High temperature braze repair of superalloys

The method for repairing a crack in an article consisting of superalloy material selected from the group that includes Ni and Co as a base material, the crack extending into the article from the surface thereof, the method comprising the steps:

• (a) mechanically removing said material adjacent that part of the crack that extends from said surface down into the article, thereby to form in the article a recess whose walls are oxide free,
• (b) filling into the recess a braze mix that consists essentially of first and second portions in powdered state, the first portion consisting essentially of said superalloy material or a material analogous thereto, and the second portion consisting essentially of a braze component containing a melting point depressant, the weight ratio of said first and second portions being less than 1.5/1,
• (c) subjecting said mix in the recess and the article material adjacent the recess to first elevated temperature under vacuum conditions and for a first time interval for causing said mix to form a melt, said first elevated temperature being less than the melting temperature of said material adjacent the recess;
• and
• (d) thereafter subjecting the melt and the article material adjacent the recess to second elevated temperature near said first elevated temperature under vacuum conditions and for an extended time sufficient to diffuse the depressant out of a melt into the recess wall and into the first portion of the mix, and thereby to increase the melting temperature of said melt to slightly below that of the article superalloy material,
• (e) said extended time including a primary interval during which the second elevated temperature remains at an initial level lower than said first elevated temperature, and at a lower level within the range 2050.degree.-2150.degree., and a secondary and subsequent interval during which the second elevated temperature remains at another level which is higher than said initial level, each of said primary and secondary intervals being less than five hours but substantially greater than said first time interval.