Effect of GA+ ion beam on the stability of retained austenite in high carbon steel

Abstract

This paper presents studies concerning the influence of the Ga+ ion beam on the stability of retained austenite in K110 cold work tool steel (X155CrVMo12). The material was first austenitized at 1200 °C to dissolve a significant amount of the alloy's carbides to obtain the largest possible volume fraction of retained austenite, which was 93% after quenching in oil. Changes in the steel's crystal structure upon interaction with Ga+ ions were observed using a combination of SEM-FIB-EBSD techniques. Selected grains in the material were sputtered with Ga+ ions of various accelerating voltages (2 kV – 30 kV) using two different doses, namely 50 and 100 pC/μm2. It was found that the application of 5 kV Ga+ ion beam is enough to induce partial transformation of austenite to BCC phase. The use of higher voltages (8–30 kV) resulted in the complete transformation of austenite. Low acceleration voltages of 2 kV, even with a high dose of 500 pC/μm2, did not induce any phase transformation and only deformed austenite's crystal structure. Moreover, it was shown that the crystallographic orientation between austenite and the Ga+ ion beam induced BCC phase is not random.