Feasibility study on joining of multi-layered W/Cu-CuCrZr-SS316L-SS316L materials using vacuum brazing

Microhardness and Tensile Strength Analysis of SS316L/CuCrZr Interface by Laser Powder Bed Fusion

Metallic joints within tokamak devices necessitate high interface hardness and superior bonding properties. However, conventional manufacturing techniques, specifically the hot isostatic pressing (HIP) diffusion joining process, encounter challenges, including the degradation of the SS316L/CuCrZr interface and CuCrZr hardness. To address this, we explore the potential of laser powder bed fusion (LPBF) technology. To assess its viability, we fabricated 54 SS316L/CuCrZr samples and systematically investigated the impact of varied process parameters on the microhardness and tensile strength of the dissimilar metal interfaces. Through comprehensive analysis, integrating scanning electron microscopy (SEM) imagery, we elucidated the mechanisms underlying mechanical property alterations. Notably, within a laser volumetric energy density range of 60 J/mm3 to 90 J/mm3, we achieved elevated interface hardness (around 150 HV) and commendable bonding quality. Comparative analysis against traditional methods revealed a substantial enhancement of 30% to 40% in interface hardness with additive manufacturing, effectively mitigating CuCrZr hardness degradation.

Microstructural and Mechanical Characterization of W-CuCrZr Joints Brazed with Cu-Ti Filler Alloy

The determination of the mechanical properties of a brazed joint is an important factor to reach the metallurgical level of a joint development. This paper evaluates the mechanical properties, and its correlation with the joint microstructure, of a W-CuCrZr joint brazed in a high vacuum furnace using 80Cu-20Ti flexible filler material in tape form. This joint is meant to be implemented in the divertor application in future fusion power plants. Main experimental parameters were a brazing temperature of 960 °C and a dwell time of 10 min. The microstructure of the joint was constituted by Cu solid solution and Cu4Ti phases. This last phase was distributed in the W-braze interface. Mechanical properties were evaluated by means of Vickers microhardness and mechanical tests by applying pure shear loads. The microhardness profile of the brazed joint indicated that W remained with the as-received hardness but CuCrZr base material was softened after the brazing procedure. Shear strength of 96 ± 15 MPa was obtained for the brazed joint and fracture propagated at the W-braze interface.