Application of the powder filler and hot isostatic pressure process to bond the hybrid structured Ni-based superalloy pieces

This study employed hot isostatic pressing (HIP) to bond directionally solidified (DS) and fine equixed grain (FEG) hybrid structured rods (CM247LC Ni-based superalloy). The bonding was facilitated using an intermediated layer (IL) formed by CM247LC powder filler. The preselected parameters for the HIP process were established based on an earlier study. The bonded samples were heat-treated to achieve the optimal strength of the bonded pieces. The test results revealed that carbides γ' and eutectic γ-γ' in the DS and FEG pieces coarsened after the HIP process. Following heat treatment, notable changes were observed in both DS and FEG. The grain size and volume fraction of the carbides and γ-γ' decreased, while γ' became a typical diced-shape phase. The IL area has the finest γ matrix grain size compared to DS and FG. In addition to the diced cube shape γ', γ-γ' was hardly observed. Furthermore, the nano- or sub-micro-sized carbides were evenly distributed within the matrix and grain boundaries, which was crucial in inhibiting fracture accumulation during tensile tests. Therefore, following the tensile tests, the fracture location tended to occur in the DS piece. This occurrence could be attributed to the DS having the largest matrix grain, the presence of the γ-γ', and the largest-sized carbides.