Gypsum bonded investment for micro-structure casting of ZnAl4

The effects of sintering temperature on the surface roughness of gypsum bonded investments were investigated to find the appropriate sintering temperature applied for micro-investment casting.The surface roughness tests were carried out at sintering temperatures ranging from room temperature to 1,000 ℃ for investment compounds mixed from calcium sulphate α-hemihydrate and quartz powder (wt.%, 6:4; 5:5, 4:6, 3:7).In this experiment, each investment compound was prepared by pouring the investment materials into a plastic bottle with the good surface roughness (Ra～0.2 μm).DTA-TG curves were measured using a thermal analyzer to investigate the difference of surface roughness at different temperatures.The results show that the surface roughness of gypsum bonded investment is temperature sensitive.The preheating temperature of the mold should be up to 600 ℃, but not over 700 ℃, and the investment compound with 60 % plaster and 40 % quartz powder is applicable for preparing the micro-structures.The micro-structures with 100 μm diameter were produced in the present studies.The results show that the surface roughness of the casting is only Ra～0.51 μm, slightly rougher than that of the investment mold.     

高温下金与石英的相互作用及其对浸金过程的影响

金在高温下可能与石英及硅酸盐类矿物相互作用,导致焙烧后矿石中金回收难度增大。于不同温度(600℃~750℃)和时间(1~4 h)条件下对石英-硫化矿-金粉混合物进行焙烧,考察焙烧渣中金的氰化浸出率。结果表明,高温会活化石英并与金相互作用,导致焙烧渣中的金难以被氰化物浸出。第一性原理计算表明,金原子在石英(101)表面的吸附能为-300.01 kJ/mol,Au-1与石英表面的Si-12距离为0.2264 nm,石英表面Si-12的电子转换到Au-1原子上,布居值和键长数据显示金原子与石英(101)表面的硅原子存在键合作用,印证了焙烧试验结果。     

消失模铸钢涂料耐火骨料烧结性的研究

以石英粉和铝矾土组成复合耐火骨料,在不同温度下进行烧结,使用BST401抗折弯仪测试烧结试样的抗弯强度,研究不同配比的耐火骨料的烧结性。研究表明,随着复合骨料中铝矾土含量的增加和烧结温度的升高,试样的抗弯强度都有增大的趋势。当铝矾土含量为60%、石英粉含量为40%、试样在1500℃时抗弯强度显著增大。并对烧结试样进行扫描电镜(SEM)分析,试样烧结良好,符合消失模铸钢涂料耐火骨料的要求。     

自修复混凝土的制备及其抗渗性能和抗盐冻性能

以氯化胆碱为促进剂,超细二氧化硅为活化剂,沸石粉为反应助剂,52.5号普通硅酸盐水泥为粘结剂,石英砂为结构增强剂,将上述原料搅拌混匀后,与水按照质量比0.4∶1配置成混凝土用修复剂,涂覆于混凝土试件表面,标准养护后得到自修复混凝土试件。考察了自修复混凝土的抗渗性能和抗盐冻性。结果表明:自修复混凝土的抗渗性和抗盐冻性得到了明显的改善,自修复混凝土的一次抗渗压力和二次抗渗压力均明显高于基准混凝土的,在NaCl溶液中,经冻融循环200次后,自修复混凝土的质量损失率较基准混凝土的减少了45%,其相对动弹模量较基准混凝土的下降趋势更缓。     

研磨温度对亲水性固结磨料垫加工性能的影响

研磨温度的升高会引起树脂基体模量的变化,从而影响亲水性固结磨料垫的加工性能。通过有限元分析软件仿真了亲水性固结磨料垫在不同研磨液温度下研磨石英玻璃的瞬态温度场,研究了不同温度条件下固结磨料垫基体的溶胀率与砂浆磨损量,探索了固结磨料垫在不同研磨液温度下的加工性能。结果表明:随着研磨液温度的升高,基体温度分布区间也随之改变,固结磨料垫基体的溶胀率与砂浆磨损量均增加,分别达到了1.43%与2.5 mg;温度升高使基体动态模量减小,材料去除率(material removal rate,MRR)和表面粗糙度R_a得到了改善,分别为8.2 μm/min和69.9 nm。因此适当提升研磨温度,能在一定程度上提高固结磨料垫的加工性能。      

