Microstructural characterisation of a Ni–Fe-based superalloy byin situsmall-angle neutron scattering measurements

Abstract

The microstructural evolution at high temperatures was studied in an experimental Ni–Fe-based superalloy DT706 by in situ small-angle neutron scattering (SANS). Modifying the alloy heat treatment to improve the microstructural stability and mechanical properties in Inconel 706 type superalloys has been a significant research goal for many years. The earlier studies of phase transformation relied mostly on optical and electron microscopy investigations of samples that were cooled down to room temperature after the high-temperature exposure. However, the kinetics of γ′ and γ′′ precipitation is very fast and new precipitation does occur during the cooling phase. So it is unlikely that the high-temperature microstructure is retained at room temperature. In this presentation, we followed the phase transformation in DT706 alloy by studying the microstructural changes occurring at elevated temperatures. The results of in situ SANS measurements are presented. Microstructure examination on differently heat-treated samples by electron microscopy gives complementary information on the phase transformation sequences. The formation and evolution of precipitates are strongly influenced by the cooling rate from the solution to the η stabilization temperature. The microstructure of DT706 alloy can be tuned using the in situ SANS results.

Enhancing the High-Temperature Strength of a Co-Base Superalloy by Optimizing the γ/γ′ Microstructure

“…Complementary in-situ and ex-situ small-angle neutron scattering (SANS) investigations were performed to get representative information from larger volumes about the temporal evolution of the γ precipitate phase. Previous studies demonstrated that two-phase superalloys can be successfully analyzed by SANS to investigate the microstructural evolution of the γ/γ microstructure during heat treatments [14][15][16][17][18]. In this study, the γ precipitate size distributions and volume fractions during the heat treatment procedures and after the full three-step heat treatment were determined quantitatively.…”

In Situ Characterization at Elevated Temperatures of a New Ni-Based Superalloy VDM-780 Premium

“…[3] In the 718-type Ni-based superalloys, the austenitic matrix (c phase) is strengthened by intermetallic precipitates of Ni 3 Al (c¢, fcc L1 2 structure) and Ni 3 Nb (c¢¢, bct DO 22 structure), and the existence of coprecipitates of both phases with different morphologies (plate, needle, cube, or disc shape) was also observed. [4,5] Other phases that can also be formed are Ni 3 Nb-based (d, orthorhombic DO a structure) and Ni 3 Ti-based (g, hexagonal DO 24 structure). The limiting service temperature (650°C) of alloy 718 is due to the instability of the c¢¢ phase, which transforms into d phase, and the alloy loses its creep resistance.…”

Formation and Dissolution of γ’ Precipitates in IN792 Superalloy at Elevated Temperatures

“…While ex-situ SANS brings information on precipitate morphology, size and specific interface in superalloys (see e.g., [8,9] and references therein), in-situ SANS studies, moreover, are able to follow the evolution of the microstructure of superalloys directly at high temperature [10][11][12][13][14]. This approach has important benefits when compared with room temperature measurements, as the Table 1.…”