Exploration of the role of diffusion-controlled dislocation climb – Recovery alone or key strain accommodation mechanism?
Committee: Tao Sun, MSE, Chair
Sean Agnew, MSE, Advisor
Jerrold Floro, MSE
James Burns, MSE
Jason Kerrigan, MAE
Laurent Capolungo, Los Alamos National Laboratory (LANL)
A major drawback of magnesium alloys, their limited formability at room temperature, is a result of its limited number of independent easy slip systems and is resolved by working the material at elevated temperature. It is widely believed that the activation of additional glide modes, namely <c+a> dislocations on pyramidal planes, provides the necessary 5th independent slip system needed to facilitate the homogeneous polycrystalline deformation generated during elevated temperature forming operations. The climb of <a> dislocations offers an alternative mechanism in Mg alloys deformed at temperatures above ~0.5Tm; however, the extent of strain accommodation by climb is currently debated. It is hypothesized that classical creep theories underestimate the strain carrying potential of dislocation climb thus relegating it to a recovery mechanism.
Prior work has illustrated the utility of monitoring crystallographic texture evolution and strain anisotropy for revealing the controlling deformation mechanisms through crystal plasticity modeling. A model which explicitly accounts for the kinematics of dislocation climb and a genetic algorithm to parameterize the model provide an efficient means of matching simulation with experimental data. Application of these new methods has revealed that significant dislocation climb (rather than extensive glide of <c+a> dislocations) provides a comprehensive explanation for the characteristic changes in strain anisotropy, texture evolution, strain rate sensitivity, and activation energy which accompany the transition into the power law creep regime. The practical utility of this new insight will be explored through the use of forming limit diagram prediction.
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Zoom Information: https://virginia.zoom.us/j/93122753707?
Meeting ID: 931 2275 3707