Ti3Al激光焊接接头EBSD试样的制备

采用电子背散射衍射(EBSD)技术研究Ti3Al基合金焊接接头的微观组织和织构对于改善焊接接头的使用性能有着重要的意义,而电子背散射衍射样品的制备质量对其成像效果有着重要影响.对比离子减薄、电解抛光和机械化学抛光3种方法制备Ti3Al基合金焊接接头EBSD试样的效果.结果表明,与其它方法相比,机械化学抛光更适合于Ti3...     

Large-scale aluminum foam plate fabricated by enhanced friction powder compaction process based on sintering and dissolution process

An enhanced friction powder compaction (FPC) process was proposed for fabricating a large plate of aluminum foam by the sintering and dissolution process. In this process, the rotating tool plunged into the die filled with a powder mixture of aluminum and NaCl during the FPC process was made to traverse perpendicularly to the direction of plunging as in the case of friction stir welding. In the enhanced FPC process, no external heat source, such as an electric furnace or a spark plasma sintering, was necessary for fabricating aluminum foam, except for the friction heat generated by traversing the rotating tool. It was found that a long plate of aluminum foam can be fabricated with a length equal to the tool traversing length. By X-ray computed tomography (CT) and scanning electron microscopy (SEM) observations of the pore structures of the fabricated aluminum foam, it was found that the entire sample had a pore structures that was similar to the NaCl morphology, regardless of the position along the traversing direction. The fabricated aluminum foam had a similar stress–strain curve to that of aluminum foam fabricated by spark plasma sintering and exhibited ductile fracture. This is considered to be attributed to the good bonding between aluminum particles in the entire sample. The fabricated aluminum foam exhibited almost the same plateau stress regardless of the position along the traversing direction.     

铸造碳化钨粉末物性对激光熔覆陶瓷颗粒增强Fe基复合材料耐磨性能的影响

为研究铸造碳化钨粉末物性对激光熔覆陶瓷颗粒增强Fe基复合材料耐磨性能的影响,将不同制备方法和粒径的铸造碳化钨粉末添加到Fe基合金粉中,在45号钢表面进行激光熔覆以获得高硬度和高耐磨的合金化层。利用金相显微镜、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、硬度计分别分析了合金化层的显微组织、物相组成以及显微硬度。利用轮式磨损试验机测试了其常温下的耐磨性能,并进行了比较。结果表明:熔覆层主要由莱氏体组成,碳化钨粉末的制备方法和粒径差异对复合材料的耐磨性能具有重要影响。等离子旋转电极雾化法制备的碳化钨粉末能起到最好的增强耐磨作用,粒径细的碳化钨粉末比粒径粗的粉末增强耐磨效果要好。     

激光冲击TC17钛合金叶片的微观组织/应力演变及缺口振动疲劳性能

目的 提高航空发动机叶片的抗疲劳性能。方法 采用高功率密度短脉冲激光冲击某型发动机TC17钛合金整体叶盘叶片模拟件,并采用飞秒激光在进气边预制缺口。通过扫描电子显微镜和透射电子显微镜表征激光冲击前后的表层微观组织。通过X射线衍射和三坐标测量仪分别测量激光冲击强化过程中的残余应力演变和宏观塑性变形,并由一阶弯曲振动疲劳对激光冲击强化效果进行评价。结果 激光冲击在TC17钛合金叶片表层诱导产生了高密度位错组织,但由于冲击次数的控制,未产生明显的晶粒细化效应。激光冲击叶盆面后,叶盆面呈现压应力状态,残余应力为330.5 MPa,叶背面呈现拉应力状态,其值为55.5 MPa。进一步激光冲击叶背面后,叶背面的拉应力转变为压应力,其值达到了267.0 MPa,叶盆面残余压应力减小,由330.5 MPa变为261.9 MPa。激光冲击叶盆面后,进气边与叶尖交点偏离初始位置0.119 1、0.129 1 mm;冲击叶背面后,位移偏离初始位置减小,分别为0.071 08、0.099 mm。激光冲击强化后,缺口振动疲劳寿命显著提升,平均循环次数由56 696周次增加到199 515周次,出现了明显的裂纹闭合效应。结论 激光冲击强化在TC17钛合金表层引入了高密度位错组织和双面贯穿式残余压应力,并将叶片宏观塑性变形控制在0.1 mm以内,在疲劳性能上获得了显著的提升。     

