Large scale stabilization of the BCC phase in copper-steel laser powder bed fusion enabling statistical microstructural analysis and mechanical testing

Abstract

It has been shown that a Body-Centered Cubic (BCC) phase appears in the L-PBF additively manufactured Copper/Steel bimetallic system, at the interface between the two materials. This study aimed to stabilize the BCC phase on a larger scale to enable statistical analysis of its effects on solidification and microstructure, as well as mechanical performance. Thermodynamic CALPHAD calculations identified a mixture of 85 % CuCrZr and 15 % 316L as optimal for BCC stabilization. This 15 % 316L addition increased laser absorptivity, reduced thermal conductivity and helped promoting a refined microstructure, a weakened texture, and a significant BCC phase formation. The BCC phase altered solidification by inducing heterogeneous nucleation, producing a bimodal microstructure. These microstructural changes markedly enhanced mechanical performance, with room-temperature compression yield strength rising from 250 MPa (CuCrZr) to 535 MPa. Finite element simulations, coupled with CALPHAD modelling, were used to investigate the influence of 316L on CuCrZr’s thermophysical properties and its role in the observed improvements. The findings of this study suggest that the presence of the BCC phase can enhance the mechanical properties of the interfacial region, and potentially influence the resistance to interfacial cracking—a common issue in multi-material printing.