The microstructure evolution of in-situ laser remelted of (Ni/Ni₃B + WC) + NiCrFeBSiC flame-sprayed coating

This article presents research results related to microstructural changes in modified flame-sprayed DURMAT 61-PTA (NiFeSiB + WC/W₂C) coating by introducing additional Metco 15E (NiCrFeBSiC) sublayers into the coating system with next laser remelting. This modification aimed to increase the adhesion of the large, high-melting and hard tungsten carbides to the substrate material and to facilitate and control the laser remelting of the coating. The modified coating was subjected to microstructural analysis regarding chemical and phase composition and hardness assessment. It was shown that the hardness of the layered (modified) coating after the laser melting process increased significantly, exceeding the additivity rules for mixtures. This suggests a noticeable synergy effect related to the mutual influence of both input materials. The research indicates that the effect responsible for the increase in hardness to approximately 61 HRC was the generation of tungsten borides as an essential strengthening phase. The probable in-situ formation of boride phases results from the primary dissolution of tungsten carbides in the matrix and the secondary formation of tungsten borides of various types. The observed synergistic effect is the essential benefit of using the above-mentioned technological concept of layered coatings, which is proposed to facilitate the preparation of technologically challenging coatings containing many phases based on tungsten carbide.