Abstract
High-entropy alloys (HEAs) are a new class of metallic materials that have attracted great attention due to their excellent properties. Spark plasma sintering (SPS), which possesses the combined effects of spark discharge and high temperature/pressure, is a promising method for fabricating high-performance HEAs. However, the low cooling rate after SPS (furnace cooling under vacuum) generally facilitates the formation of stable phases in HEAs, including brittle intermetallic phases, which are detrimental to the deformation abilities and mechanical properties of the SPSed HEAs. Here, we report a double-step ball milling approach for processing raw powders to achieve simultaneous enhancements in both strength and ductility in an SPSed face-centred cubic (FCC) CoCrCu0·5NiAl0.5 HEA. The reasons for enhancing the mechanical properties are that the coarse-scale brittle B2 phase along the grain boundary is replaced by dispersed fine-scale α-Al2O3, which results in a reduction in brittleness and an improvement in strength (via Orowan strengthening and load-transfer strengthening) caused by α-Al2O3. Through this study, a simple and effective approach is proposed that may overcome the strength-ductility trade-off for SPSed Al-containing HEAs.
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