IMPROVED MECHANICAL-PROPERTIES IN DISSIMILAR TI-AISI 304L JOINTS

The effect of low temperature post weld heat treatment on the tensile strength and bend test properties of dissimilar friction welds between titanium and AISI 304L stainless steel joints is investigated. Post w eld heat treatment at temperatures less than 873 K has no effect on jo int tensile strength properties, but markedly improves bend test prope rties. The highest bend angle is produced using a post-weld heat treat ment at 773 K for 1 h (the Larson-Miller parameter corresponding to th is treatment is 15.5 x 10(3) K h(-1)). LOW temperature heat treatment improves bend ductility, because stress relaxation occurs with minimal increase in the transition region width at the bond line region. Diss imilar joint bend testing properties decrease markedly when the width of the transition region exceeds 1-2 mu m. An explanation for the detr imental effect of thick transition regions at the joint interface regi on on the mechanical properties of dissimilar joints is proposed. It i s suggested that the development of significant triaxial stress due to the constraint imposed by large, needle-shaped intermetallic particle s promotes premature joint failure in joints containing thick transiti on regions.