非晶态Ni-W-P镀层退火晶化和激光晶化组织结构的演变

用XRD定量分析法并结合扫描电镜形貌观察,研究化学沉积高磷(13.3%)含量的Ni-W-P镀层在不同热处理条件下的晶化程度、晶粒尺寸及晶格应变等组织结构的演变规律。结果表明:高磷非晶态镀层在退火晶化过程中,Ni3P相的体积分数始终高于Ni相的,700℃时,两相的体积分数之差显著增大,镀层仍有残存的非晶相;在400~500℃之间形成的Ni3P的晶粒尺寸大于Ni的;温度为500~700℃时,Ni相的尺寸大于Ni3P的,但均未超过纳米级。镀层晶格应变表现为随退火温度的升高而降低,镀态时晶格应变最大。激光晶化处理的非晶态Ni-W-P镀层的显微结构特征介于400~500℃之间退火的镀层晶化特征。随扫描速度增加,不仅Ni3P晶粒尺寸增大,而且两相的尺寸差变大。     

激光柔性加工系统中光纤传能特性研究

介绍了光纤传能在激光柔性加工系统中的应用价值.针对Nd:YAG脉冲激光,试验研究了多模石英光纤传能特性,包括光纤输出光束空间特性和光纤传输高功率激光容量;分析了激光注入条件和光纤弯曲对光纤传能的影响.     

Collective dynamics in nanostructured polycrystalline ferroelectric thin films using local time-resolved measurements and switching spectroscopy

Grain-to-grain long-range interactions and the ensuing collective dynamics in the domain behavior of nanostructured polycrystalline Pb(Zr,Ti)O₃ ferroelectric thin films have been investigated. To identify the key factors and interactions controlling local polarization dynamics we utilize a synergistic approach based on focused ion beam (FIB) milled damage-free nanostructures to isolate single grains and grain clusters, time-resolved piezoresponse force microscopy and switching spectroscopy PFM (SSPFM) (PFM) to address polarization dynamics within individual grains, and finite-element simulations to quantify the local ferroelectric interactions and hence assess the weight of several possible switching mechanisms. The experiments find that of the three possible switching mechanisms, namely direct electromechanical coupling, local built-in electric field and strain, and grain boundary electrostatic charges, the last one is the dominant mechanism. Although finite-element simulations find that direct electromechanical coupling and local built-in field-induced switching are possible, calculations confirm that for the utilized material properties, the aforementioned mechanisms are energetically unfavored.     

In situ strain investigation during laser welding using digital image correlation and finite-element-based numerical simulation

In situ strain evolution during laser welding has been measured by means of digital image correlation to assess the susceptibility of an advanced high strength automotive steel to solidification cracking. A novel method realised using auxiliary illumination and optical narrow bandpass filter allowed strain measurements as close as 1.5?mm from the fusion boundary with good spatial and temporal resolution. A finite-element thermomechanical model of the welding process supports the experimentally measured transverse strain. The validated finite-element numerical model can be used to assess the local strain and associated stress conditions which influences weldability and in particular, solidification cracking.     

Characterization of microstructural changes during annealing of cold worked austenitic stainless steel using ultrasonic velocity measurements and correlation with mechanical properties

A technique that is sensitive to change in texture is more reliable than mechanical property measurements for the study of recrystallization behavior in alloys where recrystallization is coupled with precipitation. Hence, ultrasonic velocity measurements have been employed to characterize microstructural changes during annealing of cold worked Ti-modified austenitic stainless steel where precipitation of TiC is known to retard recrystallization. Mechanical property measurements, such as strength and hardness, could not distinguish the recovery and recrystallization regimes, and it was difficult to determine the exact time or temperature for onset of recrystallization. The variation of velocity with annealing time or annealing temperature exhibited a three-stage behavior. The velocity exhibited a slight increase in the recovery region followed by a sharp and continuous decrease in the recrystallization region and reached saturation on completion of recrystallization. Based on the microstructural investigations, the three stages were identified to be recovery, progress of recrystallization, and completion of recrystallization. Velocity measurements could sense the onset, progress, and completion of recrystallization more accurately compared with that of hardness and strength measurements.     

