Different Heat-Exposure Temperatures on the Microstructure and Properties of Dissimilar GH4169/IC10 Superalloy Vacuum Electron Beam Welded Joint

Vacuum electron-beam welding (EBW) was used to join the precipitation-strengthened GH4169 superalloy and a new nickel-based superalloy IC10 to fabricate the turbine blade discs. In this study, a solid solution (1050 degrees C/2 h for GH4169 and 1150 degrees C/2 h for IC10) and different heat-exposure temperatures (650 degrees C, 750 degrees C, 950 degrees C and 1050 degrees C/200 h, respectively) were used to study the high-temperature tensile properties and microstructure evolution of welded joints; meanwhile, the formation and evolution of the second phases of the joints were analyzed. After EBW, the welded joint exhibited a typical nail morphology, and the fusion zone (FZ) consisted of columnar and cellular structures. During the solidification process of the molten pool, Mo elements are enriched in the dendrites and inter-dendrites, and that of Nb and Ti elements was enriched in the dendrites, which lead to forming a non-uniform distribution of Laves eutectic and MC carbides in the FZ. The microhardness of the FZ gradually increased during thermal exposure at 650 degrees C and reached 300-320 HV, and the gamma ' and gamma '' phases were gradually precipitated with size of about 50 nm. Meanwhile, the microhardness of the FZ decreased to 260-280 HV at 750 degrees C, and the higher temperature resulted in the coarsening of the gamma '' phase (with a final size of about 100 nm) and the formation of the acicular delta-phase. At 950 degrees C and 1050 degrees C, the microhardness of FZ decreased sharply, reaching up to 170 similar to 190 HV and 160 similar to 180 HV, respectively. Moreover, the Laves eutectic and MC carbides are dissolved to a greater extent without the formation of gamma '' and delta phases; as a result, the absent of gamma '' and delta phases are attributed to the significant improvement of segregation at higher temperatures.