The influence of microstructure of weld metal on near-threshold crack growth behavior under the condition of low and high stress ratio has not been deeply understood. Therefore, experiments were carried out to study the influence of microstructure on the near-threshold fatigue crack growth behavior of 18Ni maraging steel and weld. Microstructure characteristics of base metal and weld metal were analyzed by optical microscope and scanning electron microscope. Results show that the segregation of elements such as Mo, Ti, and Ni leads to the formation of massive reversed austenite phases in the weld interdendritic region and correspondingly reduces the content of these elements in martensite matrix of weld metal, thereby reducing the amount of N 3 (Mo, Ti) in the weld matrix, leading to decrease of microhardness and tensile strength of weld metal compared to that of base metal. Fatigue tests demonstrate that when the stress ratio is 0.1 and fatigue crack growth rate is less than 10 −5 mm/cycle, roughness-induced crack closure effect has a great influence on crack growth behavior of base metal. The near-threshold crack growth rate of weld metal is lower than that of base metal under the stress ratio of 0.9, which can be attributed to the larger average size of martensite blocks and lower density of high-angle boundaries in weld metal than in base metal.

Dendritic growth is regarded as the intrinsic cause of failure for the lithium metal rechargeable batteries, which blame on the uneven lithium-ion flux induced by the fragile native solid electrolyte interface (SEI) film. Herein, a functional SEI film is composed of BaTiO3 (BTO) dipole in polyacrylonitrile (PAN) matrix, to regulate lithiumion flux through piezoelectric effect. It is found that, piezoelectric effect of the poled BTO film will induce a reversed local electric field on the dendrites bulge, thus reducing the aggregation of lithium-ion flow and slowing down dendrite growth. Moreover, the PAN matrix of the BTO film exhibited outstanding mechanical property of toughness and long fatigue lifespan, buffering volume change of lithium metal electrode during the plating/striping process. Under the effect of the poled BTO film, the lithium electrode achieved a flatter and smoother surface than that of native SEI film even after depositing a large area capacity of 10 mA h cm(-2). Consequently, The Li||Poled-BTO-Cu half-cell delivered 94% coulombic efficiency over 180 cycles. Furthermore, the Poled-BTO-Li||FeLiPO4 could maintain the capacity at 110 mA h g(-1) after 350 cycles.

对高氧TC4/TC17钛合金线性摩擦焊接头进行热处理,研究了不同热处理温度对异质钛合金线性摩擦焊接头显微组织及力学性能的影响.结果表明:异质钛合金线性摩擦焊接头焊缝区在TC17侧形成亚稳定β相,在高氧TC4侧形成针状马氏体相.经过热处理后,板条状α相在晶界处析出,针状α相在晶粒内部析出,并且残余α相在保温过程中发生分解,随着热处理温度的升高,析出相逐渐长大.接头焊缝及热力影响区显微硬度在热处理后显著增加.裂纹尖端张开位移(Crack tip opening displacement,CTOD)试验结果表明:接头断裂韧性薄弱区域在焊缝区及TC17侧热力影响区,热处理温度的升高可以明显提高接头薄弱区域的断裂韧性.

The safety risks brought by dendrite growth and volume changes keep investors away from commercial application, even lithium-metal material owns high energy density and low potential. The development of artificial solid electrolyte interphase (SEI) could not only solve the problems of inhomogeneity and fragility of native SEI film but also block electrochemical corrosion during long-term rest and inhibit the notorious dendrite growth. Herein, a hybrid SEI film composed of a metal Cr and fast ion conductor, LiF, is in situ generated for the lithium-metal electrode. Based on the unique property of metal Cr of high elastic modulus, anticorrosion, and especially no alloy phase with lithium, the hybrid SEI film supported by a Cr framework exhibited high mechanical strength and stability, even in a high-current-density and large area capacity plating-stripping process. The galvanic corrosion test results showed that the corrosion current of a Cr-LiF hybrid SEI film-coated lithium-metal electrode decreased to 15 nA cm(-2), only 1/15 of the bare lithium anode with native SEI. An enhanced electrochemical performance was achieved in terms of long cyclic stability at a large area capacity of 5 mA h cm(-2) in symmetric cells and high capacity retention in Cr-LiF-Li parallel to LiFePO4 full cells such as similar to 96.6% over 1000 cycles at 1C and similar to 90% over 600 cycles at 5C. Considering the moderately fabricated strategy, multiple stable mechanisms, and outstanding electrochemical performances, it is reasonable to apply this hybrid artificial SEI vastly in metal lithium batteries.

