Advances of machining techniques for gradient structures in multi-principal-element alloys

Multi-principal-element alloys (MPEAs) are attracting increasing attentions because of their high strength and ductility, high fracture toughness, excellent corrosion resistance, outstanding thermal-softening resistance and high oxidation resistance. Moreover, gradient structures (GSs) have been shown to be effective in alleviating the strength-ductility trade-off although strength and ductility are mutually exclusive properties for metals, which provides an opportunity for developing high-performance MPEAs. Here, we summarized four processing methods for creating GSs in MPEAs, including rotationally accelerated shot peening (RASP), ultra-precision machining technology (UPMT), cyclic dynamic torsion (CDT), and ultrasonic surface rolling processing (USRP). Principles, advantages, disadvantages, and typical applications of these methods are discussed in this work.