Pr激光表面合金化对Ti－6A1－4V组织热稳定性的影响

采用激光Ｐｒ合金化处理，研究了Ｔｉ－６Ａ１－４Ｖ稀土合金化快速凝固组织对热稳定性的影响。结果表明，Ｔｉ－６Ａ１－４Ｖ激光表面Ｐｒ合金化可提高其在７００℃以下的热稳定性，这是由于快速凝固过程获得的组织在高温下具有良好的抗粗化能力。ＴＥＭ分析表明，经Ｐｒ合金化的钛合金表层内形成一种含Ｐｒ的有序固溶体相，该相具有六方结构，ａ＝０．３９１４ｎｍ，ｃ＝０．６５９２ｎｍ，ｃ／ａ＝１．６８４，呈椭圆或圆形颗粒状，分布于初生β柱晶的亚胞胞壁，尺寸约０．１～０．４μｍ。在退火过程中还形成一种析出相，分布于位错线及小角晶界上，尺寸为１０～２０ｎｍ，分析了这两种析出相对组织热稳定性的积极作用。     

快速凝固金属粉末的工业化前景

本文综合评述了快速凝固工艺的技术特点以及快速凝固金属粉末的组织变化;并介绍了快速凝固粉末的压结方法和这类合金的应用。认为快速凝固金属粉末具有广泛的工业化前景,并将促进粉末冶金技术及合金化理论的发展。     

Zr-4合金激光表面Nb合金化层厚度与组织研究

研究了预涂铌的Zr-4合金经激光表面合金化（LSA）后的合金化层厚度、组织、和显微硬度，并分析了产生变化的机理。由于激光参数不同，合金化后含铌层的厚度在210～360μm之间，合金化层距表面100gm深度处铌含量在1．84～2．67wt％之间。合金化层组织为树枝晶，随着冷却速度的增加，枝晶间距变小；合金化层的显微硬度随冷却速度的增加而增加，最大达到了430HV。     

基于有限元的激光熔覆凝固过程分析

针对激光熔覆过程中温度变化对其凝固组织的影响,讨论了温度梯度G与冷却速度(即降温阶段的温度变化率)对凝固组织的影响,利用形状控制因子K分析了激光熔覆过程的凝固行为。分析结果表明:在热源中心的正下方晶粒是沿基体垂直方向析出的;冷却速度有细化晶粒的作用,冷却速度越大,晶粒越细小;熔覆材料或基材达到熔点的时间与达到最大冷却速度时间的先后顺序对其凝固组织形态有重要影响,若冷却速度先达到最大值,其组织呈胞状晶粒,否则,其组织呈柱形树枝晶。K在80×106～120×106℃.s时,凝固组织为密布排列且粒径较大的胞状晶粒;当K大于200×106℃.s时,凝固组织为柱形树枝晶。     

TC4钛合金激光熔覆熔池凝固传热研究

基于有限元法对单道单层激光熔池的凝固过程进行数值模拟,得到熔覆过程中激光熔池的温度场分布及温度梯度分布等数据信息,结合测温实验,分析了激光熔池在凝固过程中的热行为,阐述了激光工艺参数对熔池凝固传热过程的影响。结果表明:在激光单道熔覆过程中,熔池前端热量集中、熔深较大,尾部热量传递迅速、熔深较小。温度梯度在熔池前端最大值变化范围是3.04～3.89×10~6℃/m~(-1)。激光功率对熔池热传递的影响效应大于扫描速度影响效应的规律。模拟和实验结果吻合。     

光制造科学与技术的现状和展望

光制造是通过光与物质的相互作用,实现材料成形与改性的过程。其典型工具是激光。由于激光在能量、时间、空间方面的可选择范围很宽,可形成超快、超强、超短等极端物理条件,其制造过程所产生的物理化学效应、加工机理有许多不同于传统制造的独特之处,形成以超高加热速度、远离平衡态快速凝固、非接触式等为典型特征的加工方式,由此产生了一批新技术、一批新产品,使一批产品高性能化,形成了相应的高新技术产业群。概述光制造特别是激光制造技术的发展历史、现状与未来发展趋势,提出未来5～10年光制造技术基础研究领域可能存在的研究热点。     

亚快速凝固过程中瞬态界面传热的研究进展

在亚快速凝固过程中,基体与熔体间的界面传热直接影响着熔体凝固过程以及凝固坯壳的组织形貌和表面质量,而瞬态界面传热又是其中的关键问题。重点从瞬态界面传热的研究方法、影响瞬态界面热流的因素、瞬态界面热流对凝固组织的影响等三个方面综述了目前国内外瞬态界面传热的研究进展,并提出目前研究中存在的问题及今后的研究方向。     

45钢激光表面合金化层性能研究

探讨了４５钢上Ｆｅ基、Ｓｔｅｌｌｉｔｅ１２激光表面合金化层的组织和性能,分析了合金层与基体之间的显微组织、成分分布,测试了合金层的显微硬度、耐磨性和耐蚀性。试验结果表明,激光表面合金化是提高材料表面性能的一种有效方法。     

激光制造技术的应用与展望

激光制造技术是一种具有巨大发展潜力的高柔性、绿色制造技术.阐述了目前激光制造技术在不同制造领域、不同工艺范围的应用现状,包括激光焊接、激光熔覆及激光表面合金化、激光淬火、激光表面改性、激光切割、激光快速成形、激光打孔和激光纳米制造,并展望了激光制造技术未来的研究及发展趋势.     