Mechanical Properties and Microstructure of VPS and HVOF CoNiCrAlY Coatings

In this study, high velocity oxy-fuel (HVOF) and vacuum plasma spraying (VPS) coatings were sprayed using a Praxair (CO-210-24) CoNiCrAlY powder. Free-standing coatings underwent vacuum annealing at different temperatures for times of up to 840 h. Feedstock powder, and as-sprayed and annealed coatings, were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). The hardness and Young’s modulus of the as-sprayed and the annealed HVOF and VPS coatings were measured, including the determination of Young’s moduli of the individual phases via nanoindentation and measurements of Young’s moduli of coatings at temperatures up to 500 °C. The Eshelby inclusion model was employed to investigate the effect of microstructure on the coatings’ mechanical properties. The sensitivity of the mechanical properties to microstructural details was confirmed. Young’s modulus was constant up to ~200 °C, and then decreased with increasing measurement temperature. The annealing process increased Young’s modulus because of a combination of decreased porosity and β volume fraction. Oxide stringers in the HVOF coating maintained its higher hardness than the VPS coating, even after annealing.     

消失模涂料防渗与自剥离机理的研究

为研究消失模涂料的防渗与剥离情况,分别配制了以石英粉与高铝矾土为骨料的两种涂料,并在相同浇注条件下浇注铸件.采用扫描电镜及X射线衍射分别观察涂料断面微观组织及分析铸件上涂料层的物相.结果表明,浇注后以石英粉为骨料的涂料仅仅轻度烧结,而以高铝矾土为骨料的涂料生成了比骨料耐火度更高的新物质,阻挡了钢液的侵入且不与钢液发生反应.生成的新物相提高了高铝矾土涂料的防渗性并促使涂料自动剥离.     

金刚石工具预合金代钴粉末的研究及应用

近年，国内外开展了金刚石工具代钻粉末的研究。本文采用水雾化法开发了三种预合余代钻粉末：对粉末的基本属性、形貌，粉末的相组成，粉末的差热性进行了分析研究；测定了它们的烧结密度、硬度、抗弯强度、弹性模量随热压烧结温度变化的规律；采用作者自行建立的磨料磨损试验方法，测定了它们的质最磨损阿分率（即耐磨性）；测定了它们的冷压生坯密度、模拟生坯强度以及高频钎焊的结合力矩；观察了热压烧结SEM腐蚀组织和SEM断口形貌。结果表明：三种预合金粉末有着优良的低温烧结性能和耐磨性，表现出接近于超细钴和相当于国外代钴粉末的优良的物理、机械性能，对金刚石把持力高；具有高的高频钎焊结合力矩；粉末成本较低，用粉量可降低。实际切割花岗石、混凝土，切割锋利，使用寿命长。     

石英粉粒度对涂料性能影响的正交试验

在石英粉粒度对涂料性能影响的试验中,选用不同粒度的石英粉作为耐火骨料,钠基膨润土和CMC联合作为悬浮剂,淀粉水溶液和水玻璃作为粘结剂,以水为载液。首先进行单一变量试验,选出4种较为关键的性能,通过4种不同粒度的骨料搭配,按照4种不同的加入量,进行4因素4水平正交试验。采用极差法来分析各种因素对涂料性能的影响,得出综合性能最好的组合并对该组合进行性能分析。结果表明,当耐火骨料的组分:240、270、300、320号加入量比为80:80:80:20时,石英粉涂料的综合性能最好。     

Some reactive processing aspects of high-temperature aluminides Nb3Al and RuAl

In the present investigation elemental powder mixtures with nominal composition of Nb-25at. % Al and Ru-50at.% Al corresponding to Nb₃Al and RuAl intermetallic phases were prepared. Green compacts from these mixtures were reactive sintered in vacuum or hot isostatically pressed after being encapsulated and reacted in quartz capsules. In the absence of pressure, reactive sintering at temperatures up to 1800 °C did not lead to densification, and swelling effects were observed. Reactions of formation of Nb₃Al and RuAl were found to take place at different temperature regions characteristic for each aluminide system, with clear dependence of the reaction temperature on the heating rate of the powder mixtures. Dilatometry studies showed that swelling occurred instantaneously at temperatures corresponding to the reaction temperature and led to a volume increase of about 25% and 42% for Nb₃Al and RuAl, respectively. The activation energy for the reactions was estimated from the differential thermal analysis. Similar data for the NiAl intermetallic phase were also obtained for comparison. The densification behavior and the phase composition of the reaction products were investigated and correlated with the heating rate, the mutual solubility of the reactants, and the amount of liquid phase available during the reaction.     