TC17 titanium alloy which usually used on the fan and compressor disk were selected. Microstructure and mechanical property of joint were investigated. Microstructure character of different part of joint was analyzed also. Results showed that the joints included three zones, base metal（BM）, thermal mechanical affected zone（TMAZ） and weld zone（WZ）. The microstructure of joint middle part was equiaxial grains, but the bottom part was the elongated grains. Dynamic recrystallation happened at the weld zone. Tensile test result showed that joint tensile strength equal to that of the TC17 base metal. The average hardness value of the HAZ was 486 HV which was higher than that in the BM and WZ.

本文以Φ25 mm的GH4169实心棒为母材展开连续驱动旋转摩擦焊实验,在缩短量5 mm、焊接压力200 MPa、转速500～2500 r/min条件下,结合高速摄像机、红外热成像仪获得缩短速度演变及界面温度,通过光镜、扫描电镜、EBSD手段表征接头形貌演变,利用Matlab表征界面产热分布,揭示飞边成形机理.结果表明,GH4169旋转摩擦焊飞边随转速增大,依次呈现为光滑、表面弧纹、开裂形貌.800 r/min是一个临界转速判据,当转速小于800 r/min时,飞边呈光滑形貌;当转速介于800～1500 r/min时,飞边出现弧纹;当转速不低于1500 r/min时,飞边显著开裂.光滑形貌对应于较慢的飞边生长速度和较长的生长时间,飞边金属在变形、挤出界面的同时,有充分的时间再结晶软化,使表面流铺光滑;弧纹和开裂形貌对应于飞边在快速和较短时间内生长,再结晶来不及完成而发生加工硬化开裂.不同的飞边形貌,其形成机理不同:光滑形貌是塑性环(塑化金属)在界面中径到边缘处(0.43R～R)形核,随后铺展并挤出界面发生飞边连续生长现象,即飞边是塑化金属均匀流铺、挤出的结果;弧纹和开裂形貌对应于塑性环形核在界面内侧(0～0.43R),在界面压力的作用下被封闭在界面内部无法挤出,其飞边的形成,是界面持续摩擦使温度达到焊接温度后的变形挤出结果,即飞边是焊接后期界面金属快速镦粗变形形成的.不同的飞边形貌,对接头的静载拉伸强度分布影响不大,但影响到接头外缘延伸率.光滑、弧纹、开裂形貌,分别对应于接头外缘延伸率17％、9％、6％,相应的接头延伸率不均匀性从8％上升至50％、66％.

Inconel718 superalloy components were fabricated by a modified wire and arc additive manufacturing method which named ultra-high frequency pulsed gas tungsten arc welding (UHFP-GTAW) and conventional pulsed gas tungsten arc welding (CP-GTAW), respectively. The UHFP-GTAW and CP-GTAW components were both divided into two sets of specimens, and one of the two sets was prepared with solution and aging heat treatment, then the microstructure and mechanical properties were investigated. Results showed that the ultra-high frequency pulsed arc could effectively refine the morphology of precipitation strengthening phases and the grain size of matrix. The amount of Laves phase in UHFP-GTAW specimens was apparently reduced compared with CP-GTAW specimens. The reduction of area and elongation of UHFP-GTAW specimens got significantly enhanced while the tensile strength was just slightly decreased. (C) 2019 Elsevier B.V. All rights reserved.

