Solidification Microstructures of the Ingots Obtained by Arc Melting and Cold Crucible Levitation Melting in TiNbTaZr Medium-Entropy Alloy and TiNbTaZrX (X = V, Mo, W) High-Entropy Alloys.

Takeshi Nagase,Takayoshi Nakano,Kiyoshi Mizuuchi

doi:10.3390/e21050483

Takeshi Nagase, Takayoshi Nakano + Show 1 more

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https://doi.org/10.3390/e21050483

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Abstract

The solidification microstructures of the TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, and W) high-entropy alloys (HEAs), including the TiNbTaZrMo bio-HEA, were investigated. Equiaxed dendrite structures were observed in the ingots that were prepared by arc melting, regardless of the position of the ingots and the alloy system. In addition, no significant difference in the solidification microstructure was observed in TiZrNbTaMo bio-HEAs between the arc-melted (AM) ingots and cold crucible levitation melted (CCLM) ingots. A cold shut was observed in the AM ingots, but not in the CCLM ingots. The interdendrite regions tended to be enriched in Ti and Zr in the TiNbTaZr MEA and TiNbTaZrX (X = V, Mo, and W) HEAs. The distribution coefficients during solidification, which were estimated by thermodynamic calculations, could explain the distribution of the constituent elements in the dendrite and interdendrite regions. The thermodynamic calculations indicated that an increase in the concentration of the low melting-temperature V (2183 K) leads to a monotonic decrease in the liquidus temperature (TL), and that increases in the concentration of high melting-temperature Mo (2896 K) and W (3695 K) lead to a monotonic increase in TL in TiNbTaZrXx (X = V, Mo, and W) (x = 0 − 2) HEAs.

Highlights

A recently developed concept in the area of multicomponent alloys, which is known as high-entropy alloys (HEAs), has been proposed for use in a new generation of structural and functional metallic materials [1,2,3,4,5,6,7]
The peaks of the TiNbTaZr medium-entropy alloy (MEA) and the TiNbTaZrV HEA can be indexed to the body-centered cubic (BCC) phase, while the formation of a dual-BCC phase that was composed of BCC-1 and BCC-2 phases was observed in the TiNbTaZrMo bio-HEA and the TiNbTaZrW HEA
The distribution of constituent elements in the solidification microstructures was discussed based on their thermodynamics

Summary

Introduction

A recently developed concept in the area of multicomponent alloys, which is known as high-entropy alloys (HEAs), has been proposed for use in a new generation of structural and functional metallic materials [1,2,3,4,5,6,7]. RHEAs were mainly developed as high-temperature structural materials and/or radiation resistant materials [8,9,10,11,12,13]. Ti–Nb–Ta–Zr–Mo HEAs, whose constituent elements are group IV, V, and VI elements, were reported as promising metallic biomaterials [14,15,16]. HEAs and MEAs for metallic biomaterials are denoted as Entropy 2019, 21, 483; doi:10.3390/e21050483 www.mdpi.com/journal/entropy

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