Three-dimensional ultrasounds bring about crystallographic microstructure transition and mechanical performance synergy for multicomponent (FeCoNiCr)85Mo15 eutectic alloy

Three-dimensional (3D) ultrasounds were applied to the solidification process of multicomponent (FeCoNiCr) 85 Mo 15 eutectic alloy. At the small ultrasonic amplitude of 14 ​μm, the lamellar (γ+σ) eutectic was significantly refined, and the interface orientation was shifted from [001] γ //[112] σ and (−110) γ //(11-1) σ to the most stable configuration of [011] γ //[-110] σ and (-11-1) γ //(001) σ . If ultrasonic amplitude was increased, σ phase transferred from tetragonal to hexagonal close-packed (HCP) structure, while its independent nucleation and growth facilitated the formation of anomalous (γ+σ) eutectics. Once the ultrasonic amplitude reached 16 ​μm, a metastable μ phase enriched with Cr element was found in the form of lamellar (γ+μ) eutectic structure. These crystallographic structure transitions were attributed to the ultrasound induced high energy and nonlinear cavitation and acoustic streaming effects. The diverse eutectic structures obtained by 3D ultrasonic solidification brought in superior mechanical properties. The maximum yield strength and ductility were enhanced by 1.4 and 2.1 times to 2000 ​MPa and 21.4 ​%, respectively. The strengthening mechanism belonged to the refinement of lamellar (γ+σ) eutectics and the stable interface configuration secured by weak ultrasounds, whereas the increased volume fraction of the FCC-structured γ phase in (γ+σ) eutectic and the metastable (γ+μ) eutectic structure formed under strong ultrasounds contributed to enhance alloy ductility.