Defect evolution of nanocrystalline SnO2 thin films induced by pulsed delivery during in situ annealing

The microstructural defects of nanocrystalline SnO₂ thin films prepared by pulsed laser deposition have been investigated using transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. Defects inside nanocrystalline SnO₂ thin films could be significantly reduced by in situ annealing SnO₂ thin films at 300 °C for 2 h. High-resolution transmission electron microscopy showed that the stacking faults and twins were annihilated upon in situ annealing. In particular, the inside of the SnO₂ nanoparticles demonstrated perfect lattices free of defects after in situ annealing. Raman spectra also confirmed that the in situ annealed specimen was almost defect-free. By using in situ annealing, defect-free nanocrystalline SnO₂ thin films can be prepared in a simple and practical way, which holds the promise for applications as transparent electrodes and solid-state gas sensors.     

Pseudoelastic deformation and size effects during in situ transmission electron microscopy tensile testing of NiTi

The stress-induced B2–B19′ transformation in aged 51 at.% NiTi was investigated using in situ straining transmission electron microscopy (TEM). Increased applied strain along [1 1 0]_B2 transforms B2 into plates containing B19′ variants that are related by a (1 1 0)_B2 compound twin plane. This atypical twin plane is explained by relaxing the invariant plane constraint in the crystallographic theory of martensite (CTM) to an invariant line constraint. The relaxation is rationalized from the thin foil geometry. The relaxed CTM approach, coupled with conditions to maximize transformation strain along the loading axis and minimize elastic energy, predicts the observed twin interface, diffraction patterns, and interface with the B2 austenite. These results demonstrate subtleties in interpreting thin foil TEM results regarding martensitic transformations, and translating those results to bulk response.     

Effect of annealing and O2 pressure on structural and optical properties of pulsed laser deposited TiO2 thin films

In this paper, effect of annealing and O₂ pressure on the structural and optical properties of pulsed laser deposited thin films of TiO₂ is reported. XRD, FTIR spectra and SEM images confirm that at high annealing temperatures, the rutile phase and crystalline quality of thin films increases. Higher pressure of O₂ during deposition improves the rutile phase and favors the rod like growth of TiO₂ thin film. The red shift in photoluminescence (PL) spectra of TiO₂ thin films with annealing temperature is reported. Contact angle measurement data for the thin films reveals the hydrophobic nature of the films. The very low reflectivity (～10%) reported in this paper may be promising for anti-reflection coating applications of pulsed laser deposited TiO₂ thin films.     

Temperature control in laser brazing of a steel/aluminium assembly using thermographic measurements

One way of making car bodies lighter is to introduce some aluminium parts in place of steel. Steel and aluminium can be joined by laser braze welding. As in other types of thermal joining, inter-metallic phases may weaken the joint. In laser braze welding, these appear as a thin layer of brittle compounds at the steel/seam interface. Their formation is related to temperature. It has been shown that, if the layer is less than 10 μm thick, the joint is not compromised [Kreimeyer M., Sepold G. Laser steel joined aluminium-Hybrid structures, Proceedings of ICALEO'02, Jacksonville, USA; 2002]. Not only can temperature gradient be calculated by numerical simulation, but it is also possible to measure the surface temperature by thermography. We show here how thermography may be used to control temperature during laser braze welding.     

Detectability of corrosion damage with circumferential guided waves in reflection and transmission

There is an increasing interest in high frequency short range guided waves to screen or monitor for corrosion. This contrasts with long range guided waves (LRGWs) which screen pipes for large patches of corrosion and have been successfully used in corrosion management for the past twenty years. The fundamental setup described in this paper uses circumferential guided waves, which are excited at a single location on a pipe and travel around the pipe wall and are detected at the same location. The study uses a finite element model assisted method to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals. The setups themselves consist of either an axial array of transducers, for monitoring, or a single transducer which axially scans a pipe. Both setups have an array or scan pitch between either adjacent transducers or measurements. The detection capability of the fundamental Lamb wave modes (A0 and S0) in both reflection and transmission have been compared, as well as a hybrid shear horizontal wave setup, which uses the SH0 mode in reflection and the SH1 mode in transmission. A sensitivity analysis was conducted using two separate methods to determine the probability of detection (POD) for either the reflection or transmission signals. Both methods determine a POD for a specific defect, noise level, and array or scan pitch. Probability images are produced which map the POD for a range of defect sizes. For the parameters investigated in this study, it was found that in transmission large diameter defects have a higher detectability, whereas deep, narrow diameter defects are more detectable in reflection. A generalised overview of the sensitivity of short range guided waves is presented by combining both the reflection and transmission PODs. The data fused sensitivity of the S0 and SH hybrid modes are given as 0.6% and 0.75% cross sectional area (CSA) respectively, allowing for the comparison with LRGWs. The A0 mode was excluded from the POD analysis because it was much less sensitive than the other two modes.     

