Effects of tungsten and rhenium additions on phase-separation in a model Ni-Al-Cr-W-Re superalloy: A four-dimensional study

• Published in: Journal of alloys and compounds 2019-08, Vol.799, p.377-388
• Main Authors: Huang, Yanyan, Mao, Zugang, Noebe, Ronald D., Seidman, David N.
• Format: Article
• Language: English
• Subjects: Aging; Aging (metallurgy); Atom-probe tomography; Chemical composition; Chemical partition; Chemical precipitation; Chromium; Concentration gradient; Diamond pyramid hardness; Diffusion; Ni-based superalloys; Nickel; Nickel base alloys; Organic chemistry; Partitioning; Partitions; Precipitates; Precipitation; Rhenium; Solid solutions; Solution strengthening; Superalloys; Tungsten
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.05.292

The effects of a combined 1.0 at.% W and 1.0 at.% Re addition to a model Ni-10.0Al-8.5Cr at.% superalloy aged at 1073 K (800 °C) for aging times up to 256 h are investigated using atom-probe tomography (APT) and Vickers microhardness measurements. The nanoscale properties, including volume fraction, mean-volume equivalent-radius and number density of the γ′(L12)-precipitates, the chemical compositions of the γ(f.c.c.)-matrix and γ′(L12)-precipitates, the concentration profiles and partitioning ratios between the two phases, γ(f.c.c.)/γ′(L12), hetero-interfacial concentration widths, and microhardness are measured as function of increasing aging time. Localized excesses of the solvent Ni at the γ(f.c.c.)/γ′(L12) interfaces persist at aging times as long as 256 h. Transient diffusional concentration gradients associated with solute-atoms during diffusion-limited growth exist in either the γ(f.c.c.)-matrix or γ′(L12)-precipitates for the as-quenched state; these gradients disappear after 0.25 h for Al and Cr, and after 1 h for W and Re. Tungsten partitions to the γ′(L12)-precipitates and Re partitions to the γ(f.c.c.)-matrix, respectively, and this partitioning behavior enhances the partitioning of Al to the γ′(L12)-precipitates and Cr to the γ(f.c.c.)-matrix. The partitioning behavior indicates that W and Re evolve temporally more slowly than Al and Cr due to their small diffusivities in Ni. The interfacial concentration widths in the Ni-Al-Cr-W-Re alloy decrease with increasing aging time and increasing mean precipitate-radius. Adding W and Re to the base Ni-10.0Al-8.5Cr at.% alloy increases the γ′(L12)-precipitate volume fraction and the microhardness due to the increased volume-fraction and solid-solution strengthening provided by W and Re. •The effects of a combined addition of W and Re to a model Ni-Al-Cr are investigated.•Temporal evolution of the chemistry and precipitates' nanostructure is studied.•W, Re evolve more slowly than Al, Cr, and they enhance the partitioning of Al, Cr.•W, Re additions increase the precipitates' volume fraction and the microhardness.•The interfacial concentration widths decrease with aging, but they never reach zero.