Hard Magnetic Properties of Sm-Fe-C Based Alloys Prepared by Mechanical Alloying

The structure and magnetic properties of SmyFe100-1.5yC0.5y(y=8～20) alloys prepared by mechanical alloying (MA) from Sm, Fe and graphite have been investigated systematically. In order to improve hard magnetic properties of the alloys prepared by mechanical alloying, a new method consisting of re-milling and re-annealing was developed. After being re-milled and re-annealed, the Curie temperature TC of the Sm-Fe-C alloys changes. The TC of 2:17 phase increases, whereas the TC of 2:14:1 phase decreases. After being re-annealed at low temperatures, the grain sizes of hard phases are smaller than those in the alloys annealed at high temperatures. The effects of Co or Ti substitution for Fe are studied.

Identifying the optimal HVOF spray parameters to attain minimum porosity and maximum hardness in iron based amorphous metallic coatings

Flow based Erosion e corrosion problems are very common in fluid handling equipments such as propellers, impellers, pumps in warships, submarine. Though there are many coating materials available to combat erosionecorrosion damage in the above components, iron based amorphous coatings are considered to be more effective to combat erosionecorrosion problems. High velocity oxy-fuel(HVOF)spray process is considered to be a better process to coat the iron based amorphous powders. In this investigation, iron based amorphous metallic coating was developed on 316 stainless steel substrate using HVOF spray technique. Empirical relationships were developed to predict the porosity and micro hardness of iron based amorphous coating incorporating HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance. Response surface methodology(RSM) was used to identify the optimal HVOF spray parameters to attain coating with minimum porosity and maximum hardness.

Evaluation the Vickers Hardness of Denture Base Materials

The aim of this study was to evaluate the Vickers Hardness of four different denture base materials. Four different denture base materials were used in this study: Heat-cured pink acrylic resin, self-cured acrylic resin, heat-cured clear acrylic resin and polyamide denture base materials. To-tally 80 disc shaped samples which 2 mm thickness and 40 mm diameter were prepared. The samples were stored in distilled water after polished. Then, Vickers Hardness test was performed with TMTeck HV-1000B (200 gram at 15 second). The statistically analysis of obtained data was performed with use one-way analysis of variance test. The results showed that the highest Vickers Hardness value (18.57 HV) was identified in heat-cured (pink) acrylic resin, the lowest Vickers Hardness value (9.62 HV) was identified in polyamide denture base materials. The result of one-way analysis of variance test showed that there were statistically very highly significant differences between four denture base materials of Vickers Hardness (p < 0.001). The obtained data presented that the self-cured denture base acrylic resin was the hardnest denture base materials.

Effect of heat treatment on the microstructure and hardness of C-Cr-W-Mo-V-RE Fe-based hardfacing layer

After different heat treatment processes, the metal compound, the microstructure and the hardness of the C-Cr-W- Mo-V-RE Fe-based hardfacing layers are investigated by means of metallographic microscope, X-ray diffraction （ XRD ）, energy dispersive spectrum（ EDS ）, transmission electron microscope（TEM） and hardness tester. The results show that the hardfacing layers have higher tempering stability and secondary hardening property. After quenching at 820 ℃ ,the hardness value（ HRC37 ） and the microstructure of the layers are similar to that normalized at 820 - 1 000 ℃. The tempering stability and the hardness increases with increasing quench temperature, which is attributed to the amount of the alloy element in the matrix. These results are very helpful for improving the mechanical properties of the hardfacing layers.

The effect of copper valence on catalytic combustion of styrene over the copper based catalysts in the absence and presence of water vapor

Catalysts CuOx/γ,-Al2O3-IH and CuOx/γ/-Al2O3-IM were prepared, characterized, and tested for styrene combustion in the absence and presence of water vapor. The effect of copper valence of the catalysts on the catalytic activity for styrene combustion was discussed using the theory of hard soft acids and bases （HSAB）. The results showed that the existence of water vapor in feed stream inhibited the catalytic activity for styrene combustion due to the competition adsorption of water molecule. HSAB theory confirmed that the local soft acidity of the catalyst CuOx/^-AI203-1H was much stronger than that of the catalyst CuOx/^-AI203-1M because of the higher content of soft acid Cu＋ on its surface, which increased the adsorption ability toward soft base of styrene and reduced the adsorption toward hard base of water vapor, and thus increased the catalytic activity for styrene combustion and weakened the negative influence of water vapor.

