Microstructure and interfacial reactions during active metal brazing of stainless steel to titanium

Microstructural evolution and interfacial reactions during active metal vacuum brazing of Ti (grade-2) and stainless steel (SS 304L) using a Ag-based alloy containing Cu, Ti, and Al was investigated. A Ni-depleted solid solution layer and a discontinuous layer of (Ni,Fe)2TiAl intermetallic compound formed on the SS surface and adjacent to the SS-braze alloy interface, respectively. Three parallel contiguous layers of intermetallic compounds, CuTi, AgTi, and (Ag,Cu)Ti2, formed at the Ti-braze alloy interface. The diffusion path for the reaction at this interface was established. Transmission electron microscopy revealed formation of nanocrystals of Ag-Cu alloy of size ranging between 20 and 30 nm in the unreacted braze alloy layer. The interdiffusion zone of β-Ti(Ag,Cu) solid solution, formed on the Ti side of the joint, showed eutectoid decomposition to lamellar colonies of α-Ti and internally twinned (Cu,Ag)Ti2 inter- metallic phase, with an orientation relationship between the two. Bend tests indicated that the failure in the joints occurred by formation and propagation of the crack mostly along the Ti- braze alloy interface, through the (Ag,Cu)Ti2 phase layer

Investigation of microstructure and mechanical properties of Fe-V dissimilar welds

This paper presents a systematic investigation of solidification and phase formation, microstructures, and mechanical behavior of Fe-V weld metals. It is found that V weld metal is dominated by Fe25V solid solution (hardness ~ 6.1 GPa) with V-rich precipitates formed along the grain boundaries. The observed intergranular cracking is attributed to the phase separation of (αFe, V) solid solution into V-rich (V) and V-poor (Fe25V) regions at low temperature. The overall mechanical properties could be improved by using Cu20V composite filler, due to the formation of stable Fe10V and Cu solid solution phases