Coupling hot isostatic pressing and laser powder bed fusion: A new strategy to manufacture defect-free CuCrZr-316L steel multi-material structures

Multi-material laser powder bed fusion (PBF-LB) offers new design opportunities by combining multiple materials into complex 3D shapes. However, for combinations with large differences in thermal, physical or elastic properties, avoiding interfacial defects is challenging. Combining Cu alloys with stainless steel is appealing for components necessitating high thermal / electrical conductivity in some areas and high strength and corrosion resistance in others. In this work, CuCrZr-316L samples were fabricated with a recoater allowing for deposition of two powders within a layer. As-printed samples exhibit significant intermixing and two types of defects: porosity in CuCrZr and steel cracking near the interface. Subsequent hot isostatic pressing (HIP) effectively addressed these issues by closing pores and healing cracks. Despite an overall softening, CuCrZr stays harder near the interface thanks to a very fine-grained structure retained after HIP. Alternatively, when CuCrZr powder near the interface is left unmelted and subsequently sintered, regions with small equiaxed grains and Cr-rich precipitates are formed, which exhibit properties similar to those of printed and HIPed CuCrZr. Hence, locally leaving powder unmelted and sintering it proved to be a successful strategy for producing defect-free 316L-CuCrZr components via PBF-LB, provided an airtight enclosure is ensured through proper design considerations.