激光表面处理17-4PH不锈钢的电化学腐蚀行为

利用动电位极化、电化学阻抗等电化学测试技术,结合金相观察和扫描电镜(SEM)观察,系统研究了特定激光功率(1600 W)条件下激光表面强化处理工艺参数对17-4PH不锈钢在3.5% NaCl溶液中腐蚀行为的影响。结果表明：采取表面使用吸光剂X、激光扫速为6 mm/s的工艺参数处理的17-4PH不锈钢试样的耐腐蚀性能最佳。同时表明只有当吸光剂和扫描速度达到良好配合时,才能获得较为均匀的组织,从而显著提高激光表面硬化层的耐腐蚀性能。当吸光剂与扫描速度不匹配时,激光表面处理后,会产生不均匀的表面组织,材料耐蚀性能会严重下降,在腐蚀环境中使用时,易发生严重的点蚀。     

MAG焊旋转喷射过渡熔滴运动形态的相关分析

熔滴旋转喷射过渡ＭＡＧ焊是用于钢结构的一种高效焊接方法,在窄间隙焊和角焊缝时还可以克服焊接时侧壁的熔剑不良等缺陷。本文用高速摄影方法拍摄了Ａｒ＋Ｏ２保护气体时旋转喷射过渡的熔滴过渡形态,建立了液尖－液流束运动的相关分析模型,并由此分析讨论了熔滴运动的动态变化过程和旋转参数。结果表明,用本文提出的“相关分析”方法,可以确定液尖与液流束运动的主从关系。在脉冲旋转喷射过渡期间,液尖、液流束均绕焊丝轴线做     

Porous structures fabrication by continuous and pulsed laser metal deposition for biomedical applications; modelling and experimental investigation

The use of porous surface structures is gaining popularity in biomedical implant manufacture due to its ability to promote increased osseointegration and cell proliferation. Laser direct metal deposition (LDMD) is a rapid manufacturing technique capable of producing such a structure. In this work LDMD with a diode laser in continuous mode and with a CO₂ laser in pulsed modes are used to produce multi-layer porous structures. Gas-atomized Ti-6Al-4V and 316L stainless steel powders are used as the deposition material. The porous structures are compared with respect to their internal geometry, pore size, and part density using a range of techniques including micro-tomography. Results show that the two methods produce radically different internal structures, but in both cases a range of part densities can be produced by varying process parameters such as laser power and powder mass flow rate. Prudent selection of these parameters allows the interconnected pores that are considered most suitable for promoting osseointegration to be obtained. Analytical models of the processes are also developed by using Wolfram Mathematica software to solve interacting, transient heat, temperature and mass flow models. Measured and modelled results are compared and show good agreement.     

汽车稳定杆用 55Cr3弹簧钢室温旋转弯曲疲劳性能

从汽车稳定杆用钢的实际应用需求出发,采用横向轴向应变控制方法,在应变循环比 R为－1,频率 83Hz和室温环境下,测试了 55Cr3弹簧钢旋转弯曲疲劳性能,得到了试样的 S-N曲线。并通过扫描电镜观察疲劳断口,研究了 55Cr3弹簧钢旋转弯曲疲劳特性。结果显示：生产的汽车稳定杆用 55Cr3弹簧钢具有高纯净度和良好的强度与塑韧性配合,其旋转弯曲疲劳试样的疲劳极限可达 730MPa;在较高应力下,裂纹起源于试样表面因加工刀痕和擦伤等引起的缺陷,且存在多处裂纹源。     

汽车顶盖激光焊缝打磨系统的设计与应用

针对汽车顶盖激光填丝钎焊的焊缝表面存在鱼鳞纹、锯齿边等缺陷，提出一种基于自适应接触法兰、电主轴和机器人的打磨系统。通过固定在机器人末端的自适应接触法兰使打磨片以恒定压力压紧焊缝，电主轴带动打磨片高速旋转，高速旋转的打磨片磨削焊缝。介绍了该系统的硬件组成、通信架构以及打磨流程，并分析了接触法兰压力、电主轴旋转方向及转速和打磨姿势对打磨品质的影响规律。     

Functional nanostructures through nanosecond laser dewetting of thin metal films

Techniques for processing nanoscale metallic structures with spatial order and tunable physical characteristics, such as size and microstructure, are paramount to realizing applications in the areas of magnetism, optics, and sensing. This paper discusses how pulsed laser melting of ultrathin films can be a powerful but simple and cost-effective technique to fabricate functional nanostructures. Ultrathin metal films (1 nm to 1,000 nm) on inert substrates like SiO₂ are generally unstable, with their free energy resembling that of a spinodal system. Such films can spontaneously evolve into predictable nanomorphologies with well-defined length scales. This study reviews this laser-based experimental technique and provides examples of resulting robust nanostructures that can have applications in magnetism and optics.     

