Effect of Al Content on Phase Compositions of FeNiCoCrMo0.5Alx High Entropy Alloy

Valentina Andreeva,Svetlana Shalnova,Oleg Tolochko,Tatiana Larionova,Victor Klinkov,Maria Salynova,Anton Semikolenov

doi:10.3390/met11111734

Valentina Andreeva, Svetlana Shalnova + Show 5 more

Open Access

https://doi.org/10.3390/met11111734

Copy DOI

Abstract

The FeCoNiCrMo0.5Alx system with x up to 2.13 was analyzed from the point of view of evolution of the phase composition and microstructure. Cast samples were synthesized by induction melting and analyzed by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, and Vickers microhardness test methods. Phase compositions of these alloys in dependance on Al concentration consist of FCC solid solution, σ-phase, NiAl-based B2 phase, and BCC solid solution enriched with Mo and Cr. Phase formation principles were studied. Al dissolves in a FeCoNiCrMo0.5 FCC solid solution up to 8 at.%.; at higher concentrations, Al attracts Ni, removing it from FCC solid solution and forming the B2 phase. Despite Al not participating in σ-phase formation, an increase in Al concentration to about 20 at.% leads to a growth in the σ-phase fraction. The increase in the σ-phase was caused by an increase in the amount of B2 because the solubility of σ-forming Mo and Cr in B2 was less than that in the FCC solution. A further increase in Al concentration led to an excess of Mo and Cr in the solution, which formed a disordered BCC solid solution. The hardness of the alloys attained the maximum of 630 HV at 22 and 32 at.% Al.

Highlights

The concept of high-entropy alloys (HEA) arose in 2004
Despite Al not participating in σ-phase formation, an increase in Al concentration to about 20 at.% leads to a growth in the σ-phase fraction
A further increase in Al concentration led to an excess of Mo and Cr in the solution, which formed a disordered BCC solid solution

Summary

Introduction

The concept of high-entropy alloys (HEA) arose in 2004. It was initiated by the works of Cantor et al [1] and Yeh et al [2]. Later in [3,4], based on the experimental data, other criteria of multicomponent solid-solution stabilization have been proposed, namely, atomic-size difference (δ), which should not be higher than 6.6%; mixing enthalpy of solid solution (∆Hmix), which should be in the range of −15–5 KJ/mol; and Ω, defined as Tm∆Smix/|∆Hmix|, which should be ≥1.1. An addition of Nb to AlCoCrFeNi studied in [30] results in the formation of a Laves phase of the (CoCr)Nb type and BCC solid solution and an increase in strength and hardness. It is a hard and brittle topologically close packed phase, and its appearance in stainless steels usually results in the deterioration of the properties due to brittleness and the removal of Cr from the solid solution matrix [35,36]

Objectives

Methods

Results

Discussion

Conclusion