Effect of Grain Size on the Modulus of Elasticity and Strength of Synthetic Graphites

The effect of the grain size of the filler on the mechanical properties (compressive, bending, and tensile strength and modulus of elasticity) of synthetic graphite is analyzed using data for commercial structural graphites. As the mean particle size of the filler (_av) decreases from 3000 to 1 m, the modulus of elasticity increases, on the average, from 10 to 15 GPa, and the compressive, bending, and tensile strength increases by about one order of magnitude. The Griffith equation is used to evaluate the size of defects that initiate fracture (c _c) in different types of graphites. It is shown that the factors determining the critical defect size depend on the particle size of the filler. For _av > 150 m, c _c is comparable to _av or _max. In the range 30 < _av < 150 m, c _c is equal to or greater than _max. In graphites with _av < 30 m, c _c far exceeds _max and, presumably, corresponds to the particle size of the molding powder.     

Effect of Grain Size of BaTiO_{3}Ceramics on Thermal Expansion and Electrical Properties

The thermal expansion behavior and electrical resistivity of BaTiO \(_{3}\) ceramics with different grain sizes were investigated. When they were heated and subsequently cooled in the range from 25  \(^{\circ }\) C to 200  \(^{\circ }\) C, the expansion and contraction curves of BaTiO \(_{3}\) ceramics with grain sizes of 600 nm and 1500 nm were not matched well to each other, and abnormal contraction and expansion behaviors were observed. For 30 nm and 150 nm BaTiO \(_{3}\) ceramics, the expansion and contraction curves basically are straight lines during heating. The linear thermal expansion coefficients ( \(\alpha _\mathrm{L}\) ) and the electrical resistivity of BaTiO \(_{3}\) ceramics were also measured. Experimental results showed that the value of \(\alpha _\mathrm{L}\) increases and the electrical resistivity decreases gradually with reducing grain size. This phenomenon can be attributed to the combination effect of the grain boundary and oxygen vacancies.     

Radiation Resistance of Isotropic Structural Graphites

Experimental data are presented on the effect of neutron irradiation (360–400°C, neutron fluence up to 3 × 10²² n/cm², reflector of a BOR-60 reactor) on the dimensions and properties of isotropic, fine-grained structural graphites. The shrinkage rate and irradiation-induced size changes are shown to depend on the original characteristics of graphite.     

纳米氧化锆涂层晶粒度与隔热性能的关系

将纳米热障涂层隔热性能与微观组织联系起来并进行定量描述的工作还处于起步阶段,采用纳米ZrO2团聚体粉末在不同的喷涂参数下制备了3种不同的纳米热障涂层,利用扫描电子显微镜、IA-32定量金相分析软件、X射线衍射仪对其进行了观察和分析,并结合非稳态激光脉冲法与差示扫描量热仪测量了涂层的热导率.研究表明:涂层中同时存在柱状组织和纳米级等轴组织,并以柱状组织为主;随着喷涂参数的改变,二者的相对比例发生变化;纳米级等轴组织含量对涂层的平均晶粒度和热导率都有重要影响;随着涂层晶粒度的减小,热导率随之降低.     

Effect of Reagent Concentrations on the Grain Size of Chemical-Vapor-Deposited ZnSe

The effect of Zn and H₂Se concentrations on the microstructure of chemical-vapor-deposited ZnSe was studied. The average grain size was found to decrease in the flow direction and to vary nonmonotonically with depth, passing through a maximum. The factors influencing the mechanism of ZnSe deposition are discussed.     