Quantitative evaluation of reheat cracking susceptibility by in situ observation and measurement using laser confocal microscope*

In the post-weld heat treatment process, the reheat cracking which might occur in the weldments of low-alloy steels has been a serious problem. So, it is considered to be important to predict the possibility of occurrence of reheat cracking in these steels. It is however recognized as a time-consuming procedure to evaluate quantitatively the susceptibility to this type of cracking. In the present study, a new quantitative evaluation method of reheat cracking susceptibility by in situ observation and measurement using a laser confocal microscope has been proposed. Through this new method, the reheat cracking susceptibility of any kind of steels can be evaluated with the same standard. Moreover, because the position of the initial crack can be focused and the critical ductility to initiate the crack is measured by in situ observation, the reheat cracking susceptibility can be evaluated using only one specimen. So the newly developed method can provide efficient quantitative assessment of the reheat cracking sensitivity with high accuracy.     

Dielectric characterization of conducting textiles using free space transmission measurements: Accuracy and methods for improvement

The dielectric behaviour of in-situ polymerized thin polypyrrole (PPy) films on synthetic textile substrates were obtained in the 1–18 GHz region using free space transmission and reflection methods. The PPy/para-toluene-2-sulphonic acid (pTSA) coated fabrics exhibited an absorption dominated total shielding effectiveness (SE) of up to −7.34 dB, which corresponds to more than 80% of incident radiation. The permittivity response is significantly influenced by the changes in ambient conditions, sample size and diffraction around the sample. Mathematical diffraction removal, time-gating tools and high gain horns were utilized to improve the permittivity response. A narrow time-gate of 0.15 ns produced accurate response for frequencies above 6.7 GHz and the high gain horns further improved the response in the 7.5–18 GHz range. Errors between calculated and measured values of reflection were most commonly within 2%, indicating good accuracy of the method.     

A study on crystallization, optical and electrical properties of the advanced ZITO thin films using co-sputtering system

Multi-functions (conductor, semiconductor and insulator) ZnInSnO (ZITO) transparent oxide thin films have been obtained by a co-sputtering system using ITO target and ZnO target with oxygen gas contents (0-8%). The ZITO film containing a small ITO content had the lowest resistivity (good electron mobility) and higher optical transmittance. In addition, the influences of thermal treatments (post-annealing and substrate temperature) on electrical properties and optical transmittance of ZITO films were studied. Photoluminescence (PL) of the ZITO film confirmed the contribution of ITO content and oxygen gas content on the photo-emission. The ZITO film with zinc atomic concentration of 58 at.% was a good candidate for TCO material (3.08 × 10⁻⁴ Ω cm). Under the substrate temperature of 100 °C or post-annealing temperature of 200 °C, the properties of ZITO film could be improved.     

5083Al/1060Al/TA1/Ni/SUS304五层爆炸复合板退火组织演化及力学性能

为改善5083Al和304不锈钢爆炸焊接质量,提升隔热效果,本研究采用1060Al、TA1和Ni作夹层材料,制备了具有热传导梯度的五层爆炸复合板。为消除爆炸焊接后的残余应力,减少绝热剪切带和微裂纹等缺陷,采用550℃×60min退火工艺对五层爆炸复合板进行退火处理,并通过SEM、EBSD和万能试验机等手段,分析研究退火对其组织演化及力学性能的影响。结果表明：五层爆炸复合板的4个焊接界面均呈波形,且在界面处存在微裂纹、孔洞、绝热剪切带和漩涡区等缺陷。经退火处理,4个焊接界面均发生不同程度的再结晶,微裂纹、绝热剪切带等缺陷得到有效改善;5083Al/1060Al/TA1界面的β相和Al-Ti金属间化合物增多,TA1/Ni界面在原TiNi₃熔化层的基础上新增TiNi熔化层和Ti₂Ni熔化层。界面抗拉剪强度均有所降低,但均仍远高于相应国标使用要求;拉脱试样在5083Al/1060Al界面断裂分离。     