NiTi形状记忆合金激光焊接的研究进展

NiTi形状记忆合金因具有良好的形状记忆效应、超弹性、耐蚀性及生物相容性等被应用于生物医疗、航空航天及汽车等领域。激光焊接作为材料连接领域的重要技术之一,在NiTi形状记忆合金上的应用也受到了广泛关注。详细总结及分析国内外研究工作中关于NiTi形状记忆合金激光焊接接头的显微组织、力学性能、耐蚀性及生物相容性等方面的研究进展,同时分析如何提升NiTi形状记忆合金激光焊接质量的措施与机理。激光焊接过程中焊缝处镍元素的蒸发及热影响区内含镍金属间化合物的析出是导致焊接接头质量降低的根本原因,尽管通过工艺控制、焊缝合金化或焊后热处理等可提高焊接接头质量,但从目前结果来看仍有进一步提升的空间和需求。最后,结合现有研究进展及课题组的实际工作,给出NiTi形状记忆合金激光焊接未来可能的研究方向,旨在为后续的研究提供参考与借鉴。     

Influence of Rapidly Solidified Structures on Wear Behavior of Ti-6AI-4V Laser Alloyed with TiC

In this paper the influence of rapidly solidified structures on the wear behavior of Ti-6Al-4V laser alloyed with TiC is studied by using an unlubricated sliding wear test. The results show that laser surface alloying with TiC can significantly increase wear resistance of Ti-6Al-4V. The wear of Ti-6Al-4V is characterized by adhesive de-lamination and melting showing a severe wear mechanism, while after alloying with TiC, it is changed into a mild wear mechanism characterized by a smooth, worn surface. This is attributed to directional fast-growing dendrites capped by a TiN/TiC film with high hardness and framed α marlensites obtained in rapid solidification.     

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part II—simulation results and experimental validation

As the mathematical model has been developed in part I, the simulation results of the transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 aluminum alloy and the experimental validation are presented in this paper. Modeling results showed that the solute concentration in the solidified region continuously increases during the solidification process. As the temperature is lower than the coherent temperature (i.e., the temperature at which the coherent mushy zone is just formed), the strains accumulated in the coherent mushy zone increase with the increasing solid fraction. The amount of strain in the mushy zone is primarily determined by the life (i.e., time span) of the coherent mushy zone, which is determined by the solidification range and solidification time. The increased solidification range and consequently solidification time extend the life of the coherent mushy zone, which increases the amount of strain and thus increases the likelihood of solidification cracking. The modeling results are in agreement with the experimental results. Both the experimental and modeling results exhibited that solidification cracking is prone to occurring near the top surface and middle part of the weld bead and an increase of laser power leads to the higher cracking susceptibility.     

Abrasive wear study of white cast iron with different solidification rates

The abrasive wear resistance of white cast iron was studied. The iron was solidified using two solidification rates of 1.5 and 15 °C/s. Mass loss was evaluated with tests of the type pin on abrasive disc using alumina of different sizes. Two matrices were tested: one predominantly austenitic and the other predominantly martensitic, containing M₃C carbides. Samples with cooling rate of 15 °C/s showed higher hardness and more refined microstructure compared with those solidified at 1.5 °C/s. During the test, the movement of successive abrasives gave rise to the strain hardening of the austenite phase, leading to the attainment of similar levels of surface hardness, which explains why the wear rate showed no difference compared to the austenite samples with different solidification rates. For the austenitic matrix the wear rate seems to depend on the hardness of the worn surface and not on the hardness of the material without deformation. The austenitic samples showed cracking and fracture of M₃C carbides. For the predominantly martensitic matrix, the wear rate was higher at the solidification rate of 1.5 °C/s, for grain size of 66 and 93 μm. Higher abrasive sizes were found to produce greater penetration and strain hardening of austenitic matrices. However, martensitic iron produces more microcutting, increasing the wear rate of the material. The analysis of the worn surface by scanning electron microscopy indicated abrasive wear mechanisms such as: microcutting, microfatigue and microploughing. Yet, for the iron of austenitic matrix, the microploughing mechanism was more severe.     

