Boriding influence on cyclic oxidation of CrFeMnNbNi high entropy alloy

Abstract

Boriding is often used to improve the wear resistance of metals and alloys and successful results are obtained. Although boriding increases the wear resistance in HEAs, it is also important to know the oxidation behavior, especially for high temperature applications. In order to determine the cyclic oxidation behavior of boriding in HEAs, alloy CrFeMnNbNi was subjected to boriding in this study. In the CrFeMnNbNi alloy that was produced by arc melting, three phases were detected as FeNi, FeCr and Laves in the post-production analysis. With the pack boriding process, a boride zone of approximately 30–35 μm thickness and a diffusion zone of 28–33 μm consisting of different types of borides (M_xB_y) were obtained on the surface. Both HEA and borided-HEA were exposed to cyclic oxidation experiments up to 45 h at 900 °C. Mn, which has a high affinity to oxygen, caused the formation of oxides containing predominantly Mn. The presence of boride phases in the subsurface regions changed the formed oxide products. In the borided sample, oxide formations containing Mn-Fe-B were detected and showed rapid oxide growth. The oxide growth caused serious damage in some areas, weakening the oxidation resistance.