冷速对液态Ti_3Al合金快速凝固过程中微观结构变化的影响

采用分子动力学方法模拟研究了不同冷速条件下液态Ti3Al合金的凝固过程。采用对相关函数法、原子团类型指数法(CTIM)对凝固过程中团簇结构的变化进行了分析。结果表明:在以1×1012K/s,1×1013K/s,1×1014K/s三种不同冷速条件下,系统都形成了以(12 0 12 0)基本原子团为主的非晶态结构,冷速对于Ti3Al合金凝固过程微观结构的影响主要是通过(12 0 12 0)基本原子团数目变化体现出来,(12 0 12 0)基本原子团在Ti3Al合金快速凝固过程团簇结构演变中起了主要作用。冷速越低,Ti3Al合金的玻璃态转化温度越低,体统形成的(12 0 12 0)基本原子团数目越多,非晶体的结构越稳定。     

冷速路径在分析奥氏体转变组织的应用

研究Q345R低合金钢在连续冷却过程中奥氏体的相变行为及其在非恒定冷速空冷组织分析中的应用。结果表明,和温度-时间(T-t)曲线相比,冷速路径(T-v)曲线能够更加准确、直观地反映相应温度下的实际冷速,将冷速路径和CCT图叠加分析得到的转变组织和实际冷却组织相符。     

热声键合界面的微观结构特性

设计一系列的键合实验，通过扫描电镜SEM和EDS能谱测试分析热声键合界面的微观结构特性及变化规律，结果表明，热声键合界面的形状像一个中央未结合的椭圆环，键合强度取决于皱脊椭圆环结构；当作用力和功率保持不变，随着时间增加，键合区向中央延伸，当作用力和时间保持不变，随着功率的增加，焊接区里皱脊面扩大。EDS能谱测试Au—Al、Au—Ag界面的微观组织成分，证实了Au—Ag扩散偶的Kirkendall扩散效应及Au—Al键合界面可能形成金属间化合物。     

纳米晶脉冲电铸的试验研究

通过理论分析和试验研究 ,利用高频脉冲电流、高速冲液及添加剂方法 ,获得了纳米晶电铸层。分析了在脉冲电铸过程中 ,电规准及添加剂对沉积层微观结构影响     

聚合物淬火介质浓度的测量应用

聚合物水基淬火剂在生产中得到了越来越广泛的应用,但聚合物水基淬火剂在使用过程中由于降解其粘度不断减少,对流冷速不断增加,增大了变形开裂的潜在危险。为稳定和控制对流冷速,通过长期的实践,提出了使用经过粘度校正和冷速校正后的折光系数对浓度进行测控的方法,生产应用证明,该方法直接,简单,有效。     

滤饼微观结构及其测量结果的分析研究

分析滤饼的微观结构以及滤饼孔隙率计算方法的不足,探索用环境扫描电镜对滤饼进行切片扫描和断层扫描,对滤饼微观结构进行分析研究的可能性.分层测定了不同过滤压力和不同压榨压力下,过滤终了时和压榨全过程中的滤饼孔隙率以及不同压榨起始点进行压榨时的滤饼孔隙率,从而深入了解过滤过程以及不同压榨过程和压榨周期中滤饼的内部结构.并与传统的根据加压试验获得的计算数据进行了比较和分析.     

DQ50钢的显微组织对硬度的影响

试验研究了DQ 50钢显微组织对硬度的影响,以及该钢在不同冷速下得到的显微组织.研究得出该钢适宜的冷速应选为10～60℃/min.     

BM510L汽车大梁钢的连续冷却转变曲线

采用膨胀法在Gleeble-3500型热模拟试验机上测定了BM510L钢在不同冷速下连续冷却时的膨胀曲线及连续冷却转变曲线(CCT曲线);利用光学显微镜、显微硬度计研究了BM510L钢连续冷却过程中奥氏体转变后的组织和显微硬度。结果表明:随着冷速的提高,铁素体转变开始温度降低,珠光体转变终了温度也逐渐降低,当冷速大于1℃·s-1时,组织中开始发生贝氏体转变,当冷速为15℃·s-1时,组织已完全转变为贝氏体组织;随着冷速的提高,其显微硬度逐渐增大。     

基于工艺过程的工艺知识建模方法研究

对工艺经验知识进行了分析,从宏观角度出发,以工艺过程树状结构为基础建立了工艺知识的层次结构模型;从微观角度出发,以四元组结构为基础,采用自然语言和多媒体的方式建立了工艺知识的知识元结构模型.最后给出了应用实例,实例分析研究表明,该建模方法是有效的.     

