Effect of Tungsten Addition on the Nucleation of Borides in Wide Gap Brazed Joint

Abstract

Wide gap brazing (WGB) is a cost effective and reliable means to repair gas turbine hot section components with defect sizes exceeding 0.3 mm. However, it has been shown that WGB joints of nickel-based superalloys suffer from reduced ductility and thermal fatigue life due to the presence of brittle intermetallics and porosities in the brazed joint. In order to disperse the brittle intermetallic compounds, potentially increase the ductility of the repaired region, and reduce the risk of the thermo-mechanical fatigue failure, elemental tungsten (W) was added to the braze additive filler alloy IN738 by mechanical alloying. The alloyed IN738 was then brazed with the addition of 30, 50 and 80 wt% of braze alloy (BNi-9). After brazing at 1200°C for 20 minutes, microstructural analysis of WGB joints showed a decreasing trend of discrete boride size and the amount of eutectic and script-shaped borides with the increases of W. The increase in the braze alloy to additive filler alloy ratio diminished the effect of W addition due the dissolution of W particulates.

Wide-Gap Brazing of K417G Alloy Assisted by In Situ Precipitation of M3B2 Boride Particles

“…As a result, relatively large cracks or worn areas (>1.5 mm) are discovered in aerospace components, where the narrow gap TLP bonding technique would be inadequate [ 13 ]. For wide-gap brazing, the selection and design of the filler metal composition is the key factor to improve the brazing performance [ 14 , 15 , 16 , 17 , 18 , 19 ]. Considerable effort has been devoted to adding a second gap-filler powder, (hereafter termed additive powder) of similar composition to that of the base metal (BM), to the joint gap, for use with braze powder during the high-temperature brazing process [ 14 , 20 , 21 ].…”

“…Considerable effort has been devoted to adding a second gap-filler powder, (hereafter termed additive powder) of similar composition to that of the base metal (BM), to the joint gap, for use with braze powder during the high-temperature brazing process [ 14 , 20 , 21 ]. During the entire wide-gap brazing process, additive powder with a high melting point remains largely unmelted, thereby providing the necessary capillary force to retain the molten braze powder that would otherwise be too fluid to bridge the faying gap surfaces [ 16 , 17 ]. However, the formation of hard and brittle eutectic structures with uneven distribution cannot be avoided due to their sensitivity to the chemical composition of the filler metal, brazing temperature, and brazing time [ 22 , 23 , 24 , 25 ].…”

Aging Thermal Treatment in the Inconel 725 Brazed Incorporating Tungsten Nanoparticles

“…If there is a considerable formation of such phases during the thermal cycle, brazed Inconel 725 will become more susceptible to corrosion, and the mechanical properties will be detrimentally affected, giving place to fracture initiation [6]. Additionally, rhodium, a relatively expensive element, has been used for improvement of fracture toughness by modifying intermetallics [7]. On the other hand, industrial gas turbines blades fail during service due to the operation conditions in aggressive environments.…”