Directional solidification behavior of turbine blades in DZ125 alloy: design of blade numbers on assembly

The influence of blades assembly, i.e., the blade number on the solidification process, heat exchange and grain structure on a directionally solidified Ni-based superalloy DZ125 was investigated by combining the experimental and simulation results. The casting process was simulated thermodynamically by ProCAST software, where the interface heat transfer coefficient was precisely determined by a measurement with thermocouples. There is a good agreement between experimental and simulation results. It was interestingly found that with the number of blades increasing from 6 to 10, due to the decrease in radiation absorption efficiency, the maximum temperature and the heating rate decrease in the mold, during the preheat process. During the withdrawal procedure, increased assembly numbers reduce the radiation exchange from mold to the enclosure, resulting in the decrease in cooling rate and temperature gradient of the blades. At the end of withdrawal, the slower cooling rate of the outside balances the temperature distribution of internal and external surfaces on the rabbet of blade. The interface heat transfer coefficient (IHTC) values of DZ125 casting system were investigated by inverse method. Then, a series of assembly blade groups were designed and being cast and calculated. Values of IHTC are proved to be suitable for different assembly groups of casting in this case. Based on simulation and experimental results, it was interestingly found that: In the preheating process, with the number of blades increased, the maximum temperature on the mold becomes lower and the heating rate becomes slower, which result from the decrease in radiation efficiency between the mold and graphite heater. During the withdrawal, increasing assembly blade number reduced the radiation exchange from the mold to the enclosure, and it results in the cooling rate and temperature gradient on the blades getting decreased. At the end of withdrawal, the slower cooling rate leads to the temperature distribution maintaining uniformity for internal and external surfaces on the rabbet of the blade.