Microstructure and mechanical properties of Co31.5Cr7Fe30Ni31.5 high-entropy alloy powder produced by plasma rotating electrode process and its applications in additive manufacturing

Abstract

Microstructure and mechanical properties of feedstock powders critically determine the quality of additive manufacturing (AM). The present study employs a plasma rotating electrode process (PREP) to produce non-equiatomic Co31.5Cr7Fe30Ni31.5 high-entropy alloy (HEA) powders and examines variations of their microstructure and mechanical properties with powder particle size in the range of 20–106 μm. It finds that the powders possess smooth surfaces, good sphericity, and equiaxed polycrystal grains under PREP electrode rod arc speed of 32000 r/min and main arc current of 760 A. A stable FCC structure is maintained regardless of the powder particle size. Moreover, the nano-hardness of the powders generally decreases with the increase of powder particle size except for that of 50–75 μm, which is positively correlated with the change of the grain size. The finest grain size is present for powders with particle sizes of 50–75 μm, which possess the highest average nano-hardness and reduced elastic modulus. Bulk alloys fabricated by cold spray (CS) and laser cladding (LC) AM maintain the FCC structure. The CSAM bulk alloy shows early brittle fracture due to the presence of pores and prior particle boundaries resulting from insufficient plastic deformation of the powder particles. The LCAM bulk alloy presents good tensile properties with the ultimate tensile strength (UTS) and elongation to failure being 481.2 MPa and 35.9%, respectively, which can be attributed to the good cohesion and grain characteristics. The present study shall provide the field of AM with useful information in the applications of non-equiatomic PREP HEA powders.

Keywords

• High-entropy alloys
• Plasma rotating electrode process
• Additive manufacturing
• Microstructure
• Mechanical properties