New Mg_2Si based Alloy for Automobile Engine Cylinder Liner

New Mg2Si based alloy were prepared by mechanical alloying. Sintering temperature was from 825 to 865K, which indicated that few Mg2Si were produced at lower temperature while MgO were produced at higher temperature. Microstructure image showed that at sintering temperature of 855K, Mg2Si were mostly synthesized with the reaction of purity magnesia powder and silicon powder. Hardness and wear tests proved that the new synthetic silicon magnesium alloy had higher hardness and good wear resistance. Under the same testing conditions, it is found that the hardness of the new material is 420.50, and pure magnesium is only 41.65.In the same experiments it is also found that under the same pressure, pure magnesium alloys than silicon wearing capacity of pure magnesium is 2 times as high that of Mg2Si based alloy. It shows that Mg2Si based alloy is the ideal material for the wear parts of car engine cylinder liner because of its small density, stable dimension, high hardness and wear-resisting.

EFFECT OF RARE EARTH ELEMENT Er ON STRENGTHENING OF INTERFACE OF Ti（C，N） BASED CERMETS

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Application of GaN in Hard-switching Converters:Challenges and Potential Solutions

This paper overviews the benefits,challenges,research trends and potential solutions on the design and application of gallium nitride(GaN) technology in hard-switching power electronic converters from the device level up to converter level.

A Promising Initial Population Based Genetic Algorithm for Job Shop Scheduling Problem

Job shop scheduling problem is typically a NP-Hard problem. In the recent past efforts put by researchers were to provide the most generic genetic algorithm to solve efficiently the job shop scheduling problems. Less attention has been paid to initial population aspects in genetic algorithms and much attention to recombination operators. Therefore authors are of the opinion that by proper design of all the aspects in genetic algorithms starting from initial population may provide better and promising solutions. Hence this paper attempts to enhance the effectiveness of genetic algorithm by providing a new look to initial population. This new technique along with job based representation has been used to obtain the optimal or near optimal solutions of 66 benchmark instances which comprise of varying degree of complexity.

Study on Fe-based alloy Fe-Cr-Ti-C layers by reactive plasma cladding

Fe-based alloy Fe-Cr-Ti-C composite layers with and without titanium （ other powder ingredients are about the same） were fabricated on Q235 steel by plasma cladding process with high-energy plasma jet as heat source. Microstructure , phase composition and micro-hardness of the layers were investigated by optical microscope （OM）, X-ray diffraction （XRD）, electron probe microanalysis （ EPMA ） and micro-hardness tester. The results show that the grains of the cladding layers with Ti are much finer than that of the Fe-based cladding layer without Ti. Compared with the cladding layers without Ti, there are more shingle crystals in the cladding layers with Ti and the hard phase （ Cr, Fe ） 7 C3 of the eutectic in the layers increase gradually. However, as increasing titanium content in the alloy powder, the hard phase （Cr, Fe ） 7 C3 in eutectic structure of the cladding layer increases gradually, restraining （ Cr, Fe ）7 C3 carbide precipitation and decreasing the average and maximum hardness of the cladding layer.

