The effect of the volume fraction on precipitate coarsening in nickel-base superalloys and aluminium–lithium alloys

Abstract

Coarsening of γ′‐precipitates in nickel‐base superalloys and of δ′‐precipitates in aluminium‐rich aluminium–lithium alloys is investigated by analytical transmission electron microscopy. The growth rate of the particles increases with their volume fraction. This increase is described best by Ardell's [6] model. The γ′‐volume fractions of the superalloys are independent of the annealing time t. In the case of the Al–Li alloys the analogous statement holds only if t is long enough to yield average δ′‐particle radii of 9.4 nm or more. For shorter heat‐treatments the δ′‐volume fraction increases strongly with t.

Effects of a tungsten addition on the morphological evolution, spatial correlations and temporal evolution of a model Ni–Al–Cr superalloy

“…The widespread use of γ'(L1 2 )-precipitate strengthened Ni-base superalloys as a turbine blade material in high temperature commercial and military jet engines and land-based gas turbines warrants extensive study of the microstructural evolution and γ'-coarsening behavior in model γ(fcc)/γ' alloys, such as Ni-rich Ni-Al, Ni-Al-Cr and Ni-Al-Mo alloys [1][2][3][4][5][6][7][8][9][10][11][12][13]. In these alloys, elastic anisotropy leads to coherent precipitates evolving from spheres-to-cubes to arrays of cubes or to doublets or octets of smaller precipitates [1,8,[14][15][16][17], as well as face-to-face cube alignment along the elastically soft <100>-crystallographic directions [1,2].…”

“…Vickers microhardness for a 500 g load sustained for 5 s was measured on mounted samples polished to 1 µm. The average value of fifteen independent microhardness measurements made on several grains was determined and converted from kg/mm 2 to MPa by multiplying by the acceleration of gravity, 9.807 m/s 2 .…”

A correlative four-dimensional study of phase-separation at the subnanoscale to nanoscale of a Ni Al alloy

“…And yet surprisingly little experimental evidence (in systems where is greater than zero) exists to support the prediction of the LSW temporal dependency of . The experimental γ'(L12)-precipitate size distributions (PSDs) are consistently broader, flatter, and more symmetric than what the meanfield LSW model predicts [48][49][50][51][52][53]. Hence, the LSW PSD is agreed to be incorrect, as is probably the modified LSW PSD [54].…”

Nucleation, growth and coarsening of γ′-precipitates in a Ni–Cr–Al-based commercial superalloy during artificial aging

“…Although precipitation in these alloys has been studied using sophisticated experimental techniques [2][3][4][5][6], information about the early stages of decomposition, involving nucleation and growth of precipitates is still insufficient and, therefore, the physical mechanisms of these processes are not completely understood [7].…”