The anomalous dependence of coarsening behavior on gamma prime precipitate volume fraction and the evolution of the morphology of the precipitates are investigated in selected binary nickel alloys (Ni-Al, Ni-Ga, Ni-Ge, Ni-Si, and Ni-Ti). The rationale for selecting these alloys is that the lattice mismatch varies from a low of - 0.00226 in the Ni-Si alloys to a high of 0.01005 in the Ni-Ga alloys. The magnitude of lattice mismatch plays an important role in the precipitate morphology and the tendency of the precipitates to align. The equilibrium gamma prime volume fractions can be varied by an order of magnitude in these alloys. The research has two principal thrusts: (1) investigation of coarsening kinetics over a wide range of precipitate volume fraction; and (2) quantitative characterization of the morphologies of gamma prime precipitates as functions of particle size, lattice mismatch, and volume fraction. Experimental characterization methods include dark-field transmission electron microscopy, image analyzing software applied to scanned TEM negatives, and magnetic analysis to measure the variation of solute concentration. The relationship between anomalous coarsening and lattice mismatch is examined in the selected alloys. %%% Prior research on nickel-aluminum alloys has shown that when the volume fraction of gamma prime precipitate is below 0.05, the interfaces of individual large precipitates become concave. This research characterizes the evolution of gamma prime precipitate shape to determine whether the concave cuboidal shape is a thermodynamic equilibrium shape. This is important for scientific understanding because recent theoretical analyses suggest that concave cuboidal shapes are metastable. ***

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Type
Standard Grant (Standard)
Application #
9900714
Program Officer
Harsh Deep Chopra
Project Start
Project End
Budget Start
1999-05-01
Budget End
2003-04-30
Support Year
Fiscal Year
1999
Total Cost
$335,310
Indirect Cost
Name
University of California Los Angeles
Department
Type
DUNS #
City
Los Angeles
State
CA
Country
United States
Zip Code
90095