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Zirconium diboride-based ceramics were studied to explore the effects of high secondary phase content and the relative merits of silicon carbide and zirconium carbide. Densification and grain growth were not influenced by heating rate or composition. Hardness increased with silicon carbide or zirconium carbide content from 18 to 26GPa and 18 to 21.5GPa respectively. Flexural strength was controlled by grain size and mode of crack propagation, and maximized at 380MPa at 20wt% silicon carbide and 590 MPa at 50wt% zirconium carbide. Zirconium carbide enhanced flexural strength better, due to its smaller coefficient of thermal expansion mismatch with zirconium diboride.

In this work, the casting process under mechanical agitation in the semi-solid state was investigated for the production of ZK60 magnesium alloy modified with the addition of 2.5% wt ofmischmetal. The results show that this process enables the production of ingots with homogeneous chemical composition and free of shrinkage, inner defects and internal oxidation. The as-cast microstructure consists of an α-Mg matrix with globular grains reinforced by a grid of distinct intermetallics of Mg-Zn, Mg-Zn-RE and Mg-RE type along the grain boundaries. The yield strength at room temperature undergoes more than 50% increase during direct T5 aging, thus reaching 170 MPa. At 300°C, however, the dispersion of nanometric precipitates does not modify the hot deformation behavior of the aged alloy, which undergoes dynamic recrystallization in a similar manner to the as-cast alloy. DRX at 300°C is fastest for the alloy solution-treated at 500°C.

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