Topologically Close Packed Phases in an Experimental Rhenium-Containing Single Crystal Superalloy

Abstract

The kinetics, morphology and composition of the formation of TCP phases in an experimental alloy containing no tungsten is studied. At high temperature P phase forms after 20 h, whereas below 950°C the phases p and R occur. At lower temperatures a polycrystalline form of cr phase is observed which is meta-stable but acts as a nucleation site for the other phases. The phase occurrence and compositions are compared with a thermodynamic model using a rhenium-containing database, and reasonable agreement is found for the P, R and cs phases. However the model underestimates the stability of the p phase.

Creep Rupture Strength of Re and Ru Containing Experimental Nickel-Base Superalloys

“…Together with supplemental experiments in the temperature range around the incipient melting point, a consistent solution heat treatment temperature of 1340 °C was selected for all Astra-1 alloys as maximum temperature without partial melting. The required solution heat treatment time has been determined by the investigation of the segregation distribution coefficients k s after solution heat treatment times of 1,4,8,16,24 and 32 h at 1340 °C. For this purpose, EPMA analyses (electron probe microanalyzer JXA-8100, JEOL, Tokyo, Japan) of all elements were carried out by mappings of a 750x750 µm 2 area (measuring details can be found in [12]).…”

“…However, the addition of Re is limited by the highly increased susceptibility to form brittle and harming TCP-phases. To overcome this problem, the most recent alloy development led to the addition of Ru, which appears to be advantageous through microstructure stabilization with respect to TCP-formation [3][4][5][6][7][8][9][10][11]. However, additions of the elements Re and Ru also give rise to economic concerns, since both elements are short in availability and thus also fairly expensive.…”

Analytical Electron Microscopy Investigation of Topologically Close-Packed Phases in CMSX-4 Single Crystal Superalloy

“…However, the creep properties of superalloys containing high amounts of refractory elements decrease due to formation of the intermetallic topologically close-packed phases, known as TCP [1][2][3][4][5][6][7][8]. The TCP phases which were reported to be precipitated in single crystal superalloys are: σ (tetragonal, P 42/mnm), µ (trigonal, R-3m), P (orthorhombic, P nma) and R (rhombohedral, P -31m) phases [1,5,6].…”

Effect of Ruthenium on Microstructure and Stress Rupture Properties of a Single Crystal Nickel-Base Superalloy

“…It has been found that the addition of rhenium plays an important role on high temperature creep resistance in single crystal nickel base superalloys [3,4] . However, Re has a strong segregation tendency in the γ phase, and homogenization of Re is very difficult even at the temperatures above 1300 for a long time ℃ , consequently the TCP phase which is harmful to mechanical properties may precipitate during long term high temperature service [5] . Moreover, Re is rare resource and very expensive element.…”