Formation of Solidification and Homogenisation Micropores in Two Single Crystal Superalloys Produced by HRS and LMC Processes

Abstract

2)

Application of Hot Isostatic Pressing in Nickel-Based Single Crystal Superalloys

“…The volume of the interdendritic liquid phase shrinks after solidification and cannot be supplemented by other liquid phases, thus forming irregular micropores in the interdendritic region. Secondly, due to the existence of partially dissolved gas in the liquid phase during solidification, spherical pores are formed after solidification [34][35][36]. Figure 1 shows a typical as-cast microstructure of a nickel-based SX superalloy, showing that micropores are mainly formed in the interdendritic region with a size of a few microns to a ten of microns.…”

“…The cooling rate has a significant effect on the formation of pores during solidification [35][36][37], as shown in Figure 2. When the cooling rate is 0.5 °C/s, the pore volume fraction is 0.22%, and is reduced to 0.14% with the cooling rate of 1 °C/s.…”

“…Therefore, increasing temperature gradient can significantly reduce the defect rate of single crystal blades. Compared with commonly used high rate solidification (HRS) process, the liquid metal cooling (LMC) process has a higher temperature gradient and the primary dendrite arm space (PDAS) after solidification is less than 400 μm, which is about 500 μm for HRS process, resulting in lower porosity The cooling rate has a significant effect on the formation of pores during solidification [35][36][37], as shown in Figure 2. When the cooling rate is 0.5 • C/s, the pore volume fraction is 0.22%, and is reduced to 0.14% with the cooling rate of 1 • C/s.…”