Wide Gap Braze Repair of Gas Turbine Blades and Vanes—A Review

Abstract

Gas turbine blades and vanes in modern gas turbines are subjected to an extremely hostile environment. As such, sophisticated airfoil designs and advanced materials have been developed to meet stringent demands and at the same time, ensure increased performance. Despite the evolution of long-life airfoils, damage still occurs during service thus limiting the useful life of these components. Effective repair of after-service components provides life-cycle cost reduction of engines, and as well, contributes to the preservation of rare elements heavily used in modern superalloys. Among these methods developed in the last four decades for the refurbishment and joining of superalloy components, wide gap brazing (WGB) technology has been increasingly used in the field owing to its ability to repair difficult to weld alloys, to build up substantially damaged areas in one operation, and to provide unlimited compositional choices to enhance the properties of the repaired region. In this paper, the historical development of wide gap repair technology currently used in industry is reviewed. The microstructures and mechanical properties of different WGB joints are compared and discussed. Subsequently, different WGB processes employed at major OEMs are summarized. To conclude this review, future developments in WGB repair of newer generations of superalloys are explored.

An ICME Process Chain for Diffusion Brazing of Alloy 247

“…To achieve an isothermal solidification process and thus to avoid formation of brittle eutectic phases, a filler material similar to the base metal is used containing additions like boron which is a fast diffuser and acts as effective melting point depressant. For filling larger gaps, braze alloys also may be mixed with base metal powder and applied as pre-sintered preform (PSP) [35].…”

The microstructures and mechanical properties of K465 superalloy joints, brazed with different clearances

“…In addition, the pre-filling of the alloy powder did transform the morphology of the low-melting point phases from large blocky shaped and skeletal shaped to small blocky shaped or dot shaped that were dispersed throughout the brazed joint. In conclusion, the alloy powder performed three basic functions: (1) to provide capillary pressure to draw molten brazing alloy into the microgaps, (2) to act as a boron or silicon sink, and (3) to present opportunities for further alloying metals to the repaired region [16,17]. Therefore, in the study, it was proved that the pre-filling of the alloy powder selected in the paper did improve the microstructure and high-temperature tensile strength of the wide gap brazed joint of K465 superalloy.…”

“…However, the solid solution was enriched with higher levels of Ni than that of the brazing seam with 0.1 mm clearance. The reason may be that, compared to narrow gap brazing, wide gap brazing provided 500~1000 times larger surface areas to react with brazing alloy during brazing, so the reaction extent was more extensive and the elemental inter-diffusion was faster [16].…”

Influence of oxygen impurity content on transient liquid phase sintering behaviour of Cu–Ni powders

“…10 In the context of a TLPS variable melting point braze, the amount of liquid initially formed during TLP processing is particularly important as it should be sufficient to densify the braze as well as bond the faying surfaces of the substrates to be joined, yet isothermally solidify within a reasonable, known time frame. Base metal particle size a B , 7,13-15 relative diffusivities D, 14,16 base metal grain size d, 14 heating rate R H , 7,13,15,17,18 processing temperature T P , 13,15,[17][18][19] base/additive solubilities, 12,16 powder purity and morphology 13 and bulk alloy composition 7,15,17,19,20 have all been found to influence the amount of liquid formed and it's duration during TLPS.…”