Regular elemental powders were used in warm flow compaction instead of the expensive micron-sized powders to fabricate cross-shaped parts. Debinding behaviors, sintering properties and shape consistency of the sintered parts were studied. Binder removal was accomplished by heating green compacts at intermediate temperatures with optimal heating rates until the debinding temperature was reached. Results show that by controlling debinding process, complex parts with good shape consistence can be obtained by warm compaction of binder-treated powder. Fine and shiny surface was obtained and no surface defect can be observed for sintered parts debinded at 2 ℃/min, while defect can be observed in sintered parts debinded at 4 ℃/min.

The Cu-Sn binary intermetallic powders were obtained via a patented reaction ball milling technique. The Sn melt reacted with the solid-state Cu during the milling process at different temperatures for different intervals. Two kinds of binary intermetallics were obtained. For 12 h, Cu₆Sn₅ was prepared by milling Sn melt at 573 K while Cu₃Sn by milling Sn melt at 773 K. And a mixture of Cu₆Sn₅ and Cu₃Sn was fabricated at 673 K. All these intermetallic powders had mean grain sizes of less than 100 nm. A finer microstructure was obtained by milling Sn melt blended with 20%(mass fraction) Ni powders at 573 K for 12 h. The reaction mechanism and advantages were discussed in comparison with that of high-energy ball milling. The results show the solutionizing of Ni powders in the Cu₆Sn₅ intermetallic.

The sinter-hardening properties of a partially-diffuse alloyed Fe-2Cu-2Ni-1Mo-1C material were investigated. Samples were formed by die wall lubricated warm compaction method, then, sintered in hydrogen atmosphere at 1 150 ℃ for 1 h and cooled at 4.6, 2.9 and 1.5 ℃/s, respectively, from 900 ℃ down to 600 ℃. Effects of cooling rate on mechanical properties and microstructure of the material were discussed. The results show that when the cooling rate increases, the tensile strength of the material increases, while, the elongation shows opposite result. The sintered material has a tensile strength of 872 MPa and an apparent hardness of HB 257 at a cooling rate of 4.6 ℃/s. Slight shrinkage is observed. Heterogeneous microstructures containing martensite, bainite, pearlite and nickel-rich retained austenite are observed in the material. Higher martensite content can be obtained at higher cooling rate, while, at lower cooling rate, pearlite and retained austenite dominated the microstructure.

The microstructural evolution of nanocrystalline Cu-10%Nb(mass fraction) alloy during mechanical alloying (MA) was investigated by using X-ray diffraction, optical microscopy(OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. Upon milling of Cu-Nb powders with coarse grains, the grain size is found to decrease gradually with lengthening milling time, and reach the minimum value (about 9 nm) after 100 h milling. The microstrain and the microhardness of the powders increase during the grain refinement. And Cu lattice parameter increases steadily over 100 h milling. The mechanisms of solid solution extension during milling were discussed. The results show that up to 10%Nb can be brought into solid solution by MA. The extension of solid solution is found to relate closely with the formation of nanocrystalline

The size, crystal structure and phase transformation of Ni_49.8Mn_28.5Ga_21.7 alloy particles prepared by planetary ball milling (PBM) and vibration ball milling (VBM) were investigated by SEM, XRD and DSC. The results show that the particles milled by PBM for 4 h exhibit irregular polyhedron, with the size distribution between 5 μm and 40 μm. These particles present disordered fct structure with no phase transformation behaviour. When annealed at 600 ℃ for 1 h, the crystal structure of the particles evolves from disordered fct to Heusler completely. The particles milled by VBM for 4 h exhibit flaky shape, with the size distribution from 3 μm to 30 μm. The particles present disordered fcc structure with no phase transformation behaviour. However the crystal structure of these particles doesn’t transform from disordered fcc to Heusler completely after annealing at 600 ℃ for 1 h, for the severe lattice distortion induced in the VBM process is not eliminated entirely

The nano-composite powders of CeO₂/Zn were prepared with high energy ball milling and the nano-composite materials of CeO₂/Zn were fabricated with vacuum sintering powder metallurgy. Meanwhile, the composite and structure were analyzed by the means of XRD and FESEM. From the comparison of different nano-CeO₂ contents composites, the best corrosion resistance and hardness, and the optimum content of nano-CeO₂ were achieved. The result shows that corrosion resistance, hardness and uniformity of metal structure can be improved significantly with nano-CeO₂; at the same time, the optimal corrosion resistance, hardness and microstructure are obtained when the mass fraction of nano-CeO₂ is 1%.

