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Wide gap brazing (WGB) of X-40 cobalt based superalloy was conducted in this study using BNi-9 braze alloy with X-40 and IN738 additive alloys. A groove was machined into X-40 bars with a nominal width of 6·35 mm before filler application. Following brazing at 1200°C for 15 min, the microstructure of the as brazed joints was examined using SEM, EDS and nanoindentation technique. Both WGB joints with X-40 and IN783 additive alloys contained primary matrix phase in addition to a number of boron containing phases which assumed either eutectic or discrete forms. Nanoindention testing revealed that these boron containing phases exhibited hardness values several times higher than the base alloy and matrix phase contributing to the embrittlement of the braze joint. Porosity was also observed in both types of WGB braze joints, the degree of which was greatest in the braze joints with IN738 additive alloy. Tensile testing at 950°C showed that the yield strength of both WGB joints was higher than that of the baseline specimens while the ultimate tensile strength of the WGB joints was lower than that of the baseline X-40. The ductility of the WGB joints was significantly inferior to that of the baseline X-40, particularly for WGB with IN 738 additive alloy.

This sttidy investigates the effects of the deposition process and coating composition on microstructural and tribological properties of TiN-and CrN-based coating systems. Coatings were produced using various PVD-based processes-electron beam (EB), cathodic arc (CA), and plasma enhanced magnetron sputtering (PEMS). All coated samples were evaluated for their composition, microstructure, and surface morphology. Coating mechanical properties such as hardness. Young's modulus, and coefficient of friction were also studied and related to their microstructures, wear, and erosion resistances. It was found that hardness (H), Young's modulus (E), and coefficient of friction had impact on both wear and erosion rates. In particular, the H^IE^ ratio was inversely proportional to the specific wear rate. For erosion behavior, higher H^IE^ ratios relate to lower erosion rates at low impingement angles, whereas higher H^IE^ ratios relate to higher erosion rates at high impingement angles.

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.