还原碳化法制备超细碳化铬粉末

以纳米Cr_2O_3和乙炔黑为原料,经高温还原碳化制备超细Cr_3C_2粉末,研究反应温度、反应时间以及配碳量对Cr_3C_2粉末的粒度与游离碳含量的影响。通过热力学计算,只有当温度高于1 350 K时还原碳化反应才有可能进行,采用纳米Cr_2O_3可显著降低反应温度,在1 573 K下焙烧6 h碳化率即达到98.20%;Cr_3C_2粉末的游离碳含量随配碳量增加而显著提高,配碳量(质量分数)为理论配碳量的1.05倍时制得游离碳含量为0.23%、氧含量为0.91%(均为质量分数)、平均粒度为1μm的Cr_3C_2粉末,该粉末达到硬质合金及热喷涂应用的要求。     

平整压下率对TS290组织性能的影响

 为了研究平整压下率对TS290组织性能的影响,为品种开发制定合理的工艺参数提供参考,采用激光共聚焦显微镜检测了样品显微组织,采用TEM观察了样品位错形态及其分布,采用拉伸试验机检测了样品力学性能。结果表明,随着平整压下率从0增大到3.0%,TS290屈服强度先减小后增大,抗拉强度先缓慢增加后趋于平稳。加大平整压下率对组织细化作用有限,但可以显著增大基体位错密度,进而提高材料屈服强度。平整压下率控制在2.0%左右时,试验钢屈服强度为290 MPa,抗拉强度为400 MPa,洛氏硬度为59.0,性能达到TS290质量设计要求。     

碳化硼陶瓷力学性能及其影响因素

碳化硼的力学性能与其他陶瓷材料一样,对结构十分敏感.在工艺控制过程上看,不可能制得结构完全相同的材料,文献报道的计算式和数据亦非常分散.作者测定了用热压方法制得的碳化硼陶瓷(表现密度为2.1～2.3g/cm~3,晶粒度为12μm)的抗弯强度、抗压强度、弹性(弯曲)模量和泊松比.同时,通过文献检索,搜集了各种公式和数据,并对本实验结果进行了综合分析,得出了有关的计算式和性能值.     

基于增材制造的硬质合金粉末研究现状

硬质合金是由难熔金属碳化物（WC,TiC,NbC等）和金属粘结相（如Fe,Ni和Co）组成,通过粉末混合、压制然后烧结而成。然而传统的粉末冶金成形方法模具成本高,难以形成复杂零件。相比之下,增材制造（3D打印）采用数字化叠层加工技术,能够实现快速精准的成形。研究与开发适于增材制造的硬质合金粉末是其中的关键一步,目前,增材制造的硬质合金粉末制备方法主要分为以下4类:机械合金化法、球形WC粉末表面包覆技术、喷雾干燥技术、等离子体球化技术,这4种方法在制备原理、成本和成形方法的灵活性上均有所不同。因此,综述了适用于增材制造成形的硬质合金粉末的4种制备方法,并对制备粉末的特性以及成形性能进行了对比,总结了粉末制备原理、各自的优缺点以及适用的增材制造成形工艺,希望可以推动增材制造成形硬质合金的研究发展。     

烧结温度对碳化硅陶瓷力学性能的影响

采用硼、碳助剂无压烧结制备碳化硅陶瓷。针对烧结温度与碳化硅烧结体密度、抗弯强度以及硬度之间的关系进行了试验研究,并对不同温度下制备的烧结体进行了显微结构形貌观察和XRD图谱分析。结果表明,烧结温度在2190～2220℃范围内可以制备密度高、力学性能好的碳化硅陶瓷。其相对密度超过96%;抗弯强度接近400MPa;维氏硬度23GPa以上。在试验温度范围内,密度与抗弯强度之间的关系近似为线性关系,密度越高抗弯强度和硬度性能越好。     

Effect of distribution of B4C on the mechanical behaviour of Al-6061/B4C composite