采用响应面法对超高频电弧增材制造工艺(UHFP-GTAW)进行了优化.通过建立函数关系得到了焊缝尺寸关于焊接电流、送丝速度及焊接速度的多元二次回归模型,并运用方差分析验证了回归模型的可靠性.设置优化条件选取了相应的焊接参数,并将焊缝尺寸的预测结果与试验结果进行了对比.结果 表明,模型预测尺寸与实际试验测得的焊缝尺寸误差分别为焊缝宽度5.4％和焊层高度6.6％.对沉积成形的GH4169高温合金薄壁构件分别进行了水平方向和垂直方向的拉伸力学性能测试,其强度极限分别达到1130.93和1126.04 MPa,断后伸长率分别为18.1％和16.56％,断面收缩率分别达到20.6％和20.2％.

对TC17钛合金平板的氩弧焊焊接和焊后热处理过程进行了数值模拟,模型中考虑材料相变和蠕变,计算得到焊接和热处理过程中的温度场演变情况和热处理前后残余应力分布规律.结果 表明,由于存在较大的热输入,焊后产生了较大的残余应力,焊缝附近的HAZ区域纵向残余拉应力达到了650MPa左右,热处理后降低至160MPa左右.采用小孔法和X射线衍射仪测量了试件的残余应力,模拟计算得到的残余应力值与小孔法测试结果符合性较好.

立足航空发动机整体叶盘叶片发生损伤后采用线性摩擦焊进行修复的背景需求,针对航空发动机常用的TC17钛合金,开展激光成形制备一侧焊接台后再线性摩擦焊的典型接头组织分析、力学性能测试以及断口分析,重点分析了接头中激光沉积区组织在线性摩擦焊前后演变特征及与力学性能影响关系,结果表明,缩短量的大小决定了接头中含有的激光成形区组织多少,参与焊接过程的激光成形沉积区组织发生了明显的再结晶,原始的粗大晶粒破碎,晶粒内部析出细小 α 相,三种典型接头的拉伸性能均与母材相当,当焊缝中挤出去除沉积区组织时,接头高周疲劳强度可达到母材的90％ 以上.

采用超高频脉冲电弧增材工艺成形了GH4169高温合金薄壁件,并制定了两种热处理制度.试样分为3组:未热处理组、固溶+时效组和均匀化+时效组,并对电解腐蚀后的显微组织进行了对比和分析.结果表明,未经热处理的组织主要为粗大枝晶,晶间有较多的Laves相,在超高频电弧的作用下,其组织比常规脉冲电弧沉积成形得到的组织尺寸更小;固溶+时效处理后的组织,γ基体上分布着大量片状δ相、γ″相和一定量的γ′相,残留有少量Laves相;均匀化+时效后的组织,δ相基本消失,基体上分布有大量颗粒状的γ″相和γ′相,及少量的小块状Laves相和碳化物.

文中针对航空发动机风扇及压气机盘TC17钛合金材料,开展了接头组织分析、拉伸性能测试及硬度测试,分析了接头不同部位组织特征及形成原因.结果表明,接头明显分为母材区(BM)、热力影响区(TMAZ)和焊合区(WZ),焊接接头中部热力影响区的组织表现为等轴晶粒,而靠近焊缝边缘处热力影响区的晶粒表现为沿着受力方向被拉长,焊合区发生了动态再结晶;接头的拉伸性能与母材相当;接头热力影响区的硬度高于母材和焊合区,平均硬度为486 HV.

针对热处理前后TC17(α+β)/TC17(β)钛合金线性摩擦焊接头组织和性能进行了对比分析.结果表明,焊态时焊缝区组织发生动态回复和再结晶,两侧的热力影响区组织均被不同程度地拉长,热处理后焊缝中的亚稳相分解析出弥散的α和β相,TC17(α+β)侧热力影响区的初生α相有所长大.焊态接头焊缝区显微硬度比母材低,接头的抗拉强度和屈服强度略低于母材,分别达到母材的91.9％,96.2％,接头拉伸性能试件断裂位置均在焊缝区;经过热处理,母材显微硬度未发生明显变化,焊缝区显微硬度显著提高,接头抗拉强度和屈服强度达到与母材相当,与焊态相比分别提高11.9％,8.2％,接头拉伸性能试件断于母材区.

