Directional solidified (DS) turbine blades are widely used in advanced gas turbine engine. The size and orientation of columnar grains have great influence on the high temperature property and performance of the turbine blade. Numerical simulation of the directional solidification process is an effective way to investigate the grain's growth and morphology, and hence to optimize the process. In this paper, a mathematical model was presented to study the directional solidified microstructures at different withdrawal rates. Ray-tracing method was applied to calculate the temperature variation of the blade. By using a Modified Cellular Automation (MCA) method and a simple linear interpolation method, the mushy zone and the microstructure evolution were studied in detail. Experimental validations were carried out at different withdrawal rates. The calculated cooling curves and microstructure agreed well with those experimental. It is indicated that the withdrawal rate affects the temperature distribution and growth rate of the grain directly, which determines the final size and morphology of the columnar grain. A moderate withdrawal rate can lead to high quality DS turbine blades for industrial application. directional solidified (DS) turbine blade, Cellular Automation (CA), numerical modeling and simulation Citation: Zhang H, Xu Q Y, Tang N, et al. Numerical simulation of microstructure evolution during directional solidification process in directional solidified (DS) turbine blades.
The spiral selector is the key part for producing single crystal (SX) blades and ensures the integrity of crystal, which mainly includes starter block and spiral part. In this work, the influence of spiral part on the grain selection process was studied. Both of the metallography results and EBSD results proved that the prior location and the special orientation of the second dendrite arms were important for the grains competitive growth during the directional solidification process. Based on the experimental results, two geometrical restrict mechanisms of grain selection were proposed. They were the competitive stimulating effect on the second dendrite arms in horizontal direction, which was resulted from the spiral arc shape, and the growing blocking effect on the primary dendrites in vertical direction, which was resulted from the take-off angle of the spiral part. These models could successfully explain the grain selecting effects of the spiral part. The modified cellular automaton
:With the universal improvement of the manufacturing requirements of temperature-resistant high-end equipment in industry,the existing alloy systems and traditional manufacturing processes have difficulties in meeting the current requirements.High-entropy alloys and laser additive manufacturing technology are coupled to provide a new solution for the overall manufacturing of large-size and complex high-end equipment parts in China. On the one hand, a variety of high-entropy alloys such as WNbMoTa and NbMoTa are formed by the laser cladding deposition. The grain size of the formed alloys is small and the constitutional segregation is not obvious. Among them, the yield strength of NbMoTa alloy under 1 000 ℃ reaches to 530 MPa, higher than GH4169, DZ125 high-temperature alloys used in domestic aero-engine turbine blades and T111, C103, Nb-1Zr refractory alloys used in domestic aerospace industry. On the other hand, the thermal stress and strain during high-entropy alloys forming are simulated based on FD-FE simulation, solving the problem that the samples are easy to warp in the process of selective laser melting.
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