In the present work some properties of nanopowders and possible areas of their applications are discussed. Main attention is paid to the use of nanodispersed powders (NDP) in new materials production technologies.
Phase contents and elemental composition of ultradispersed powders obtained by the electrical explosion of tin-leadalloy powders are investigated. It is demonstrated that during the explosion and subsequent cooling, surface layers of powder particles are enriched in lead compared to the initial alloy. The thermal stability of powders oxidizing in air is also investigated.
The feasibility of obtaining highly dispersed aluminum oxide powders by the electrical explosion of aluminum conductors in an inert gas atmosphere and the subsequent oxidation of aluminum particles by water prior to their contact with air is demonstrated. For a specific surface area of the initial aluminum powder of 6.5/g, the corresponding specific surface area of the resultant aluminum oxide nanopowder was as large as 300/g.
The mechanical alloying effect has been studied on the three Cu-based alloy systems with a positive heat of mixing. The extended bcc solid solution has been formed in the Cu-V system and an amorphous phase in the Cu-Ta system. However, it is round that a mixture of nanocrystalline Cu and Mo Is formed in the Cu-Mo system. The neutron diffraction has been employed at a main tool to characterize the detailed amorphization process. The formation of an amorphous phase in Cu-Ta system can be understood by assuming that the smaller Cu atoms preferentially enter into the bcc Ta lattice during ball milling.
Interpenetrating phase composites of -Cu system were produced via Spark-Plasma Sintering (SPS) oi nanocomposite powders. Under simultaneous action of pressure, temperature and electric current titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a fine-grained skeleton. Increasing SPS-temperature and he]ding time promote densification due to local melting of copper matrix When copper melting is avoided the compacts contain 17-20% porosity but titanium diboride skeleton is still formed representing the feature of SPS . High degree of densification and formation of titanium diboride network result in increased hardness of high-temperature SPS-compacts.
Mechanically-alloyed NiAl powder was sintered by Spark-Plasma Sintering (SPS) process. Densification and behavior mechanical property were determined from the experimental results and analysis ,such as changes in linear shrinkage, shrinkage rate, microstructure, and phase during sintering process, Victors hardness, and transver.ie-rupture-strength (TRS). Above 97% relative density was obtained after sintering at 115 for 5 min. Crystallite size determined by the Scherrer method was approximately 50 nm. From the X-ray diffraction analysis it was confirmed that the sintered bodies were composed mainly of NiAl phase together with NiAl phase. Measured Vickers hardness and TRS value were 55510 and 139375 MPa , respectively.
Pure WC powders which does not include a binder phase were consolidated by spark plasma sintering (SPS) process at 1600~185 for 0~30 min under 50 MPa. Microstructure alid mechanical properties of binderless WC prepared by SPS were investigated. With increasing sintering temperature, sintered density and Vickers hardness of binderless WC increased. The fracture toughness of binderless WC was 7~15 MPa depending on the sintered density and decreased with increasing the Vickers hardness. It is found that the binderless WC prepared by SPS at 175 for 10 min under 50 MPa showed nearly full densification with fine-grained structure and revealed excellent mechanical properties of high hardness (~HV 2400) and considerably high fracture toughness (~7 MPa ).
Resistance sintering under ultra-high pressure if developed to fabricate W-Cu composite containing 5 to 80v/o copper. The consolidation was carried out under pressure of 6 to 8 GPa and input power of 18 to 23 kW for 50 seconds. The densification effect and microstructure of these W-Cu composites are investigated. The effect of W particle size on ,sintering density was also studied. The micro hardness was measured to evaluate the sintering effect.
A chemical vapor condensation (CVC) process using the pyrolysis of metal-organic precursors was applied to produce the nanosized powders. Morphology and phase changes of the synthesized powder as a function of CVC parameters were investigated by XRD, BET and TEM. The agglomerated nanosized monoclinic powders with nearly spherical shape and 10-38 nm in mean diameter could be obtained. Conditions to produce the nanopowders are presented in this paper
Thin Ag films deposited onto substrates by DC magnetron sputtering and thereafter annealed ,it temperatures 100-50 are investigated by scanning tunneling and atomic forte microscopy. It is shown that the film surface topography and microstructure are considerably changed as a result of annealing. To provide a quantitative estimation of the surface topography changes of Ag films the surface fractal dimension was calculated. Elasticity and hardness of the films are studied by a nanoindentation technique. The films are found to have value of elastic modulus close to that of bulk silver while their hardness and yield stress are essentially higher.
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.
Distributions of diamond particles protruding on the surface of worn diamond segments in circular saw has been investigated. Scanning electron microscope was used to examine the worn ,surface and radial saw blade wear and grinding ratio was measured. The number of protruded diamond particle was approximately 50% of the total number of particles, and that was independent of diamond particle concentration and table speed. It was also noted that the inter-particle distance did not follow a symmetric function like Gaussian distribution function, instead it fitted well with a probability density function based on gamma function. The distribution of inter-particle spacing, therefore, was analyzed using a gamma function model.