Elasto-Plastic-Creep Characteristics of BAg8 Brazing Filler Metal Estimated by Tension-Strain Maintenance Test

This paper discusses the efficient estimation method of the elasto-plastic-creep characteristics of BAg8 (72%Ag28%Cu) brazing filler metal for joining the cemented carbide of K20 (WC-Co) to the alloy tool steel of SKS3. For the estimation, so-called "tension-strain maintenance test" which consists of a tensile part and a stress relaxation part was employed. The advantage of this estimation method is that once this test has been conducted using only 1 specimen at a temperature, the elasto-plastic-creep characteristic of the specimen at the temperature can be estimated. Especially, the creep characteristics can be estimated without conducting long-term creep test. Therefore, by conducting tension-strain maintenance tests, the elasto-plastic-creep characteristics of BAg8 at 3 different temperatures were estimated. Based on the estimated results, the material constants for an elasto-plastic-creep constitutive model were determined at the 3 temperatures, and then they were expressed as a function of temperature to describe the deformation of BAg8 at arbitrary temperature. Using the constants for the elasto-plastic-creep constitutive model, some simulations of basic deformation, such as time-dependent pure tension and stress relaxation at different 2 temperatures were conducted. Then, by comparing the simulations with the experiments, it was found that the deformation behaviors in the experiments were almost predicted by the simulations. Moreover, the elasto-plastic-creep FEM analysis of the brazing process for joining K20 and SKS3 with BAg8 was conducted by employing the constitutive model with the material constants used for the above basic simulations. The residual stress distributions in the analyzed result were compared with the X-ray residual stress measurement results of an actual brazing joint. As a result, the residual stress distributions in the analysis approximated those in the actual brazing joint well. Namely, the elasto-plastic-creep characteristics of BAg8 could be estimated efficiently by the tension-strain maintenance tests using only 3 specimens.