ZnO压敏陶瓷热处理的正电子湮没寿命谱研究

在常温下测量了ＺｎＯ压敏陶瓷经不同方法热处理后的正电子湮没有寿命谱，结果表明，与无热处理比较，７５０℃×２ｈ的氧化热处理基本不改变缺陷强度Ｉ２；随后进行的７５０℃×２ｈ还原热处理则使Ｉ２明显降低，氧化热处理和还原热处理均使缺陷寿命τ２延长。根据正电子理论和ＺｎＯ压敏陶瓷晶界缺陷模型，该结果支持适当温度下的氧化热处理使氧离子Ｏ吸会于晶界中这一假设，同时，我们还得出：晶界吸附的Ｏ并非Ｂｉ２Ｏ３相变的结     

Ni-Co-Cr高温合金中3d电子作用的正电子湮没研究

利用正电子湮没技术测量了纯金属Ni、Co、Cr以及3种不同成分的Ni-Co-Cr合金的正电子湮没辐射Doppler展宽谱,分析了形成Ni-Co-Cr合金时3d电子的作用.结果表明,3种纯金属中Ni的3d电子信号较强,当增大Ni-Co-Cr合金中Ni原子的比例时,导致正电子与自由电子湮没的几率增加和合金中的金属键增强,从而提高了合金的韧性.Ni-Co-Cr合金的实验熵谱与其合成熵谱保持了较好的一致性,表明Ni-Co-Cr合金中不同原子之间主要以金属键相结合,这也成为Ni-Co-Or合金具有较好金属延展性的重要原因.     

An Inductive Technique for Electrical Conductivity Measurements on Molten Metals

A computer-controlled rotational technique to measure the electrical resistivity of solid and molten metals was developed. The electrical resistivities of pure metals (aluminum, indium, lead, and tin) and the low-melting point alloy LMA-158 in the solid and liquid states were measured. The results also show that there is a linear relationship between electrical resistivity and temperature in both the solid and the liquid states of the test materials. Good agreement was found between the experimental data and predictions from the literature. The data were used to estimate the temperature coefficients of electrical resistivity of test specimens over a wide range of temperatures including the melting point of the metals. Good agreement between experimental data and predictions made by previous researchers for the temperature coefficients was achieved.     

Defects and Electron Densities in TiAl-based Alloys Containing Mn and Cu Studied by Positron Annihilation

The defects and electron densities in Ti50Al50, Ti50Al48Mn2 and Ti50Al48Cu2 alloys have been studied by positron lifetime measurements. The results show that the free electron density in the bulk of binary TiAl alloy is lower than that of pure Ti or Al metal. The open volume of defects on the grain boundaries of binary TiAl alloy is larger than that of a monovacancy of Al metal. The additions of Mn and Cu into Ti-rich TiAI alloy will increase the free electron densities in the bulk and the grain boundary simultaneously, since one Mn atom or Cu atom which occupies the Al atom site provides more free electrons participating metallic bonds than those provided by an Al atom. It is also found the free electron density in the grain boundary of Ti50Al48Cu2 is higher than that of Ti50Al48Mn2 alloy, while the free electron density in the bulk of Ti50Al48Cu2 is lower than that of Ti50Al48Mn2 alloy. The behaviors of Mn and Cu atoms in TiAI alloy have been discussed.     