The 1.0%Al₂O₃/Cu (mass fraction) composite was prepared by hot pressing (HP), then treated by rolling to get a full density. The microstructures and the micro area element distribution of the composite were analyzed by SEM. The density, electric conductivity and tensile strength were also investigated. The experimental results show that the alumina particles are more dispersed and become smaller through a single-pass rolling. The pore existing in the composite is eliminated or closed under the rolling force. The relative density increases from 98.4% to 99.2%. The electric conductivity increases from 88.9%IACS to 91.2%IACS. The tensile strength is increased by 47% from 300 MPa to 440 MPa.

The effect of post annealing on the phase transformation of Ni₅₂Mn₂₄Ga₂₄ ferromagnetic shape memory alloy particles prepared by ball milling was studied. Ni₅₂Mn₂₄Ga₂₄ alloy particles at micron scale were prepared successfully by ball milling the crushed bulk alloy. SEM observation reveals that the shape of the as-milled particle is regular polygon and a lot of cracks can be seen at the surface of the particles. For as-milled particles, the widening of characteristic peak can be found in the XRD pattern, and no transformation characterization can be detected by DSC. Post annealing at the elevated temperature will recover the transformation behavior of milled particles to the same level as that of bulk sample. It is shown that with increasing annealing temperature above 400 ℃, M_s decreases and A_s increases, while the magnetic transition temperature keeps constant. XRD results indicate that the change of grain size of the particles results in such an effect of post annealing.

A Ni-Cr/BN composite was produced by a active sintering process. The powder of nickel carbonyl，Cr₂O₃ and C were used as the original materials，and a hexagonal BN(h-BN) powder was added as a solid lubricant. The influence of sintering temperature，heating rate and holding time on the properties of Ni-Cr/BN were studied. The composition and microstructure of Ni-Cr/BN were analysed by X-ray diffraction(XRD) and the optical microscopy(OM). The frictional behavior and hardness were measured with ring-block friction testing machine and Brinell hardness tester respectively. The results show that Ni-Cr is the matrix and a low-melting eutectic compound is the bonding phase in the composite. The porosity reaches 48% and the value of hardness reaches HB18 when the composite is fabricated at 1 100 ℃ for 1 h. Its wear rate is 7.44×10^{−5 g/min, and the average friction coefficient is 0.266. These properties make such composite suitable for use as self-lubricating material.}

The properties and forming process of prealloyed powder metallurgy (PM) Ti-6Al-4V alloy were researched for application of high performance of titanium parts. Hot isostatic press (HIP) technology and two kinds of powders were used in the prealloyed processing to get full density material. Tensile properties, impact toughness and fracture toughness of PM Ti-6Al-4V alloy were studied and discussed. The microstructures were examined with optical microscope and the morphologies of powders were observed by SEM. Forming processes were performed to fabricate PM titanium parts. The experiment results show that the prealloyed PM Ti-6Al-4V alloy has same good properties as wrought material and the complex shape PM parts can be near-net-shaped. Some of the parts have been commercially used. This indicates that the prealloyed process should have bright prospects in making high-performance, complex shape and low-cost titanium alloy parts.

A new type of hybrid SiC foam-SiC particles-Al composites used as an electronic packaging substrate material were fabricated by squeeze casting technique. The mechanical properties and the fracture mechanism of the hybrid composites were investigated. The influence of SiC particles and foam hybrid reinforcement on the behavior of the composites was studied. The results show that the interface bonding in the hybrid composites is good for the composites with the unique double interpenetrating structure. The compressive strength of the hybrid composite reinforced by the SiC with the volume fraction of 59.9% is 680 MPa, which is higher than that of any other composites with the same volume fraction of SiC particles reinforcement.