基于工艺过程的工艺知识建模方法研究

对工艺经验知识进行了分析,从宏观角度出发,以工艺过程树状结构为基础建立了工艺知识的层次结构模型;从微观角度出发,以四元组结构为基础,采用自然语言和多媒体的方式建立了工艺知识的知识元结构模型。最后给出了应用实例,实例分析研究表明,该建模方法是有效的。     

基于有限元的激光熔覆凝固过程分析

针对激光熔覆过程中温度变化对其凝固组织的影响,讨论了温度梯度G与冷却速度(即降温阶段的温度变化率)对凝固组织的影响,利用形状控制因子K分析了激光熔覆过程的凝固行为。分析结果表明:在热源中心的正下方晶粒是沿基体垂直方向析出的;冷却速度有细化晶粒的作用,冷却速度越大,晶粒越细小;熔覆材料或基材达到熔点的时间与达到最大冷却速度时间的先后顺序对其凝固组织形态有重要影响,若冷却速度先达到最大值,其组织呈胞状晶粒,否则,其组织呈柱形树枝晶。K在80×106～120×106℃.s时,凝固组织为密布排列且粒径较大的胞状晶粒;当K大于200×106℃.s时,凝固组织为柱形树枝晶。     

燃烧室新型迷宫复合冷却结构二维壁温数值模拟

针对燃烧室新型迷宫复合冷却结构,采用数值模拟方法研究了该冷却结构的流场结构和内外壁温分布情况,获得了结构内部的流场及多层壁温的分布规律,并且计算了席壁层热侧面的压力分布情况。计算结果表明,迷宫复合冷却结构沿轴向的壁温梯度较全气膜冷却结构更加平缓,外侧壁最高温度较全气膜冷却结构低大约200 K左右。     

中速定向凝固K10高温合金的组织和偏析的研究

本文利用最新研制的ZMLMC（区域熔化液态金属冷却）超高温度梯度定向凝固装置研究了钴基高温合金K10在中等冷却速率下定向凝固时的微观组织变化和枝晶偏析及其与凝固参数的关系。结果表明,钴基高温合金K10在中速定向凝固后,其一次枝晶间距比传统的HRS法定向凝固组织细化5倍以上,并在一定的冷却速率下获得了二次分枝被强烈抑制、一次轴呈平行排列的定向凝固超细柱晶组织,在所研究的冷却速率范围内,合金元素Cr、Mo和Ni在枝晶干与枝晶间的偏析比均随冷却速率的增大而趋于1,枝晶偏析得到抑制甚至消除。     

Differential membrane-based nanocalorimeter for high-resolution measurements of low-temperature specific heat

A differential, membrane-based nanocalorimeter for general specific heat studies of very small samples, ranging from 0.5 mg to sub-μg in mass, is described. The calorimeter operates over the temperature range from above room temperature down to 0.5 K. It consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: (i) The resistive thermometer, made of a Ge(1 - x)Au(x) alloy, displays a high dimensionless sensitivity ∣dlnR∕dlnT∣ ? 1 over the entire temperature range. (ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. (iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. This gives high resolution and allows continuous output adjustments without additional noise. (iv) Absolute accuracy is achieved via a variable-frequency-fixed-phase technique in which the measurement frequency is automatically adjusted during the measurements to account for the temperature variation of the sample heat capacity and the device thermal conductance. The performance of the calorimeter is illustrated by studying the heat capacity of a small Au sample and the specific heat of a 2.6?μg piece of superconducting Pb in various magnetic fields.     

High performance temperature controlled UHV sample holder

A requirement of many surface science studies is the capability to alter a sample temperature in a controlled mode. Sample preparation procedures such as heating or cooling ramps, high temperature spikes, fast annealing, or simply maintaining a sample at a very high, or very low, temperature are common. To address these issues, we describe the design and the construction of a multipurpose sample holder. Key points of this design are operation in an extended temperature range from liquid nitrogen (LN(2)) temperature to approximately 1300 K, temperature control during heating and cooling, low thermal inertia with rates up to 50 K s(-1) (heating) and -20 K s(-1) (cooling), and small heated volume to minimize background problems in thermal desorption spectroscopy (TDS) spectra. With this design the sample can be flash heated from LN(2) temperature to 1300 K and cooled down again in less than 100 s. This sample holder was mounted and tested in a multitechnique apparatus and adds a large number of sample preparation procedures as well as TDS to the list of already available surface analysis techniques.     