表面扩散合金化对ZM5镁合金冲蚀磨损性能的影响(英文)

将ZM5镁合金置入铝、锌混合粉末中,在氩气保护下,于温度(390±5)°C保温8h进行表面固态扩渗合金化处理。研究表面固态扩渗合金化处理前和处理后ZM5镁合金在两种不同冲蚀磨损环境中(油和石英砂,水和石英砂)的冲蚀磨损行为。结果表明:当冲蚀磨损介质为油和石英砂时,冲蚀磨损表面形貌为切削沟痕。油对试样的腐蚀很弱,切削磨损是主要的磨损机制。当冲蚀介质为水和石英砂时,冲蚀磨损试样表面为腐蚀坑和裂纹。水的腐蚀和石英砂的冲刷作用加剧试样的磨损质量损失。在相同的冲蚀介质中,经过表面固态扩渗合金化处理的试样的耐冲蚀磨损性能均比未经过表面固态扩渗合金化处理的试样好。     

电熔刚玉对硅基陶瓷型芯性能的影响

以石英玻璃粉为原料,石蜡为增塑剂,添加质量分数0%～30%的电熔刚玉为矿化剂,通过热压注法成功制备了硅基陶瓷型芯,研究了电熔刚玉含量对方石英析晶和硅基陶瓷型芯综合性能的影响。结果表明：随着电熔刚玉含量的增加,样品的收缩率逐渐增加,气孔率先减小后增大,致密化程度增加;而抗弯强度和高温抗蠕变性能呈现先增强后减弱的趋势。当添加10%电熔刚玉时,样品表现出优良的综合性能,收缩率为1.02%,气孔率为20.91%,体积密度为1.7083 g/cm³,室温和高温抗弯强度分别为14.83和20.96 MPa,高温挠度为0.39 mm。     

Finite element analysis of single layer forming on metallic powder bed in rapid prototyping by selective laser processing

A method for calculating the distribution of temperature and stress within a single metallic layer formed on the powder bed in rapid prototyping with the selective laser melting method is proposed. The solidified layer is assumed to be subjected to plane-stress deformation and the two-dimensional finite element methods for heat conduction and elastic deformation are combined. In the simulation, the finite element mesh is constructed on the surface of the powder bed. The heat caused by laser irradiation is given to the elements under the laser beam. Shrinkage due to solidification is assumed to result in only the change of the layer thickness. In the elastic finite element simulation, the Young's modulus of the solidified part is expressed as a function of temperature. To simplify the calculation, the whole area is treated to be continuous, and the powder bed and the molten part are assumed to have a very small Young's modulus. The heat conduction and the elastic finite element calculations are carried out alternately. The obtained results of deformation and tensile stress distribution show the possibility and places of cracking of the layer during forming.     

Recycling water glass from wet reclamation sewage of waste sodium silicate-bonded sand

Wet reclamation of waste sodium silicate-bonded sand produces much alkaline sewage and causes pollution. Recycling water glass from wet reclamation sewage of the waste sodium silicate-bonded sand can solve pollution issues and generate economic benefits. In this work,the wet reclamation sewage was filtered,and the filtrate was causticized with a quicklime powder to produce a lye. The effects of causticization temperature,causticization time,and the amount of quicklime powder on the causticization rate were studied. The lye was used to dissolve the silica in the filtration residue to prepare a sodium silicate solution. The effects of the mass of filtration residue,dissolution temperature,and dissolution time on sodium silicate modulus were studied. Finally,the recycled water glass was obtained by concentrating the sodium silicate solution,and the bonding strength of the recycled water glass was tested. The results showed that the causticization rate could be improved by increasing the amount of quicklime powder,causticization temperature,and causticization time,and the highest causticization rate was above 92%. Amorphous silica in the filtration residue dissolved in the lye. Increasing the amount of the filtration residue,dissolution temperature,and dissolution time could improve the sodium silicate modulus. The bonding strength of the recycled water glass was close to that of commercial water glass. The recycled water glass could be used as a substitute for the commercial water glass.     

