Interaction of interstitial solid-solution impurities and dislocation motion in body-centered cubic metals
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
The project investigated the dislocation-mediated plasticity which causes the brittleductile transition in pure Cr and which appears to be related to the role of impurities and their interference with the thermally-activated dislocation mobility. Based on established theories of kink-pair nucleation on screw dislocation, the uniaxial stress formalisms have been reformulated for hardness and subsequently applied to the experimental data. The combination of newly acquired resolution of temperaturedependent hardness and activation volume allowed to identify an impurity induced solute-drag strength contribution superimposed on the temperature-dependent and strain-rate dependent kink-pair nucleation limited strength. Detailed analysis of the kink-pair nucleation limited plasticity regimes allowed for the identification of the line tension model regime and elastic interaction regime at low temperatures (i.e., high hardness) and elevated temperatures (i.e., low hardness), respectively. At even higher temperature, the nanoindentation data did not reveal a measurable strain rate and temperature dependent hardness beyond the experimental scatter and therefore, revealed athermal strength contribution presumably related to athermal strengthening mechanisms (e.g., forest hardening). These presumable athermal Knee hardness is also superimposed on the hardness contribution related to the thermally-activated kink-pair nucleation. Moreover, the project developed an equilibrium molecular dynamics method to determine the mobility of dislocations in the limit of zero stress. The molecular dynamics simulations revealed also two temperatures regimes for even the mobility of edge dislocations. The resulting implications are currently investigated in context of the influence microstructural constrains on the intrinsic mobility of extended dislocation lines.