Influence of Si and Ge Microalloying Additions and Plastic Deformation on Precipitation Processes in Al-Cu Based Alloys

The combined effect of micro-alloying with Si and Ge and/or plastic deformation prior to ageing at 160°C on age hardening has been studied in an Al-2 at% Cu alloy. The results obtained indicate that the hardness response is faster and the peak hardness is higher when plastic deformation and micro-alloying are applied together than performing each procedure individually. Different amounts of deformation, ranging from 0% to 30% have been utilized. An optimum deformation degree for the hardening response has been established around 8% for the Al-Cu-Si-Ge alloy. Characterization by transmission electron microscopy (TEM) shows that the peak hardness is due to a complex microstructure that contained θ" disc shaped precipitates, rod-shaped Si-Ge precipitates and θ' plates that were heterogeneously nucleated on the Si-Ge particles. Pre-deformation has been found to stimulate the growth of the θ' plates due to enhanced diffusion along dislocation cores. Increasing deformation reduces the influence of the Si-Ge precipitates on heterogeneous nucleation, leading to reduced peak hardness and faster over-ageing.

Does Missing Data in Studies of Hard-to-Reach Populations Bias Results? Not Necessarily

Missing data are always an issue in community-based longitudinal studies, calling into question the representativeness of samples and bias in conclusions, the research has generated. This may be due to the difficulty of implementing random sampling procedures in these studies and/or the inherent difficulty in sampling hard-to-reach segments of the population being studied. In fact, the ability to accurately study hard-to-reach populations in light of potential bias created by missing data remains an open question. In this study, missing data are defined as both failure to interview potential research participants identified in the sampling frame and failure to retain enrolled research participants longitudinally. Using the sample from the Mobile Youth Survey, a multiple-cohort, longitudinal study of adolescents living in highly impoverished neighborhoods in Mobile, Alabama, we examined sample representativeness and dropout to determine whether missing data led to a nonrepresentative, and therefore, biased sample. Results indicate that even though random procedures are not strictly used to draw the sample, (a) the sample appears to be largely representative of the population that was studied, and (b) attrition is largely uncorrelated with characteristics of those who dropped out. This suggests that it is possible to study with validity hard-to reach populations in community settings.

Effect of Precipitation on the Hardness of Ternary Metallic Glass

The present study reports effects of annealing treatment on the hardness of Ce75Al23Si2 rare earth-based metallic glasses (REMG). Then specimens were annealed at 100&deg;C, 200&deg;C, 250&deg;C, 270&deg;C, and 290&deg;C five different temperatures for 30 minutes. After that, three different characteristic methods, including microindentation, X-ray Diffraction (XRD), and scanning electrical microscope (SEM) were conducted on the as received REMG sample and five annealed samples. XRD data demonstrate that the crystallization occurs in the sample at the annealing temperature as low as 200&deg;C. The microindentation measurement shows that hardness of the REMG sample does not change at all before crystallization occurs in the sample and increases with the annealing temperature in the range of 200&deg;C to 290&deg;C. The average crystal size in the annealed samples was estimated using Debye-Scherrer equation to be 28-42 nm, in consistent with the SEM observation, indicating that nano-crystalline domains may give rise to the enhancement of hardness.

Refractory Hard Alloys Elaborated by Casting of Ternary (Co, Ni Fe)-30Cr-2.5 to 5 wt% C Compositions

Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume fractions in chromium carbides (even more than 50%) may be obtained in a metallic matrix by this way. However graphite may also appear in very low quantities in the carbon-richest alloys. The hardness increases with the carbon content (up to 1000 Hv30kg) but it may be a little lowered when graphite is also present. The results show that very hard alloys may be simply obtained by casting of rather cheap elements.

环片硬度对金基合金导电环摩擦磨损性能的影响

通过摩擦磨损试验、寿命试验和表界面分析方法研究了不同硬度的AuAgCu合金环片与AuNi合金刷丝在大气环境下的摩擦特性和磨损形貌特征.结果表明,随着导电环环片硬度由200.4 HV提高到243.6 HV,摩擦系数显著降低,环片磨痕宽度有所减小;环片与刷丝接触部位均存在典型的黏着磨损形貌特征,刷丝磨损区域形貌不规则,但硬环的磨损区域呈现出明显的犁削状划痕形貌;硬度不同的环片与刷丝对摩产生的磨屑均为薄片状且无团聚,磨屑成分与环片金属材料成分一致.此外,通过寿命试验前、后导电环环片和刷丝的质量分析可知,环片硬度的提高可显著降低导电环环片的磨损量.可见,在一定范围内提高导电环环片硬度,可以获得较好的减摩抗磨效果,为后续电接触材料对偶摩擦副的配副提供了试验和理论依据.

