Microstructural, Mechanical and Electrochemical Characterization of a Flame Sprayed NiFeCrBSi/WC Cermet Coating

Abstract

To increase the lifetime of drilling bits, these components are usually covered with hard metal matrix composites. Nowadays, nickel based metal matrix composites arise as substitutes to cobalt-based ones. The challenge now is to provide an efficient coating with low cost. The aim of this paper is to exploit the characteristics of a newly designed flame sprayed NiFeCrBSi-WC composite coatings. The experimental activities were carried out using the scanning electron microscopy, for the microstructural analysis of coating. Additionally, micro-hardness and nano-indentation tests were carried out to evaluate the resistance of the coatings against penetration. Moreover, the electrochemical behavior was assessed in NaCl and Na₂SO₄ aqueous solutions. The ionic concentrations were varied between 1 g/l to 35 g/l. The results show that the microstructure is dendritic and characterized by the presence of hard chromium carbides and nickel grains in the inter-dendritic space. The coating was subject to a slight decarburization. The presence of carbides and the decarburization make the microhardness of the matrix fluctuates between 300 HV to 900 HV. For the electrochemical response, the increase in ion concentration induces a decrease in the corrosion resistance. In Na₂SO₄ aqueous solutions, the charge transfer is roughly constant for the concentrations above 1 g/l.