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中国有色金属学会会刊：英文版 2004年第3期14卷 510-515页

作者：丰平熊惟皓李鹏余立新夏阳华 State key laboratory of die & mould technology

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.

关键词：火花等离子烧结金属陶瓷粉末冶金相变显微结构硬质相 TEM SPS 纳米相

Effects of molybdenum on the microstructure and mechanical properties of Ti(C,N)-based cermets with low Ni

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Rare Metals 2006年第1期25卷 90-95页

作者： WANG Saiyu XIONG Weihao YAN Mingshuang FAN Chou the stale key laboratory for die ＆ mould technology Huazhong University of Science and Technology Wuhan 430074 China Huangshi Institute of technology Huangshi 435003 China

The effects of Mo on the microstructure and mechanical properties of Ti（C,N）-based cermets with low Ni have been studied systematically. Different contents of Mo （4-12 wt.%） were added into Tl（C,N）-based cermets. Specimens were fabricated by conventional powder metallurgy and vacuum sintered at temperatures of 1440, 1450, and 1460℃ individually. The microstructure and fracture morphology were investigated by scanning electron microscope, and the mechanical properties such as transverse strength and hardness were measured. The results show that the microstructure is uniform and the thickness of rim phase is moderate when the content of Mo is 8 wt.%; the mechanical properties of the specimens sintered at 1450℃ are better than those sintered at 1440 and 1460℃. The integrated properties of transverse strength and hardness are the best when the content of Mo is 8 wt.% and the sintering temperature is 1450℃.

关键词： Ti(C,N)-based cermets microstructttre mechanical properties Mo content

Electrochemical performance of microarc oxidation films formed on AZ91D alloy in two group electrolytes

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中国有色金属学会会刊：英文版 2005年第4期15卷 777-783页

作者：王立世蔡启舟魏伯康刘全心 State key laboratory of die and mould technology Huazhong University of Science and Technology

The phase composition and electrochemical performances of microarc oxidation（MAO） films prepared on AZ91D alloy by using step-down current method in a phosphate electrolyte（P-film） and silicate electrolyte（Si-film） were studied. The results show that P-film is mainly composed of Mg, MgAl2O4 and MgO, and Si-film is composed of Mg2SiO4 and MgO. There clearly exists a fluoride-enriched zone with the thickness of about 12μm for P-film and 0.71μm for Si-film at the MAO coating/substrate interface. The electrochemical tests show that both P-film and Si-film can enhance the corrosion resistance of AZ91D magnesium alloy significantly. The corrosion failure process of the two films in 5%（mass fraction） NaCl solution is quite different.

关键词：有色金属电化学 AZ91D合金氧化反应

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

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中国有色金属学会会刊：英文版 2004年第3期14卷 485-490页

作者：余立新熊惟皓郑勇李国安 State key laboratory of die & mould technology College of Materials Science and Engineering

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.

关键词：粉末冶金碳化钛氮化钛金属陶瓷烧结显微结构性能

Preparation of Al matrix nanocomposites by diluting the composite granules containing nano-SiCp under ultrasonic vibaration

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Journal of Materials Science & technology 2018年第9期34卷 1609-1617页

作者： Shulin Lü Pan Xiao Du Yuan Kun Hu Shusen Wu State key laboratory of Materials Processing and die & mould technology Huazhong University of Science and Technology

In this work, an efficient process by diluting the nano-SiCp/Al composite granules in the molten matrix under ultrasonic vibration（UV） was developed to prepare metal matrix nano-composites（MMNCs）.Millimeter-sized composite granules with high content of SiC particle（8 wt%） were specially fabricated by dry high-energy ball milling（HBM） without process control agent, and then remelted and diluted in molten Al alloy under UV. The MMNCs melt was finally squeeze cast under a squeeze pressure of 200 MPa, Microstructure of the composite granules during dry HBM was investigated, and the effect of UV on microstructure and mechanical properties of the MMNCs was discussed. The results indicate that nano-SiC particles are uniformly distributed in the nano-SiCp/Al composite granules, which are covered by vestures of pure Al. During diluting, nano-SiC particles released from the composite granules are quickly dispersed in the molten matrix by UV within 4 min. Microstructure of MMNCs is significantly refined under UV and squeeze casting, eutectic Si phase modified to fine islands with an average length of 1.4 μm. Tensile strength of the squeeze cast MMNCs with 1 wt% of nano-SiC particles is 269 MPa, which is improved by 25% compared with the A356 alloy matrix.

关键词： Al matrix nano-composites Dry high-energy ball milling Ultrasonic vibration Composite granules Microstructure

Modelling of dynamic recrystallization kinetics of 300M steel at high strain rates during hot deformation

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Science China(Technological Sciences) 2019年第9期62卷 1534-1544页

作者： GUO Peng DENG Lei WANG XinYun LI JianJun State key laboratory of Materials Processing and die & mould technology Huazhong University of Science and Technology

The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization(DRX) kinetics models suitable for strain rates where there are no stress peaks in the flow curves using the existing Avrami equation, and the optimal processing parameters for forging can be scarcely *** this study, the high-temperature flow and DRX behavior of 300M steel are investigated by performing isothermal compression tests at temperatures between 1173–1423K with strain rates between 0.001–50 s-1. Distinct stress peaks can be found in the flow curves at low strain rates, and the average grain size decreases with the increase in the strain rate at the same temperature. The DRX mechanism is a discontinuous DRX, and the grain boundary migration plays an important role in the DRX process. In contrast, no stress peak is observed in the flow curves at high strain rates, and the average grain size no longer decreases with the strain rate increase at the same temperature. The DRX mechanism in this case is a continuous DRX. The demarcated strain rate is calculated based on the characteristics of the obtained flow curves and grain sizes. The recrystallization volume fraction model and prediction grain size model at high strain rates are established. In combination with the existing DRX kinetics models at low strain rates, the processing parameters can be optimized to produce components with excellent mechanical properties.