In this work, the effect of mixing parameters on the distribution of B₄C in 6061-Al alloy and its correlation with mechanical behaviour was studied. 6061-Al alloy powder was mixed with 10 mass-% B₄C powder in a ball mill and powder rotator mixer by varying mixing time from 1 to 5?h. Mixing was performed in both wet and dry conditions in a ball mill while only dry condition was used in the powder rotator mixer. The green compacts were sintered at 630°C. The quadrat method was used to quantify the distribution of B₄C particles in the microstructures of sintered Al/B₄C composite. The results showed that the distribution was improved with mixing time but the density, hardness and compression strength of Al/B₄C composites were reduced with time during ball milling. On the other hand, the distribution of reinforcement, density, hardness and compressive strength of Al/B₄C composites was improved with mixing time in the powder rotator mixer.     

碳含量对脱β层硬质合金组织和性能的影响

本文通过一步烧结法制备了三种不同含碳量的WC-Ti(C,N)-(Ti,W)C-(Ta,Nb)C-Co脱β层硬质合金,通过扫描电镜(SEM),电子探针微区分析仪(EPMA)分析合金的微观组织和成分分布,以及测定维氏硬度HV30,断裂韧性KIC等性能指标,研究碳含量对其微观组织和物理力学性能的影响,研究结果表明:在三个合金的表层均形成了缺Ti,Ta,Nb的立方相,而富Co粘结相的脱β层。微量的C含量变化对合金的组织和性能产生重要的影响,合金的脱β层厚度和WC的平均晶粒度均随着C含量的增加而增大。随着碳含量的增加,维氏硬度HV30降低,断裂韧性KIC增加。     

纳米钨铜复合粉末的制备与微观形貌

首先采用高浓度湿磨法制备超细WO3-CuO混合粉末,800℃空气中焙烧90min后得到CuWO4-WO3前驱体粉末,再通过氢气还原获得超细W-Cu复合粉末。将该复合粉末与直接还原超细WO3-CuO混合粉末所得的W-Cu复合粉末进行对比,并研究还原温度对W-Cu复合粉末的微观形貌、成分与粒度的影响。结果表明:经过30h高浓度湿磨,WO3-CuO混合粉末的中位径由44.88μm降至0.28μm,焙烧后得到的CuWO4-WO3粉末平均粒径小于0.7μm且分散良好。由CuWO4-WO3还原获得的W-Cu复合粉末细小、分散均匀,还原温度对其形貌影响不大,由WO3-CuO混合粉末直接还原得到的W-Cu复合粉末由大量W-Cu纳米颗粒构成,随还原温度升高,纳米W-Cu颗粒逐渐长大。     

冷轧压下率对TRIP钢组织与力学性能的影响

研究了含铝TRIP钢在相同的热处理条件和不同冷轧压下率时的组织和力学性能。结果表明,随着冷轧压下率增加,材料组织细化,屈服强度连续升高;而抗拉强度和伸长率则由于晶粒细化以及TRIP效应,先升高后降低。冷轧压下率74%时材料的综合性能最佳,此时带状组织的危害也有所减轻或消失。     

Y_2O_3对硬质合金晶粒尺寸和摩擦磨损性能的影响

研究了稀土Y2O3对WC-10Co硬质合金晶粒尺寸、矫顽力的影响,对比了Y2O3含量0.10%(质量分数,下同)和0.30%硬质合金的摩擦磨损性能。结果表明:微量Y2O3能细化WC晶粒,有效改善合金的硬度,影响硬质合金的磁性能。低于0.15%时,WC-10Co合金晶粒尺寸随着Y2O3增加而明显细化,硬度显著增加;Y2O3含量达到0.2%以上,WC-10Co合金的晶粒尺寸基本稳定,硬度也变化不大。在相同条件下,细晶粒0.30%Y2O3的WC-10Co硬质合金比0.10%Y2O3的WC-10Co硬质合金的摩擦因数稍高,但磨损体积损失低于0.10%Y2O3合金。     

Effect of mechanical activation on carbothermal reduction of chromite with graphite

Abstract

The carbothermal reduction of mechanically activated chromite with graphite under an argon atmosphere was investigated at temperatures between 1100 and 1400°C and the effects of the mechanical activation on chromite structure were analysed by X-ray diffraction, scanning electron microscopy and specific surface area measurement. An increase in specific surface area resulted in more contact points. The activation procedure led to amorphisation and structural disordering in chromite, and accelerated the degree of reduction and metallisation in the mixture of chromite and graphite.