铝合金时效硬化的正电子湮没研究进展

介绍了正电子湮没的试验原理,以及正电子寿命谱和符合多普勒展宽等试验技术。总结了近几年来正电子湮没技术在铝合金时效研究中的应用进展,展示了正电子湮没技术是如何通过对合金时效中微结构变化的研究,获得溶质偏聚动力学及空位-溶质相互作用等重要信息。     

Thermophysical Property Measurements on Niobium and Titanium by a Microsecond-Resolution Pulse-Heating Technique Using High-Speed Laser Polarimetry and Radiation Thermometry

A microsecond-resolution technique was used to measure the heat of fusion, specific heat capacity, and electrical resistivity of niobium and titanium in the temperature range of 1600 to 3200 and 1500 to 2200 K, respectively. The method is based on rapid resistive self-heating of a wire-shaped specimen by a current pulse from a capacitor–discharge system. Melting of the specimen occurs in approximately 50 s. Measured quantities are the current through the specimen, the voltage across the specimen, the radiance from the specimen, and its normal spectral emittance, as functions of time. The true temperature of the specimen is computed from the values of the normal spectral emittance and radiance temperature of the specimen at each instant. The latter quantities are measured by means of high-speed laser polarimetry and radiation thermometry, respectively.     

检测激光多普勒信号的新方法

为了准确地检测激光多普勒信号,提出了一种新的信号检测方法。在算法中应用梯度下降方法推导出算法的系统方程,并且应用庞加莱映射稳定原理给出系统稳定的存在条件。应用该算法能够检测激光多普勒信号,估计多普勒频移。测试结果表明,测出数据的相对误差小于0．7％。     

在中低温条件下环境辐射对光谱发射率测量的影响

讨论了有效光谱发射率和有效亮度温度的概念。介绍了光谱发射率的测量方法及测量装置。在考虑到环境辐射的情况下,给出了光谱发射率的计算方程,指出中低温条件下的光谱发射率测量必须考虑环境辐射的影响,否则会出现较大的误差。     

Study of artificial aging in AlMgSi (6061) and AlMgSiCu (6013) alloys by Positron Annihilation

We investigate the artificial aging process of the weldable Al-alloys AA-6013 (AlMgSiCu) and AA-6061 (AlMgSi) by positron annihilation spectroscopy and Vickers micro-hardness measurements. We find a correlation between a minimum of the measured positron lifetime and the maximum hardness. To explain these findings AlZn will be discussed as a well known example of positron interaction with different types of precipitations in aluminum. Additionally, we calculate positron annihilation parameters for pure Al, Si, Mg, and finding support for our interpretation. For AA-6013 and AA-6061 the increase of the average positron lifetime after reaching the maximum hardness is attributed to the formation of semi-coherent precipitates. Hence, using positron annihilation it is possible to follow very sensitively the precipitation sequence even in technical aluminum alloys. Finally, we discuss which implications the aging may have on microstructural changes.     

Thermal and Electrical Conductivity Measurements on Aluminum Foams

Metal foams are one of the most interesting types of materials although there is limited information concerning their thermal and electrical conductivity. Closed cell different density Alporas foams are investigated, which has one of the most homogeneous cell size distribution recently. Comparative method has been chosen to determine the thermal conductivity of the samples in the function of the temperature at 30, 100, 200, 300, 400, 500 °C. For measuring the electrical conductivity of aluminium foams a special low frequency eddy current measuring apparatus was used. The ratio of thermal and electrical conductivity was calculated and shown an increasing function by the density of the foams.     

MgAl2O4透明陶瓷的正电子湮没寿命谱研究

采用正电子湮没寿命谱的方法研究了Mg-Al尖晶石透明陶瓷被电子,质子辐照后的缺陷情况,以及在γ射线辐照下,缺陷情况随γ射线剂量的变化规律,并研究了其退火特性。     

激光多普勒效应微纳测量技术的研究

研究MEMS系统中可动构件(膜、梁、梳、面、弹簧)在承受压力、弯曲等机械负荷及热负荷下的性能，重要途经是测量其在各种条件下的运动量(振动、位移等)．提出了一种MEMS构件微小振动、位移测量系统，采用外差法激光多普勒技术，通过对信号的频谱分析，确定了信号处理单元的适宜频带宽度．对调相多普勒跟踪信号进行相干解调及频率／电压转换，可以实时地得到被测的速度、位移、加速度、频率等参量．实现的测量分辨力为20nm．