Redistribution of carbon and oxygen in semicrystalline molybdenum during annealing

Conclusion An increase in the annealing temperature of deformed molybdenum containing 0.011% of interstitial elements in the 1150–1550°C interval effects a steady increase in the amount of carbon and oxygen atoms on the grain boundaries as a result of their segregation from the grain body. After annealing above 1350°C (an average grain size d30 m), the process of the outflow of interstitial elements onto the boundaries takes place incompletely, as a result of which a supersaturated solid solution is formed in the grain body. Subsequent annealing at 1150°C for 4 h leads to an additional increase in the oxygen content and to the formation of molybdenum-carbide particles on the boundaries; this causes a small decrease in the strength characteristics, and a sharp decrease in plasticity characteristics.Institute of Powder Metallurgy, Academy of Sciences of the Ukrainian SSR, E. O. Paton Institute of Electric Welding, Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 28–30, December, 1986.     

In situ thermal imaging and three-dimensional finite element modeling of tungsten carbide–cobalt during laser deposition

Laser deposition is being used for the fabrication of net shapes from a broad range of materials, including tungsten carbide–cobalt (WC–Co) cermets (composites composed of a metallic phase and a hard refractory phase). During deposition, an unusual thermal condition is created for cermets, resulting in rather complex microstructures. To provide a fundamental insight into the evolution of such microstructures, we studied the thermal behavior of WC–Co cermets during laser deposition involving complementary results from in situ high-speed thermal imaging and three-dimensional finite element modeling. The former allowed for the characterization of temperature gradients and cooling rates in the vicinity of the molten pool, whereas the latter allowed for simulation of the entire sample. By combining the two methods, a more robust analysis of the thermal behavior was achieved. The model and the imaging results correlate well with each other and with the alternating sublayers observed in the microstructure.     

Changes in the density of steel during plastic deformation and annealing

Conclusion The volumetric method was used to study the formation of microcracks during plastic deformation of annealed and normalized steel 70. It was found that the number of microcracks formed increases with the coarseness of the original structure. Defects occurring with substantial plastic deformation of annealed steel with a structure of coarse lamellar pearlite are healed by brief heating to temperatures above 1100°.Institute of Metal Physics, Academy of Sciences of the USSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 21–23, January, 1971.     

Role of side assisting gas on plasma and energy transmission during CO2 laser welding

In this paper, the effect of how the side assisting gas influences the laser-induced plasma and energy transmission in CO₂ laser welding is studied. Under different configurations of the side assisting gas, the optical emission and spectrum signals from the laser-induced plasma were obtained and compared. From signal analysis and evaluation of weld results, it shows that the application of side assisting gas greatly suppresses the laser-induced plasma and enhances the efficiency of laser energy transmission, which in turn results in a sound weld quality with full penetration. A physical model of plasma consisting of diffusive plasma and residual plasma was also proposed and validated to illustrate the role of side assisting gas. The results suggest that the diffusive plasma can be blown away by the side assisting gas. This observation provides a promising solution to increase the absorption rate and utilization efficiency of the laser energy during laser welding by diminishing the diffusive plasma through side assisting gas.     

Elucidation of the effect of welding speed on melt flows in high-brightness and high-power laser welding of stainless steel on basis of three-dimensional X-ray transmission in situ observation

This research was performed with the objective of clarifying the effect of welding speed on melt flows during melt-run welding of SUS304 stainless steel plates with a 6-kW power laser beam on the basis of three-dimensional X-ray transmission in situ observation. As welding speed increased from 25 to 250 mm/s, three kinds of welds characterized by porosity formation and no defects or underfilling due to spatters were produced. The average and the maximum values of measured melt flow velocity were 3 and 10 times higher than the welding speed, respectively. Two kinds of circulation flows at the inlet or the tip of a keyhole were confirmed to control heat transfer in a molten pool. It was found that the circulation flows were so sensitive to the welding speed that bubbles resulting in porosity or spatters were often formed. According to X-ray observation of the formation of spatters with tungsten carbide (WC) tracers, as the melt flow rose along the keyhole wall, the velocity was accelerated from 0.24–0.54 m/s near the keyhole inlet. Consequently, the melt flows made the convex surface behind the keyhole grow higher, resulting in spattering.