Laser–ultrasonic absorption measurements in low carbon steels

We have refined the contactless laser–ultrasound reverberation technique to measure ultrasonic absorption on small metallic samples. In this technique, a sample is supported by a holder which is ultrasonically decoupled from the sample. A pulsed laser is used to generate an acoustic pulse. After the pulse has mode converted and scattered sufficiently to fully insonify the sample, the decrease in the noise-like ultrasonic signal is recorded as a function of time using a laser-interferometer. A joint time–frequency analysis technique is used to extract an absorption spectrum from the signal. In this paper, the technique is demonstrated in a frequency bandwidth ranging from 1 to 7 MHz, and in a dynamic range of 0.003 to 0.3 dB μs⁻¹. Measurements made on samples of three low-carbon steel grades, namely ultra low carbon (ULC), low carbon (LC), and high strength, low-alloy steels (HSLA), clearly show that ultrasonic absorption varies with steel grade. The technique was utilized to study the effect of a magnetic field on the ultrasonic absorption of an annealed ultra low carbon steel sample. It was found that magnetoelastic effects are responsible for a large fraction of the total absorption.     

Fe---Cr---Ni---Mo---C alloys produced by laser surface alloying

Several Fe---Cr---Ni---Mo---C alloys were produced by laser alloying on plain carbon steel substrates, using the blown powder technique. It was found that a careful selection of the laser treatment parameters results in alloyed layers free of defects and with a homogeneous chemical composition. The structures were martensitic, fully austenitic and austenitic-ferritic, depending on the chemical composition. The high cooling rates were found to affect the austenitic-ferritic structures, which showed a larger quantity of δ ferrite than that predicted by the Shaeffler diagram. Surface alloys produced by laser processing, with chemical composition similar to that of conventional austenitic stainless steels, showed better pitting corrosion resistance than their bulk counterparts produced by conventional techniques, despite their higher carbon content.     

Measurement of milling tool vibrations during cutting using laser vibrometry

Spindle and tool vibration measurements are of great importance in both the development and monitoring of high-speed milling. Measurements of cutting forces and vibrations on the stationary spindle head is the most used technique today. But since the milling results depend on the relative movement between the workpiece and the tool, it is desirable to measure on the rotating tool as close to the cutters as possible. In this paper the use of laser vibrometry (LDV) for milling tool vibration measurements during cutting is demonstrated. However, laser vibrometry measurements on rotating surfaces are not in general straight forward. Crosstalk between vibration velocity components and harmonic speckle noise generated from the repeating revolution of the surface topography are problems that must be considered. In order to overcome the mentioned issues, a cylindrical casing with a highly optically smooth surface was manufactured and mounted on the tool to be measured. The spindle vibrations, radial tool misalignment, and out-of-roundness of the measured surface were filtered out from the signal; hence, the vibrations of the cutting tool were resolved. Simultaneous measurements of cutting forces and spindle head vibrations were performed and comparisons between the signals were conducted. The results showed that vibration velocities or displacements of the tool can be obtained with high temporal resolution during cutting load and therefore the approach is proven to be feasible for analysing high-frequency milling tool vibrations.     

Transformation potential predictions for the stress-induced austenite to martensite transformation in steel

The stress-induced transformation behavior of retained austenite is considered in this work. With the development of transformation-induced plasticity (TRIP) steels this deformation mode is of growing importance. Twinned martensite structures were calculated using the crystallographic theory of martensite. An available work criterion was used to predict the transformation potentials for 16 different in-plane stress states for sheet sample geometry. By rotating the twinned martensite structures over all crystallographic orientations using Euler angles, the magnitude of the transformation potential was plotted as an orientation distribution plot for comparison with typical texture components. From these data, the Brass and Copper orientation components that are typical in retained austenite such as in TRIP steels were found to have low transformation potential values. Grains aligned with these orientations would require higher stresses to transform than other orientations, and may therefore never transform. This correlates to experimental observations that heavily deformed TRIP steel contains residual retained austenite.     

光纤激光毛化机器人系统

光纤激光作为第三代激光技术的代表,具有其他激光器无可比拟的技术优越性和广阔的应用发展空间,将会逐步取代全球大部分高功率CO2激光器和绝大部分YAG激光器。利用光纤激光器的优点,集成开发了第五代全新的光纤激光机器人毛化系统,系统以光纤激光器为载体,协同机器人及其他设备来完成轧辊毛化作业。光纤激光毛化柔性工作站与传统的CO2激光毛化设备相比取得了多项重大突破,如系统采用普通机床代替昂贵的磨床实现毛化功能,不仅节约大量的设备投资费用,并大幅度提高生产效率;系统对轧辊旋转时的轴向跳动容忍度大,毛化速度大幅度提高;光纤激光毛化技术可实现毛化点形貌的任意设计以及毛化点的有序、无序排列;毛化成本大幅度降低,没有三废,是一种绿色制造技术。     

