Transformation induced plasticity (TRIP) steels are a class of steels with exceptional formability properties, due mainly to the presence of meta-stable retained austenite which transforms to martensite under loading, locally hardening the steel. The volume fraction and mechanical stability of the retained austenite play an important role in producing the high formabilities of TRIP steels. In this thesis, two separate morphologies of retained austenite, equiaxed versus lamellar, have been produced through thermo-mechanical processing of a single common TRIP steel chemistry. The sheet formability characteristics of these two microstructures were examined, with varying volume fractions of retained austenite, through uniaxial tensile and in-plane plane-strain (IPPS) testing. It was found that higher levels of retained austenite produced better formability properties for both microstructures and strain paths. In uniaxial tension it was seen that the the lamellar microstructure attained higher strains at maximum load, and exhibited more sustained instantaneous n values than the equiaxed structure, despite having a lower volume fraction of retained austenite. IPPS testing was performed using an optical measurement of local strain and a comparative forming limit based on differences in strain rate between a developing neck and the surrounding material. It was found that the lamellar microstructure performed better than the equiaxed microstructure for this strain path, achieving higher strains before reaching the comparative forming limit. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2010-01-25 16:36:07.598

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The blending of lignin as a component in a thermoplastic blend poses a challenge in the form of dispersion and compatibility. Polyesters such as poly(lactic acid) and poly(butylene adipate-co-terephthalate) offer the best opportunity of compatibility in melt blending with lignin due to their ability to form hydrogen bonds. The fractionation of lignin into more homogeneous fractions offers better dispersion and more consistent properties, retaining the toughness of the original polymer in addition to bridging stress transfer between PLA and PBAT. Functionalization of lignin was done by lactic acid grafting. The resulting blend of PLA/PBAT/modified fractionated lignin showed improved interaction between lignin and PLA, but reduced compatibility between lignin and PBAT. This thesis provides a deeper understanding on the effect of lignin heterogeneity, its fractions, and the functionalization of lignin on lignin and bioplastic blends to further the use of a largely produced industrial by-product in high value applications. / Natural Sciences and Engineering Research Council (NSERC) – Lignoworks Biomaterials and Chemicals Strategic Research Network, Canadian Foundation for Innovation (CFI), Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)

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