Microstructure and mechanical behavior of laser aided additive manufactured low carbon interstitial Fe49.5Mn30Co10Cr10C0.5 multicomponent alloy

Laser aided additive manufacturing(LAAM)was used to fabricate bulk Fe49.5Mn30Co10Cr10C0.5 interstitial multicomponent alloy using pre-alloyed powder.The room temperature yield strength(σy),ultimate tensile strength(σUTS)and elongation(εUST)were 645 MPa,917 MPa and 27.0％respectively.The as-built sample consisted of equiaxed and dendritic cellular structures formed by elemental segregation.These cellular structures together with oxide particle inclusions were deemed to strengthen the material.The other contributing components include dislocation strengthening,friction stress and grain bound-ary strengthening.The high εUTS was attributed to dislocation motion and activation of both twinning and transformation-induced plasticity(TWIP and TRIP).Tensile tests performed at-40℃and-130℃demonstrated superior tensile strength of 1041 MPa and 1267 MPa respectively.However,almost no twinning was observed in the fractured sample tested at-40℃and-130℃.Instead,higher fraction of strain-induced hexagonal close-packed(HCP)ε phase transformation of 21.2％were observed for fractured sample tested at-40℃,compared with 6.3％in fractured room temperature sample.     

以金属氧化物为原料改进燃烧法合成γ-LiAlO_2（英文）

提出一种合成γ-LiAlO_2的替代解决方案—改进燃烧法直接合成γ-LiAlO_2,并将其用于相对简单的反应体系中,原料为非氧化性化合物如Al_2O_3和LiOH,燃料为尿素。采用1:1、1.5:1和2:1的非化学计量Li/Al摩尔比,在900和1000°C下反应5 min,制备LiAlO_2,并对其组织和结构进行表征。考察Li/Al摩尔比对材料形貌和高γ射线辐照下材料稳定性的影响。结果表明,所得粉体的晶体结构为?-LiAlO_2和?-LiAlO_2,其取决于Li/Al摩尔比。因此,用该方法可以成功合成微砖状、多面体状和层状?-LiAlO_2,而无需任何后续处理。γ辐照结果表明,所得到的?-LiAlO_2不分解,只形成少量的Li_2CO_3;由此可以确定,辐照会导致固结,不利于氚的有效提取;结果证明,用燃烧法生产高纯度?-LiAlO_2不需要硝酸盐前驱体。     

大型水电工程前期准备延期的影响类型分析

讨论了成本考虑不足与水电工程项目施工前准备阶段延期的负面影响,以及发展中国家不能及时有效地交付项目与稀有资源浪费间的冲突。建议项目员工、开发商、政府官员和国际金融机构重视延期成本,找到成本与效益的平衡点。     

生物基油对白炭黑填充天然橡胶胶料加工性能和硫化特性的影响

通常使用的石油基加工油,比如重质环烷油(HNO)和轻质环烷油(LNO)具有潜在的致癌性。本文研究了一种新型生物基油——茶籽油(TO)可能会成为通用加工油的替代品。在进行试验对比时,还选择了另外两种生物基油,分别是棕榈油(PO)和椰子油(CO)。试验结果表明,所有研究的生物基油的热稳定性均高于轻质环烷油(LNO),在白炭黑填充天然橡胶(NR)配方中,配合生物基油的混炼胶加工性能比添加石油基油的胶料更加优异。主要表现为:生物基油的热稳定性高,在相同混炼条件下,与添加石油基油的混炼胶相比,添加生物基油能够提高白炭黑与天然橡胶的混合效率,改善白炭黑在天然橡胶基质中的分散性,提高混炼胶的塑化效果。加工油的不同类型和用量对混炼胶的硫化特性影响很小。通过试验结果分析,所研究的TO、PO和CO生物基油很有可能成为石油基加工油的替代产品。     

Critical parameters near the ferromagnetic-paramagnetic phase transition in La0.67–xYxBa0.23Ca0.1MnO3 compounds（x=0.10 and x=0.15）

