The synergistic effect of Re and W on the evolution of TCP phases in Nickel-based superalloys

Abstract

In this work, the synergistic effect of Re and W on the evolution of the topological close-packed phases (TCP) in Nickel-based superalloys were studied by means of Thermo-Calculation (TC), solidifying slowly, Differential Thermal Analysis (DTA), and solution-aging treatment. The specimens were analyzed by means of SEM-EDS, TEM-SADP, and EPMA. The calculated results indicated that the P phase precipitated prior to the μ phase with the temperature decrease, and both phases μ and P coexisted in a certain temperature range when the content of Re was higher ( Re: 5–7 wt%) and the content of W was lower ( W:4–6 wt%); Only phase μ precipitated from the alloy when Re content was less than 4 wt% and W content was higher than 7 wt%. The experimental results showed that the μ phases were slats-like and distributed in parallel in different orientations; and the μ/P intergrowth phases with coherent relationship were short rod-like. In addition, the gathered μ/P intergrowth phases around the big blocky-like γ' phases were found in alloys solidified slowly, which was prone to cause holes. Based on phase-transition temperature obtained by combining calculation and DTA, the solution-aging process of the alloys were determined. After solution-aging treatment, the long strip shape μ phases and short rod-like μ/P intergrowth phases distributed uniformly in the matrix, and the big blocky-like γ' phases and holes disappeared. The experimental results showed that the total amount of TCP phase decreased and the P phase gradually disappeared when the content of Re decreased and the content of W increased. The research results had a guiding role in optimizing the composition of alloys and predicting the safety performance of aerocraft during the flight cycle.