In-situ reactive synthesis and characterization of a high entropy alloy coating by laser metal deposition

Abstract

In this study, we investigate the influence of in situ reactive synthesis of Ti6Al4V– AlCoCrFeNiCu high entropy alloys by laser metal deposition on the microstructural and mechanical properties of the as-built alloy as opposed to the traditional method of mixing powders via a ball mill prone to contamination and segregation. We explore the capability of a new alloy design by combining two base alloys via in situ reactive alloying, delivering the Ti6Al4V and AlCoCrFeNiCu high entropy alloy powders from multiple powder feeders and regulating their feed rate ratios. The nano mechanical, tribological and microstructural morphologies of the alloys were characterized using a nanoindentation tester, a tribometer, XRD and SEM, respectively. The results showed that satelliting the high entropy alloys powder and the Ti6Al4V powder fraction using double powder feedstock had a homogeneous distribution with dendritic structures. Optimization was achieved at a laser power of 1600 W, a scan speed of 12 mm/s and a powder flow rate of 2 g/min. The surface roughness (Ra) for Ti–6Al–4V, AlCoCrCuFeNi and (Ti–6Al–4V)-(AlCoCrCuFeNi) alloy was 0.5 µm, 0.63 µm and 0.80 µm, respectively. The high wear resistance of the novel Ti6Al4V– AlCoCrFeNiCu alloy was influenced by the hardness of the alloy which was higher than the Ti6Al4V alloy and the AlCoCrFeNiCu alloy. This study successfully defines the capabilities of in situ fabrication of high entropy alloys and presents novel techniques for multiple powder preparation of high entropy alloys using laser additive manufacturing, to permit the next generation of compositionally graded materials for aerospace components.