高温低周疲劳损伤对FGH96合金力学性能影响的实验研究

通过设计FGH96粉末高温合金的高温低周疲劳试验和高温单轴拉伸试验,研究了不同应力水平下高温低周疲劳损伤对合金力学性能的影响,结合对断口形貌的观察和成分分析,分析了合金力学性能改变的微观机理。结果表明,受疲劳载荷作用期间位错运动的影响,合金的屈服强度、抗拉强度在损伤前期表现出上升的趋势;损伤后期,随着材料内部裂纹的不断增多及扩展,合金的弹性模量、抗拉强度不断退化。合金力学性能的变化与疲劳加载的应力水平表现出明显的相关性。断口显微组织分析表明,随着损伤程度的增加,合金高温拉伸断裂模式由韧性逐渐向脆性转变,高温氧化加速了断裂模式的转变。     

精密铸造废弃型壳的回收与再利用

对废弃型壳(水玻璃+石英粉)的处理后再利用进行了研究.结果表明,在处理得到的粉、砂中按比例加入新的粉、砂,其各项性能指标都有所改善,有回收利用的价值.     

超细钼粉制备技术的研究现状与进展

金属钼因低的热膨胀系数、高温强度、高弹性模量等特性,广泛用于航空航天、军工、石油化工以及核工业等尖端行业,是推动高科技领域发展不可或缺的材料。钼粉作为钼制品的基础原料,其物化性质与钼制品的性能密切相关。相比于普通钼粉,超细钼粉具有更大的比表面积、更高的活性以及更低的烧结温度。目前制备超细钼粉的方法主要有热还原法和热分解法,热还原法通过调整还原工艺达到阻止晶粒长大的目的;而热分解法的发展主要涉及到装备的升级改造与工艺的优化完善。本文着眼于超细钼粉的制备工艺、反应机理以及产物状态,重点分析了典型工艺的发展历程和技术特点,总结了超细钼粉制备技术的研究现状与进展,提出当前技术工艺所面临的问题以及未来的研究方向,以期为超细钼粉制备工艺的发展与工业化应用提供思路。     

镍基粉末冶金FGH95高温合金的拉伸及低周疲劳性能研究

在420～650℃的温度范围内,研究了PM FGH95高温合金在应变率0.0001～0.01 s-1范围内的拉伸性能及在不同应力比R=-1及R=0下的低周疲劳性能.拉伸试验结果表明:在此温度范围内,应变率对弹性模量、拉伸屈服强度及塑性模量的影响可以忽略不计;并且应变率自0.0001 s-1增大至0.01 s-1时,弹性模量、拉伸屈服强度及塑性模量受温度的影响也不明显.PM FGH95合金受材料微结构的影响很大,材料含有的微缺陷对其力学性能有非常不利的影响.LCF试验结果表明:PM FGH95合金是循环硬化材料.当应力比R=-1时,温度对LCF寿命的影响很小;但在应力比R=0时,LCF寿命受温度的影响很大,且随着温度的增加材料的低周疲劳寿命减小.SEM断口扫描发现,断裂表面有很多的解理面,但没有疲劳条带,且此断裂模式下没有明显的塑性变形,所以FGH95合金的低周疲劳寿命几乎是由裂纹萌生阶段决定的.     

超磁致伸缩复合材料的静态弹性模量及抗压强度

采用粘结技术制备出了性能良好的磁致伸缩复合材料，着重研究了合金含量、粉末粒度、磁场取向、粉末表面处理对样品的静态弹性模量及抗雎强度的影响规律。结果表明，粉末粒度、粉末表面处理对复合材料的抗压强度及静态弹性模量均有较大的影响；合金含量、磁场取向对复合材料的静态弹性模量影响不大，其中合金含量对复合材料的抗压强度有较大的影响。     

Effect of synthesis conditions on the properties of wet spun polypyrrole fibres

High molecular weight doped polypyrrole (PPy) has been synthesized by the incorporation of the di(2-ethylhexyl) sulfosuccinate dopant anion which renders the polymer soluble in various organic solvents. The intrinsic viscosity of PPy solutions show that the molecular weight of PPy is very sensitive to the polymerization temperature. A significant increase in molecular weight was achieved by reducing the polymerization temperature from 0 to −15 °C. The resultant solutions were amenable to a wet-spinning process that produced continuous, doped polypyrrole fibres. The ultimate tensile strength, elastic modulus and elongation at break of the higher molecular weight fibres were 136 MPa, 4.2 GPa and 5%, respectively. These values were 500%, 250% and 280% higher than obtained from the lower molecular weight fibers. X-ray diffraction showed that the low temperature PPy powder exhibited a similar degree of ordering to the standard PPy powder. UV and FT-IR spectroscopy showed that the conjugation length of PPy could be increased significantly depending on the polymerization conditions. Cyclic voltammetry demonstrated the electroactivity of the polypyrrole fibres. These fibres are likely to be important for bionic, electronic textile, artificial muscles, battery and sensor applications.