Microstructural refinement and tensile properties of Fe65.7Ni11.7Ti1Mo6.6Co15 HEA undergoing multiple LSP

Seeking for the Fe65.7Ni11.7Ti1Mo6.6Co15 high entropy alloy (HEA) with well-performed mechanical properties is indispensable for its wide applications. Herein, the HEA was fabricated via vacuum induction melting at 1923 K, and then subject to LSP treatment by one to three coverage layers. The corresponding microstructure features were observed and a systematic work of the strengthening mechanism were revealed. Moreover, the uniaxial tensile testing was performed and the fracture behaviors of the tensile specimens as a function of the coverage layer are also determined. It evidently shows that, the significant LSP-generated grain refinement process attributes to the following two modes: (i) interactions of multidirectional dislocation motion subdividing the β phases into refined equiaxed grains, and (ii) numerous new formed parallel lath martensite in γ phases divided by vertical DWs resulting in slender lath grains. In addition, the tensile properties and fracture behaviors of the HEA subjected to LSP treatment strongly depend on the coverage layer. With increasing the coverage layer of LSP, both the ultimate tensile strength and the ductility of the material are improved. Thus, the typical cleavage fracture pattern gradually evolves into the brittleness and ductility mixed fracture pattern.