Key Engineering Materials Vols. 368-372

Abstract: The composition, microstructures and properties of the Ti(CN) based cermets have been characterized by using SEM/BSE and energy spectrometer. Results shows that the carbon content of the cermets through N2 and Ar sintering was lower by 0.5% than vacuum sintering and the nitrogen content of the cermets through N2 sintering was higher by 20~25% than the Ar and vacuum atmosphere sintering. When sintered in Ar or N2, the balance between the carbon and nitrogen in the cermets was broken to form a surface defects, which would result in poor properties. The structure of vacuum sintering is more uniform and the properties are better.

Abstract: Aluminum nitride (AlN) powder was synthesized by gas reduction–nitridation of γ-Al2O3, using NH3 as the reactant gas. The results showed that AlN can be fabricated by this process at 1100°C for over 480 min in the flowing NH3 atmosphere. However, no AlN was found in the products synthesized at 1300°C and 1400°C, which was different from the former reports. A series of experiments with different parameters were carried out, and the effects of reacting temperature and time on the synthesis of AlN were investigated. The reaction mechanism was also studied.

Abstract: Based on the empirical electron theory (EET) of solids and molecules, the valence electron structures (VESs) of TiC-Mo(Ni)-Fe system were calculated by building proper structure model. The results indicate that additives of Mo and Ni improve the interface conjunction factors of the cermets in different ways. By adding Mo, the VESs of the ceramic phase are improved for the formation of the rim phase (Ti1-xMox)C, which leads to the enhancement of the interface conjunction, while the improvement of the VESs on metal phase by adding Ni is due to the formation of the Fe100-yNiy. Mo and Ni additives increase the interface electron density of cermets, that is, the adding of the Mo and Ni enhance the overlapping grade of the electron cloud on interface and increase the binding energy of the interface, which is propitious to the wettability. The best wettability was found at x=0.5 or y=30.

Abstract: Fe-SiAlON-MoSi2 composites were prepared using FeSi75, α-Al2O3, and MoSi2 powders as starting materials at 1400 oC, 1500 oC, 1600 oC and 1700 oC, respectively, for 3h in a flowing nitrogen under the pressure of 0.9MPa. The results showed that the main phases of Fe-SiAlON-MoSi2 composite were β-SiAlON with deferent Z-values, MoSi2, and Fe3Si. Z-value of the obtained β-SiAlON depanded on α-Al2O3 content and the sintering temperature. The morphology of SiAlON phase changed from fibre-like of low Z-value to hexagonal prism-like of high Z-value.

Abstract: A new near-net-shape technology, namely, self-reactive spray forming, to prepare ceramic preforms with low cost was proposed by combining the self-propagating high-temperature synthesis (SHS) with the metal spray forming. The feasibility of the technology was illustrated. And TiC-TiB2 -based structural ceramic was prepared by the new technology. The microstructure of the self-reactive spray formed preforms was analyzed. It was shown that the self-reactive spray formed preforms are composed of four kinds of structure, which takes on the characteristics of rapid solidification. They are griseous continuous base phase TiC0.3N0.7, black columnar grain TiB2 with the size of 100nm-1μm, white by-product phase TiO2 distributing along the boundary of the base phase, and a few of black anomalous pores respectively.

Abstract: Ti0.6Cr0.4OxNy bimetallic metal oxynitride nano powder was synthesized by ammonolysis of the nanosized Cr2O3/TiO2 composite powder with n(Ti):n(Cr)=6:4 at 800oC for 8 h. The precursor and the resulting oxynitride were characterized by Auger electron spectroscope (AES), X-ray diffraction analysis (XRD), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and BET surface area techniques. The result indicated that the precursor was homogenous mixture of Cr2O3 and TiO2 with high BET surface area. The as-synthesized oxynitride powder contains only Ti0.6Cr0.4OxNy with cubic structure. The BET surface area of the oxynitride powder is 37.42 m2/g and the particle size is in the range of 20~30 nm.

Abstract: The Al/AlN bonded corundum based multiphase material was prepared by raw materials of fused alumina and metallic aluminum powder by in situ reaction at 1100°C for 3h in N2 . The XRD analysis showed that the mineral phases of prepared material are corundum, metallic aluminum and AlN respectively. The SEM investigation revealed that both tetragonal whiskers and hexagon powders of AlN were formed. The results of hydration tests indicated that the rate of weight gain and pulverization of the material were negligible and the ratio of residual crushing strength was kept at a high level. The XRD patterns of samples after hydration tests identified that the AlN phase still remained although a small amount of AlOOH and Al(OH)3 was formed due to the hydration of AlN. It is believed that the limited hydration of AlN should be contributed to the dissolution of O element to AlN. The hydration mechanism of AlN was discussed.

Abstract: The 5-axis milling processes were conducted with several uncoated WC-Co tools, which are with taper ball end mills with four flutes. There is a severe problem of high rate of tool failure, which has led to the high cost and low productivity of the milling process. In order to find out the real reason, some former work, which included the tool geometry analysis, tool path and tool posture analysis, as well as the cutting force calculating, had been done. It has been found that most of the tool failures are resulted from cutting edge chipping or the workpiece material of titanium alloys attached to the tool. Meanwhile, a suddenly applied load or an abrupt unloading of the tool at the end of a cut is another important factor. Moreover, the tool materials had been analyzed, which included the element composition analysis with XRD, the microstructure analysis with SEM. XRD results indicate the cobalt at the tip of tool is less than at the shank of tool. SEM results indicate there are micro-cracks concentrated in the cutting edge area. The tool material failure mechanism will be set up based on the tool material analysis in this study.

Abstract: In the present study, steel-bonded cemented carbide GT35 has been fabricated from natural ilmenite by in-situ carbothermic reduction and vacuum pressureless sintering. The effect of different carbon source on the mechanical properties and microstructure of GT35 composite was studied. The quality of the composite synthesized from natural graphite is higher than those from other carbon source. Some good results were obtained from experiments: the density is about 6.2g/cm3, and the bending strength is 1390MPa, which higher than that of other samples. The structures and ingredient of different carbon source were analyzed to elucidate their different performance in the reactions.

Abstract: Laser cladding experiment was carried out with a 5 kW continuous wave CO2 laser by preplacing Ni75Si25 and Ni78Si13Ti9 powders onto Ni-based superalloy substrate. The microstructure of the specimens was monitored by using optical and scanning electron microscopy. The chemical compositions of the alloys and their phases were obtained using X-ray diffraction and energy dispersive x-ray spectroscopy. The phase transformation temperatures were determined by non-isothermal differential scanning calorimetry tests. The microhardness of the laser cladded sample was measured.