Phase evolution, microstructure, and mechanical behaviors of the CrFeNiAlxTiy medium-entropy alloys

Abstract A series of Co-free CrFeNiAlxTiy medium-entropy alloys (MEAs) were designed and prepared. The effect of Al and Ti addition on phase evolution, microstructure, nano- and marco-mechanical behaviors were systematically investigated and analyzed. The density of the CrFeNiAlxTiy MEAs was measured by the Archimedes method. With the content of Al and Ti increasing, the density of the CrFeNiAlxTiy system decreased. The density of the CrFeNiAl0.3Ti0.3 MEA is only 6.9294 g/cm3. The microstructural analysis indicated that the addition of Al element increased the volume fraction of BCC phase, while the Al and Ti addition increased the volume fraction of BCC and B2 phases. The mechanical tests suggested that the hardness, compressive yield strength, fracture strength, specific yield strength, and specific fracture strength all increased with the Al and Ti addition. The CrFeNiAl0.3Ti0.3 MEA possessed high Vickers hardness, compressive yield strength, fracture strength, specific yield strength, and specific fracture strength, whose values are 551 HV, 1712 MPa, 3700 MPa, 247.06 MP cm3/g, and 533.96 MP cm3/g, respectively. Furthermore, the compressive plasticity of the CrFeNiAl0.3Ti0.3 MEA is also very large (∼39.8%). The CrFeNiAl0.4Ti0.2 MEA also displayed outstanding mechanical behaviors just as the CrFeNiAl0.3Ti0.3 MEA, whose Vickers hardness, yield strength, and compressive plasticity are 580 HV, 1600 MPa, and 45%, respectively. The good combination of strength and compressive plasticity of CrFeNiAl0.3Ti0.3 and CrFeNiAl0.4Ti0.2 MEAs could attribute to the peculiar microstructure. The phase formation criteria and strengthening mechanism were discussed. This study provides insights not only into the BCC/B2-containing MEAs but also into the future development of MEAs with high-performance, low-cost, and low-density for industrial applications.