微细光成型固化工艺参数优化

为了分析紫外光对液态光敏树脂进行曝光固化成型过程中工艺参数对固化物的形状和精度的影响,根据自行研制的实验系统的大量数据,对线形固化中的主要工艺参数进行了分析和优化。结果表明,在单层液态树脂膜厚30 μm,曝光光束功率0.15 μW,扫描速度15 μm/s以及工作距650 μm时能够得到具有较高精度线宽和线高的固化直线段,利用优化的工艺参数,成功实现了三维微小实体结构的成型制造。     

Micro-stereolithography photopolymer solidification patterns for various laser beam exposure conditions

Micro-stereolithography is a novel micro-manufacturing process that fabricates 3D microstructures by solidifying the photopolymer using a UV laser in a layer-by-layer fashion. In this paper, variation in the photopolymer solidification pattern due to the scanning pattern and pitch of a focused laser beam was investigated experimentally. Also, experiments were conducted to determine the effects of the layer thickness on the solidification width and depth in multi-layer solidification. The experimental results were compared to numerical simulations. The results showed that a zigzag-shaped scanning pattern was faster and more stable than a crank-shaped pattern. It was also determined that the scanning pitch should be selected according to solidification depth and width for a given scanning pattern, and that the layer thickness has little effect on the solidification depth. Based on the results, several microstructures were successfully fabricated, such as a micro-tube with a helical separation wall and a microlink.Nomenclature P_L The power of the laser beam - The wavelength of the laser beam - f The focal length of the focusing lens - z The depth from the surface of photopolymer - V_S The scanning feed of the laser beam - W₀(z) The Gaussian half-width of the focused laser beam at a given depth z - E_C The critical exposure of the photopolymer - D_P The penetration depth of the photopolymer - W_{0 min} The Gaussian half-width at the focal point - R The Gaussian half-width of the laser beam that passes into the focusing lens - w The scanning width of the laser beam - L The solidified width of the photopolymer - h The solidified depth of the photopolymer - D₁ The layer thickness - D₂ The total solidified depth in a multi-layer solidification     

Wear Reduction of Borosilicate Glass Microballs Using Vapor-Phase Lubrication With n-Pentanol

The effect of n-pentanol vapor-phase lubrication on the wear mechanism of borosilicate glass was investigated. Glass microballs with a diameter of ～60 μm were slid against a silicon wafer under a normal load of 100 μN up to a sliding distance of ～210 km. It was shown that wear volume of the microball could be reduced by ～18 times using n-pentanol vapor-phase lubrication. The wear mechanism was assessed using 3D laser microscopy and scanning electron microscopy. Abrasion was identified as the main mechanism of wear for the borosilicate glass under n-pentanol vapor-phase lubrication condition. In addition, despite the fact that lubrication was supplied to the sliding interface as a vapor, it was sufficient to prevent agglomeration of wear debris, which aided in decreasing abrasion.     

Numerical modeling on the formation process of keyhole-induced porosity for laser welding steel with T-joint

A mathematical model of laser welding steel with a T-joint was developed in this paper to investigate the formation process of keyhole-induced porosity, helping to understand the mechanism of porosity formation in laser welding steels with heavy section. Solidification model and adiabatic bubble model were coupled in this model, which could more approximately reflect the formation process of bubble and its evolution into porosity. The volume-of-fluid (VOF) method was taken to track free surfaces of keyhole and porosity. The numerical results showed that the unstable keyhole during the laser welding process induced the collapse of keyhole and then resulted in bubbles in the molten pool. These bubbles moved following with the fluid flow in the molten pool, where some bubbles could escape out of molten pool under the competition of flow and solidification speed. But some bubbles captured by a solidified wall during the migration process in the molten pool would evolve into porosities. It was also found that some bubbles formed adjacent to a fusion line were easier to be captured by a solidification surface, which could give explanation for some porosities occurring close to the fusion line. A good agreement of simulation and experimental results proved the reliability of this mathematical model, while the mechanism of porosity formation was better clarified with this model.     

Microstructure and tribological properties of laser clad γ/Cr7C3/TiC composite coatings on γ-TiAl intermetallic alloy

In order to improve the wear resistance of the γ-TiAl intermetallic alloy, microstructure, room- and high-temperature (600 °C) wear behaviors of laser clad γ/Cr₇C₃/TiC composite coatings with different constitution of NiCr–Cr₃C₂ precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr₇C₃ and TiC carbides and the inter-primary γ/Cr₇C₃ eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equilibrium solidified reinforced Cr₇C₃ and TiC carbides and the positive contribution of the relatively ductile and tough γ/Cr₇C₃ eutectics matrix and their stability under high-temperature exposure.     

锰硼奥氏体基高铬铸铁的组织结构及抗磨性研究

研究了四种不同含B量的Fe-Cr-Mn-C-B系铸造合金的铸态组织结构及摩擦磨损特性。结果表明：硼碳化物体积分数随B含量增加而增大，并可按等量原子比估算。由于含B合金基体表面更易摩擦诱发马氏体相变，且产生表面细晶强化作用，显著提高了滑动磨损的抗磨性。含硼0．3％时，滑动磨损的抗磨性是25Cr马氏体基合金的4倍，是Mnl3铸钢的7．6倍。