燃气轮机燃烧室冲击射流冷却火焰筒壁的结构参数研究（英文）

The flame temperature in the combustor of a gas turbine is usually as high as 2000 K, while the maximum temperature that can be endured by metal materials is less than 1200 K at present. Therefore, various protective and cooling measures are needed to ensure the operation life of the liner wall which wraps the flame. The lean premixed combustor can meet the increasingly stringent emission requirements, but it requires more air for premixed combustion and then less air for cooling and dilution. In order to obtain a better impingement jet cooling structure, this paper studied the impingement jet cooling structure with vertical circular holes of equal diameter under single outlet condition. The structural variables studied include the jet hole diameter D, the impinging distance Z, the jet hole length(jet plate thickness) t, and the jet-to-jet spacing X is ignored. Among them, X/D(the ratio of the jet-to-jet spacing to the jet diameter) is inversely correlated with the mass flow rate. Within the constant X/D being equal to 10, the influence of D, Z and t on the average heat transfer coefficient h of the target surface under same mass flow was determined by means of conjugate numerical heat transfer analysis and orthogonal test. The results show that Z has significant influence on h, D has moderate influence on h, and t has negligible influence on h. Further, by means of regression orthogonal test, the influence trend of parameters Z and D on h at X/D=10 was studied. The optimal values of Z and D within the research scope were found.     

Temperature directly affects the rate of irradiation-induced mass loss from phosphatidylcholine multilayers

We monitored the mass thickness of egg yolk phosphatidylcholine multilayers at several temperatures during electron irradiation. The rate of irradiation-induced mass loss was reduced substantially when this specimen was cooled to liquid nitrogen temperature from room temperature. Additional cooling to liquid helium temperature caused an additional reduction of mass-loss rate. The characteristic doses D(1/e), which are the slopes of the logarithm of the differential mass thickness against dose, were approximately 7 x 10(3) e/nm2 at 290 K, 8 x 10(4) e/nm2 at 130 K, and 1.4 x 10(5) e/nm2 at less than 10 K. The fractions of the original mass thickness that remained after arbitrarily high doses were about 69% at 290 K, 72% at 130 K, and 77% at less than 10 K.     

Freeze-substitution and isothermal freeze-fixation studies to elucidate the pattern of ice formation in smooth muscle at 252 K (-21°C)

Taenia coli muscle was cooled to 252 K in the presence of the cryoprotectant dimethyl-sulphoxide, at cooling rates known to reduce viability by significantly different amounts. The reduction in viability was known to be related to ice formation. Freeze-substitution and isothermal freeze-fixation studies were carried out to determine the distribution of ice within the muscle at this temperature. Freeze-substitution using ethylene glycol was unsuccessful but a new method, using high concentrations of the cryoprotectant as the substituting solvent, was able to maintain ice configurations at this relatively high substitution temperature. The results of freeze-substitution in dimethylsulphoxide were confirmed by isothermal freeze-fixation when both techniques were conducted under identical cooling conditions. The results indicated that the functional differences produced by cooling muscle at either 0·3 K min^?1 or 2 K min^?1 were related to the distribution of the ice phase within the tissue.     

An automated laser thermometer for studying plasma processes in the microtechnology

The design and characteristics of an automated temperature sensor of dielectric and semiconductor substrates in apparatuses for film deposition and etching of microstructures are considered. The temperature is measured via the laser interference thermometry technique as wavelengths of 0.633 and 1.15 μm of a He-Ne laser. A signal-to-noise ratio of ～30 dB attained in the system is such that the device is sensitive to a change in the substrate temperature of 0.01 K. The heating and cooling of the wafer are recognized automatically and displayed via a graphic interface in real time. An interferogram recorded during substrate heating or cooling, the time dependence of the temperature after the discharge initiation, and the temperature dependence of the substrate-heating power are displayed on the monitor. For 0.5-mm-thick silicon substrates, the measurement range at a wavelength of 1.15 μm extends from cryogenic temperatures to 650 K.     

A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ≈400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/√Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.