 0.05%) is deposited by oxide-free molten droplets in the open atmosphere owning to the in-situ de-oxidizing effect of B.