Method of diffusion bonding of nickel based superalloy substrates
A method of transient liquid phase bonding includes the use of an interlayer between the two substrates to be bonded that is alloyed with a melting point reducing element. The interlayer forms a liquid during the bonding process, resulting in superior surface contact between the interlayer and substrates during the bonding process. As the melting point decreaser diffuses out of the interlayer, the interlayer resolidifies, at which point bonding continues under the principles of diffusion bonding.
1 . A method of bonding a set of substrates, comprising:
providing a pair of substrates, each substrate defining a joining surface;
providing an interlayer over at least one joining surface by a procedure selected from the group consisting of electroless plating, spraying, and application of a foil, the interlayer being alloyed with a melting point reducer;
positioning the substrates with the joining surfaces facing each other; and
pressing the substrates together while subjecting the substrates and interlayer to a temperature above the melting point of the interlayer; whereby the interlayer melts to provide essentially complete surface to surface contact between each joining surface and the interlayer.
2 . The method according to claim 1 , further comprising reducing a surface roughness of each joining surface prior to providing an interlayer over each joining surface.
3 . The method according to claim 2 , wherein the surface roughness is reduced to a level wherein an average surface roughness is below about 30 μin.
4 . The method according to claim 1 , wherein the substrates are nickel, cobalt, and iron based superalloys.
5 . The method according to claim 1 , wherein the interlayer is nickel alloyed with boron.
6 . The method according to claim 5 , wherein the interlayer includes about 0.1% to about 6% boron.
7 . The method according to claim 1 , wherein bonding includes diffusion of the melting point reducer into the substrates after the interlayer has melted, resolidification of the interlayer, and diffusion bonding.
8 . The method according to claim 1 , wherein the interlayer has a thickness of about 0.0001 inch to about 0.001 inch.