Journal of Composite Materials

In order to improve the in situ oxidation kinetic condition of Al in Cu matrix, Cr, instead of Al was in situ oxidized to form Cu/Cr₂O ₃ composites in the present investigation, Cu-Cr powders with different solubilities after mechanical activation were utilized to synthesize Cu/Cr ₂O₃ composites, and their microstructure and stability were analyzed. The results show that although the Cu-Cr powders suffer from the same mechanical activation; Cr₂O₃ particles formed by the powders with different solubilities have great differences in size, amount, and distribution. In the range of experiments, the Cu/Cr₂O ₃ composite formed by Cu-Cr powders with 67% solution has large amounts of finer Cr₂O₃ particles uniformly distributed in Cu matrix and the best stability at elevated temperatures.

Yttria-stabilized tetragonal zirconia/20 wt% alumina (TZP-3Y20A) composites were fabricated by spark plasma sintering at various sintering temperatures over the range of 1000—1400^°C. Hydroxyapatite (HA) additive was added in volume fractions of 10—50% in order to increase the biocompatibility of the composite. The densification behavior of the TZP-3Y20A composite and that of the composites with HA were investigated. In the case of TZP-3Y20A composites, the density increases steadily with temperature and reaches a maximum value of 97.8% of the theoretical density at 1400°C. The solution interface formed between zirconia (ZrO₂) and alumina (Al ₂O₃) strengthens the bond between ZrO₂ and Al ₂O₃ grains and facilitates densification. In the case of TZP-3Y20A/HA composites, sintering at 1400°C led to the formation of tricalcium phosphate in the samples, which resulted from the decomposition of HA due to its limited thermal stability at high temperature; no reaction was observed between ZrO₂ and HA. The addition of HA imposes a barrier effect on the diffusion between ZrO₂ and Al₂O₃ grains, thus limiting the grain growth of ZrO₂ and Al₂O ₃.

The compressive response of an alumina-filled epoxy composite material was characterized at various strain rates using a Kolsky bar and universal testing frame (MTS). In the Kolsky-bar experiments, dynamic stress equilibrium and constant strain-rate deformation in specimens were achieved using pulse-shaping techniques. The effects of specimen aspect ratio and interfacial friction on the dynamic response of the material were examined. Compressive stress-strain curves for the composite were obtained at strain rates ranging from 9.4 × 10^-4 to 1.35 × 10³ s^-1 which exhibited strong strain-rate sensitivity. A material response model, which agrees well with the experimental measurements for the strain rates examined in this study, is also described.

Dry oxidizing methods have been widely used to modify surface properties of polymer and ceramic substrates. Compared to other dry oxidizing methods, ultraviolet light/ozone (UV/O₃) treatment has hitherto attracted less attention, mainly due to relatively weak oxidizing power. With optimized processing conditions, however, UV/O₃ treatment can be better capable of offering desired effects associated with appropriate surface modifications. Incorporation of nanoscale reinforcements, e.g., carbon nanotubes (CNTs) and graphite, into a polymer matrix creates a new class of composites that possess unique mechanical and functional capabilities. A proper surface treatment is critical to dispersing the reinforcements in the matrix, hence to provide adequate adhesion between the reinforcements and the matrix. In this article, a review is provided on the underlying mechanisms of and the advantages arising from UV/O₃ treatment of polymer substrates and nanoscale carbon materials. Special focus is placed on the relationship between the changes in chemical composition, morphology, functional groups of the treated surface and the corresponding improvements in adhesion and wettability of the substrate, dispersion of nano-reinforcements, as well as the properties of the nanocomposites made therefrom.