Exceptional cryogenic tensile properties of K4169 superalloy by micro-grain casting process

The simultaneous provision of strength and ductility of casting superalloy is challenging. In this work, a micro-grain casting process was applied to produce grain-refined K4169 alloy, which exhibited a superior combination of tensile ultimate strength, yield strength and elongation of 1204 MPa, 1041 MPa and 21.0 % at 23 °C. The tensile strengths were significantly enhanced without elongation weakened compared with the conventional casting one, which exhibited values of 947 MPa, 813 MPa and 20.0 %, respectively. As temperature decreased to −196 °C, the elongation of micro-grain K4169 further increased to 26.1 % while decreased to 13.5 % of the conventional one resulting from the different twinning tendencies related to grain refinement. This is because twinning occurs predominantly in grains orientated close to the 〈111〉 // tensile axis, and micro-grain casting process improves the probability for grains to meet this crystallography condition. The deformation twins together with stacking faults and Lomer-Cottrell locks ensured continuous work hardening, resulting in the delayed onset of necking and a better elongation. This work highlights the excellent mechanical properties of micro-grain K4169 and anticipates its enormous application potential. Moreover, the results of micromechanical behavior-microstructure-property relationship may improve the understanding of the plastic deformation of K4169 alloy and guide a further upgrading.