Wf. Gale et X. Wen, Ni3Al based composite interlayers for wide gap transient liquid phase bonding of NiAl-Hfsingle crystals to a nickel base superalloy, MATER SCI T, 17(4), 2001, pp. 459-464
The formation of undesirable second phases, for example sigma and/or carbid
es, represents a major problem during transient liquid phase (TLP) bonding
of NiAl alloys to nickel base superalloys, Unlike many other TLP bonding sy
stems, the formation of these second phases does not appear to be associate
d directly with the presence of the interlayer, Instead, the formation of s
econd phases in the bonds results from a combination of extensive interdiff
usion between the two substrates and the low solubility, in NiAl, of common
alloying additions to nickel base alloys (such as Cr, Mo, and W), The use
of a composite interlayer consisting of NiAl las a non-melting constituent)
and copper las a liquid former) allows very short bonding times and this h
as been found previously to suppress the formation of rr and carbides, duri
ng bonding. In contrast, the use of NiAl-Cu composite interlayers had littl
e effect on the formation of second phases during post-bond heat treatment
and this represents a considerable problem. Hence, the present paper invest
igates the use of an alternate, Ni3Al-Cu, interlayer, which is able to prev
ent the entry of Cr, Mo, and W into the NiAl alloy and hence suppress the f
ormation of undesirable second phases (such as sigma) during post-bond ther
mal exposure.