Effects of thermal spraying technique on the remelting behavior of NiCrBSi coatings

Abstract

This study aims to understand and quantify the influence of the deposition technique on the remelting parameters, microstructure, microhardness, and abrasive behavior of NiCrBSi coatings. An experimental study was conducted on the microstructure and mechanical properties of Ni-based alloys sprayed onto an AISI 304 substrate using two different techniques, namely the flame spraying oxygen–fuel and high-velocity oxygen–fuel techniques, followed by surface flame melting. The microstructures of the resulting coatings were analyzed using optical microscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and X-ray diffraction. The spraying technique is critical for the remelting temperature and time. The microstructures of the deposited coatings in the as-sprayed and remelted samples exhibited similar phases; however, their morphology, size, and distribution were dependent on the deposition technique and remelting parameters, namely temperature and time. Abrasive wear and Vickers microhardness tests were performed. The remelted coatings exhibited higher microhardness, enhanced cohesion of the coating splats, and decreased coating porosity, which decreased wear loss. Although the oxygen–fuel technology after remelting exhibited a relatively larger phase size and lower microhardness than those obtained by high-velocity oxygen–fuel after remelting, a lower wear loss was obtained for the oxygen–fuel. Therefore, this study focused on understanding the effects of as-sprayed and remelted microstructures on wear and microhardness. These findings provide a new understanding of the combination of thermal spraying and remelting techniques for controlling the microstructure and mechanical properties of NiCrBSi coatings.