Effect of Grain Size on the Weldability of Cast Alloy 718

Electron beam welding was conducted on cast alloy 718 with varying grain sizes obtained using Microcast (MX™) and conventional cast (CC) techniques. The average value per section of Total Crack Length (Av. TCL) was measured on each cross section and used to represent the material's weldability. It was found for the first time that the grain size had a reduced effect on the weldability of cast alloys, relative to that reported in the literature for wrought alloys; i.e., increased grain size in the range of 90-3000 microns resulted in improved weldability. This was determined to be related to the probability of welds intersecting grain boundaries and causing grain boundary microfissuring. The conclusion from the experimental analysis is corroborated by the use of a Weibull-type analysis to evaluate the probability of a weld microfissure occurring relative to the grain size. As grain size increases, the probability of the weld intersecting the grains is reduced, and thus, the likelihood of microfissuring is reduced. With regard to a single crystal, there are no grain boundaries intercepting the weld (probability = 0), and thus, microfissuring related to constitutional liquation of primary carbides, or segregation of species to grain boundaries would not occur.     

Effect of Grain Size on the Ionic Conductivity of Silver Halides

An equation is derived for the ionic conductivity of silver halide emulsion grains with dimensions comparable to the Debye length of intrinsic defects. The conductivity of the grains is shown to be inversely proportional to the grain size. The surface potential distribution depends on both the shape and size of the grains. The surface charge density, surface potential, and volume potential are estimated for octahedral, cubic, and tabular AgBr grains.     

金刚石膜内晶粒尺寸和取向对其热导率的影响

研究了金刚石膜内晶粒尺寸和取向程度对金刚石膜热导率的影响。通过对衬底表面进行不同研磨时间的处理和适当的工艺条件，采用灯丝热解化学气相沉积（ＨＦＣＶＤ）的方法在单晶硅衬底上形成了具有不同晶粒尺寸和不同程度（１００）晶面取向的金刚石膜，并研究了其热导率。结果表明，由大晶粒和较高程度（１００）晶面取向的晶粒构成的金刚石膜具有热导率特性。     

晶粒尺寸对Cu-30%Zn合金形变孪晶厚度的影响

对于面心立方结构的纳米金属,晶粒尺寸对孪生厚度(孪生核)的影响虽已有研究,但仍有待深入。本论文以Cu-30%Zn合金为模型材料,通过高压扭转变形技术、等径角挤压连同轧制技术变形得到晶粒尺寸在5~500nm的样品。透射电子显微镜观察发现:变形孪晶的片层厚度随晶粒尺寸的减小而减小,当晶粒尺寸小于20nm以后,孪晶厚度为(111)晶面间距(层错);另外,层错存在于各个不同尺寸范围的晶粒内,表明层错不受晶粒尺寸影响。研究结果表明在低层错能超细晶材料中,孪生变形是通过从晶界连续发射不全位错(层错)形成的。     

Effect of Grain Size Distribution on the Performance of Perpendicular Recording Media

Micromagnetic simulations of perpendicular recording in hard disk storage media have been performed with model media of variable microstructural disorder. Simulations indicate that increasing disorder, either due to size and shape distribution or due to disordered packing, decreases signal and increases noise. The mechanism observed in the model is that, in a disordered microstructure, there is a distribution of magnetostatic and exchange coupling between grains that acts to create clusters of grains that act collectively. These clusters increase the auto-correlation function of the spatial distribution of magnetization that is a measure of the magnetic feature size. Consequently, the transition width between recorded bits increases and the position variation of the transition locations (jitter) increases, so that signal-to-noise ratio (SNR) falls. The results suggest that microstructurally ordered media will exhibit higher performance, and that such effects may ultimately demand the use of self-assembled or patterned media with regular packing and very narrow size distribution     

Effect of Cooling Conditions on Grain Size of AZ91 Alloy

The grain size of AZ91 alloy was investigated in terms of the effects of cooling rate, superheat and steel gauze. It was found that rapid cooling rate and low superheat favoured the achievement of fine grain structures. The gauze had a less profound effect on the grain size in AZ91 magnesium alloy than that in A356 aluminum alloy. The mechanisms by which these factors affect grain refinement of AZ91 have also been discussed.     

