Strengthening CoCrFeNi high entropy alloys via additive manufacturing with laser shock modulation of melt pool

A novel synchronous laser shock modulation of melt pool (LSMMP) method was proposed to enhance melt pool convections and inhibit columnar crystal growth mainly found in additive manufacturing high entropy alloys (HEAs) via an additional second pulsed laser. The effect of laser shock on the microstructure of HEAs under the same additive manufacturing parameters was discussed assisted by finite element method (FEM). Results of electron backscattered diffraction (EBSD) show that grain refinement occurs in LSMMPed HEAs under optimal parameters. The strengthened plane texture is observed in the LSMMPed HEAs from three crystallographic orientations of [100], [110], and [111]. The Vickers hardness of HEAs is enhanced by grain refinement and there is no elemental segregation in the LSMMP process. The validation of LSMMP by tensile tests also indicates that the LSMMPed HEAs have better ductility. The present results demonstrate the fast real-time interference capability of LSMMP in metal additive manufacturing. • An effective in-situ modulative tool of laser shock modulation of melt pool (LSMMP) was studied to control additive manufacturing. • The process and extent of melt pool oscillation caused by different pulsed laser energies were recorded. • An optimal LSMMP parameters is beneficial for changing grain type and refining grain. • Strength of CoCrFeNi HEAs is enhanced by grain refinement in the LSMMP process. • A better ductility of CoCrFeNi HEAs with ultimate tensile strength of 652 MPa and elongation of 42.1% was obtained.