Papers by Author: Christopher R. Hutchinson

Abstract: A physically-based model for nucleation during discontinuous dynamic recrystallization (DDRX) has been developed and is coupled with polyphase plasticity and grain growth models to predict the macroscopic stress and grain size evolution during straining. The nucleation model is based on a recent description for static recrystallization and considers the dynamically evolving substructure size. Model predictions are compared with literature results on DDRX in pure Cu as a function of initial grain size, deformation temperature and strain-rate. The characteristic DRX features such as single to multiple peak stress transitions and convergence towards a steady-state stress and grain size are quantitatively reproduced by the model.

Abstract: A physically-based model is proposed for the competitive precipitation of multiple phases (bcc-Fe, Fe3B, Nd2Fe14B, Nd2Fe23B3, NdFe4B4 and Fe2B) from an amorphous Fe-B-Nd matrix. These materials form the basis of a class of nanocomposite hard magnets. The nucleation and growth of the different phases are calculated using computational thermodynamics and kinetics tools with input from a thermodynamic assessment of this system. In some alloy compositions, the phase formation sequence during crystallization shows significant sensitivity to the heating-rate. Model calculations illustrate that this effect cannot be explained by homogeneous nucleation and growth of the phases. The possible role of heterogeneous nucleation is briefly discussed.

Abstract: A brief overview of the role of computational materials science and engineering in the ARC Centre of Excellence for Design in Light Metals is presented. A recent example of designing precipitate structures in Al alloys for simultaneous increases in strength and elongation is used to highlight the spirit of the approach.

Abstract: The comparative effectiveness of solute Nb and NbC particles at impeding grain boundary motion is treated theoretically. It is shown that, for a steel containing ~0.05 at% Nb (~0.1 wt%Nb), under typical recrystallization conditions, solute Nb is more effective in the ferrite, whereas in the austenite, depending on the exact recrystallization temperature, either solute Nb or NbC precipitates may be more effective.

Abstract: The microstructural evolution and associated strengthening during isothermal ageing of an Al-3Cu-0.05Sn reinforced by non-spherical θ' (Al2Cu) precipitates is studied. Emphasis is placed on the plate shape of the θ'. It is found that the microstructure parameters governing the magnitude of the precipitation strengthening effect are completely different from the classical case of spherical precipitates. New possibilities for microstructure design are discussed.

Abstract: The work hardening behavior of an Al-3Cu-0.05Sn (wt %) alloy was studied using tensile tests and Bauschinger tests. Emphasis is placed on the influence of the precipitation state (number density, size distribution and volume fraction) and separating the isotropic and kinematic components of the work hardening.

Abstract: It has recently been observed that the creep resistance of Al-Cu based precipitation hardened alloys may be enhanced through use of the underaged temper. We have treated this problem theoretically by considering the motion of a dislocation through a precipitation hardened structure and discuss the physical origin of the enhanced creep resistance in the underaged condition. The variation in expected creep resistance as a function of aging treatment is calculated and the possible generality of the experimental observations is considered.

Abstract: The kinetics and morphology of the grain boundary grooving of Zn bicrystals with 16° <1010> tilt GB by Sn(Zn) melt has been studied at 325°C in equilibrium conditions in vacuum. It is shown that grooving process is interface controlled at least on the first stage. Groove walls mobility is evaluated. Changing of GB grove shape from “faceted walls” corner for annealing time < 78 h to concave “Mullins type” groove for annealing time > 78 h at the same experimental temperature was observed for the first time.

Abstract: A physically based model is used to analyze quantitatively, the relative contributions of solute Nb and strain-induced NbC precipitation to the retardation of static recrystallization during the interpass time. The model explicitly takes into account the time evolution of strain-induced precipitation and its interaction with recovery and recrystallization. It is thus possible to quantitatively model the recrystallization kinetics taking into account: i) the effect of solute drag on the boundary mobility, ii) the effect of particle pinning (Zener drag) on the driving force for boundary motion, and iii) the effect of dislocation pinning by strain-induced precipitates, on the recovery kinetics and the nucleation of recrystallization. The analysis shows that there is an optimum partitioning of Nb between matrix solute and strain induced precipitates. This optimum partitioning maximizes particle pinning while ensuring an adequate solute drag effect to prevent the boundary from breaking away from solute atmosphere. The optimum partitioning of Nb between the matrix and the precipitates is shown to depend upon the temperature window of rolling, pass reduction and interpass time. The effect of delaying the kinetics of strain-induced precipitation of NbC through large Mn addition is shown to be an advantage for ensuring adequate solute drag in the low temperature, large pass deformation schedule used in near-net shape processing of thin slab or thick strip castings.