TC17 titanium alloy sheet is welded with tungsten inert gas arc welding (TIG) and electron beam welding (EBW),and tensile tests are carried out.Based on tensile test result and fracture morphology,relationship between mechanical properties with microstructure of welded joint is analyzed.The research results show,when TC17 alloy is heated by TIG arc,grains in the weld bead and heat affected zone (HAZ) are badly coarsening.The heat affected zone of EBW is relatively narrow,and there is no coarse grain zone.Tensile strength of two welding methods are both strong as the base metal and the relative elongation is deceased,mainly because of the microstructure change of the heat affected zone and the weld.Compared with EBW,the micro structure of TIG joint is more coarse.

文中针对航空发动机涡轮盘的典型材料DD6单晶和FGH96粉末合金材料，开展了异种材料线性摩擦焊工艺研究。研究了DD6／FGH96的可焊性，并对DD6／FGH96线性摩擦焊接头进行了组织观察和力学性能测试。结果表明，焊接后FGH96侧组织有明显变形区，而DD6侧组织变形不明显。两种材料焊缝区的γ′相均发生了溶解，而且尺寸也发生变化。拉伸测试结果表明，断裂均发生在DD6单晶侧，接头抗拉强度可与DD6单晶母材相当。

为解决摩擦焊中的产热问题,引入了摩擦阻抗的概念,并将其中的摩擦阻抗划分为滑动摩擦阻抗和粘着摩擦阻抗.结合旋转摩擦焊、搅拌摩擦焊相关研究,从塑性环(或塑化区)的萌生、生长,以及搅拌摩擦焊的周期性现象切入,给出了两种摩擦焊过程中不同的摩擦阻抗演变机制,努力回答了摩擦产热与变形产热作用时空及贡献大小等长时间困扰学术界的问题.

航空发动机按用途分为军用航空发动机和民用航空发动机.军用航空发动机是决定现代战争胜负的重要因素,并对国民经济和科技发展有着巨大的带动和促进作用,其发展水平是一个国家综合国力、工业基础和科技水平的集中体现,是国家安全的重要战略保障.

In order to study the effect of the ac-tive lfux using before welding and the heat treatment after welding on the microstructure and property of TC17 TIG weld joint, the tensile test and hardness test for the weld joint under different welding parameters are carried out in this study. The optical microscope (OM) and the scanning electron microscope (SEM) are used to observe the micro-structure and the fracture surface of the tensile test. The results show that the using of the active lfux could prevent the weld joint from the air hole defect, and after which, the heat input, the grain growth trend of the heat affected zone (HAZ) and the asymmetric for the grain size of the HAZ are decreased. Elements of Sn and Zr diffuse equably under the heat treatment process and weld joint is mark-edly strengthened. For the TIG weld joint of TC17 plates, the excellent microstructure and properties can be obtained under both using active lfux before welding and heat treat-ment after welding.

2011年是苏联亡党亡国20周年。20年前,苏联放弃了社会主义发展道路,改行西方的多党制、议会制和自由市场经济模式。20年后,俄罗斯收获了什么？本专题研究报告是六集版电视片《苏联亡党亡国20年祭——俄罗斯人在诉说》的解说词。俄罗斯人的诉说为我们进一步客观认识并正确评价苏联解体事件提供了较为生动的教材,对广大群众特别是青少年增强中国特色社会主义信念、广大党员特别是党员领导干部坚定共产主义理想,必将起到有益的作用。

The TIG welding method, iflled with TA2 welding wire, is used to research the microstructure and mechanical property of the weld joint. The orthogonal experiment between coating active lfux before welding and heat treatment after welding is carried out to investigate the inlfuence of the common treatment way for the weld-ing process on the properties of the weld joint. Results show that, the weld joint of TC17 titanium alloy has the obvious areas, named weld zone (WZ), fusion line and the heat affected zone (HAZ). The microstructure of the WZ has a character of columnar crystals and the air holes are observed in this zone. The microstructure of the HAZ is relatively large and the softening of the weld joint is obvi-ously compared with the base metal. The tensile intensity of the weld joints after welding reaches 85% of the base metal, and this value could be more than 90% after heat treatment. The weld joints after heat treatment have good tensile property and creep deformation at high temperature, which shows that the TC17 titanium alloy has relatively good weld ability.