Phase transformations in Ag70.5Cu26.5Ti3 filler alloy during brazing processes

 

Chem. Met. Alloys 1 (2008) 323-332

 

Sviatoslav HIRNYJ, J. Ernesto INDACOCHEA

 

Phase transformations that occur in the brazing alloy Ag70.5Cu26.5Ti3 are described. The liquid segregation paths and the liquid composition path are presented. The evolution of the liquid and the concentration of titanium in the liquid are plotted versus temperature. With increasing temperature the activity of titanium in the liquid increases and is sufficient for reactive brazing even before the alloy is completely melted and liquid is segregated. In the liquid, copper suppresses the activity of titanium while silver enhances it. The activities of titanium in both segregated liquids are identical, though the concentrations are very different. Thus, both liquids Ц Ag-Cu-rich L1 and Cu-Ti-rich L2 Ц are equally reactive and responsible for wetting and spreading, not just L2, as often believed. The major differences (including gravimetric) between L1 and L2 and the effect of preferential segregation of Ag to the free surface of the liquid on surface tension are discussed.

 

 

SEM image of an as-received brazing alloy Ag70.5Cu26.5Ti3 (CB4).

 

Keywords

Silver-copper eutectic / Titanium / Active filler metal / Reactive brazing / Segregation / Phase diagram