Microstructure and Mechanical Properties of Sintered and Heat-Treated HfNbTaTiZr High Entropy Alloy

Jaroslav Málek,Radim Kocich,Jakub Čížek,František Lukáč,Lenka Kunčická,Jiří Zýka

doi:10.3390/met9121324

Abstract

High entropy alloys (HEAs) have attracted researchers’ interest in recent years. The aim of this work was to prepare the HfNbTaTiZr high entropy alloy via the powder metallurgy process and characterize its properties. The powder metallurgy process is a prospective solution for the synthesis of various alloys and has several advantages over arc melting (e.g., no dendritic structure, near net-shape, etc.). Cold isostatic pressing of blended elemental powders and subsequent sintering at 1400 °C for various time periods up to 64 h was used. Certain residual porosity, as well as bcc2 (Nb- and Ta-rich) and hcp (Zr- and Hf-rich) phases, remained in the bcc microstructure after sintering. The bcc2 phase was completely eliminated during annealing (1200 °C/1h) and subsequent water quenching. The hardness values of the sintered specimens ranged from 300 to 400 HV10. The grain coarsening during sintering was significantly limited and the maximum average grain diameter after 64 h of sintering was approximately 60 μm. The compression strength at 800 °C was 370 MPa and decreased to 47 MPa at 1200 °C. Porosity can be removed during the hot deformation process, leading to an increase in hardness to ~450 HV10.

Highlights

The concept of the so-called “high entropy alloys” (HEAs), known as “multi-principal element alloys” (MPEAs) or “complex concentrated alloys” (CCAs)[1], has been attracting attention since its formulation in the early 2000s by Yeh et al [2] and Cantor et al [3]
The concept of High entropy alloys (HEAs) is different from other alloys of modern structural materials which may consist of multiple metallic elements [4,5]
The HfNbTaTiZr alloy was synthesized from elemental powders via the powder metallurgy process consisting of mixing, cold isostatic pressing and sintering

Summary

Introduction

The concept of the so-called “high entropy alloys” (HEAs), known as “multi-principal element alloys” (MPEAs) or “complex concentrated alloys” (CCAs)[1], has been attracting attention since its formulation in the early 2000s by Yeh et al [2] and Cantor et al [3]. The concept of HEAs is different from other alloys of modern structural materials (e.g., composites) which may consist of multiple metallic elements [4,5]. The traditional design of new alloys with one principal element is replaced by a new group of materials with multiple elements. The matrixes of high entropy alloys are typically bcc or fcc, but recently even HEAs with the hcp matrix have been reported [1,11,12,13,14]. The HEAs with the bcc matrix usually exhibit high strength and lower plasticity whereas fcc HEAs have lower strength and high plasticity [1,6]

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