电流辅助微成形技术研究进展

高强难变形金属材料微成形中普遍存在成形温度高、表面氧化严重、模具寿命低等问题,迫切需要发展提高难变形材料微成形潜力的新原理、新方法和新工艺。电流辅助微成形技术可以明显改善材料的塑性流动能力、优化微观组织、改善表面质量、提升构件综合力学性能,在突破高强难变形材料制造瓶颈方面具有巨大潜力。基于此,从电流诱发的非热电致塑性效应(电子风)、焦耳热效应和次生效应(裂纹愈合、局部电势)等方面综合评述了电致塑性效应的物理机制,分析了电流激励下材料成形性和应力降等力学性能的响应规律,并从电流对材料回复、再结晶及相变等微观组织的影响方面探讨了电致塑性效应的微观作用机理,进而讨论了近年发展的一些电流辅助微成形工艺,总结并提出了电流辅助微成形技术在理论和工艺方面面临的挑战。

纳米多层金属复合材料研究进展

向金属中加入纤维、颗粒、晶须等增强体是提高金属复合材料力学性能的重要途径。而现代工业的不断发展对材料的多功能性提出了更高的要求。为改善材料的综合性能,保证其在高温、辐照等极端条件下的使用,研究人员设计了由纳米级交替层组成的材料体系——纳米多层金属复合材料。由于其具有极高的界面密度,可以有效地阻碍位错移动从而强化材料,同时促进了辐照缺陷的吸收,有效减轻金属的辐照损伤,在快堆、聚变堆等先进核反应堆中具有重要的应用前景。近年来,纳米多层金属复合材料在国内外得到了广泛而深入的研究,在制备技术、结构表征和综合性能等研究方面取得了长足的进步。以Cu/Nb纳米多层复合材料为例,综述了其制备技术、变形行为及热稳定性、抗辐照性、导电性等综合性能的研究进展,并探讨了纳米多层金属复合材料的发展趋势及应用前景。

特种能场微成形技术研究进展

随着微成形加工尺度范围的不断延伸,单纯依靠模具施加载荷(力场)的微成形技术难以突破成形尺度极限,因此迫切需要发展塑性微成形新原理、新方法和新工艺。针对微成形尺度效应这一基本科学问题,将电场、电磁场和超声波等特种能场应用到微成形技术中,利用特种能场与材料相互作用产生的物理效应,突破微成形尺度极限并扩大可加工材料的范围,从而实现跨尺度、多材料和可控微成形。特种能场微成形技术将极大地促进微成形技术的发展和应用,成为微/纳制造技术领域一个重要研究方向。

Investigation of FE Model Size Definition for Surface Coating Application

An efficient prediction mechanical performance of coating structures has been a constant concern since the dawn of surface engineering. However, predictive models presented by initial research are normally based on traditional solid mechanics, and thus cannot predict coating performance accurately. Also, the high computational costs that originate from the exclusive structure of surface coating systems （a big difference in the order of coating and substrate） are not well addressed by these models. To fill the needs for accurate prediction and low computational costs, a multi-axial continuum damage mechanics （CDM）-based constitutive model is introduced for the investigation of the load bearing capacity and fracture properties of coatings. Material parameters within the proposed constitutive model are determined for a typical coating （TIN） and substrate （Cu） system. An efficient numerical subroutine is developed to implement the determined constitutive model into the commercial FE solver, ABAQUS, through the user-defined subroutine, VUMAT. By changing the geometrical sizes of FE models, a series of computations are carried out to investigate （1） loading features, （2） stress distributions, and （3） failure features of the coating system. The results show that there is a critical displacement corresponding to each FE model size, and only if the applied normal loading displacement is smaller than the critical displacement, a reasonable prediction can be achieved. Finally, a 3D map of the critical displacement is generated to provide guidance for users to determine an FE model with suitable geometrical size for surface coating simulations. This paper presents an effective modelling approach for the prediction of mechanical performance of surface coatings.

