Nickel-based Single Crystal Alloy Research Articles

Directional coarsening in nickel-base single crystals with high volume fractions of coherent precipitates

Directional coarsening has been investigated experimentally in two nickel-base single crystal alloys with high volume fractions of precipitates. The initial elastic stresses due to the positive or negative misfit of the coherent precipitates biased the orientation of the precipitates developed during coarsening. However, directional coarsening of the precipitates did not occur until some limited amount of creep deformation was initiated. With the application of an external stress, dislocations penetrated preferentially into the most highly stressed matrix channels and directional coarsening occurred by coalescence of the γ′ precipitates in the plane of the initially less highly stressed channels, where the misfit stresses were not altered by the presence of misfit relieving dislocations. The diffusional processes responsible for rafting apparently operate on the local scale of the precipitates, with preferential local dissolution of the γ′ and diffusional flow of alloying elements around the periphery of the precipitates.

APFIM characterization of single-crystal PWA 1480 nickel-base superalloy

An atom-probe field-ion microscopy and analytical electron microscopy characterization of a PWA 1480 nickel-based single-crystal alloy has revealed a high number density of 5 to 10 nm diameter γ precipitates in the interior of coarse cuboidal γ′ precipitates in material that was heat-treated for 4 h at 1288°C, 4 h at 1079°C and 32 h at 871°C. Atom-probe analysis revealed that the chromium, cobalt and tungsten partitioned preferentially to the γ precipitates and γ matrix and the aluminum, titanium and tantalum partitioned to the γ′ precipitates. No evidence of tungsten clustering in the γ matrix was found.

Analysis of Subgrain Boundaries in the y’ Phase of a Nickel-Base Single Crystal Alloy After High Temperature Creep

Analysis of Subgrain Boundaries in the y’ Phase of a Nickel-Base Single Crystal Alloy After High Temperature Creep