Characterization of phase transformation and microstructure of nano hard phase Ti(C,N)-based cermet by spark plasma sintering

By means of optical microscope , scanning electron microscope （SEM） and transmission electron microscope （TEM）, the process of densification, the characterization of phase transformation and the microstructure for spark plasma sintering （SPS） nano hard phase Ti（C,N）-based cermet were investigated. It is found that the spark plasma sintering （SPS） enables the nano hard phase Ti（C,N）-based cermet to densify rapidly, however, the full densification of the sintered samples can not be obtained. The rate of phase transformation is significantly quick. When being sintered at 1 200 ℃ for 8 min, Mo2C is completely dissolved, and TiN dissolves into TiC entirely and disappears. Above 1 200 ℃, Ti（C,N） begins to decompose and the atoms of C and N separate from Ti（C,N） resulting in the generation of N2 and the graphite. Due to the denitrification and the graphitization, the density and the hardness of sintered samples are rather low. The distribution of grain size of the sample sintered at 1 350 ℃ covers a wide range of 90500 nm, and most of the grain size are about 200 nm. The hard phase is not of typical core-rim structure. Oxides on the surface of particles can not be fully removed and present in sample as titanium oxide TiO2. Graphite exists in band-like shape.

Effect of sintering on microstructures and properties of sub-micron Ti(C,N)-based cermets

The influence of different sintering processes, including vacuum sintering, vacuum sintering followed by HIP and sintering-HIP, on the microstructure and properties of sub-micron Ti(C,N) cermets with various binder contents was studied. Image analysis based on back-scattered electrons image observations was used to determine the morphologic and structural characteristics. Transverse rupture strength(TRS), hardness, fracture toughness were measured and TRS data were treated by Weibull statistics further. It is shown that a very significant improvement in TRS can be obtained by HIP or sintering-HIP treatment for the alloys with lower and middle binder content at the controlled cooling rate, but the effect is not obvious for the alloys with higher binder content. HIP is also helpful for improving the hardness of sub-micron Ti(C,N) cermets, however, but can lower the fracture toughness. The variation of these properties was interpreted in terms of the difference in morphologic and structural characteristics.

The Conductivity of Co-dopant Ceria Electrolyte

A kind of novel ceria electrolyte was examined.Various trivalent oxides were added as co-dopants to Ce 0.8Gd 0.2O 1.9,and their effects on the conductivity of ceria electrolyte were discussed.It has been found that the co-dopant of trivalent oxides of Sm,Nd,La and Y improves the ionic conductivity notably.Furthermore,the fine original powders,co-dopant and higher sintering temperature may hasten the sintering.

Preparation of ultrafine Ti (C, N)-based cermet using oxygen-rich powders

The availability using oxygen-rich powders to prepare ultrafine Ti(C,N)-based cermets was investigated. The deoxidation process, denitrification phenomenon and the effect of deoxidation on microstructure and mechanical properties of sintered samples were discussed, respectively. The results show that oxygen in the samples prepared even with high oxygen contained in starting powders can be almost completely cleaned away through suitable sintering process. The ultrafine oxygen-rich powders have a significant effect on microstructure, which promotes the formation of white core phase. A ultrafine Ti(C,N)-based cermet with mean particle size of 0. 30 μm, uniform microstructure and excellent mechanical properties is successfully prepared. It is also found that there exists severe denitrification phenomenon in the preparation process of ultrafine Ti(C,N)-based cermet.

Mathematical Model for Tempering Time Effect on Quenched Steel Based on Hollomon Parameter

Through the differentiating and integrating process, a mathematical model for tempering time effect on quenched steel was derived based on the attribute of state function and the general equation of Hollomon parameter, which correlates the tempering hardness with the tempering time at different tempering temperature. Using the established model, the linear relationship between the tempering hardness and the tempering time in logarithm was proved theoretically, and the tempering hardness for various tempering time was reduced to the measurement and calculation of a hardness experiment tempered for 1 h at different tempering temperatures. Moreover, the hardness of steel 42CrMo and T8Mn tempered for various times at 200-600℃ was calculated using this method. The predicted results are in good agreement with those of the available experiments.

Microstructure Characteristics of Inconel 625 Superalloy Manufactured by Selective Laser Melting

Selective laser melting （SLM）, an additive manufacturing process, is capable of manufacturing metallic parts with complex shapes directly from computer-aided design （CAD） models. SLM parts are created on a layer-by-layer manner, making it more flexible than traditional material processing techniques, in this paper, Inconel 625 alloy, a widely used material in the aerospace industry, were chosen as the build material. Scanning electron microscopy （SEM）, electron back scattering diffraction （EBSD） and X-ray diffraction （XRD） analysis techniques were employed to analyze its microstructure. It was observed that the molten pool was composed of elongated columnar crystal, Due to the rapid cooling speed, the primary dendrite arm space was approximately 0.5 μm and the hardness of SLM state was very high （343 HV）. The inverse pole figure （IPF） indicated that the growing orientation of the most grains was 〈001〉 due to the epitaxial growth and heat conduction. The XRD results revealed that the austenite structure with large lattice distortion was fully formed. No carbides or precipitated phases were found. After heat treatment the grains grew into two microstructures with distinct morphological characters, namely, rectangular grains and limited in the molten pool, and equiaxed grains along the molten boundaries. Upon experiencing the heat treatment, MC carbides with triangular shapes gradually precipitated. The results also identified that a large number of zigzag grain boundaries were formed. In this study, the grain formation and microstructure, and the laws of the molten pool evolution were also analyzed and discussed,