The doped SiC powders were prepared by the thermal diffusion process in nitrogen atmosphere at 2 000 ℃. Graphite film with holes was used as the protective mask. The dielectric properties of the prepared SiC powders at high frequencies were investigated. The complex permittivity of the undoped and doped SiC powders was measured within the microwave frequency range from 8.2 to 12.4 GHz. The XRD patterns show that before and after heat treatment no new phase appears in the samples of undoped and nitrogen-doped, however, in the aluminum-doped sample the AlN phase appears. At the same time the Raman spectra indicate that after doping the aluminum and nitrogen atoms affect the bond of silicon and carbon. The dielectric real part (ε′) and imaginary part (ε") of the nitrogen-doped sample are higher than those of the other samples. The reason is that in the nitrogen-doped the N atom substitutes the C position of SiC crystal and induces more carriers and in the nitrogen and aluminum-doped the concentration of carriers and the effect of dielectric relaxation will decrease because of the aluminum and nitrogen contrary dopants.

The C_sf/Si₃N₄ composites were prepared by hot-press sintering method using α-Si₃N₄ power, short carbon fibers and La₂O₃-Y₂O₃ sintering additives. The mechanical and microwave dielectric properties of C_sf/Si₃N₄ composites were studied and discussed. The results show that the addition of the short carbon fibers can not destroy the relative density of the sintered samples, but it deteriorates the flexural strength of the sintered samples, so the flexural strength of the silicon nitride matrix is the highest among the samples. The real part (ε′) and the imaginary part (ε″) of the permittivity of C_sf/Si₃N₄ composites greatly increase with increasing volume fraction of the short carbon fibers, achieve the maximum 73.1 and 101.5, respectively. A strong frequency dependence of the imaginary part (ε″) of the permittivity is observed.

Nano-SiC powders doped by B were synthesized through the carbothermal reduction of xerogels containing the tributyl borate. The results show that the 3C-SiC with minor phase of 6H-SiC is generated at 1 700 ℃, and that there are not the characteristic peaks of any boride in the XRD patterns, which indicates that the boron is available only on the crystallization of 3C-SiC. The Raman spectra of the samples also show the characteristic bands of 3C- and 6H-SiC at 788 and 965 cm⁻¹. But the bands at 1 345 and 1 590 cm⁻¹ are characteristic peaks of amorphous carbon materials. The intensities of peaks at 788 and 965 cm⁻¹ increase with B content in Raman spectra, which also shift to higher wavenumber with the increasing B. The microstructure of SiC powder is composed of agglomerated particles with diameters ranging from 30 to 100 nm. The results of dielectric property show that the sample with 0.005 B has the largest values in ε′ and ε″ among the four samples due to the existence of the intrinsic defects. But the absence of the relaxation polarization leads to low values of all the samples.

The nano-TiC_p/W and micro-TiC_p/W composites containing 1% TiC(mass fraction) particles with average particle sizes of 50 nm and 1.5 μm were fabricated respectively by high energy ball milling and vacuum hot pressing (VHP) at 2 373 K, 30 MPa, in a vacuum of 1×10⁻³ Pa. Microstructure and mechanical properties of the composites were examined at room temperature. The results show that both n-TiC and μ-TiC particles are homogeneously distributed in the as-sintered composites. The size of n-TiC particle is about 100 nm, and that of μ-TiC particle is about 1 μm. The additions of n-TiC and μ-TiC particles both result in higher mechanical properties compared with monolithic W. The improved mechanical properties may be mainly attributed to the grain size strengthening, dispersion strengthening and grain boundaries strengthening. The addition of n-TiC particles to tungsten is found to have beneficial effects on the mechanical properties than that of μ-TiC due to its small size.

The suitable test equipment for wire-drawing was designed. Wire-drawing tests were carried on with this equipment for TiC/Al₂O₃ ceramic wire-drawing die. Effect of lubrication medium and drawing velocity on the drawing force was investigated. The wear mechanisms of the ceramic drawing dies were investigated. Worn bore surfaces of the ceramic drawing dies were examined by scanning electron microscopy. The results show that lubricant media have great influence on the drawing force. The drawing force is the smallest when a grease lubricant is used. But alteration of drawing velocity has scarcely any influence on the drawing force. Detailed observations and analyses of the die wear surface reveal that the most common failure of the ceramic drawing die is the wear in the invariable zone and bearing zone owing to the greater press stresses. Abrasive and adhesive wear are found to be the predominant wear mechanisms for ceramic drawing die.