发展中的电弧等离子体温度场诊断技术

综述了几种电弧等离子体温度场的诊断技术,阐述了光谱多线解析法、多通道辐射高温计法、散斑照相法的测量原理和光路设计,分析比较了光谱多线解析法、多通道辐射高温计法、散斑照相法等方法的优缺点.提出了发展测量方法稳定可靠,测量精度高,实现电弧燃烧的实时、在线测量技术的必要性.     

不同基板预热温度对激光金属沉积成形过程温度场的影响

为降低成形过程的热应力,抑制成形过程裂缝的产生,减小成形过程试样和基板的翘曲变形,激光金属沉积成形往往需要进行基板预热,因此研究不同基板预热温度对激光金属沉积成形过程温度场的影响具有非常重要的意义．根据有限元分析中的“单元生死”技术,利用APDL编程建立了基板预热对激光金属沉积成形过程温度场影响的三维多道多层数值模拟模型,详细分析了基板未预热和分别预热到200,300,400,500,600 ℃时对沉积成形过程温度场和温度梯度的影响．通过中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,在与模拟过程相同的参数下,利用镍基合金粉末在基板未预热和分别预热到300,400,500,560 ℃时进行了成形试验,试验结果跟数值模拟结果吻合较好．     

Using optical vortex to control the chirality of twisted metal nanostructures

We discovered for the first time that light can twist metal to control the chirality of metal nanostructures (hereafter, chiral metal nanoneedles). The helicity of optical vortices is transferred to the constituent elements of the irradiated material (mostly melted material), resulting in the formation of chiral metal nanoneedles. The chirality of these nanoneedles could be controlled by just changing the sign of the helicity of the optical vortex. The tip curvature of these chiral nanoneedles was measured to be <40 nm, which is less than 1/25th of the laser wavelength (1064 nm). Such chiral metal nanoneedles will enable us to selectively distinguish the chirality and optical activity of molecules and chemical composites on a nanoscale and they will provide chiral selectivity for nanoscale imaging systems (e.g., atomic force microscopes), chemical reactions on plasmonic nanostructures, and planar metamaterials.     

Steady temperature field in the elements of optical systems

We study an approximate method for the analytic determination of steady temperature fields in the elements of optical systems. The method assumed can be used to study temperature fields of other objects with a curvilinear boundary.     

The use of laser interference methods for acoustic field diagnostics

The limits of applicability of different schemes of experimental equipment and methods of processing the dynamic signal, which adapt laser interference technologies for acoustic-field diagnostics in a liquid, depending on the extent of the medium and the frequency and intensity of the acoustic field are determined. The results of measurements of the intensity of an acoustic field are presented and their errors are estimated. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 55–59, January, 2008.     

Joining ceramic to metal using a powder metallurgy method for high temperature applications

Fecralloy was successfully joined to calcia stabilised zirconia (CSZ) using a mixture of Fe, Cr and Al powders as a brazing filler and a screen printing and powder metallurgy method. The joining process was achieved at 1000 °C for 5 h in vacuum. During the joining process the filler wetted the surfaces of the CSZ and the Fercalloy foil, and formed a Fe(Cr, Al) alloy. The joint produced using the filler of (Fe-30Cr-5Al)-0.06 (Y₂O₃) (wt.%) showed good thermal stability and good thermal cycling oxidation resistance at temperatures up to 850 °C in air, even though the joint contained some porosity.     

Determining of laser surface treatment parameters used for light metal alloying with ceramic powders

There are presented in this paper the investigation results of microstructure as well hardness investigation of the surface layer of cast aluminium alloys in as‐cast state and after laser surface treatment using a high power diode laser (HPDL) with Al₂O₃ ceramic powder. The purpose of this work was to determine the proper laser treatment conditions for surface treatment of the investigated alloys and to describe the structural changes occurred in the surface layer after laser treatment. For investigation of the obtained structure there was used light as well scanning and transmission electron microscopy. The morphology and size of the ceramic powder particles as well the structure of the remelted aluminium surface layer was possible to determine. After the laser surface treatment carried out on the aluminium cast alloys there are visible structural changes concerning the microstructure as well as distribution and morphology of the fed particles occurred in the sample surface. Concerning the laser treatment conditions for surface hardening also the laser power and ceramic powder feed rate was studied. The structure of the surface laser tray changes in a way, that there are zones detected like the remelting zone and the heat influence zone. This investigation with appliance of a high power diode laser for Al alloys makes it possible to obtain or develop an interesting technology very attractive for different industry branches.     

