Yield-stress anomaly in equiatomic ZrNbTiVHf high-entropy alloys

TL;DR

This study investigates the unusual increase in yield stress with temperature in ZrNbTiVHf high-entropy alloys, revealing a yield-stress anomaly between 500 and 800 K and analyzing the underlying deformation mechanisms.

Contribution

It provides the first detailed experimental analysis of the yield-stress anomaly in ZrNbTiVHf high-entropy alloys, including thermodynamic activation parameters and deformation behavior.

Findings

Yield stress increases with temperature between 500 and 800 K.

Flow stress shows minimal strain-rate dependence in the anomaly range.

Regular deformation behavior with linear temperature dependence outside the anomaly range.

Abstract

We have carried out plastic deformation experiments on single-phase samples of the body centered ZrNbTiVHf high-entropy alloy between room temperature and 1150 K. The experiments were carried out on polycrystalline samples with two different grain sizes, in compression at a true constant strain rate of 10-4 1/s. Incremental tests such as stress-relaxation tests, strain-rate changes and temperature changes were carried out in order to determine thermodynamic activation parameters of the plastic deformation process. The material displays a yield-stress anomaly in the temperature range between about 500 and 800 K, where the yield stress increases with increasing temperature. In the same temperature range, we find an extremely low strain-rate dependence of the flow stress, which is reflected in almost constant flow-stress values in stress-relaxations and strain-rate changes. At temperatures below 400 and above 800 K we find regular plastic deformation behavior with a linear temperature dependence of the yield stress of about -1.1 MPa/K, an activation volume of around 1.8 nm3 and 0.2 nm3 at low and high stresses, respectively, and an activation enthalpy of 2.7 eV in the high-temperature range.