Microstructure-fracture toughness relationship of vanadium alloy/stainlesssteel brazed joints

In this work, brazing V-5Ti-5Cr to 304 stainless steel (SS 304) using Au-18 Ni alloy as filler material was conducted under high vacuum condition. Sess ile drop technique was used to determine the wettability of filler alloy to the stainless steel and the vanadium alloy substrates upon which the relat ionship between the contact angles with time was obtained. Tensile tests we re performed on unnotched and notched specimens to demonstrate the overload ing behavior and the fracture toughness of the base materials and the braze d 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 tha t the Au-18Ni filler material exhibited good wettability with the SS 304 an d 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 GP a. The fracture toughness (K,,) of this joint was 19.1 MPa rootm. The fract ure surface of the joint showed well brazed area with good wettability and proper amount of residual filler material which came from the solidificatio n of residual liquid filler alloy of Au-Ni. The failure of the joint occurr ed along the interface of the vanadium/filler under static load. (C) 2001 P ublished by Elsevier Science B.V.