Method to determine the optical properties of turbid media

A novel method to determine the optical properties, namely, absorption coefficient, scattering coefficient, and anisotropy factor of turbid solutions, single constituent or multiconstituent, is presented. Turbid solutions of milk, ink, and a mixture of both were illuminated by a laser beam and measurements were carried out in scattered light. Experimental results were matched to the corresponding results of Monte Carlo simulation to obtain the optical properties of the turbid media.     

Simulation of temperature distribution in single metallic powder layer for laser micro-sintering

Simulation of temperature distribution in single metallic powder layer for laser micro-sintering (LMS) using finite element analysis (FEA) has been proposed, taking into account the adoption of ANSYS μMKS system of units, the transition from powder to solid and the utilization of moving laser beam power with a Gaussian distribution. By exploiting these characteristics a more accurate model could be achieved. The effects of the process parameters, such as laser beam diameter, laser power and laser scan speed on the temperature distribution and molten pool dimensions have been preliminarily investigated. It is shown that temperature increases with the laser power and decreases with the scan speed monotonously. For the laser beam diameter during single-track, the maximum temperature of the powder bed increases with the decrease in the laser beam diameter, but far from the center of the laser beam area, the temperature increases with the laser beam diameter. The molten pool dimensions in LMS are much less than that in classical selective laser sintering (SLS) process. Both molten pool length and width decrease with the laser beam diameter and the laser scan speed, but increase with the laser power. The molten pool length is always larger than the molten pool width. Furthermore, the center of molten pool is slightly shifted for the laser multi-track.     

Calculation of the temperature field in laser irradiation of a laminar composite

Using the solution of a boundary-value problem of nonstationary heat conduction, we suggest an approach to determining the temperature in laser irradiation of the surface of a two-period laminar semiinfinite body.     

A novel approach to determine high temperature wettability and interfacial reactions in liquid metal/solid interface

In many technical processes, high temperature wetting of a liquid metal phase on a solid substrate occurs via an extensive chemical reaction and the formation of a new solid compound at the interface. For instance, good adhesion of the zinc coating to the steel surface is one of the most important requirements that the hot-dip galvanizing process has to fulfill. Good adhesion directly depends on the formation of a defect-free Fe₂Al₅ inhibition layer at the interface. The complex surface chemistry of oxides on the steel surface which is a result of segregation and selective oxidation upon recrystallization annealing significantly influences the kinetics of the correlated reactive wetting. This article presents the development of a novel advanced technique for the investigation of high temperature wetting process up to a temperature of 1100 K and provides first new insights in the mechanisms of the reactive wetting process in presence of oxides on the surface. The method is based on the sessile drop method with an additional spinning technique to get rid off the liquid metal phase at any chosen wetting time, thusly opening the way to access the interfacial reaction layer directly. The presented work focuses on model alloys of interest which are mainly relevant to the industrial steel grades. Emphasis is put both on the wettability of liquid Zn and on the interfacial reactions during reactive wetting process. Insights into such reactive phenomena are fundamental demand to improve the hot-dip galvanizability of advanced high strength steel grades.     

激光多道熔覆温度场的计算与分析

以45钢板材上熔覆三道Ni60自熔性合金粉末为例,对送粉式激光熔覆多道搭接情况下的温度场进行计算,得到了熔覆过程中基体上各点的温度变化规律及固定时刻熔覆层的温度分布曲线,分析了多道熔覆时温度场的变化规律.计算结果表明基体表面激光经过的中心点温度变化呈锯齿状,而离激光光源较远的基体上各点温度达到最大值存在一个滞后时间.多道搭接情况下,熔池内的最高温度,后两道熔覆层要略高于第一道熔覆层,且对于后两道熔覆层起熔时刻和熔覆结束时刻熔池内的最高温度明显高于熔池内的平均最高温度.     

High-temperature ellipsometer system to determine the optical properties of materials

A high-temperature ellipsometer system was developed that permits determination of the optical properties of solid and liquid bulk samples for temperatures as high as 2300 °C. The angles of incidence may be varied from 40° to 50°. The system was tested with a silicon wafer sample in inert gas environments of helium, argon, and nitrogen. In addition the possible sources of error in the inferred refractive index, especially in the context of Faraday effects, were assessed.     

