Fabrication of Dense Ultrafine TiAl Alloys by Spark Plasma Synthesis from Mechanically Activiated Powders

Powder of Ti-46at%Al alloy was synthesized through mechanical activation（MA） and then sintered and concurrently consolidated in a short sintering time of 900 s by using a spark plasma sintering（SPS） process. The XRD and SEM profiles show that the microstructures of TiAl alloys contained γ TiAl and small amount α-2 Ti3Al phase, whose amount can be controlled by the sintering temperature. The compacts retained the original fine-grained fully densified bodies by avoiding an excessively high sintering temperature. The alloys sintered at higher temperature with this process showed a coarser microstructure. So it is possible to produce dense nanostructured TiAl alloys by mechanically activated spark plasma sintering （MASPS） within a very short period of time.     

Densification behavior of high Nb containing TiAl alloys through reactive hot pressing

Densification behavior of high Nb containing TiAl alloys through reactive hot pressing was investigated. The results showed that the density of the sample hot pressed at 1400°C could reach a near full density of 98.37%. However, the densification abnormality was observed at 1500°C. The diffusion of elemental Nb during microstructural evolution is an important aspect affecting densification, which will form pore nests. With the increase of hot pressing temperature, the diffusion of Nb becomes more adequate. HIP （Hot isostatic pressing） treatment can only decrease porosity to some extent, but cannot eliminate it completely.     

Strain rate sensitivity of tensile properties in high Nb containing TiAl alloys

The effect of strain rate on the yield strength of high Nb containing TiAl alloy was studied. The results show that the strain rate sensitivity varies with the test temperature, and the yield strength is not sensitive to the strain rate at room temperature but significantly sensitive to the strain rate at high temperature. An increase of the strain rate or a decrease of the temperature results in an obvious change of fracture mode. It is found that the strain rate sensitivity of this alloy varying with temperature is due to the dislocation climb generated at high temperature.     

Fabrication of in situ Ti2AlN/TiAl composites by reaction hot pressing and their properties

Ti2AIN/TiAI composites with different volume fractions of reinforcement were successfully fabricated by hot-pressing sintering method （reaction hot pressing） using Ti, Al and TiN powders as starting materials. The synthesis process includes four stages： first, the reactions between Al and Ti powers and between Al and TiN powders respectively occur and result in TiAl3 phase; secondly, AI powders in the sample are exhausted; the remaining Ti cores react with TiAl3 layer to form Ti-Al intermetallics; moreover, a few Ti2AlN particles precipitate from the TiAl3 phase; thirdly, Ti-Al intermetallics react with the remaining Ti cores to form Ti3Al and TiAl phases. TiAl phase and original TiN powers are in direct contact each other; finally, the residual TiN powers react with TiAl phase and result in a plenty of TizAIN phase. Compared with TiAl matrix, the hardness, elastic modulus and high-temperature compressive strength of Ti2AlN/TiAl composite are improved obviously and they are all enhanced with increasing the volume fraction of Ti2AlN phase.     

Relationships between the precipitation of α2 ordered phase and alloying elements/electron concentration in α+α2 titanium alloys

Some experimental α α2 alloys were prepared by the addition of tin or aluminum elements into Ti-55 alloy. These alloys were designed with varied electron concentration values and named as Sn-rich alloys and Al-rich alloys, respectively. The precipitation and growth of α2 ordered phase in the tested alloys under various heat treatment conditions were investigated. Some comparisons among the experimental results were performed and discussed in detail. Stronger precipitation and growth of α2 ordered phase were caused in Al-rich alloys but relatively weak change in Sn-rich alloys with increasing the electron concentration. The precipitation of α2 ordered phase in Al-rich alloys is stronger than that in Sn-rich alloys when the electron concentration value is the same for the two alloys.     

碳、铌对Inconel 718合金熔敷层组织与性能的影响

为了提高Inconel 718合金焊接接头的塑、韧性，开发了具有良好力学性能和热加工性能的镍基高温合金焊接材料.通过适当调整Inconel 718高温合金中的碳、铌含量，并在一定工艺参数下进行熔敷，然后再进行扩散退火和固溶、时效处理；研究了C、Nb含量变化对Inconel 718高温合金熔敷层的组织和性能的影响.实验结果表明：焊后熔敷层的组织主要由γ固溶体构成，枝晶间出现白色的Laves相；经扩散退火处理后，Laves相发生溶解；在相同的处理条件下，熔敷层的屈服强度和硬度对碳、铌成分的变化比较敏感.     

