Wide gap brazing with prepacks of nickel base braze mixes

Abstract

Vacuum brazing of wide gaps has been used increasingly to repair hot section components of second generation aeroengines over the years. It has also been extended to repair first generation components and those components too badly damaged for weld repair alone, and used in situations where welding will cause appreciable mechanical distortion. In the present investigation, the effects of material and process parameters on the formation of various types of constituent void, namely, interfacial, interstitial, and shrinkage voids, in nickel base wide gap brazes produced by prepacking with dry braze mix powders of Nicrobraz LC and Nicrogap 116 are reported. The results showed that the size and number of interfacial and interstitial voids increased with gap depth and width, and with gap filler content in the braze mix, but decreased with increasing brazing temperature. At intermediate and high gap filler contents, shrinkage voids were not readily observable as they were absorbed into other constituent voids. At low gap filler contents, shrinkage voids were numerous and small at high brazing temperatures but could become isolated and large at low brazing temperatures. The findings were compiled into braze quality control charts delineating the regions of gap filler content and brazing temperature over which a gap of a certain depth can be soundly brazed without the formation of constituent macrovoids. The present work showed that gap depth is an important parameter which must be considered in wide gap brazing with prepacking of nickel base braze mixes. Large interfacial and interstitial voids were common features for gaps 6 mm or larger in depth, unless brazing was conducted at sufficiently high temperatures with braze mixes with gap filler contents of less than 30%.

MST/3110