关键词： 300M steel flow curves demarcated strain rate dynamic recrystallization grain size

Microstructural evolution of Mg9AlZnY alloy with vibration in lost foam casting during semi-solid isothermal heat treatment

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中国有色金属学会会刊：英文版 2010年第S3期20卷 768-773页

作者：赵忠樊自田蒋文明董选普 State key laboratory of Material Processing and die & mould technology Huazhong University of Science and Technology

The nearly equiaxed grains of Mg9AlZnY alloy were obtained by vibrating solidification in lost foam casting(LFC) and the microstructure of Mg9AlZnY alloy was *** this basis,the morphology and size of α-Mg grains fabricated by semi-solid isothermal heat treatment(SSIT) at 530 ℃ and 570 ℃ holding different time were *** results show that the main constituent phases of Mg9AlZnY alloy are α-Mg,β-Mg17Al12 and Al2Y,and the Y can greatly refine α-Mg *** distribution of α-Mg grains equivalent diameters between 20 and 100 μm is up to 87%,and the average roundness of α-Mg grains reaches 1.37 in the specimen obtained at 570 ℃ and holding time 60 *** to the analysis of solidification kinetics and thermodynamic,binary eutectic with low melting point melts firstly on SSIT *** the liquid fraction increases with the solute diffusibility,both of the shape and size of α-Mg grains change *** the liquid fraction reaches equilibrium,the α-Mg grains are gradually spheroidized under the interfacial tension,and then the α-Mg grains begin to combine and *** of α-Mg dendritic grains on SSIT process is obviously different from that of equiaxed grains.

关键词： lost foam casting(LFC) semi-solid isothermal heat treatment(SSIT) microstructural evolution magnesium alloy

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

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International Journal of Minerals,Metallurgy and Materials 2015年第12期22卷 1273-1282页

作者： Hang Zhao Jian-jun Li Zhi-zhen Zheng Ai-hua Wang Qi-wen Huang Da-wen Zeng State key laboratory of Material Processing and die & mould technology Huazhong University of Science & Technology

In this work, an in situ synthesized TiC-reinforced metal matrix composite （MMC） coating of approximately 350-400μm thickness was fabricated on a gray cast iron （GCI） substrate by plasma transferred arc （PTA） surface alloying of Ti-Fe alloy powder. Microhard- ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy （SEM） and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual anstenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures （473 K and 623 K）, and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam- ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc- ture and to the presence of TiC particles.

关键词： gray cast iron composite coatings particle-reinforced composites titanium carbide surface alloying microstructure wear

Microstructure and Properties of In Situ Si and Fe-rich Particles Reinforced Al Matrix Composites Assisted with Ultrasonic Vibration

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Acta Metallurgica Sinica(English Letters) 2014年第5期27卷 862-868页

作者： Shulin Lü Shusen Wu Chong Lin Ping An State key laboratory of Materials Processing and die & mould technology Huazhong University of Science and Technology

In this research, the in situ Si and Fe-rich particles reinforced Al matrix composites were fabricated by rheocasting （RC） process assisted with ultrasonic vibration （USV）. After USV treatment, the polygonal primary Si crystals were refined into particles with average diameter of about 15-23 μm, and the fraction of primary Si declined to about 5.4-6.5 vol%. The coarse plate-like δ-Al4（Fe,Mn）Si2 phase was transformed into fine particles with average diameter of about 17-20 μm, and the fraction of particle-like Fe-bearing particles is about 3.6-5.3 vol%. The ultimate tensile strength of the RC composites increases with the increase of Fe content at 350 ℃. The increase of the elevated temperature strength of the composites is mainly attributed to the refinement of δ-Al4（（Fe,Mn）Si2 phase and the increase of the volume fraction of the Fe-bearing compounds. Compared with the composites without USV, the RC composites assisted with USV have thinner mechanical mixing layer in wear test, which corresponds to smaller wear rate.

关键词： Fe-bearing phase Metal matrix composites Microstructure Properties Ultrasound

Structural transformation and rheological processes in bulk metallic glass Zr_(41)Ti_(14)Cu_(12.5)Ni_(10)Be_(22.5)

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中国有色金属学会会刊：英文版 2004年第2期14卷 218-222页

作者：王敬丰蒲健邹辉甘章华柳林肖建中 State key Lab of die and mould technology

The temperature dependence of strain and strain rate of the Zr41Ti14Cu12.5Ni10Be22.5（Vit1） bulk metallic glass （BMG） under constant heating condition was derived from the static extension method with a dynamic thermal mechanical analyzer （DMA）. A few strain rate peaks, which corresponds to the glass transition and multistep crystallization in the differential scanning calorimeter （DSC） examination, were observed in the curves of the relation between strain rate and temperature. The onset of viscous flow and the end of glass transition are interrelated, the first and second strain rate peaks correspond with the first and second crystallization transition processes, respectively. The influence of stress on strain and strain rate was researched. It is found that the rheological behaviour of BMG Vit1 changes from elasticity to anelasticity, finally to the Newtonian viscous flow along with increasing temperature.

关键词： Zr41Ti14Cu12.5 锆合金大块金属玻璃流变学结构转变 BMG DMA DSC