Evaluation of speed of melt evacuation in the technology of laser cutting of metals by the optical correlation method

A multichannel pyrometer was used to determine the speed of melt evacuation from an irradiated zone in laser-cutting technology with auxiliary gas. Local pulsations of brightness temperature were measured in four areas of ～0.1 mm in diameter each spaced by 0.6 mm along the cutting front. A method is described for measuring the displacement rate of temperature heterogeneities during melt motion by mutual correlations of brightness-temperature pulsations calculated in neighboring areas. The necessity of preliminary frequency filtration of the measurement data may be due to propagation of a nonlinear wave in the melt on a metal surface under the impact of a gas jet.     

The effects of solid-state phase transformation upon stress evolution in laser metal powder deposition

To investigate the influences of solid-state phase transformation on stress evolution during multi-pass laser metal powder deposition (LMPD) process, a 3D finite-element (FE) thermo-mechanical model considering phase transformation has been established. The influences of phase transformation such as mechanical properties changes, volume change and transformation induced plasticity (TRIP) are taken into account. Furthermore, the influences of high magnitude stress upon martensitic transformation characteristic temperature and TRIP are considered. The temperature and history (microstructure) dependent material properties used in the present research are obtained by experiments. The stress field during LMPD process is analyzed with and without solid-state phase transformation, respectively. Stress measurement of X-ray diffraction (XRD) method is applied to deposited samples, and the measuring data are compared with the computational predictions. The results show that phase transformation has a dominant effect on the stress evolution, longitudinal residual stresses significantly reduced as a result of solid-state phase transformation. In addition, the effect of stresses on martensitic transformation temperature is important for accurate prediction of residual stresses (stress state after cooling of the clad to ambient temperature). Residual stresses are lower when the phase transformation temperature is reduced.     

Study on the interaction between the shape and the temperature field of the melt in the electromagnetic shaping process

Based on analyses for the electromagnetic pressure on the melt and the heat induced in the melt, the ratio of heat to pressure Q₀/P_m is defined, to give the relationship between Q₀/P_m and the thickness a, the electromagnetic parameter (μγ) of the melt and the electric current frequency f under the electromagnetic confinement and shaping process. If Q₀/P_m is large, any adjustment to the melt shape will easily cause a variation of the temperature in the melt. In this situation, there appears to be a more sensitive interaction between the shape and the temperature field and a more narrow adjustment range for the process. Experiments on thin plate samples with a cross-section of 6 mm×18 mm are done with two kinds of induction coils. The results show that when a coil with a trumpet inside wall is used and the positions of the melt top and the S/L interface are properly selected, the melt periphery is nearly vertical and the temperature gradient ahead of the S/L interface is high. Under these conditions, a more stable and wider coupling between the shape and the temperature field is continuously maintained and samples with a smooth surface and unidirectional crystals are successfully obtained.     

Nonsteady thermocapillary mass transfer in the laser alloying of metals

This article examines convective mass transfer of an impurity in a shallow bath of molten metal with allowance for the motion of the fusion front during the laser alloying of metals.Notation r, z, cylindrical coordinates - t time - T_i temperature of the liquid (i=1) and solid (i=2) phases - q(r) absorbed energy flux - k concentration factor - T_m melting point - L heat of fusion - density - _i, _i thermal conductivity and diffusivity - T₀ initial temperature - , absolute and kinematic viscosities of the melt - v_r, v_z projections of the melt velocity on the coordinate axes r and z - p pressure - surface tension Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 799–805, May, 1989.     

Study on the interaction between the shape and the temperature field of the melt in the electromagnetic shaping process

Based on analyses for the electromagnetic pressure on the melt and the heat induced in the melt, the ratio of heat to pressure Q₀/P_m is defined, to give the relationship between Q_o/P_m and the thickness a, the electromagnetic parameter (μγ) of the melt and the electric current frequency/under the electromagnetic confinement and shaping process. If Q_o/P_m is large, any adjustment to the melt shape will easily cause a variation of the temperature in the melt. In this situation, there appears to be a more sensitive interaction between the shape and the temperature field and a more narrow adjustment range for the process. Experiments on thin plate samples with a cross-section of 6 mm × 18 mm are done with two kinds of induction coils. The results show that when a coil with a trumpet inside wall is used and the positions of the melt top and the S/L interface are properly selected, the melt periphery is nearly vertical and the temperature gradient ahead of the S/L interface is high. Under these conditions, a more stable and wider coupling between the shape and the temperature field is continuously maintained and samples with a smooth surface and unidirectional crystals are successfully obtained.