Influence of testing temperature on the mechanical performance of brazed conventionally and additively manufactured 316L stainless steel joints

In this work, brazed joints between samples of 316L stainless steel (316LSS) are formed using the Ag155 brazing filler metal. As an additional aspect of the investigation, the joints combine stainless steel formed by conventional processing and by additive manufacture (AM). These samples are then tested to determine their shear response with temperature, employing a bespoke test design comprising a set of three cylindrical samples held together with two brazed joints. Multiple samples are tested at 20 and 500 °C and single samples at intermediate temperatures. A shear strength above 200 MPa is retained up until 200 °C, and, despite significant differences in steel microstructure, the conventional or AM processing of the 316LSS does not affect joint failure. At higher temperatures, there is a progressive decrease in both the failure strength and the ductility of the joint. The reasons for the behavior are traced to changes, potentially associated with a transformed layer in the steel near to the joint, in the operating failure mechanism as determined by observations of the failure surfaces of the joints. These results highlight the importance of systematic investigations of the strength of brazed joints with temperature and correlation of these to the joint microstructure.