On a effectué une investigation de la réduction carbothermique avec du graphite, de la chromite activée mécaniquement, en atmosphère d’argon, à des températures entre 1100 et 1400°C, et l’on a analysé les effets de l’activation mécanique sur la structure de la chromite par diffraction des rayons x, par microscopie électronique à balayage et par mesure de la surface spécifique. Une augmentation de la surface spécifique résultait en des points de contact plus nombreux. La procédure d’activation menait à une structure plus amorphe et en désordre de la chromite et accélérait le degré de réduction et de métallisation dans le mélange de chromite et de graphite.     

Effects of chromium sources on the microstructure and properties of TiC-steel composites

The composites of low alloy steel reinforced with TiC particles (36?wt-%) were prepared by conventional powder metallurgy process in this paper. The chromium in the steel matrix was provided by pure chromium powder (PCP), low carbon ferrochrome powder, medium carbon ferrochrome powder (MCFP) and high carbon ferrochrome powder. The SEM was used to observe the particle morphology and microstructure. Density, hardness and transverse rupture strength (TRS) of the samples were tested. The results show that the composite prepared with the PCP as a chromium source has low hardness and TRS and the composites prepared with different ferrochrome powders have higher hardness and TRS. The microstructures of the samples prepared with different chromium sources have some differences and provide the differences in mechanical properties and fracture morphology. The sample prepared with the MCFP as chromium source has the highest comprehensive performance after tempering: hardness 70 HRC and TRS 1752?MPa.     

机械活化条件下超细铁矿粉氢基还原特性及机制

摘要：通过热重法研究了不同机械活化程度的铁矿粉氢基还原特性,并分析和探讨了其还原反应机制。实验结果表明,机械活化对氢气还原铁矿粉有促进作用,机械活化时间越长,还原特征温度越低,还原反应所需的活化能也越低,但反应机制未发生变化,反应的限制性环节是其界面反应。机械活化明显影响到超细铁矿粉的逐级反应,对于未经活化的铁矿粉而言,逐级反应层次极不明显,而对于活化后铁矿粉的逐级反应层次随着活化时间的增加越发分明。     

Direct chromium alloying by smelting reduction of mill scale and low grade chromite ore

Direct alloying is the process in which all of the elements needed for alloying can be reduced from their oxides in a furnace or a ladle. This process is one way of reducing the amounts of energy and materials, reducing the loss of alloying elements, and improving working condition. Mill scale produced in rolling mills is considered a rich iron source (> 67% Fe) with minimum impurities. In this paper, iron high-Cr alloy was produced by a direct alloying with chromium in carbo- thermal reduction using fine of low grade chromites ore and mill scale. The smelting experimental heats were carried out in a 5?kg pilot plant submerged electric arc furnace. The charging materials and reduction parameters were varied and the optimum conditions for obtaining alloy with the highest metallic yield and the highest iron and chromium recovery were determined. When using coke as the reducing agent in stoichiometric amounts, for a mixture of mill scale (55%) and chromite ore (45%), 89.1% of the iron and 72.5% of the chromium were recovered, producing iron high-Cr alloy containing 17.9%Cr, 3.73%C, 0.46%Mn and 1.47%Si. The maximum iron and chromium recoveries obtained were 99.3% and 72.5%, respectively when using excess carbon. The present study clarifies the possibility of using a mixture of chromite ore , mill scale and coke as the precursor for direct chromium alloying. This method offers an alternative process route with cheaper raw materials and fewer process steps (by avoiding the step of ferrochrome production) for producing high chromium iron or steel alloys.     