Effect of Ultrasonic Vibration on Deformation in Micro-blanking Process with Copper Foil

Effect of ultrasonic vibration on deformation in micro-blanking was investigated with copper foils of different grain sizes using a developed device. It is found that maximum shearing strength is decreased by ultrasonic vibration, and this effect becomes bigger for coarse grain than that for fine grain, which can be attributed to acoustic softening effect considering the absorbed acoustic energy. Surface roughness R_a of smooth zone decreases for the polishing effect of vibration at the lateral contact surface. When ultrasonic vibration is applied, the sheared deformation area becomes relatively narrow, and it leads to the reduction of radius of rollover. The analysis of cross section in sheared deformation area shows that the crack initiation is inhabited for the existence of acoustic softening, and the proportion of smooth zone is increased. Also, angle of crack propagation becomes smaller because of periodic strain, and the angle of facture surface is decreased. As a result, the quality of micro-sheet parts is improved by applying ultrasonic vibration.

Quasi Ellipsoid Gear Surface Reconstruction Based on Meshless Local Petrov-Galerkin Method and Transmission Characteristic

Special transmission 3D model simulation must be based on surface discretization and reconstruction, but special transmission usually has complicated tooth shape and movement, so present software can＇t provide technical support for special transmission 3D model simulation. Currently, theoretical calculation and experimental method are difficult to exactly solve special transmission contact analysis problem. How to reduce calculation and computer memories consume and meet calculation precision is key to resolve special transmission contact analysis problem. According to 3D model simulation and surface reconstruction of quasi ellipsoid gear is difficulty, this paper employes meshless local Petrov-Galerkin （MLPG） method. In order to reduce calculation and computer memories consume, we disperse tooth mesh into finite points--sparseness points cloud or grid mesh, and then we do interpolation reconstruction in some necessary place of the 3D surface model during analysis. Moving least square method （MLSM） is employed for tooth mesh interpolation reconstruction, there are some advantages to do interpolation by means of MLSM, such as high precision, good flexibility and no require of tooth mesh discretization into units. We input the quasi ellipsoid gear reconstruction model into simulation software, we complete tooth meshing simulation. Simulation transmission ratio during meshing period was obtained, compared with theoretical transmission ratio, the result inosculate preferably. The method using curve reconstruction realizes surface reconstruction, reduce simulation calculation enormously, so special gears simulation can be realized by minitype computer. The method provides a novel solution for special transmission 3D model simulation analysis and contact analysis.

激光清洗技术研究进展及挑战(特邀)

开展激光高效清洗基础理论及装备的研究是对《中国制造2025》纲要的具体落实,符合我国可持续发展战略,有利于提高航空航天、轨道交通、海洋船舶等装备的自动化程度,对于我国产业结构的升级与优化具有重要意义。尽管国外发达国家在激光清洗的基础理论、工艺探索、工程应用方面开展了大量的工作,但仍普遍存在构件清洗效率低、耦合机制不清晰、评价标准和在线监测技术有待完善等问题。针对我国航天、高铁、海洋等领域对激光清洗的重大需求,以航天新一代固液冲压发动机的TA15钛合金进气道、高铁车体特征件和转向架零部件、海洋船舶制造中的舱口盖等大型复杂构件为研究对象,介绍了激光清洗机制及工艺、清洗过程中多元参数的在线监测、清洗智能装备技术等方面的研究进展,以期为我国未来智能激光制造的可持续发展提供一定参考。

激光抛光技术研究进展与发展趋势

近年来,制造业进入了新的发展时期,对表面抛光技术提出了新的要求,激光抛光技术的快速发展为表面抛光智能化高效化提供了新的途径。激光抛光技术具有无污染、应用广、抛光质量稳定和易实现自动化等优点,是一种极具发展前景的工业抛光技术。但是目前激光抛光技术还不够成熟,仍有一些技术难点亟待解决。从激光抛光机制、激光抛光工艺和激光抛光新技术等方面梳理了近年来激光抛光技术的发展现状,阐述了激光类型、材料特性、工艺参数、抛光机制和抛光质量等多个维度的相互关系,总结了激光抛光技术需要解决的问题,并浅析了激光抛光技术未来的发展趋势。