The critical properties of the mixed manganite La0.67–x Y x Ba0.23Ca0.1Mn O3 with x=0.10 and x=0.15 around the paramagnetic(PM)-ferromagnetic(FM) phase transition were investigated through various techniques. These involved modified Arrott plots, Kouvel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for(x=0.10) La0.57Y0.10Ba0.23Ca0.1Mn O3(β=0.312±0.002 and γ=1.147±0.003 at T C=299.23±0.05 K). Moreover, the estimated critical exponents of(x=0.15) La0.52Y0.15Ba0.23Ca0.1Mn O3 were β=0.286±0.004 and γ=0.943±0.002 at T C=289.53±0.06 K. The critical exponents’ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–x Y x Ba0.23Ca0.1Mn O3 phase diagram. Expressing the field dependence as ΔS M∝H n allowed us to establish a relationship between the exponent n and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence of ΔS M.     

Separation of hematite from banded hematite jasper (BHJ) by magnetic coating

The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.     

Strain rate dependency and fragmentation pattern of expanding warheads

For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.     

Effect of the addition of rare earths on the activity of alumina supported copper cobaltite in CO oxidation,CH4 oxidationand NO decomposition

The effect of the addition of small amounts of rare earths(Ln=La, Ce, Nd and Gd) to alumina supported copper-cobalt spinel oxide on the catalysts efficiency in CO and CH4 oxidation and in NO decomposition was investigated. Samples of Ln/Cu Co/Al catalyst were prepared and characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), atomic absorption spectroscopy(AAS), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), H2-temperature-programmed reduction(H2-TPR), electron paramagnetic resonance(EPR) spectroscopy and low temperature nitrogen adsorption. The results showed that the addition of rare earths changed the surface state of the alumina supported copper-cobalt spinel catalyst. As a result, partial reduction of copper species was observed as well as migration of these species between the surface and the bulk. The Ln/Cu Co/Al catalysts behaved differently in oxidation and reduction processes. In oxidation processes where oxide structure was important, Ce/Cu Co/Al and Nd/Cu Co/Al were the most active catalysts. The catalyst Ce/Cu Co/Al was the most active in the oxidation reactions because of the availability and favorable surface distribution of the redox couples Cu+/Cu2+ and Ce3+/Ce4+. In NO decompostion, Ln-modified catalysts significantly improved the selectivity of the process to N2.     

ZrCuAlNi系大块金属玻璃的非晶形成能力、热学和力学性能（英文）

分析ZrCuAlNi系大块金属玻璃的非晶形成能力、热学和力学性能。运用密实堆积和动态脆性指数模型从理论上确定合金的成分。采用铜模吸铸法在氩气保护下制备圆柱形和圆锥形铸锭。用X射线衍射表征圆锥形铸锭以便确定非晶结构。结果表明:两种合金的临界非晶直径为3 mm。用差示扫描量热法(DSC)分析其热行为,加热速率分别为0.5、0.67和0.83 K/s。γ参数、过冷液相区ΔT_x和约化玻璃转变温度T_(rg)等这些实验所得的参数均表明其具有高的非晶形成能力。非晶成分显示其脆性指数为40。合金的压缩试验采用的应变速率为0.016 s~(-1),得到弹性模量约为83 GPa,总应变约为5%,屈服强度为1.6 GPa,硬度为4 GPa。运用密实堆积和动态脆性指数模拟可以预测ZrCuAlNi系合金的非晶形成成分。     

一种用于故障隔离的参数区间包络线计算方法

基于参数区间的故障隔离方法的核心工具是区间判断阈值曲线,其计算一直是制约该方法发展的问题。参数区间动态轨迹包络线作为区间判断阈值曲线具有能够适用于多重参数故障隔离等优点,但包络线计算中的包裹效应问题在该领域内一直未能得到很好解决。介绍一种基于上、下函数的包络线计算方法,有别于区间算法计算的包络线随着迭代的进行而迅速变得肥大的可能性,采用该方法的仿真实验表明其计算的包络线的包裹效应得到很大程度上的减轻,可有效用于故障隔离的区间判断。