Prediction of the Thermodynamic Processes of Phase Separation in Single-Crystal Refractory Alloys Based on Nickel
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PREDICTION OF THE THERMODYNAMIC PROCESSES OF PHASE SEPARATION IN SINGLE-CRYSTAL REFRACTORY ALLOYS BASED ON NICKEL А. А. Hlotka1, 2 and S. V. Haiduk1
UDC 669.245.018.044: 620.193.53
We simulate thermodynamic processes of phase separation, which exert significant influence on the temperature characteristics of single-crystal refractory alloys based on nickel (RABN). By using an empirical approach, we deduce new relations for the ratios K γ ′ and K γ taking into account the joint
influence of alloying elements on the temperature characteristics of multicomponent compositions of single-crystal alloys. It is shown that, as the ratio K γ ′ increases, the critical temperatures become
higher and, hence, the thermal stability of the entire system increases. The computed values of the critical temperatures for CMSX-10K alloy are in good agreement with the experimental values and their difference does not exceed 1%. We present the dependences of the ratio K γ on the alloying system
of RABN and analyze the effect of alloying on the liquidus temperature of the alloys. Finally, we present the ratios of the content of alloying elements and regression models with the help of which it is possible to predict the width of the range of crystallization temperatures and the optimal temperature of homogenization for specific alloys. Keywords: single-crystal refractory based on nickel alloys, thermodynamic processes of phase separation, critical temperatures.
Introduction As one of the key problems in the present-day aircraft engine building, we can mention the possibility of increasing the working temperature of the gases. It is worth noting that the temperature of hydrogen-containing gases at the intake of the turbine increased from 1200°K in engines of the second generation to 1800–1950°K in engines of the fifth generation. About 70% of this increment was obtained as a result of the perfection of the systems of air cooling of gas-turbine blades. The remaining 30% were attained by improving the mechanical properties of refractory alloys based on nickel (RABN) and used for casting of single-crystal blades [1–7]. In order to determine the optimal composition of alloys used for single-crystal casting, we minimized the disbalance of the alloying system, attained the optimal ratio between γ -solid-soluble reinforcing elements and γ ′ -forming elements, and excluded some elements, such as Nb, Hf, and V, from the alloying system. Moreover, in selecting the most promising compositions of developed alloys, we take into account the temperature of complete dissolution of the γ ′ -phase in a matrix γ -solid solution t c. d. (solvus γ ′ ), the temperature t eut of local melting of the nonequilibrium eutectic (peritectic) γ + γ ′ , the solidus temperature t S , and the liquidus temperature t L . The maximal values of these temperatures determine the serviceability and creep resistance of RABN. In order to increase the critical temperatures t c. d., t eut , t S , and t L , it is necessary to guarantee 1 2
Zaporizhzhya National Technical Universit
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