铝合金微型热管分流挤压模具变形分析与优化研究

研究铝合金微型热管这类微型复杂空心挤压型材极易产生内腔偏心缺陷的问题,提出相应的挤压模具的结构设计原则。基于Altair Inspire Extrude Metal有限元分析软件,分析挤压比、焊合室高度、模芯间距和工作带长度对模芯变形的影响规律。模拟结果表明,焊合室高度和模芯间距对模芯变形的影响比较显著,而挤压比和工作带长度影响微弱。当焊合室高度提高至某一阈值时,模芯的最大变形量随着焊合室高度增加。模芯间距存在最优值,偏离该值会促进模芯变形。挤压试验结果表明,在较优的模具结构参数下获得壁厚尺寸精度±0.04mm的微型热管型材,对应的主要模具结构参数为挤压比137、模芯间距28 mm、焊合室高度8 mm和工作带长度3 mm。

Enhancement in boiling heat transfer performance using reduced graphene oxide coating with controllable components and porous structures

Enhancement in boiling heat transfer performance is significant for addressing thermal management bottlenecks of advanced electronic systems.Reduced graphene oxides(rGO)are regarded as promising candidates for thermal management due to their excellent thermal properties,chemical stability and adjustable wettability.In this study,rGO coatings with micron pores and controllable oxygen contents are prepared on Al substrate via cathodic electrophoretic deposition and subsequent thermal annealing,leading to enhanced pool boiling performance.The heat transfer coefficient for Al/rGO450is 37.2 kW m-2K-1,which is increased by 112.6%compared with bare Al,also outperformed previously reported Al based substrates.It is assumed that the hydrophilic and aerophobic r GO coatings effectively promote the liquid infiltration and bubble departure during pool boiling process.Importantly,repeatability tests indicate the durable stability of vertically oriented rGO nanosheets.Reverse nonequilibrium molecular dynamics simulation indicates that the interfacial transmission coefficients of Al/rGO increase after thermal annealing,indicative of the enhanced heat transfer performance of heterogeneous interface.Our study opens a new avenue for endowing metal substrates with high pool boiling performance using porous carbon coating nanoengineering strategy with controllable morphology and components.

TA15钛合金氧化膜激光清洗温度场有限元模拟

激光清洗是一种利用短脉冲高功率密度激光辐照清洗对象,通过激光和清洗对象发生复杂的物理化学作用,实现污染物被去除的非接触式清洗方式.激光清洗机制十分复杂,主要包括光致分解、光致剥离和光致振动,均与激光清洗过程的温度场分布规律密切相关.本文采用Comsol Multiphysics商业模拟软件,建立了TA15钛合金氧化膜激光清洗有限元仿真模型,分析了光斑形状、激光能量与加载方式、脉冲宽度等对钛合金氧化膜激光清洗过程温度场变化的影响规律.结果表明,在毫秒脉冲激光作用下基材损伤严重,脉冲宽度越短表面热扩散越小,方形平顶光斑较高斯光斑加热更均匀,矩形脉冲较高斯光斑维持高温时间短,基材不易损伤.当方形平顶微秒脉冲激光以矩形加载方式时,钛合金氧化膜激光清洗效果最佳.

TA15钛合金齿轮结构电流辅助微成形工艺研究

针对钛合金室温塑性差、高温成形模具易损坏、成形精度差等问题,提出了TA15钛合金微齿轮结构电流辅助微成形工艺。利用有限元模拟和实验相结合的方法,分析了浮动成形和分流孔直径对微齿轮电流辅助成形载荷和流动行为的影响规律。结果表明浮动成形降低了微齿轮的成形载荷并有利于齿形下端角的填充,中空分流时分流孔直径为2.3~2.5 mm成形载荷和坯料填充流动最佳。对微齿轮结构进行显微组织和成形性能分析,结果显示,齿形填充完整度较好,金属流线沿轮廓分布,齿面力学性能分布均匀,等轴组织基本被保持。

超细晶镁合金电流辅助微拉伸变形行为研究

针对传统粗晶镁合金材料塑性差、成形精度低的问题,提出了超细晶镁合金电流辅助微成形新方法。利用高压扭转技术制备了平均晶粒尺寸约110 nm的超细晶AZ31镁合金,分别对粗晶和超细晶镁合金材料进行了电流辅助微拉伸变形行为研究,发现电流辅助下材料的流动应力明显降低,且相同条件下超细晶镁合金的抗拉强度较低,而伸长率较高。粗晶试样和超细晶试样的断口形貌明显不同,粗晶镁合金的变形不均匀,韧性断裂后产生局部熔断;超细晶镁合金变形均匀,从试样外表面形成裂纹后产生整体熔断。在此基础上,绘制了超细晶镁合金电流辅助微成形热加工图,结果表明,超细晶镁合金功率耗散效率更高,成形性能明显优于粗晶镁合金。