不同添加剂对钛酸铝热膨胀系数影响的研究

钛酸铝是一种优异的高熔点、低膨胀无机非金属材料．为提高其强度、抑制其热分解,往往在钛酸铝中引入添加剂．本文研究了单一添加剂和复合添加剂对钛酸铝膨胀系数的影响．结果表明：引入少量的稀土元素氧化物能显著降低钛酸铝的热膨胀系数．引入1～4mol％CeO₂或2mol％La₂O₃可使钛酸铝的膨胀系数降至接近于零．这就为开发零膨胀材料提供了新的方法．在钛酸铝中引入1～4mol％Fe₂O₃,其膨胀系数保持不变．在含有4mol％Fe₂O₃的钛酸铝中再引入SiO₂,钛酸铝的膨胀系数增大,而加入另一种稀土元素氧化物则能降低其膨胀系数．三种添加剂的适当配比能将钛酸铝的膨胀系数调整至最小．这对于引入复合添加剂对钛酸铝的改性是很有意义的．     

Bulk Expansion Effect of Gallium-Based Thermal Interface Material

The bulk expansion effect of gallium-based thermal interface materials (GBTIMs) was experimentally disclosed and clarified for the first time. GBTIMs were prepared under low (26 %) and high (96 %) relative humidity for a short (2 h) and long (5 h) time periods. An evident volume expansion phenomenon was observed with adequate humidity. Higher humidity resulted in bigger expansion rate and expansion coefficient. The expansion coefficient could reach surprisingly large value of 1.5 for GBTIMs under 96% relative humidity. Assuming that the volume change was related to chemical reactions in the mixture, SEM and XRD were adopted to determine the structure and phase components of the samples. The gases produced in the expansion process were detected with gas chromatography and a large amount of hydrogen was found. The results indicated that the hydrogen produced by the reaction between gallium oxide \(\hbox {Ga}_{2}\hbox {O}\) and water in GBTIMs caused the expansion effect. The corroded GBTIMs were mainly composed of gallium oxide \(\hbox {Ga}_{2}\hbox {O}_{3}\) and became loose and porous solids after expansion. Thermal conductivity decreased dramatically after the expansion process due to the composition and structure changes. From the view point of application, the ambient humidity and oxidation degree must be controlled during preparation of such thermal interface material to avoid its bulk expansion effect.     

碳纳米管对水泥基材料热膨胀性能的影响

在水泥基中掺入不同比例的碳纳米管,制备出碳纳米管水泥基复合材料。测量其在室温~600℃的热膨胀性能,并根据DSC/TG、XRD图谱,孔径分布图和扫描电镜图从微观尺度分析其变化规律的机理。结果表明,从室温到150℃掺入各比例碳纳米管的水泥基复合材料热膨胀率变化趋势相似,热膨胀率为正值而出现微膨胀;150℃~590℃热膨胀率为负值且逐渐减小,试件持续收缩。当碳纳米管的掺量为水泥的0.3%时热膨胀曲线始终在其他掺量之下,热膨胀率达到最小值。这表明,碳纳米管掺量为0.3%的材料水化反应充分,产生大量的水化硅酸钙凝胶,收缩明显、密实度显著提高。掺入0.3%的碳纳米管可有效阻止供暖管道局部混凝土的膨胀,提高结构的耐久性。     

Effect of the Isotopic Composition of Fe on Its Linear Thermal Expansion Coefficient

Inorganic Materials - The linear thermal expansion coefficients (LTECs) of isotopically natural Fe (natFe) and samples isotopically enriched in 56Fe (99.945 wt %) and 57Fe (90.954 wt %) have been...     

Effect of Differential Thermal Expansion Coefficient on Stresses Generated in Coating

Two different spraying powders [81FVNS and 80% (443)+20% (105)] were plasma sprayed on two types of substrates (AISI 316 and Ti) in order to verify the effect of differential thermal expansion coefficient (DTEC) between coating and substrate on the final residual stresses generated in the coating. Modulus of elasticity (E) was evaluated for the substrates and coatings (as a composite beam). Free-standing coatings were used to measure the thermal expansion coefficient, as a function of temperature, of the actual coatings with all defects, impurities and typical lamella structure. The results show that the residual stresses seems to be less dependent on the linear thermal expansion coefficients mismatching between substrate and coating, reflecting the importance of the other sources of stresses. i.e. quenching or deposition stresses induced during spraying. The suitable heat treatment condition of the coated samples may release some or most of the residual stresses. However in some cases the sign of the stress was completely changed as a result of neglecting the quenching stresses.     

