Bangsheng Li

Design of non-equiatomic medium-entropy alloys

High-entropy alloys have attracted much attention due to their unique microstructures and excellent properties. Since their invention more than ten years ago, research attention has been mainly focused on the study of multicomponent alloys with equiatomic or near-equiatomic compositions. Here we propose a novel design of non-equiatomic medium-entropy alloys that contain one matrix element and several equiatomic alloying elements. To verify the utility of this new design, a series of Co-free Fex(CrNiAl)100−x (at.%, 25 ≤ x ≤ 65) medium-entropy alloys were designed from the much-studied FeNiCrCoAl high-entropy alloy. Detailed characterization reveals that the alloys exhibit novel two-phase microstructures consisting of B2-ordered nanoprecipitates and BCC-disordered matrix. As the alloys deviate far from equiatomic composition, the structure of the nanoprecipitates transfers from a spinodal-like intertwined structure to a nanoparticle dispersed structure. Previous parametric approaches to predict phase formation rules for high-entropy alloys are unable to describe the phase separation behaviors in the studied alloys. Our findings provide a new route to design medium-entropy alloys and also demonstrate a strategy for designing nanostructured alloys from multicomponent alloy systems through simple variations in non-equiatomic compositions.

RESEARCH OF MECHANICAL PROPERTY GRADIENT DISTRIBUTION OF Al-Cu ALLOY IN CENTRIFUGAL CASTING

Al-Cu alloy castings are obtained using centrifugal casting. The regularity of mechanical property gradient distribution of Al-Cu alloy castings with the same centrifugal radius at different positions is investigated. The result shows that the tensile strength, yield strength, elongation and microscope hardness exhibit the following gradient distribution characteristic — high on both sides and low on the center. The trend of mechanical property gradient distribution of Al-Cu alloy increases with the increase in the rotation speed. Moreover, the mechanical properties of casting centerline two sides have asymmetry. The reason is that the grain size of casting centerline two sides and Al2Cu phase and Cu content change correspondingly.