Microstructure-fracture toughness relationship of vanadium alloy/stainless steel brazed joints

In this work, brazing V-5Ti-5Cr to 304 stainless steel (SS 304) using Au-18Ni alloy as filler material was conducted under high vacuum condition. Sessile drop technique was used to determine the wettability of filler alloy to the stainless steel and the vanadium alloy substrates upon which the relationship between the contact angles with time was obtained. Tensile tests were performed on unnotched and notched specimens to demonstrate the overloading behavior and the fracture toughness of the base materials and the brazed joint. Fracture surface was examined for both the V-5Ti-5Cr and the joint to identify the failure mechanisms under static loadings. It was found that the Au-18Ni filler material exhibited good wettability with the SS 304 and V-5Ti-5Cr. The ultimate tensile strength of the brazed joint reached 245 MPa. The strain to failure was about 1.3%. Young's modulus was about 351 GPa. The fracture toughness (K,,) of this joint was 19.1 MPa rootm. The fracture surface of the joint showed well brazed area with good wettability and proper amount of residual filler material which came from the solidification of residual liquid filler alloy of Au-Ni. The failure of the joint occurred along the interface of the vanadium/filler under static load. (C) 2001 Published by Elsevier Science B.V.