Interactive Effect of Grain Orientation and Grain Size on Magnetic Properties of Fe-78 wt% Ni Ribbons

Fe-78 wt% Ni ribbons were prepared by the melt spinning technique and the interactive contribution of the grain size and grain orientation on the magnetic properties was examined. Heat treatment at 673 K for 1 h followed by furnace cooling was performed to show the annealing impact. At three wheel speeds of 10, 20, and 30 m/s, the saturation magnetization nearly does not change. High wheel speed and heat treatment are inclined to promote the growth of <001> grains. Although the <001> orientation is not the easy axis of magnetization, the improvement of the texture in this direction makes the coercivity decrease, which counteracts the inverse effect of the grain size at high wheel speed. It indicates that for preparing soft magnetic ribbons, the interactive contribution of grain orientation variation and the grain size should be considered.     

晶粒尺寸对耐候钢抗大气腐蚀性能的影响

细化晶粒能有效提高耐候钢的力学性能,但是,随着晶粒尺寸的减小,晶粒尺寸对耐候钢的耐腐蚀性能的影响是怎样的,有必要进一步研究.因此,对不同晶粒尺寸耐候钢进行了模拟工业大气周期浸润实验室加速试验,并通过金相扫描、X射线衍射、交流阻抗谱等手段对锈层进行了分析.结果发现,在腐蚀初期还没有形成致密内锈层前,细晶粒比大晶粒的腐蚀更快一些,形膜要快.在腐蚀后期形成致密的内锈层后,细晶粒和大晶粒的腐蚀速率基本一致;耐候钢晶粒尺寸不影响其耐蚀性能.     

稀土氯化物对磷化膜层晶粒及膜重的影响

稀土作磷化促进剂,稳定性好,有利于环保,有利于提高磷化效率和质量.在磷化液中加入不同稀土(Re)氯化物,探讨了其对6061铝合金磷化膜膜重的影响.利用SEM和XRD观测了磷化膜晶粒的形貌和粒径.结果表明:适量(10～50 mg/L)稀土离子的加入使得磷化膜膜重增加,晶粒细化,在此范围内Re含量越大、Re离子半径越大,则膜重越大.而当稀土含量超过60 mg/L时,反而不利于磷化膜的生成,磷化膜膜重减轻.     

原奥氏体晶粒尺寸对珠光体钢组织及韧性的影响

探索了奥氏体晶粒尺寸对珠光体等温转变组织特征以及对韧性性能的影响规律.研究表明,在相同等温转变温度下,珠光体片层间距无明显变化,随奥氏体晶粒尺寸的增加,先共析铁素体量减少而珠光体团尺寸增加.珠光体断裂韧性受控于裂纹前沿塑性影响区尺寸(1～2)δc,其中δc为临界裂纹张开位移,当原奥氏体晶粒大于(1～2)δc时,裂纹扩展阻力主要来自穿越珠光体片层α、θ相的颈缩、破断.当原奥氏体晶粒尺寸接近或小于(1～2)δc时,裂纹主要沿晶界、珠光体团界、α+θ片层界面扩展,通过扩展路径发生多次弯折消耗能量,随原奥氏体晶粒尺寸增加,准静态断裂韧度J变化幅度较小.而冲击韧性缺口前沿塑性影响区远大于原奥氏体晶粒,大角度晶界将促使裂纹的转折而提高扩展阻力,提高裂纹前沿塑性区大角度晶界密度有利于提高冲击功,冲击韧性A随晶粒尺寸的增加显著下降.