Residual stresses and interface strengths in MoSi2/stainless steel 316L joints produced by metallic-glass brazing

The residual stresses in molybdenum disilicide (MoSi2)/stainless steel 316 L joints were evaluated using X-ray diffraction (XRD) and instrumented inde ntation techniques. These joints were produced by high-temperature brazing using a cobalt-based metallic glass (METGLAS 2714A). Joining was completed in two different ways, either by feeding excess braze into the braze gap up on heating or by constraining the MoSi2/stainless steel assembly with an al umina (Al2O3) fixture during the heating cycle. These steps were necessary to ensure the production of a high-quality void free joint. The indentation results show higher tensile residual stresses in the stainless steel for t he joint with the external constraint, in comparison to the unconstrained s tate. In contrast, the compressive residual stresses in the MoSi2 las measu red by XRD) were lower in the constrained state relative to the unconstrain ed state. These results and a lack of residual stress balance indicate that the stress state in the braze is significantly different under the two joi ning conditions and the volume of the braze plays an important role in the development of the residual stresses. Push-out tests carried out on these j oints gave higher joint strengths in the unconstrained as compared to the c onstrained condition. The results of this study have important implications on the selection of the appropriate joining process (use of constraint vs extra braze).