# Al and Cu Effect on the Microstructure and Mechanical Properties of HEA Based on the AlCoCuFeNi System

## TL;DR

This study examines how varying Al and Cu levels in a high-entropy alloy affect its microstructure and mechanical properties, finding that non-equiatomic variants offer better strength and ductility.

## Contribution

The paper introduces new insights into the influence of Al and Cu on the mechanical behavior and microstructure of HEAs in the AlCoCuFeNi system.

## Key findings

- Reduced Al and Cu contents result in a single-phase microstructure with improved ductility and impact strength.
- Non-equiatomic variants achieve a tensile strength of 450 MPa with 60% elongation, compared to 80 MPa in the equiatomic variant.
- Fractography confirms a ductile fracture mode in the modified alloys.

## Abstract

Three variants of high-entropy alloys (HEAs) from the AlCoCuFeNi group, containing different amounts of Al and Cu, were developed and produced via induction melting and casting into ceramic moulds. The ingots were homogenized at 1000 °C for 10 h. Analyses revealed that variations in Al and Cu concentrations led to significant changes in the material’s microstructure, hardness, strength, and impact strength. In the equiatomic variant, differential scanning calorimetry revealed a peak associated with the phase transformation, indicating that this alloy’s microstructure consists of two distinct phases. In contrast, when the concentrations of Al and Cu are reduced, a single-phase microstructure is observed. The equiatomic variant (used as a reference) is characterized by its hardness and brittleness, exhibiting slight ductility, with a tensile strength of 80 MPa, a hardness of 400 HV5, and an impact strength of 1.9 J/cm2. However, with adjusted Al contents of 1/2 and Cu contents of 1/4, the alloy displays exceptional strength combined with good plasticity, achieving a tensile strength of up to 450 MPa with 60% elongation, and an impact strength of 215 J/cm2. The non-equiatomic variants exhibit a comparatively more straightforward microstructure and enhanced ductility, which may facilitate easier processing of these alloys. Fractography investigation revealed a ductile mode of fracture in the samples.