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<p>With the poor room temperature formability of magnesium, rare earth (RE) additions have proven a promising avenue for wrought magnesium products. However, not much is known regarding the effect of these elements on strength and ductility. Stanford et al. (2010b) summarized it best: “Although the addition of rare earth elements offers the possibility of greatly improved mechanical properties, we still lack fairly basic knowledge about the behaviour of these alloying elements”[p.6773]. Through a systematic study across three Mg-RE binary systems, the effect of gadolinium, samarium and scandium on solution strengthening, work hardening behaviour and strain rate sensitivity of Mg-RE binary alloys have been characterized.</p> <p>The results suggest that samarium offers the greatest solid solution strengthening in both tension and compression relative to the other two binary systems. For the binary alloys explored, only gadolinium and samarium in compression followed the Labusch theory of solution strengthening; in which the yield strength scales with c^2/3 . Gadolinium additions provide the largest strength and ductility in tension and compression. Increasing solute content in the binary systems leads to a decrease of the strain rate sensitivity of the alloys. At the highest level of solute, both Mg-Gd and Mg-Sm exhibit negative strain rate sensitivity under tension. In compression, Mg-Gd also exhibits a negative strain rate sensitivity at the highest level solute, whereas Mg-Sm has a low, but positive value. The asymmetry in work hardening behaviour and the form of the flow curves between tension and compression is the result of the difference in the dominating modes of deformation at a given stage of the plastic flow. The extent of the work performed established the hardening levels and thermodynamic deformation parameters which control the flow stress and work hardening behaviour, that can be applied in future work.</p> / Master of Applied Science (MASc)

The objective of this research was to investigate the hydrophilic and mechanical properties of kenaf fiber treated with vinyl tris(2-ethoxymethoxy) silane (VTEMS) and the resulting fiber/resin composite. The hypothesis was that silane-modified kenaf fibers, when used to make Sheet Molding Compounds (SMCs), would improve the water resistance and mechanical properties compared to unmodified kenaf fibers, and these potentially improved SMCs may be a useful material for the automotive and other industries. Fourier transform infrared (FTIR) spectroscopy was used to analyze the modified fibers and the resulting SMCs, and some silica-lignocellulosic bonding was observed. The water absorption of composites decreased as the loading of the silane reagent increased. The MOR and MOE mechanical properties of the SMCs also initially improved as the silane reagent levels increased from 0 (untreated) to 10% silane, but at levels above 10% VTEMS no further enhancement in the mechanical properties was obtained.

Intermetallic composites of molybdenum disilicide reinforced with various amounts of silicon carbide particulate were produced by combustion synthesis from their elemental powders. Elemental powders were mixed stoichiometrically then ball-milled. The cold- pressed mixture was then chemically ignited at one end under vacuum at approximately 700°C. The combustion temperature of the process was approximately 1600°C which was lower than the melting point of molybdenum disilicide. This processing technique allowed the fabrication of the composites at 700°C within a few seconds, instead of sintering at temperatures greater than 1200°C for many hours. The end product was a porous composite, which was densified to >97% of the theoretical density by hot pressing. The grains of the matrix were 8-14 μm in size surrounded by SiC reinforcement of 1-5 μm. The morphology and structure of the products were studied by x-ray diffraction and scanning electron microscopy (SEM). Samples were prepared for hardness, fracture strength, and toughness testing at room temperature. There were improvements in the mechanical properties of the composites with increasing SiC reinforcement. The hardness of the materials increased from 10.1 ± 0.1 GPa (959 ± 13 kg/mm2) to 11.7 ± 0.6 GPa (1102 ± 52 kg/mm2) to 12.7 ± 0.4 GPa (1199 ± 36 kg/mm2) with the 10 vol% and 20 vol% SiC reinforcement, respectively. The strength increased from 195±39 MPa to 237±39 MPa with 10 vol% and to 299 ± 43.2 MPa with a 20 vol% SiC reinforcement. The fracture toughness increased from 2.79 ± 0.36 MPa.m1/2 to 3.31± 0.41 MPa.m1/2 with 10 vol% SiC and to 4.08± 0.30 MPa.m1/2 with 20 vol% SiC. The increase in hardness and flexural strength is due to the effective load transfer across the strong interface in the composites. The main toughening mechanism is crack deflection by the residual stress in the materials, induced by the differences in the thermal expansion coefficients and the elastic moduli of the matrix and reinforcement. / Thesis / Master of Engineering (ME)