Refractory high-entropy alloys (RHEAs) have excellent mechanical properties and thermal stability. A unique light emission phenomenon appeared during the cutting of the WNbMoTaZr RHEA, which may cause injury to operators and ignite combustibles. In this work, the light emission characteristics under varying cutting parameters as well as the generation mechanisms were investigated. The light emission was observed when the cutting speed reached 50 m/min. It was found that the light emission is caused by the exothermic oxidation of Zr in chips, due to the rise in cutting temperature. With the change of cutting depth and feed rate, chip width and curvature also changed, affecting the Zr content and heat accumulation, which in turn influenced light emission and chip melting. Since most of the cutting heat was taken away by the chips, light emission had a limited effect on the machined surface quality. Thereafter, the formation mechanism of the recrystallized grains, existing on the chip melting surface, was analyzed, which is substantially different from the recrystallization mechanism under high-speed cutting. The results indicate the redistribution of elements on the melting surface of the chip, and the formation of recrystallized grains enriched with Nb and Ta elements. This was attributed to the combination of heat generated by light emission and cutting, which melts the chip surface and causes dynamic recrystallization.
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