Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

3D FEM analysis of welding residual stress and deformation of aero-engine blisk

Aero-engine blisk welded by electron beam welding(EBW) method is a complicated structure. Fixtures were used to control the deformation of blisk during its manufacturing process. Finite element method was utilized to study the evolution of the welding residual stress and deformation of this structure. In which an attenuation function was applied to the double ellipsoid heat source model based on the characteristic of EBW, and the effects of fixtures on the welding residual stresses and deforamtion were also reserached. The simulation results showed that the temperature contour of weld cross section vertical to the weld centerline followed a “V” shape. Moreover, large welding residual stress and distortion were found in the interface between blisk and fixtures. The stress concentration was reduced sufficiently in starting and end part of weldment as the fixtures were removed after welding process, while the removing operation had almost no effects on the welding residual stress in the middle section of weld bead.     

热障涂层的CMAS腐蚀失效及对策研究综述

研制具有长寿命、高性能的热障涂层（TBCs）,是制造我国大功率航空发动机、发展新一代超音速战机的一项十分紧迫的任务。由于外来沉积物CaO-MgO-Al2O3-SiO2（CMAS）渗入涂层而导致TBCs失效的现象越来越受到人们的重视,在过去的一段时间里,很多学者对CMAS渗入后涂层的失效机理进行了大量的研究并尝试了一些缓解CMAS渗入涂层的方法。本文针对当前应用最为广泛的“层状多孔结构”的等离子喷涂涂层及“细长柱晶结构”的电子束辅助物理气相沉积涂层,系统地梳理了近年来国内外学者对TBCs在CMAS渗入条件下的失效机制及涂层缓解CMAS渗入方面的最新研究成果,为制备高性能的TBCs提供帮助。     

脉冲离子束辐照致TiD_2膜力学性能的变化

金属氢化物(MH_x)应用于反应堆中子慢化剂、激光离子源片材料、中子发生器用靶时,会经历极端非平衡束流的辐照。本工作提出利用TEMP-6型强流脉冲离子束装置产生的强流脉冲离子束(high intensity pulsed ion beam,HIPIB)辐照Ti D_2膜,评估极端束流对膜力学性能的影响因素和影响程度。采用涂层附着力自动划痕仪、维氏显微硬度计对原始和辐照后的Ti D_2膜进行测试分析。研究结果发现:多次HIPIB的辐照效应导致膜面重熔再结晶,使其内部结构趋于更加致密化和平整化,能降低材料的摩擦系数并在一定程度上提高其初始临界载荷;D的释放有助于膜面韧性、显微硬度的提高,从而减轻了其塑性形变程度。     

强流脉冲电子束作用下纯钛的微观组织结构变化及其性能研究

目的提高纯钛表面的耐腐蚀性能。方法本实验主要分两步进行,首先进行金相样品的制备,然后利用强流脉冲电子束对材料表面进行改性处理,最后利用扫描电镜(SEM)、X射线衍射仪(XRD)、硬度检测,电化学检测等检测手段进行探讨研究。结果扫描电镜分析结果表明,强流脉冲电子束处理后,样品表面出现了熔坑,并且随着脉冲次数的增加,熔坑数量逐渐减少,这主要归因于强流脉冲电子束的净化除杂作用。X射线衍射分析发现,强流脉冲电子束处理后,衍射峰出现了宽化和向高角度偏移现象,主要归因于脉冲处理后合金表面的晶粒细化和表面应力、晶格常数的降低。另外,电化学测试表明,强流脉冲电子束处理后金属表面的耐腐蚀性明显增加,自腐蚀电流密度从强流脉冲电子束处理前的27.3μA/cm~2变化到25次脉冲处理后的6.3μA/cm~2,主要归因于强流脉冲电子束的净化除杂作用以及熔坑等结构缺陷的消失。显微硬度分析发现,经过强流脉冲电子束处理后由于样品表面的残余应力和孪晶等结构缺陷的存在,样品表面硬度明显降低。结论强流脉冲电子束处理后,纯钛的耐腐蚀性能增加,晶粒细化,硬度有所降低。     

基于线阵列探测器的多角度平行投影数据及其图像重建算法

针对工业断层CT进行三维结构成像的应用需求,提出了由多角度的平行投影数据重建三维CT图像的TV-ART迭代算法的新实现方法,其中将Chambolle方法推广至三维情形并用于求解CT图像全变差(TV)最小。使用该方法进行TV求解的重建图像的质量优于基于最速下降法或共轭梯度法的TV-ART迭代算法。此外,该方法具有高度并行性,适合在GPU,FPGA等高速并行计算硬件上实现,从而可以大幅提高图像重建速度。在扫描时间相同的情况下,该方法重建的三维CT图像质量优于已有方法,特别是显著提高了CT图像的轴向分辨率。     

EB-PVD梯度热障涂层的制备及其热疲劳性能

采用ＥＢ－ＰＶＤ的方法,连续蒸发按一一分比混合的Ａｌ＋Ａ１２Ｏ３＋ＺｒＯ２混合源,在Ｎｉ基高温合金基体上制备了一种新型结构的热障涂层,ＳＥＭ和ＥＤＳ的观察、分析表明,这作层实现了由金属粘结层向陶资顶层的微观结构的梯度过渡和化学成分的连续变化。涂层的基本结构为ＮｉＣｏＣｒＡ１Ｙ／Ｎｉ３Ａｌ＋Ａ１２Ｏ３／Ａ１２Ｏ３ＺｒＯ２／ＺｒＯ２。这北度热障涂层在１０５０℃的抗高温氧化性能优于传统的二层结构的热障涂     

疲劳裂纹对悬臂梁振动特性影响的理论分析

研究了疲劳裂纹对悬臂梁的固有频率及强迫振动响应的影响,使用余弦函数描述疲劳裂纹的开合过程。计算结果表明,疲劳裂纹不仅使悬臂梁的固有频率下降,而且引起非线性强迫振动响应。     

Ultra fine finishing of diamond tools by ion beams

The principles of ion beam machining and its apparatus are described, and several examples are given of ultra fine forming or sharpening diamond tools by ion beams. Problems, such as a sub-micrometre tip radius or elliptical tips are discussed, and it is concluded that ion beam machining combined with mechanical pre-finishing can be useful for forming or sharpening diamond tools.     

射频超导腔用高纯铌材制备

采用高真空电子束炉不少于3次熔炼的方式制备了大规格高纯铌铸锭。高纯铌铸锭的纯度达到99.99%,剩余电阻率比值(residual resistivity ratio,RRR)稳定地大于300,满足了射频超导腔用高纯铌材料的要求。高纯铌铸锭的RRR值主要受H、N、O、C等间隙元素的影响,随着熔炼次数的增加,气体元素可有效去除,RRR值也稳步增长。高纯铌化学元素的检测精度不能完全与RRR值对应,应结合两参数来评价高纯铌铸锭的品质。