Segregation and Homogenization of Refractory Elements in Re-containing Ni-Based Superalloys with Wide Variation of Dendrite Arm Spacing
摘要
Segregation behavior of elements and their responses to a solution heat treatment were investigated as a function of secondary dendrite arm spacing (SDAS) using a model Ni-based superalloy containing 4 wt pct Re. Five materials with SDAS ranging from 4.5 to 47 µm were prepared through various solidification processes. Reducing SDAS to approximately 20 µm or less was found highly effective in achieving a nearly fully homogenized state through a relatively simple heat treatment at 1320 °C for 2 hours. Smaller SDAS values resulted in lower segregation amplitudes of Re and W in the as-cast condition, and the shorter diffusion distances facilitated efficient homogenization during the solution heat treatment. The solution heat treatment reduced the segregation amplitude of Re by only 46 pct in a material with large SDAS of 47 µm compared to the as-cast state, while in a material with SDAS of 19 µm Re segregation was reduced by 86 pct. No detectable segregation remained in a material with SDAS of 4.5 µm after the solution heat treatment. For materials with smaller SDAS, an additional experiment was performed to assess the potential for enhancing the levels of alloying elements.