Quenching Differential Thermal Analysis and Thermodynamic Calculation to Determine Partition Coefficients of Solute Elements in Simplified Ni-Base Superalloys

Abstract

In this article, a profile-fitting methodology was developed to measure the partition coefficients of solute elements during the solidification of Ni-base alloys. Better agreement with the theoretically calculated values is expected if the accuracy of the composition and the homogeneity of the model alloys are enhanced. Regular differential thermal analysis (DTA) measurements were consistently higher than the theoretical transition temperatures, and the differences were smaller when compared to the predictions performed with the thermodynamical database developed by Du et al. The better agreement between the experimental results and the theoretical predictions made with the newly developed database suggests that improvements in the accuracy of the theoretical predictions can still be obtained and are necessary for accurate freckling prediction. Quenching modified DTA (MDTA) experiments were proven to be appropriate for directly measuring the average partition coefficients of the solute elements. Regarding the cooling rate of the first stage of the quenching experiments, it was assumed successfully that the cooling rate prior to the quenching step of 0.083 Ks À1 was sufficiently slow to permit easy quenching, while being fast enough for the primary solidification reaction to depart from the equilibrium model and being closer to the Scheil model of segregation. The minimization of the error function defined from the Scheil equation was found to be an appropriate method for describing the segregation profiles of the quenched samples and permitted good estimations of the partition coefficients of the solute elements. The reliability of the methodology was found to be satisfactory given that the magnitudes calculated for the partition coefficients of the solutes in the multicomponent alloy 718 were found to be very close to the values reported in the literature.

Phase Transition of Peritectic Steel Q345 and Its Effect on the Equilibrium Partition Coefficients of Solutes

“…The equilibrium partition coefficient of solutes in steel highly depends on the phase constitution of the mushy zone, the temperature, and the alloy components [10,11]. To date, some of papers have reported on the evolution of the equilibrium partition coefficient via experiment [1,12] or thermodynamic calculation [10,13].…”

“…To date, some of papers have reported on the evolution of the equilibrium partition coefficient via experiment [1,12] or thermodynamic calculation [10,13]. However, phase transition was not considered in these studies.…”

Removal of casting defects from CMSX-4®and CMSX-10®alloys by electropolishing in a novel electrolyte; Deep Eutectic Solvent

“…The γ phase occupies approximately 70% of the overall volume and elements in the superalloy such as Al, Ti, Ta are found in the highest concentrations in this region. Elements such as, Cr, Re, W, tend to aggregate towards and remain in the γ phase [6][7][8][9][10][11][12]. During withdrawal from the furnace and subsequent solidification, surface oxide scale is often formed on the casting as a result of the differential thermal contraction of the ceramic mould and the cooling metal.…”

Electrolytic processing of superalloy aerospace castings using choline chloride-based ionic liquids

“…A range of superalloy materials has been developed to service these demanding environments and modern aerospace turbine blades are cast from nickel based systems (CMSX4, CMSX10N) in which there are many other minor components such as Re, W, Ta, Al, Ti and others that have specific roles enhancing phase segregation and resulting in a lattice like metallurgical microstructure. [1][2][3][4][5][6][7][8][9] To improve the strength and durability, turbine combustion blades are cast as single crystal components using the investment vacuum casting method. [10][11][12][13][14] This method eliminates grain boundaries in adjacent crystallites reducing the instance of crack propagation, fracture and subsequent failure.…”