添加W对Ti-Al-Cr-Nb铸态合金高温变形的影响

通过非自耗电弧熔炼及氩气保护浇铸方法，合成不同W含量的Ti-Al-Cr-Nb合金。采用高温拉伸测试及显微组织观察，研究添加W对Ti-Al-Cr-Nb铸态合金的显微组织及其高温变形影响。研究结果表明：W的添加使Ti-Al-Cr-Nb合金的铸态组织得到细化；在800℃时基体合金的伸长率从0．62％提高到90％；在高温变形过程中，添加W使Ti-Al-Cr-Nb铸态合金的最大伸长率从620％降低到200％，而最大伸长率相应的温度从850℃增大到1050℃。不同W含量的Ti-Al-Cr-Nb铸态合金在800～1100℃的高温变形机制主要是晶粒滑动，而添加W使晶粒滑动的协调过程由晶界扩散转化为体扩散。     

Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu (wt%, signed as 3C), fabricated by traditional cast (TC) and spray forming (SF) processes, were investigated by dif-ferential scanning calorimetry (DSC) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that Al7Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K. and 800-815 K, respectively. The transformation fromβ-Al5FeSi toδ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K. and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature ofδ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation ofδ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.     

Ni_（78.6）Si_（21.4）合金的深过冷与凝固组织演化

深过冷技术研究是凝固科学中重要的研究领域之一.文中采用玻璃熔融净化与循环过热法使Ni78.6Si21.4合金获得了318K的过冷度,研究了其凝固组织随初始过冷度（ΔT）的演化规律,并对凝固组织中的亚稳相进行了分析.研究发现：当ΔT〈193K时,凝固组织为Ni3Si＋（Ni3Si＋α-Ni）非规则共晶;193K〈ΔT〈250K,凝固组织为α？Ni＋（Ni3Si＋α-Ni）非规则共晶;ΔT〉250K时,凝固组织为完全的非规则共晶;随过冷度的增加,过冷合金熔体中依次出现了亚稳相Ni31Si12相和Ni3Si2相.     

Microstructure and mechanical properties of FGBA/BG air cooling bainitic steels containing niobium

The effect of different Nb additions on the mechanical properties and microstructure evolution of grain boundary allotriomorphic ferrite(F_(GBA)) / granular bainite(B_G) air cooling bainitic steels was investigated.The results indicate that the tensile strength and yield strength increase by 157 and 97 MPa,respectively with the addition of 0.02wt%Nb.The steel acquires superior strength and toughness with the addition of 0.06wt%Nb.The results of scanning electron microscopy and transmission electron micro...     

铌与溴邻苯三酚红和二安替比林甲烷多元络合物测定铌

探讨了在聚乙烯醇(PVA)存在下,铌与溴邻苯三酚红及二安替比林甲烷的协同显色反应.在优化条件下,体系所形成的多元络合物最大吸收波长位于565nm处,表观摩尔系数为ε565=1 34×105L·mol-1·cm-1,相关系数γ=0 9992,铌量在0～0 48mg/L范围内符合比尔定律.考察了20多种共存离子对体系的影响,结果表明在有掩蔽剂存在下干扰较少.以此体系建立的方法用于测定合金钢、矿样中铌的含量,结果与标准值相符.     

钽铌冶炼过程高氟氨氮废水综合治理研究

研究综合治理钽铌冶炼过程中含有高质量浓度NH4^ 、F^-、SO4^2-工业废水的技术．在蒸发过程中利用NH4HF2、(NH4)2SO4的溶解度随温度变化不同的特性，采用分步结晶法可使这两种化合物基本分离．对尚未分离的含少量NH4HF2的固体混合物，根据固体混合物组分的升华-裂化温度不同，(NH4)2SO4相对稳定，将NH4HF2(沸点240℃)蒸发，可使NH4HF2与(NH4)2SO4彻底分离．采用蒸发-分步结晶-裂化工艺，能有效地降低钽铌冶炼厂工业废水中的NH4^ 、F^-和SO4^2-，制备的NH4HF2可达到国家标准．     

Nb对Ti处理的ELC-BH钢板组织和性能的影响

Ti处理的超低碳高强度烘烤硬化钢板中加入少量Nb将导致烘烤硬化性严重损害,深冲性和塑性削弱,强度增加.研究表明,固溶C原子减少、退火组织的晶粒细化和γ纤维织构发展受阻是性能变化的根本原因.     

