Investigation of the Interface between Laser-Melted CoCr and a Stainless Steel Substrate

Abstract

Recent advances in laser technologies offer significant flexibility in the additive manufacturing domain. Extensive work was focused on material processing using laser-directed energy deposition for repairing parts. This pilot study investigated the use of selective laser melting (SLM) for depositing a superior material such as CoCr on an existing stainless steel base. The interface between these dissimilar materials was analyzed. During fabrication, both metals were gradually mixed in the liquid state as the first CoCr powder layer was melded on the steel base without obvious defects. According to SEM and EDAX, the heat-affected zone has a limited depth (<20 µm). XRD patterns recorded across the CoCr–304 interface show a homogenous mixture of γ(Fe) and α(Co) solid solutions. The microporosity calculated by CT was under 0.5%. Microhardness was measured at and near the interface region, showing that the intermixing zone has high hardness (470–480 HV1), which may be related to the fine-grained microstructure. Mechanical testing reveals that the adhesion strength at rupture is 35% higher compared with the ultimate tensile strength of 304 steel. This adhesion strength can be attributed to the complete melting of CoCr particles after laser irradiation and to the reduced thickness of the HAZ and the IZ.

Keywords

• selective laser melting
• CoCr
• adhesion strength
• microhardness
• X-ray computed tomography
• scanning electron microscopy