Investigations on the Influence of Liquid-Assisted Laser Ablation of NiTi Rotating Target to Improve the Formation Efficiency of Spherical Alloyed NiTi Nanoparticles

In this work, the liquid-assisted laser ablation of NiTi rotating target has been used as a promising technique for generating spherical NiTi alloy nanoparticles with higher formation efficiency. Nd: YAG nanosecond laser with three different laser wavelengths (355, 532 and 1064 nm), three different laser fluences (30, 40 and 50 J/cm²) and three different rotational speeds (10 RPM, 20 RPM and 30 RPM) of target has been used to ablate the nitinol (Ni-55%, Ti-45%) target. The influences of different laser parameters (wavelengths and fluences) and different RPMs have been studied on the size, morphology and formation of alloy nanoparticles. It has been observed that the formation efficiency is maximum (39.9 mg/h) for smaller size nanoparticle (~40 nm) at 355 nm wavelength, 50 J/cm² fluence and 10 RPM rotational speed. On the other hand, we find that the formation efficiency (10.5 mg/h) is lowest with a bigger size of nanoparticle (~110 nm) at 1064 nm wavelength, 50 J/cm² fluence and 30 RPM speed. Therefore, this is a promising technique to synthesize spherical alloy nanoparticles with higher ablation efficiency. Thus, the higher ablation of particles helps to improve the optical absorption of the colloidal solution as optical absorption has a direct relation with the particle concentration. The shape and size of particles were characterized through SEM and DLS analysis whereas the crystallinity was confirmed through TEM and XRD analysis, respectively. Moreover, the elemental analysis was done with the help of XPS and EDS and optical absorption through UV–Vis spectrum analysis.     

激光冲击工艺对钛合金疲劳寿命的影响

研究激光加工工艺对Ti6A14V航空钛合金叶片表面粗糙度和残余应力的影响，并分析影响表面质量的激光加工工艺参数；探讨表面粗糙度和表面残余应力对叶片疲劳寿命的影响。结果表明，采用激光冲击航空叶片，叶片表面残余压应力大大增强，从而使得其抗疲劳破坏能力增强，而表面粗糙度减小；在激光脉冲功率允许的范围内，选择合适的冲击参数能有效降低叶片表面粗糙度，而表面残余压应力对疲劳寿命的影响起主导作用。     

The Influence of the Laser Energy on the Thermal Diffusivity Evaluation of TBC by Laser Flash

Laser Flash is considered the standard technique for measuring the thermal diffusivity of solids. The interaction between TBC and the laser energy is studied because very low thermal effusivity and thermal diffusivity of TBC can produce very high temperature increase on the surface and temperature gradient within the sample. In such a case, microstructural modifications of TBC can be generated. In this work, such phenomena are studied experimentally on free standing TBC samples.     

Influence of a pulsed laser regime on surface finish induced by the direct metal deposition process on a Ti64 alloy

The direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allows generating a prototype or small series of near net-shape structures. Despite numerous advantages, one of the most critical issues of the technique is that produced pieces have a deleterious surface finish which requires post machining steps. Following recent investigations where the use of laser pulses instead of a continuous regime was successful to obtain smoother DMD structures, this paper relates investigations on the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titanium alloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate a specific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laser heating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsed mode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger and stable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients and Marangoni flow in the external side of the fusion zone were assumed to be the main reasons for surface finish improvement. Additional results indicate that combining the benefits from a pulsed regime and a uniform laser irradiation does not provide further reduction of surface roughness.     

Nanoscale femtosecond spectroscopy for material science and nanotechnology

The design and implementation of a novel facility to perform ultrafast spectroscopy and three-dimensional (3D) fabrication at the nanoscale is reported. Single and multiphoton femtosecond excitation coupled to a laser scanning confocal microscope and a photon counting streak camera system allows to perform photoluminescence (PL) spectroscopy with in-plane spatial resolution of the order of 100 nm and temporal resolution of ∼2 ps. The facility combines high performance imaging capabilities in 3D with high sensitivity detection system and time-resolution of the photoluminescence. Imaging and spectroscopy are performed on the same spatial position thus allowing a direct correlation of the morphological features with the spectroscopic properties. The use of a laser scanning confocal microscope gives the advantages of far-field microscopy (possible sample perturbation as in the case of near-field technique is prevented) with spatial resolution well below the diffraction limit, and fast laser scanning for fast data acquisition and lower sample photodegradation. A possible application of this optical nano-probe is in the spectroscopic investigation and imaging of the active areas of molecular electronic and optoelectronic devices, such as TFTs, LEDs and PVs cells. The morphology of active layers within working devices can be correlated to field distributions, charge flows, charge recombination and light emission. We show the potential of this novel experimental set-up for the study of organic, hybrid, biological nanostructures and nanodevices.