Residual stress generation in tungsten-copper brazed joint using brazing alloy

Abstract

Understanding the residual stress state in brazed joints is crucial for operational design and life time performance of the part in service. High magnitude residual stresses are expected in the joined materials following cooling from brazing temperatures (≈950C) due to large mismatches in material properties such as coefficient of thermal expansion and Young's modulus (E). This paper aims to further understanding of the residual stresses caused when brazing tungsten to copper using a eutectic gold-copper brazing alloy. This configuration is potentially useful for future divertor designs. Finite Element Analysis (FEA) has been used to predict the brazing induced stresses and residual stress measurements were carried out on the brazed joint by X-ray diffraction (XRD) to validate the prediction model. Large residual stresses are predicted and measured in the tungsten; however there is disagreement in the nature of the stress. Predicted stresses are highly tensile in nature close to the brazing interface, whereas the measured stresses are highly compressive. The disagreement is believed to be caused by the model not accurately simulating the complex brazing process. Residual stress measurements on the copper were not possible due to texturing during brazing, grain growth and significant inelastic strains. Misalignment of parent materials was also observed to significantly affect residual stresses.