Comparison of single crystal Ni based superalloy repair by gas tungsten arc and electron beam processes

A Ni based single crystal superalloy has been subjected to both gas tungsten arc (GTA) and electron beam (EB) welding, relative to gas turbine repair. Gas tungsten arc welding was used to simulate a blade tip repair, while the EB welds were carried out to simulate replacement of an airfoil. The GTA weld build-up was carried out using three filler metals, low strength alloy 625, FM-92 of intermediate strength and high strength alloy 738. Metallography showed that neither filler types resulted in any weld cracking; however, depending on the processing conditions, the EB welds either did not crack, cracked somewhat, or cracked extensively, but only in the weld metal. Also weld shape is considered as an important factor on the incidence of cracking. Orientation image microscopic analysis showed that cracking was not present in the weld of the GTA deposit, even though stray grains were present, whereas the EB weld cracked extensively, being associated with stray grain formation.