Hydrogen reduction characteristics and mechanism of ultrafine iron ore powder under mechanical activation

The hydrogen based reduction characteristics of iron ore powder with different degrees of mechanical activation were studied by thermogravimetry, and the reduction reaction mechanism was analyzed and discussed. The experimental results show that mechanical activation has a facilitating effect on the reduction of iron ore powder by hydrogen, and the longer the mechanical activation time, the lower the reduction characteristic temperature and the lower the activation energy required for the reduction reaction, but the reaction mechanism remains unchanged, and the restrictive step of the reaction is its interfacial reaction. Mechanical activation obviously affects the step by step reaction of ultrafine iron ore powder, for the unactivated iron ore powder, the step by step reaction level is extremely insignificant, while for the activated iron ore powder the step by step reaction level becomes more and more distinct with the increase of activation time.     

硼和铬对多晶Fe83Ga17合金磁致伸缩和室温力学性能的影响

研究了添加B和Cr对多晶Fe₈₃Ga₁₇合金磁致伸缩和拉伸力学性能的影响.结果表明:在Fe₈₃Ga₁₇合金中添加原子分数1%的B,不仅提高了合金的磁致伸缩性能,而且还大幅提高了合金的室温力学性能,抗拉强度达到548MPa,延伸率达到3.56%.B元素以Fe₂B相的形式偏聚在晶界,细化了合金晶粒,增加了合金晶界结合力,抑制了沿晶脆断.添加原子分数2%的Cr,Cr固溶在Fe₈₃Ga₁₇合金中,同时提高了合金的磁致伸缩性能和室温力学性能,(Fe₈₃Ga₁₇)₉₈Cr₂合金最大磁致伸缩系数达到7×10^-5,延伸率也较Fe₈₃Ga₁₇合金有所增加,达到0.6%.     

电石渣为钙源的硅热法炼镁煅烧过程

电石渣是化工行业用乙炔法生产乙炔气或聚氯乙烯树脂的工业废渣,其主要成分为Ca(OH)2,是高碱性物质,属于较难处理的工业废弃物.现有处理电石渣的工艺都存在不足之处,因此电石渣的综合利用是近年来研究的重点与热点问题.本文提出以电石渣为钙源的硅热法炼镁工艺,可综合利用电石渣,将其与菱镁石、萤石和硅铁制成预制球团,用于真空热...     

冷轧压下率和退火温度对H62黄铜组织性能的影响

利用OM、SEM和室温拉伸试验系统研究了冷轧压下率和退火温度对黄铜组织性能的影响.结果表明:随压下率和退火温度的增加,H62黄铜晶粒尺寸均逐渐增大,强度逐渐降低,伸长率先上升后下降;400℃退火时,α相开始发生再结晶,β相沿α相晶界均匀分布,500℃及以上退火时,α相已完成再结晶,β相将逐渐回溶到α基体中;H62黄铜在56.5%的冷轧压下,600℃退火时能获得最优的力学性能.     

Effect of nickel additions on the oxidation kinetics of double titanium and chromium carbide powder

The effect of powdered nickel additions (10–33 mass %) on the oxidation kinetics of double titanium-chromium carbide produced by the method of self-propagating high-temperature synthesis, and also that of plating the synthesized carbide powder with nickel (26 mass %) was studied. The effect of nickel concentration and powder particle size on the oxidation resistance at different temperatures was different. However, it can be stated that plating the carbide powder with nickel increased its oxidation resistance at all temperatures in the range 600–1000°C, excepting 700°C. The degree of oxidation of the carbide and nickel constituents were estimated. Activation energies for the initial and parabolic stages of oxidation were determined. Translated from Poroshkovaya Metallurgiya. Nos. 1/2(411), pp. 76–82, January–February, 2000.     

“前驱体+真空碳热还原”法制备超细Mo_2C粉末的研究

利用"前驱体+真空碳热还原"法制备了超细Mo_2C粉末,采用XRD、FESEM等表征手段研究配碳量、合成温度以及保温时间对Mo_2C粉末微观形貌和物相组成的影响。结果表明:在配碳量为150%(质量分数)、合成温度1 150℃、保温2.0 h条件下制备的超细Mo_2C粉末,粒径约为100~500 nm。