Investigation of microstructural changes in INCONEL 706 at high temperatures by In-Situ small-angle neutron scattering

Abstract

The Ni-Fe based superalloy INCONEL 706 (IN706) has a complex microstructure and many A 3 B type phases, e.g., Ni 3 Al ␥Ј, Ni 3 Nb ␥Љ, Ni 3 Nb ␦, or Ni 3 Ti precipitates can form. The various precipitates can also have different morphologies, i.e., plate, needle, cube, or disc shape, and some of them exist as co-precipitates-␥Ј/␥Љ. In the present study, in-situ measurements by small-angle neutron scattering (SANS) were performed to monitor the microstructural evolution at elevated temperatures. The SANS measurements were complemented by microstructural observations at room temperature by scanning electron microscopy and transmission electron microscopy (SEM and TEM). It is demonstrated that plates and ␥Љ needles form directly at high temperatures. Cooling from high temperature produces fine dispersions of ␥Ј/␥Љ precipitates, which coarsen on reheating to lower stabilization temperatures (893 and 993 K). The final morphology of the ␥Ј/␥Љ co-precipitates, i.e., compact/noncompact type very much depends on the stabilization temperature and the cooling rates from prior higher-temperature stabilization steps.

Characterization of Gamma Prime (γ′) Precipitates in a Polycrystalline Nickel-Base Superalloy Using Small-Angle Neutron Scattering

“…At high volume fractions, this model accounts for the scattering across the particles and between them. SANS studies of precipitate distributions in nickel superalloys have been conducted by a number of research groups, [13][14][15][16][17][18] each offering different approaches to the data analysis. A technique written by Strunz et al, [18] known as the transformed model fitting procedure, has been developed, [19] increasing the realism to model more complex microstructures.…”

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

“…The precipitation aging step, comprised only of a single aging at 993 K (instead of the double aging at 993 and 893 K, followed for INCONEL 706), [3] was used as the lower-temperature aging, which is mainly responsible for the stabilization of ␥ Љ phase in INCONEL 706; [17] this step was thought to be unnecessary in ␥Ј-stabilized DT706. [17,19] B. Metallography Specimens for SEM were prepared by conventional mechanical grinding and polishing. The exact cooling rates of the MST-1 heat treatment (performed by the alloy manufacturer on the forged bar) are unknown.…”

“…The diagram shows the scattering cross-section d⌺/d⍀ (proportional to the intensity) [24] plotted as a function of the scattering-vector magnitude Q. [17] The sample that was not subjected to the stabilization heat-treatment step (i.e., the DA sample) is the only one to show increased scattering in the high-Q region (i.e., at Q Ͼ 0.03 Å Ϫ1 ). The data can be interpreted following the EM investigations and earlier observations on similar SANS investigations of INCONEL 706.…”

“…[17] In-situ neutron scattering measurements, made from studying the phase transformations at high temperatures, will be presented separately. Ex-situ SANS measurements performed at ambient temperature are presented here and are compared with similar measurements previously made on INCONEL 706.…”

Artificial neural network prediction of aging effects on the wear behavior of IN706 superalloy

“…For this purpose, there has been a growing interest in research on IN 706 superalloy [1][2][3]. IN 706 superalloys have been replacing steel parts used in gas turbines due to their higher mechanical strength, formability and good machinability in addition to their strength at high temperatures.…”