Joining of high thermal-expansion mismatched C-SiC composite and stainless steel by an Ag + Ti + Mo mixed powder filler

Abstract

Abstract High thermal-expansion mismatched C-SiC composite and 304 stainless steel have been bonded by a 72Ag + 18Ti + 10Mo (at%) mixed powder filler. At the bonding temperature (1020 °C), the filler was in semi-solid state, i.e. solid-liquid mixed state of Mo particles, TiAg grains and Ag(Ti) liquid. Microstructural analysis indicated that the high activity and viscosity of the semi-solid filler help to obtain a large-thickness homogeneous joining layer (∼416 mm), in which Mo particles were clad by (Ti,Mo) solid solution and uniformly dispersed in Ag matrix together with the TiAg grains. The large thickness joining layer mainly composed of low coefficient of thermal expansion (CTE) Mo particles and ductile Ag matrix can effectively reduce the high residual stresses of the joint caused by the thermal-expansion mismatch between the dissimilar materials. Additionally, interfaces between the base materials and the joining layer were well bonded without continuous layered brittle compounds. The interfacial reaction products at C-SiC side were TiC, Ti5Si3 and Ti3SiC2 grains in Ag matrix. At 304 interface, Ti2Ni + Ti(Fe,Ni) compounds grew in columnar and gathered nearby. The characteristics of the joining layer and the bonding interfaces contribute to the high joint strength. The average shear strength of the joint at room temperature was 156 MPa.