Influence of Ruthenium on Topologically Close Packed Phase Precipitation in Single‐Crystal Ni‐Based Superalloys: Numerical Experiments and Validation

Abstract

The suppression of topologically close-packed phases (TCP) in nickel-based single-crystal superalloys by the addition of ruthenium is modeled with a fully multicomponent mesoscale precipitation model based on the numerical Kampmann-Wagnermethod using thermodynamic CALPHAD-calculations. For the application of the model in ruthenium-containing superalloys, mobility assessments of the binary systems nickel-ruthenium (Ni-Ru) and nickel-rhenium (Ni-Re) were performed to create a new mobility database. It is postulated that the dominating effect of ruthenium regarding more sluggish TCP-phase precipitation is a change of interface energy reducing the number of precipitates nucleating. The precipitation sequences occurring during TCPphase precipitation can be explained using CALPHAD thermodynamics.

Effect of ruthenium on the precipitation of topologically close packed phases in Ni-based superalloys of 3rd and 4th generation

“…Several possible mechanisms for this effect were proposed based on experiments [10,[17][18][19][20] and simulations [21,22]. Among the solubility related mechanisms, 'reverse partitioning' [18][19][20] or increased solubility of Re and W within the c-matrix phase [10,17] was suggested.…”

“…Alternatively, a change in TCP/matrix interface energy [21,22] was considered as a potent factor influenced by Ru. However, as TCP phases exhibit very small sizes in the early stages of precipitation and are very sensitive to alloy chemistry, it was difficult to draw the final conclusions without advanced high-resolution characterization and quantitative description of phase transformation.…”

Microstructural stability of TMS-238™ Ni-base superalloy during long-term exposure at high temperature

“…To achieve this goal, Ru is frequently added to the alloy's composition. It is proposed that the diffusion coefficient between the TCP phase and the matrix interface decreases with the addition of Ru [6][7][8]. On the other hand, in high generation Ni-base alloys, high concentration of refractory elements such as Re, W, Cr and Mo can be observed.…”

“…It becomes more and more state of the art to support the estimation of the microstructure evolution during long-term annealing, by incorporation of CALPHAD modelling approach into the evaluation process. The examples of such investigations were presented in other works [9][10][11]. For reliable simulations, high-quality experimental data are crucial for initial setup and calibration.…”