Directional recrystallization processing

The technical objective of the proposed effort is to utilize directional recrystallization, and in particular the effects of texture, solutes, and particle size and spacing, to provide unique control over microstructural evolution.

The proposed effort is motivated by the published use of directional recrystallization to produce single crystals and columnar-grained microstructures with enhanced properties. The proposed research will determine the effects of both solutes and particles in a model system of nickel-aluminum. The particles will be finely-dispersed Ni3Al, which can dissolve during annealing. The effort will also characterize how the solute and particles affect the texture after deformation and subsequent annealing, in addition to the role of particle dissolution, in order to establish how columnar grains and single crystals can be produced in alloy systems. Two Ni-Al alloys will be cast: one with a composition below the solubility limit to examine the effects of aluminum solute on directional recrystallization of nickel, and one which will form Ni3Al precipitates upon heat treatment. After casting, the alloys will be homogenized and annealed at different temperatures for different times to provide Ni3Al particles of a variety of sizes and spacings. The proposed research will seek to determine particle dispersion parameters both after heat-treatment and after directional annealing using a Field Emission Gun (FEG) TEM and SEM. The alloys will be cold-rolled (previously demonstrated to produce single crystal nickel by directional recrystallization), and then recrystallized to produce fine primary-recrystallized grain structures. EBSPs will be used to determine the grain orientations and grain boundary misorientations both before and after recrystallization. The primary recrystallized material will then be directionally annealed using a variety of hot zone temperatures, and the resulting materials will be characterized during interrupted runs using optical microscopy, secondary electron imaging, and EBSPs, with a particular focus on: the size and orientations of the primary-recrystallized grains directly ahead of the directionally grown single crystal or columnar grains, the misorientations between the growing single crystal or columnar grains and the primary recrystallized matrix, and the extent of precipitate dissolution around the growing crystal interface.

Faculty contact: Ian Baker