0.2%氢对Ti-22Al-25Nb合金O相转变和B2相再结晶的影响

通过对Ti-22Al-25Nb合金置氢,研究氢对Ti-22Al-25Nb合金O转变及B2再结晶过程的影响。结果表明,在添加质量分数0.2%的氢后Ti-22Al-25Nb合金的热处理过程中,相变过程加快,相变点降低。并且氢促进B2相再结晶过程,960℃时的晶粒尺寸从135μm细化到60μm。在升温过程中氢促进强化相O相分解为B2相,并促进α2相从颗粒状转变为条状。在750℃保温时氢促进O相在晶界处优先析出并迅速长大,氢加快了B2→O相的转变过程。

TiAl基合金在置氢退火过程中γ相120°<111>孪晶界形成机制研究

利用金相显微镜、扫描电镜、EBSD技术、透射电镜和X射线衍射研究了铸态和锻态Ti-46Al-2V-1Cr-0.3Ni合金退火过程中氢对γ相120°<111>孪晶界的影响规律。结果表明,氢可以促进铸态和锻态合金γ相的静态再结晶,并且再结晶程度随氢含量的增加而增大;大量再结晶晶粒具有120°<111>孪晶界,并揭示了120°<111>孪晶界含量与氢含量的关系。氢致120°<111>孪晶界增多的原因是氢减弱了γ相的弹性各向异性。

Improvement of multi-functional properties by fabricating micro-pillar arrays structures on zirconium alloy surface

Although using the microstructure of a surface to enhance specific functions has immense applicability in numerous fields,few studies have been conducted on the multi-functional properties of nuclear fuel elements in harsh environments.In this study,surfaces with zirconium alloy micro-pillar arrays were prepared using micro-milling and ultraviolet nanosecond laser technology,and their functional properties such as the wettability,structural stability,and corrosion resistance were investigated.It was found that the geometric dimension of the micro-pillar arrays prepared using these two methods could meet the design requirements,but the micro-milling process had the best dimensional accuracy.Micro-nano multi-scale structures were obtained by laser ablation.However,these multi-scale structures exhibited weak structural stability,and the nanostructures were easily corroded.By contrast,the micro-pillar arrays manufactured using micro-milling were confirmed to have better structural stability and corrosion resistance.On one hand,the area mass loss of the micro-milled structure was lower than that of a flat surface after experiencing high-pressure fluid scouring at 8 and 38 m/s.On the other hand,the oxidation weight gain of the surface with the micro-milled structure was lower than that of a flat surface,and the oxide film was 22.5% thinner after 100 days of deionized water corrosion at 360℃ and 18.7 MPa.

Mechanism and morphology evolution of the O phase transformation in Ti-22Al-25Nb alloy

The phase transformation and microstructure in Ti-22Al-25Nb alloy are extremely complex.In this work,the morphology evolution of the O phase during the heating and cooling process was investigated by electron backscatter diffraction(EBSD)and first-principles calculations.The results show that the O→α_(2)phase transformation process during the heating process is as follows:spheroidization of the O phase occurs first,then theα_(2)phase nucleates in the spheroidized O phase,grows and replaces the O phase,completing the O→α_(2)phase transformation.In the meanwhile,the diffusion of Nb from Nb-poor O to Nb-rich B2 phases is a back-diffusion process.According to first-principles calculations,the driving force of the O→α_(2)phase transformation is the difference in the free energies of formation for the two phases(0.09 eV/atom).When the Nb content is greater than 15.625%,the lattice distortion of theα_(2)phase sharply increases,and the distortion energy drives the back-diffusion of Nb.During the cooling process,theα_(2)→O phase transformation is difficult and slow due to the difficult diffusion of Nb from the B2 toα_(2)phases.When holding for 60 min at 960℃,the coarseα_(2)phase gradually transforms to the O phase from the margin to the inside,forming a dispersed mixed structure of the O andα_(2)phases.During the B2→O transformation,the nucleation of the O phase induces a high stress region,in the range of approximately 200 nm.