A comparative study on the InterPulse TIG repairing of Inconel 738 alloy using Inconel 625 and Pmet 838 feeding wires

Abstract Repairing is considered as a practical and economic scheme to effectively extend the lifetime of components made of Inconel 738 (IN 738), which has been widely used in hot sections of jet engines and industrial gas turbines. In this study, the feasibility of repairing IN 738 substrates was investigated using InterPulse tungsten inert gas (TIG) welding with Inconel 625 (IN 625) and Pmet 838 as feeding materials. It was shown that single-pass deposition achieved sound metallurgical bonding under three different TIG parameters, with no cracks observed in any of the specimens. Under multi-pass repairing, γ ′ dissolution was observed in the heat-affected zone (HAZ), and cracks were observed neither in the multi-pass deposited layers nor the HAZ. The Pmet 838 deposited layer was quasi-homogeneous and entirely devoid of γ ′; the IN 625 multi-pass deposited layer, however, exhibits pronounced mesoscopic segregation with significantly lower hardness than the IN 738 substrate. The Pmet 838 deposited layer demonstrates considerably higher hardness than that of the IN 738 substrate, primarily attributed to the existence of dense cellular structures. The hardness in the HAZ of both specimens decreases with increasing the distance from the fusion line to the base metal, which may be associated with gradient variations of the cellular structures. After annealing at 920 °C for 150 h, the average Vickers hardness of the Pmet 838 multi-pass deposited layer decreased from 486.1 ± 13.9 HV 0.2 to 378.2 ± 6.2 HV 0.2 , even though copious precipitation of γ ′ was observed in it, which is attributable to the disappearance of the cellular structure; in contrast, the IN 625 deposited layer exhibited heterogeneously distributed γ ′ precipitates and needle-like δ phase, corresponding to the aforementioned mesoscopic segregation, resulting in an increase in the average Vickers hardness from 252.1 ± 6.6 HV 0.2 to 317.6 ± 17.4 HV 0.2 .