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

THERMOTRANSPORT OF SOLUTES IN LIQUID SILVER.

Abstract Thermotransport studies have been made for liquid silver which contained trace amounts of gold, antimony and sulfur. Capillaries containing silver and homogeneously distributed solute were sub­jected to a temperature gradient and solute redistribution at the stationary state was determined by sectioning and radiotracer technique. The net heat of transport was obtained from the slope of a plot of the logarithm of solute concentrations versus reciprocal of absolute temperature. The segregation was rather small for Au but pronounced for Sb and S. Values of Q* for Au, Sb and S are 1688 cal/mole, -6768 cal/mole and -29,000 cal/mole respectively. The experimental results are discussed in terms of the various factors which contribute to the heat of transport. </jats:p