Joining of Cf/SiC composite and stainless steel via Ag+Ti filler in-situ alloying

Abstract

Abstract The microstructure and formation mechanism of the Cf/SiC composite and stainless steel joints brazed with Ag+Ti filler were investigated. The effects of Ti content (10%˜40%, at %), bonding temperature (990˜1080 °C) and holding time (15˜60 min) on microstructure and mechanical properties of the joints were discussed. The results indicated that a large-thickness interlayer was formed after bonding, in which in-situ formed TiAg particulates and residual Ti particles were dispersed in Ag matrix. Compared with the common composite interlayers, the interlayer formed via Ag+Ti in-situ alloying had more and finer reinforcing phases without reducing the activity of the filler material. The ductile Ag matrix contributed to accommodate the large strain mismatch by elastic deformation. The interfaces between the adjoining materials and the interlayer were well-bonded without any cracks. At Cf/SiC side interface, TiC, Ti5Si3 and Ti3SiC2 grains were generated from SiC matrix and carbon fibers were exposed. A meshing interface was formed, which was beneficial to arrest and deflect cracks and improve the shear strength of the joints. Kirkendall voids were observed at 304 side interface. Especially they were formed in the joints prepared using high Ti content filler materials (Ag+30%˜40%Ti, at %) or bonded at relatively low joining temperature (990 °C). When the content of Ti was fixed, the joint shear strength increased firstly and then decreased with the bonding temperature. Different Ti contents corresponded to different peak bonding temperatures. The holding time had a similar effect on the joint strength as bonding temperature. The maximum joint shear strength at room temperature was 141 MPa obtained at 1020 °C for 30 min with Ag+30 at %Ti composite filler.