Differential equations for a dynamic thermal conductivity experiment

The mathematical model that describes a dynamic thermal conductivity experiment is reconsidered by taking into account the role of thermal expansion. Two differential equations are presented that take into account the various physical phenomena occurring in a long thin rod directly heated by a current pulse. One of the two equations keeps variables space and time completely separate and is particularly useful for computer simulations.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

封闭循环TEA CO2激光器用催化剂的实验研究

在不同的催化剂和不同温度的条件下,用磁氧分析仪监测了封离型TEA C0₂激光器中O₂含量随时间或脉冲次数的变化。对实验现象进行了分析。对几种催化剂的特性给出了详细的比较。     

The development of a high-speed spindle measurement system using a laser diode and a quadrants sensor

Reducing the manufacturing time is the trend of precision manufacturing, and the precision of a work-piece is very important for manufacturing industry. High-speed cutting is becoming more widely used and the high-speed spindle is a very important element, whose precision may affect the overall performance of high-speed cutting. Most of the studies on high-speed cutting are focused on the cutting force, the vibration of the spindle and the effects of the spindle's thermal expansion; however, the measurement of the high-speed spindle continues to use the conventional spindle measurement method.As with the measurement of the high-speed spindle, more strict demands are set on the dynamic balance of cutting tools and the bandwidth of the measurement systems when compared with common spindles. The capacitance displacement sensor has been employed for the spindle error test. The precision of the measurement system is limited by the reference (such as a master ball or a master cylinder). Also the capacitance sensor and the reference must be grounded together. This paper presents a simple spindle measurement system using a laser diode and a quadrants sensor, with accuracy up to 1 μm, within 300,000 rpm for various spindles. The system does not need any reference and it is easy to set up. This system can be applied to measure the spindle errors, the spindle speed and the spindle indexing.     

Structure, hyperfine interactions and magnetization studies of mechanically alloyed Fe50Ge50 and Fe62Ge38

X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used to study the structure and some magnetic properties of Fe₅₀Ge₅₀ and Fe₆₂Ge₃₈ prepared by mechanical alloying from the elemental powders. In both cases in the early stages of milling the intermediate paramagnetic FeGe₂ phase was formed. The mechanical alloying process of Fe₅₀Ge₅₀ resulted in the formation of the paramagnetic FeGe (B20) phase with an average crystallite size of about 15 nm. In the case of the Fe₆₂Ge₃₈, the ferromagnetic Fe₅Ge₃ (β) phase with a Curie temperature of about 430 K was obtained. The average crystallite size was about 9 nm. The average hyperfine magnetic field of about 16 T allowed it to determine that more than four germanium atoms exist in the nearest environment of the ⁵⁷Fe isotopes in the Fe₅Ge₃ phase.     

Formation of WC/Ni hard alloy coating by laser cladding of W/C/Ni pure element powder blend

WC/Ni coating was formed by laser cladding of a W/C/Ni powder blend. The formed WC crystals have rectangular or quadrangle cross-section shapes with size of 2–30 μm. Step, twist and cross growth morphologies of WC formation were observed. The coating contains WC, CW_3, WNi, FeW₃C, Fe₆W₆C, W₃O, W, C, and (Fe,Ni) phases.     

Laser Dressing of Metal Bonded Diamond Wheel

In this study, a laser beam is used as a non-contact thermal dressing tool for a bronze bonded diamond wheel. The pulsed-Nd:YAG laser beam is irradiated on the wheel surface and the bond material partially removed by laser irradiation only. In order to efficiently remove the bond material, it is necessary to direct an air jet on the spot irradiated by the laser so as to blow away the molten binder before it solidifies again. Less damage of diamond particles such as micro-cracks or graphitization occurs. In grinding with a laser-dressed wheel, the grinding forces are almost the same as those for a conventionally dressed wheel. Consequently, effective laser dressing can be expected with the associated dressing conditions.     

Mapping and Modelling Single Scan Track Formation in Direct Metal Selective Laser Melting

When a laser beam scans the surface of a metallic powder bed, the resulting track may be continuous with a crescent shape cross-section, continuous with an elliptical section, discontinuously irregularly broken, discontinuously balled or only partially melted. This paper reports experimental observations of what CO₂laser powers and scan speeds lead to what type of track, for M2 and H13 tools steels and 314S stainless steel powder beds. It also presents measurements of bed physical properties relevant to predicting the behaviour and the results of modelling that agree with the experiments. The results are placed in the broader context of selective laser melting build strategies     

镁合金表面激光电弧复合熔覆 5556 铝合金工艺研究

铝合金熔覆是轻量化镁合金表面涂层防护的重要方法。 本研究使用 AZ80A 镁合金作为基材, 使用 5556 铝 合金作为熔覆合金, 并使用激光电弧复合熔覆进行了铝合金熔覆层制备。 对熔覆层组织进行了分析, 重点研究了 激光摆动对熔覆层品质的影响。 结果表明, 当激光无摆动时, 熔覆层宽度有限, 无法正常形成各道次熔覆层的有 效搭接, 且缺陷较多。 在增加激光摆幅的情况下, 激光加热能量会更均匀地在镁合金基材表面分散, 有效增加了 熔宽, 提升了各道次熔覆层的搭接率, 促进内部缺陷更少、 品质更高的连续熔覆层的形成。     

Effect of laser fluences on the structure of carbon nitride films deposited by direct current plasma assisted pulsed laser ablation

Carbon nitride films were deposited by direct current plasma assisted pulsed laser ablation of a graphite target under a nitrogen atmosphere at room temperature. The surface morphology, composition and bonding structure of the deposited films were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, Raman, and X-ray photoelectron spectroscopy (XPS). The effect of laser fluences in the range 0.5–3 J/cm² on the surface morphology, composition and bonding structure of the carbon nitride films were systematically studied. As laser fluence is increased, AFM results show a great decrease in the surface roughness of carbon nitride films. FTIR and XPS results indicate an increase in the N/C ratio and the content of N atoms bonded to sp³ C, as well as a decrease in the content of H atoms and the content of N atoms boned to sp² C in the deposited films, and Raman spectra indicate an increase in the content of disordered sp² C atoms and the sp² cluster size. The increase in the film density and the decrease in the particle fraction contribute to the decrease of surface roughness with increasing laser fluence.     

Cr3Si／Crl3Ni5Si2金属间化合物合金组织与高温滑动磨损性能的研究

利用水冷铜模激光熔炼炉制得了由初生枝晶Cr3Si和枝晶间Cr3Si／Crl3Ni5Si2共晶组成的金属间化合物合金。利用OM，SEM，TEM，EDS和XRD分析了该金属间化合物的显微组织，在400℃，500℃和600℃条件下测试了其耐磨性能。结果表明，由于Cr3Si和Crl3NisSi2硬度高、原子键合力强、组织细小、均匀，在高温滑动磨损条件下具有优良的耐磨性能。