Repair of trailing edge of C1023 NGVs by a gouge-and-braze technique

Abstract

A gouge-and-braze technique has been investigated as an alternative to repair cracks sustained at the trailing edges of C1023 nozzle guide vanes. Slots of four different widths, namely, 0.3, 0.6, 0.9 and 1.2 mm, were gouged at the trailing edge, either by a low-speed diamond-impregnated saw or by electro-discharge machining (EDM), to simulate the crack gouging process. The slots were then blasted with glass beads, SiC particles or nickel powder. Then, they were pre-packed with braze mixes, with an excess of braze mixes deposited on top of the slots, and brazed in vacuum at high temperature. A few slots were also similarly brazed but in the as-gouged conditions. The results show that the as-saw cut slots can be brazed readily but it is not so for the as-EDM slots. Blasting by glass beads, SiC particles or nickel powder is effective in improving the wetting characteristics of slot surfaces. The results further show that slots wider than 0.3 mm can only be successfully brazed with braze mixes containing 30 to 50% of gap filler. The advantages and limitations of using filler metal alone instead of braze mixes as excess filler deposit on top of the slots are also investigated.