Full-composition-gradient in-situ alloying of Cu–Ni through laser powder bed fusion

Abstract

Multi-material laser powder bed fusion has long been a challenge in additive manufacturing, especially in terms of controlling spatial variations and joining multiple materials. The challenge is even greater when multi-material components have different physical properties (e.g., different thermal expansions, thermal conductivities and laser reflectivities). The aforementioned scenario is applicable to copper–nickel (Cu–Ni) alloy. The simultaneous printing and controllable mixing of pure Cu and pure Ni within a single print have not been accomplished due to the substantial disparity in the physical properties of pure Cu and pure Ni. In this work, a full composition with different mixing proportions (100 % Cu to 100 % Ni) was fabricated in a single printing process through in-situ alloying based on our process of micro laser powder bed fusion. A transition from a columnar grain to a quasi-equiaxed grain morphology with texture variation from <110> to <111> was found in the full–composition–gradient of the Cu–Ni alloy. Microstructural variations, such as fine grain strengthening and grain boundary strengthening, greatly affected the mechanical properties of the alloys: the ultimate tensile strength ranged from 303 to 488 MPa and the yield strength ranged from 231 to 445 MPa. Moreover, the electrical conductivity of the alloys with a compositional gradient ranged from 3.6 % IACS to 96 % IACS due to the electron scattering induced by lattice distortion. In summary, a full-composition Cu–Ni gradient alloy was fabricated through in-situ alloying adopting micro laser powder bed fusion for the first time, enabling the investigation of the evolution of the microstructure and properties of the alloy as the alloy composition varies.