Coupling Plasticity to Phase Transformations in Metastable Structural Alloys

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In the design of structural components the designer ideally seeks materials that have maximum strength and deformability (ductility). The former allows less material to be used to withstand a given force, while the latter confers toughness (the ability to absorb energy prior to failure). Unfortunately, in the majority of materials these two properties are mutually exclusive, i.e. increasing the strength generally leads to a reduction in ductility. While this compromise has its origins in the fundamental atomic properties of materials, there is an increasing awareness that material design can circumvent the intrinsic strength - ductility relationship. This proposal seeks to focus on the use of controlled deformation (strain) induced phase transformations to achieve improvements in both strength and ductility under monotonic and cyclic loading conditions. This approach will be investigated in alloys of commercial significance (steels and magnesium alloys) specifically selected to allow for the change of the material from one state to another during deformation. Tools will be developed to predict the coupling between strength, ductility and the changes induced by the phase transformation. Atomic scale simulations will be used, for example, to systematically investigate the events that trigger the change from one state to another. Advanced characterization tools will be used to assess the mechanical behaviour and phase transformation concurrently. The results will contribute to our fundamental understanding of the limits of the intrinsic relationship between strength and ductility but will also provide practical tools for materials design of value to the Canadian manufacturing industry.