Wide Gap Braze Repair Using Vertically Laminated Repair Scheme

Abstract

Wide Gap Braze Repair Using Vertically Laminated Repair SchemeRepair of after-service gas turbine hot section superalloy components provides considerable saving in life-cycle cost of engines. Whereas a number of methods have been used in the past to repair these superalloy components, wide gap brazing technology has provided a practical alternative to repair difficult-to-weld alloys with substantial damages. In this paper, the historical development of wide gap repair technologies is reviewed first. Subsequently, the recent development in utilizing a vertically laminated structure to repair a large and deep gap (up to 16 mm) in one brazing cycle will be discussed. The microstructure resulted from this repair scheme will be evaluated and compared with conventional wide gap braze with slurry and that of the Liburdi powder metallurgy (LPM™) process. It is observed that in conventional wide gap brazing with premixed slurry, the presence of intermetallic compounds can be effectively reduced by reducing the ratio of braze alloy to gap filler, which, however, also contributes to the increased occurrence of macroscopic voids in the wide gap joint. The LPM™ method, on the other hand, can achieve a macroscopically void-free repair of gap (up to 6 mm) and minimize the formation of intermetallics. By using a vertically laminated repair scheme it is shown that the process is able to repair a deeper gap (up to 16 mm) with no macroscopic defects and reduced intermetallic compounds.

Wide Gap Brazing of Inconel 738LC Nickel-Based Superalloy: Metallurgical and Mechanical Characteristics

“…DURING gas turbine operations, the hot section components, including the stationary and rotary parts are subjected to thermal and mechanical fatigue, oxidation, creep, hot corrosion, and foreign objects damage. [1][2][3] Nickel-based superalloys are used at high operating temperatures of the turbine, due to their corrosion resistance and high strength. In modern gas turbine engines, the use of higher gas pressures and operating temperatures are required to achieve higher efficiency and output.…”

Diffusion brazing repair of IN738 superalloy with crack-like defect: microstructure and tensile properties at high temperatures

“…However, the components are degrading by thermal fatigue, oxidation and creep during serving at the harsh conditions. As the high cost of manufacturing new turbine components, the repair techniques of the superalloys have already attracted wide attention [2][3][4]. Nickel superalloys, especially those with a high content of Al and Ti (Al + Ti > 6 wt-%), have poor weldability due to their high susceptibility to solidification cracking within fusion zone and heat-affected zone (HAZ) during welding or post-weld heat treatment [5][6][7][8].…”

Microstructure of diffusion-brazing repaired IN738LC superalloy with uneven surface defect gap width

“…However, buckets (blades) are often subjected to fatigue cracking when engines are operated at high temperature and varied stresses. Since manufacturing replacement buckets (blades) is very costly, effective repair and restoration rather than replacement can reduce the overall operating cost [2].…”