Mössbauer investigations of the σ-phase in the AlxCrFeCoNi high entropy alloys

Abstract

In this work we analyse the formation of sigma phase in AlxCrFeCoNi (x = 0–1.5) alloys. In order to characterise the AlxCrFeCoNi system, we decided to investigate 5 additional samples corresponding to the individual phases of alloys for x = 1 and 1.5. They were annealed at 600–1000∘C for 24 h. For each of those five samples scanning electron microscope, SEM, XRD and Mössbauer measurements were performed. The SEM/BSE images allowed identify the number of different phases present in the samples and EDX method gave elemental composition of every phase. The XRD technique helped identify those phases, and thanks to Mössbauer spectroscopy we were able to determine the percentage of each of them. The SEM/EDX measurements also revealed spherical Al precipitations which can be clearly divided into two groups in respect of diameter distribution. The analysis of the Mössbauer spectra revealed magnetically split and a paramagnetic component for phases rich in Cr as well as for a phase rich in Al and Ni. We established that the sigma phase is formed in the phase rich in Cr, and has a secondary character. We also provide the degree of transformation to sigma phase for every sample.