煤的结构基因与煤基碳材料构建研究进展

“双碳”目标的实现必将带来煤炭作为燃料用量的迅速减少,寻找煤炭的高附加值利用途径是煤炭行业可持续发展的迫切需求。简要介绍了基于单原子组装的无烟煤催化石墨化研究和焦炭催化石墨化研究,以及碳化硅炉炉芯石墨产品和特征,其晶体片径可达100um及以上,且受煤及煤基中间体结构的影响较少。重点介绍了无烟煤、烟煤、褐煤的结构特征与碳材料构建,研究发现煤的结构基因对煤基碳材料的构建有着决定性影响。无烟煤高固定碳含量的稳固碳结构有利于形成高强度的多孔炭和增碳补强剂等碳材料,无烟煤基高温石墨片径在几微米左右,片层平行度较差、交叉较多,适用于制备大规格炭电极的多晶石墨电极、电解槽、化学惰性通道。以烟煤为原料的煤沥青和焦炭中的炭青质是构成褶皱石墨的良好前驱体,煤沥青经针状焦石墨化因包含晶体液相生长过程,晶体片径尺寸可达数十微米以上,所形成的褶皱石墨经球团和浸渍包覆可以作为锂离子电池良好的负极储锂材料;焦炭中非晶态的固定碳也是制备硬碳材料的良好原料。褐煤稀疏的大分子架构和多孔颗粒形态有利于浸渍类碳材料的构建,是制备催化剂载体的优质原料。

煤基硬炭在钠离子电池负极材料中的应用研究进展

煤炭是全球储量最丰富、分布最广泛且使用最经济的能源之一。在可预见的未来,煤炭仍将是世界主要能源。在“双碳”背景下,探索煤炭资源的高效清洁利用是一项重要而紧迫的工作。本文简述了硬炭在钠离子电池中的存储机理,分析了以4种不同变质程度的煤作为前驱体调控硬炭结构的方式和电化学性能的差异,总结了煤基硬炭材料在钠离子电池应用中存在的共性问题,指出了目前煤基硬炭的研究重点和改进方向。研究成果可为煤基硬炭原料选择、结构调控、缺陷设计等提供参考。

基于困难样本对激励的小样本图像分类方法

使用少量标签样本训练得到的传统模型往往预测精度低、泛化能力弱,很难应用到实际生产中.针对小样本图像提出一种基于困难样本对激励分类方法,包括预训练阶段和元学习阶段.预训练阶段在基类数据集上训练编码器,并作为元学习阶段的初始特征编码器;元学习阶段将进一步优化此编码器,元训练过程使用本质特征法降低异常样本对质心的影响;结合度量学习与元学习设计了困难样本对激励损失函数,从样本对角度出发,在训练过程中引导模型扩大正负样本间距离,使同类样本更加紧凑.在公开数据集mini-ImageNet,tiered-ImageNet上进行实验的结果表明,分类精度分别为64.12%,70.15%,验证了所提方法的有效性和可行性.

低阶煤基炭材料研究进展

低阶煤因其储量丰富、富含多环芳烃有机物、含碳量高、成本低等特点,被认为是炭材料的优质前驱体。然而,由于不同低阶煤的灰分、微观结构、界面的差异,导致了煤基炭材料结构、性能难以有效调控的问题。近年来,研究人员提出了低阶煤基炭材料微观结构、表界面调控的有效方法。本文重点总结了低阶煤制备吸附活性炭、电容炭、硬炭、石墨和纳米炭材料的差异化策略,进一步讨论了煤种和工艺对煤基炭材料的微观结构、界面特性和官能团种类等的影响。同时介绍了煤基炭材料在吸附、超级电容器和碱金属电池中的应用。最后,展望了低级煤基炭材料未来研究的方向和挑战。