Uncovering the critical factor in determining the residual stresses level in Si3N4–GM filler alloy–42CrMo joints by FEM analysis and experiments

The influence of gradient materials (GM) filler alloy on the distribution of thermal stresses and on the bending strength of the brazed Si3N4–42CrMo steel joints was examined by using finite element modeling (FEM) computations in combination with experiments. In order to form a smooth thermal expansivity change across the whole joint, a novel GM filler alloy was fabricated by stacking each layer with different content of Mo particles (Ag–Cu–Ti+Mo) addition together. We examined the effect of GM compositions, layer numbers and thicknesses on the residual stresses in the brazed joint. In particular, the monolayer composite filler produced by incorporating 10 vol% Mo particles induced the minimum residual stresses in the joint, agreeing with the experimental results. The results indicated that the CTE mismatch between the joined materials and the ability of plastic deformation in the filler alloy were two factors that determine the residual stresses level in a brazed joint. The results reported here will provide us guidance to choose an appropriate filler alloy for improving the ceramic–metal joint performance.