Microstructural characterization of a modified 706-type Ni-Fe superalloy by small-angle neutron scattering and electron microscopy

Abstract

The new Ni-Fe-based superalloy DT706, derived from INCONEL 706, is the object of studies for potential uses in turbine-disk applications at temperatures above 973 K. This alloy aims at improving the microstructural stability while preserving the excellent machinability and good mechanical properties of the base material. This article is the first of a two-part study concentrating on the characterization of the microstructure of the DT706 precipitates, depending on the heat-treatment conditions. Analyses were performed by means of ex-situ small-angle neutron scattering (SANS) measurements, together with conventional scanning electron microscopy (SEM) and transmission electron microscopy (TEM) microscopy, on experimentally-heat-treated samples. The results, when compared to a similar analysis previously made on INCONEL 706, showed that the precipitation characteristics of DT706 reflect compositional changes, but are still remarkably dependent on the cooling stages between the different heat-treatment steps.

Quantitative Characterization of Precipitate Microstructures in Metallic Alloys Using Small-Angle Scattering

“…The precise measurement of precipitate volume fraction requires the measurement of the integrated intensity, which is the integral from 0 to infinity of I AE q 2 (Eq. [7] above). Since the experimental measurement is always made over a limited q-range, a precise measurement is possible only if proper extrapolations are made both for the low-q and high-q regions.…”

“…In the direct method, a certain distribution function of the precipitates is assumed, the scattering of which can be calculated and fitted to the experimental data as a function of the parameters of this function. For instance, a log-normal size distribution of precipitates is often assumed in the literature, [6][7][8][9][10] the size and dispersion of which can be adjusted. Other distributions, or combinations of several distributions, can naturally be used as well.…”

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

“…It is especially crucial to control the evolution of the different phases at high temperature in order to tailor the mechanical properties. [6][7][8][9] The aim of increasing the operation temperature of the Ni-based superalloys, which allows engine manufacturers to improve fuel efficiency and, thus, results in reduced emissions, forces the development of materials stable at higher temperatures. The last few decades the scientific community has put great effort into the development of Ni-based alloys with operation temperatures above 650°C while keeping the good processing C. SOLI´S, J. MUNKE, and R. GILLES are with the Heinz MaierLeibnitz Zentrum (MLZ), TU Mu¨nchen, Lichtenbergstr.…”