Microstructure and mechanical properties of CoCrNiVAlx multi-principal component alloy

Multi-principal component alloy has been proved to form disordered solid solution in most cases. However, multi-principal component alloy with single phase solid solution has a few disadvantages in mechanical properties, such as low strength or poor plasticity. Aiming at CoCrNi-based multi-principal component alloy with low strength, this paper proposed a method to enhance the multi-principal component alloy through composition design. CoCrNiVAlx multi-principal component alloy was melted by non-consumable vacuum arc melting, and the content of σ phase in the multi-principal component alloy was changed by adjusting the content of Al element. With the addition of Al element, the fcc disordered phase in the multi-principal component alloy gradually went to the ordered L12 phase with the same structure. When the amount of Al was 1.5 wt%, the compressive strength reached 2347 MPa and the hardness reached 760.8HV, which were 30% and 20% higher than the compressive strength (1828 MPa) and hardness (619.3HV) of CoCrNiV multi-principal component alloy, respectively. With the further increase of Al element to 2.0 wt%, the σ phase in the multi-principal component alloy increased further, resulting in the simultaneous decrease of strength and plasticity. The strengthening mechanism of multi-principal component alloy was analyzed, and the strengthening action of L12 phase was confirmed. The results showed that the strengthening of multi-principal component alloy was mainly provided by L12 phase strengthening (1229.55 MPa, 52.39%) and grain boundary strengthening (376 MPa, 16.02%). This paper provided a probable strategy to increase the strength of the multi-principal component alloy, which opened up a new idea for the composition design of multi-principal component alloy.