Study on rolling process optimization of high carbon steel wire

The existing problems in the manufacture of SWRH82B high carbon steel wire were discussed by sampling and testing the microstructure and properties of the steel from the workshop. To solve the problems, the experimental parameters for thermal simula- tion were optimized, and the thermal simulating experiments were carried out on a Gleeble1500 thermal simulator. The process pa- rameters for the manufacture were optimized after analysis of the data, and the productive experiments were performed after the wa- ter box in front of the no-twist blocks was reconstructed, to control the temperature of the loop layer. The results from the productive experiments showed that the cooling rate of 10-15°C/s was reasonable before phase transformation, about 5°C/s during phase trans- formation, and 600-620°C was the suitable starting temperature for phase transformation. The ultimate strength of the φ11.0 mm wire was increased to 1150-1170 MPa with an increase of 20-30 MPa, the percentage reduction of section was to 34%-36% with an increase of 1%-3% by testing the finished products after reconstruction.     

Solvent extraction of niobium from alkali solution by methyltrioctylammonium chloride

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Microstructural characterizations and mechanical properties of Mg-8Sn-1Al-1Zn-xCu alloys

Microstructural characterization and mechanical properties of as-cast Mg-8Sn-1Al-1Zn-xCu（x=0wt%, 1wt%, 1.5wt% and 2.0wt%） alloys were studied by OM, Pandat software, XRD, SEM, DSC and a standard universal testing machine. The experimental results indicate that adding Cu to TAZ811 alloy leads to the formation of the AlMgCu and Cu3 Sn phases. Tensile tests indicate that yield strength increases fi rstly and then decreases with increasing Cu content. The alloy with the addition of 1.5wt% Cu exhibits optimal mechanical properties among the studied alloys. The improved mechanical properties can be ascribed to the second phase strengthening and fi ne-grain strengthening mechanisms resulting from the more dispersed second phases and smaller grain size, respectively. The decrease in ultimate tensile strength and elongation of TAZ811-2.0wt% Cu alloy at room temperature is ascribed to the formation of continuous AlMgCu and coarse Mg2 Sn phases in the liquid state.     

Electrochemical synthesis, characterization and thermal properties of niobium ethoxide

Niobium(V) ethoxide (Nb(OEt)₅) was synthesized by electrochemical reaction of ethanol with niobium plate as the sacrificial anode, stainless steel as the cathode and tetraethylammonium chloride (TEAC) as the conductive additive. The condensates were isolated by vacuum distillation under 5 kPa. The product was characterized by Fourier transform infrared (FT-IR) spectra, Raman spectra and nuclear magnetic resonance (NMR) spectra. The results indicate that the product is niobium ethoxide. Thermal properties of niobium ethoxide were analysed by TG/DTG. Vapour pressure was calculated from the Langmuir equation and the enthalpy of vaporization was calculated from the vapour pressure-temperature data using the Clausius-Clapeyron equation. The concentrations of impurity metallic elements in the sample were detected by ICP-MS. It is shown that the purity can reach 99.997%. The volatility and purity of the niobium ethoxide ensure that it could be a good precursor for chemical vapor deposition and atomic layer deposition of niobium oxide layers.     

快速凝固条件下Cu-Cr合金的液相分解

采用快速凝固方法研究了Cu100-xCrx(x=2，25和35％)合金凝固行为．利用带有能谱(EDS)的扫描电子显微镜(SEM)分析了Cu—Cr合金的显微组织形貌和成分．实验结果证实，Cu—Cr合金在快速凝固过程中发生了液相分解，在较大的富Cr液相分解球中可观察到来自于二次相分解的、更细小的富Cu粒子．与Cu—Co和Cu-Fe液相分解组织不同，快速凝固Cu-Cr合金的大尺寸液相分解球不是由相互表面界限明确的、尺寸更小的液相分解球所组成，而是一个整体结构．     

Microstructural characterization and mechanical properties of self-reinforced Si3N4 ceramics containing high oxynitride glass

Self-reinforced Si3N4 ceramics containing high oxynitride glass have been fabricated by the control of microstructure evolution and β-SiaN4 grain growth. The effects of the size distribution of the elongated β-Si3N4 grains, and the β-SiaN4 grain growth as well as the oxynitride glass chemical characteristic on the microstructure and mechanical properties were investigated. The experimental results show that the β-Si3N4 grains in high oxynitride glass grow to elongated rod-like crystals and form the stereo-network structure. Under the sintering conditions of 1800℃ and 60 rain, a quite uniform microstructure with an average aspect ratio of 6.5 and an average of 1 I.tm can be obtained. A large amount of oxynitride glass phase with high nitrogen content enhances the elevated temperature fracture toughness because of its high softening temperature and high viscosity. In the present material, the crack deflection and pullout of the elongated rod-like β-SiN4 grains are the primary toughening mechanisms.