Phase transformations
in Ag70.5Cu26.5Ti3 filler alloy during brazing
processes
Chem.
Met. Alloys 1
(2008) 323-332
https://doi.org/10.30970/cma1.0071
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 – Ag-Cu-rich L1 and Cu-Ti-rich L2
– 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