We present a detailed study on the electronic structure, mechanical properties, phase stability, and thermodynamic properties of four polymorphs of crystalline zirconium hydride by using density functional theory within the generalized gradient approximation. An analysis of electronic structure shows that the zirconium hydrides retain metallic bonding over the whole hydrogen composition range. The calculated mechanical properties indicate that -Zr 2 H and γ-ZrH are ductile, while δ-ZrH 1.5 and ε-ZrH 2 are brittle compared with R-Zr. The hydrides change from ductile to brittle in the order of -Zr 2 H, γ-ZrH, ε-ZrH 2 , and δ-ZrH 1.5 . The formation enthalpies are negative for the four hydrides at the ambient pressure indicating that they are thermodynamically stable. Only the δ phase is thermodynamically stable in the whole pressure range. As the temperature increases, the decomposition reactions of the four hydrides are more and more favorable thermodynamically. The δ phase is thermodynamically easier to decompose than the others in the whole temperature range.

Ceramic nanoparticle-reinforced aluminium metal matrix composites (AMMCs) have superior mechanical properties compared with matrix alloys, exhibiting great potential in structural applications in industries such as the aerospace and automotive sectors. This research proposes a new method for distributing SiC nanoparticles in an aluminium matrix alloy by powder metallurgy. The mixing of aluminium powder and SiC nanoparticles was processed by a two-step procedure, which included ultrasound-assisted stirring and planetary agitation. After that, the mixing powder was subjected to compaction, sintering and extrusion. A blank sample and three composite sheets containing 1, 2 and 3 wt % SiC nanoparticles were prepared and the mechanical properties were investigated by micro-hardness and tensile tests. A scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) were used for microstructural analysis of the composite. Experimental results revealed that by adding 1, 2, 3 wt % SiC nanoparticles, hardness was increased by 26%, 34.5%, 40.0% and tensile strength was increased by 22.3%, 28.6% and 29.3%, respectively. The grain size of the aluminium matrix decreased with the addition of SiC nanoparticles. Moreover, a decrease of elongation was observed with the increasing weight fraction of SiC.

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Microstructure evolution of 15 wt% boron carbide particle reinforced aluminum matrix composites (B4C/Al composites) with titanium addition during liquid-stirring process was dynamically characterized in this paper. B4C particles were rapidly dispersed under the mechanical stirring. Many B4C clusters were formed in the melt before 20 min, but gradually scattered in matrix beyond 20 min, owing to further reactive wetting through interface reaction in addition to stirring. After rapid improvement, distribution uniformity slowly approached to completely uniform distribution during 20–55 min, even better than random distribution at 55 min. Interface reaction produced Al3BC, TiB2, and AlB2 by B4C erosion and Al3Ti decomposition; however, AlB2 only precipitated in matrix after long time stirring. The growth of TiB2 transformed from a fine layer to discretely coarse crystals on the B4C surface. Reaction mechanism and relationship between reactive wetting and particle dispersion were discussed.