The effect of Cu content on microstructure and mechanical properties of nano-sized Cu dispersed nanocomposites was investigated. The nanocomposites with Cu content of 2.5 to were prepared by reduction and hot-pressing of powder mixtures. The nanocomposites with Cu content of 2.5 and exhibited the maximum fracture strength of 820MPa and enhanced toughness compared with monolithic . The strengthening was mainly attributed to the refinement of matrix grains. The toughening mechanism was discussed by the observed microstructural feature based on crack bridging

The microstructure and mechanical property of hot-pressed composites with a different temperature for atmosphere changing from H to Ar have been studied. When atmosphere-changed from H to Ar gas at 145, the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when atmosphere-changed at low temperature of 110 the composite showed more homogeneous microstructure, higher fracture strength and smaller deviation in strength. Based on the thermodynamic consideration and microstructural analysis, it was interpreted that the Cu wetting behavior relating to the formation of CuAlO is probably responsible for strong dependence of microstructure on atmosphere changing temperature. The reason for a strong sensitivity of fracture strength and especially of its deviation to atmosphere changing temperature was explained by the microstructural inhomogeneity and by the role of CuAlO phase on the interfacial bonding strength.

Nanostructured Cu-AlO composite powders were synthesized by thermochemical process. The synthesis procedures are 1) preparation of precursor powder by spray drying of solution made from water-soluble copper and aluminum nitrates, 2) air heat treatments to evaporate volatile components in the precursor powder and synthesis of nano-structured CuO + O, and 3) CuO reduction by hydrogen into pure Cu. The suggested procedures stimulated the formation of the gamma-AlO, and different alumina formation behaviors appeared with various heat treating temperatures. The mean particle size of the final Cu/AlO composite powders produced was 20 nm, and the electrical conductivity and hardness in the hot-extruded bulk were competitive with Cu/AlO composite by the conventional internal oxidation process

Ni coated composite was successfully Prepared by the electroless deposition Process. The average size of Ni particles coated on the matrix powder was about 20 nm. It was hard to find any reaction compound as an impurity at interface between and Ni particles after sintering. The characterization of microstructure crystal structure and fracture behavior of the sintered body were investigated using XRD, TEM and Victors hardness tester, and compared with those of the sintered monolithic body. Many dislocations were observed in the Ni phase due to the difference of thermal expansion coefficient between and Ni phase, and no observed microcracks at their and Ni interface. In the /Ni composite, the main fracture mode showed a mixed fracture with intergranular and transgranuluar type having some ,surface roughness. The fracture toughness was slightly increased due to the plastic deformation mechanism of Ni phase in the /Ni composite.

Elemental powders are used in high energy milling processes for the synthesis of new compounds. The low temperature solid state reactions during milling in inert gas atmosphere may result in intermetallic phases, carbides, nitrides or silicides with a nanocrystalline structure. To obtain dense materials from the powders a pressure assisted densification is necessary. On the other side the defect-rich microstructure can be used for activated sintering of elemental powder mixtures to obtain dense bodies by pressureless sintering. Results are discussed for nanocrystalline cermet systems and for the sintering of aluminides and silicides

Plastic deformation was observed by TEM around the intragranular SiC particles in the matrix for nanocomposite system. The dislocations are generated at selected planes and there is a tendency for the dislocations to form a subgrain boundary structure with low-angel grain boundaries and networks. In this study, dislocation generated in the matrix during cooling down from sintering temperatures by the highly localized thermal stresses within and/or around SiC particles caused from the thermal expansion mismatch between matrix and SiC particle was observed. In monolithic and microcomposite system. These phenomena is closely related to the plastic relaxation of the elastic stress and strain energy associated with both thermal misfitting inclusions and creep behaviors. The plastic relaxation behavior was explained by combination of yield stress and internal stress.

Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for and nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.

The microstructure and mechanical properties of nanocomposites synthesized by chemical processing were investigated. The nanocomposites containing 15 vol% hexagonal BN (h-BN) were fabricated by hot-pressing powders covered with turbostratic BN (t-BN). The t-BN coating on particles was prepared by heating particles covered with a mixture of boric acid and urea in hydrogen gas. TEM observations of this nanocomposite revealed that nano-sized h-BN particles were homogeneously dispersed within grains as well as at grain boundaries. The strength and thermal shock resistance were significantly improved in comparison with the microcomposites.