力学失配对电子束焊接接头疲劳裂纹扩展行为的影响

研究了高温合金电子束焊接接头区的疲劳裂纹扩展行为,深入分析了接头区力学失配对疲劳裂纹扩展方向及疲劳裂纹扩展速率的影响规律。结果表明,由于力学不均匀性的影响,电子束焊接接头的疲劳裂纹扩展具有不稳定性,位于高匹配焊接区的疲劳裂纹偏离原裂纹扩展方向,跨越焊接区与母材,呈复合型扩展;焊接区疲劳裂纹的集团使得裂纹尖端有效应力强度因子减小,因而焊缝区裂尖局部有效裂纹扩展驱动力下降,导致接头的疲劳裂纹扩展速率下     

TC4钛合金窄间隙激光填绞股焊丝焊接接头组织及性能

文中对比研究了30 mm厚TC4钛合金电子束焊接头和母材的高周疲劳性能,发现接头的高周疲劳性能与母材非常接近。在文中试验条件下,电子束焊接头在循环周次为2×10⁶时的高周疲劳强度为474 MPa,达到母材的94.2%。观察电子束焊接头和母材的高周疲劳断口形貌,发现接头和母材的疲劳源均位于试样表面。疲劳裂纹扩展区都发现疲劳辉纹,相同载荷条件下,母材高周疲劳断口中辉纹的间距较小,约为1.49 μm,电子束焊接头的相邻辉纹间距为2.14 μm。在接头和母材的疲劳瞬断裂区还发现大量韧窝,呈现出典型的韧性断裂特征。文中还对比了母材、热影响区和焊缝区的疲劳裂纹扩展速率,发现热影响区的抗疲劳裂纹扩展性能最弱。分析认为,热影响区的高硬度是导致其抗疲劳裂纹扩展性能弱于其他区域的重要原因。

     

GH625合金氩弧焊焊接接头的疲劳裂纹扩展性能

研究了钨极氩弧焊GH625高温合金焊接接头的室温疲劳裂纹扩展行为。采用金相显微镜及扫描电镜对其焊接接头的显微组织和疲劳裂纹扩展断口形貌进行观察。结果表明,GH625高温合金的钨极氩弧焊焊接接头主要是由枝晶状焊缝组织和γ奥氏体等轴晶母材组成,焊缝区析出大量的白色针状δ-Ni3Nb相和块状颗粒状Laves相;其焊接接头的显微硬度高于母材;室温下,在低ΔK区间,GH625高温合金钨极氩弧焊焊接接头的疲劳裂纹扩展速率比母材低,这是由于焊缝处硬质的析出相、二次裂纹以及扩展路径的曲折多样使得其裂纹扩展时需要消耗更多的能量;在高ΔK区间内,焊接接头疲劳裂纹扩展速率高于母材。     

6N01铝合金MIG焊接头疲劳裂纹扩展性能研究

研究了6N01铝合金MIG焊接头不同区域的疲劳裂纹扩展速率,对接头的宏观形貌、显微组织、显微硬度和疲劳断口进行了分析。结果表明,焊缝区为等轴树枝晶,接头热影响区主要由淬火区和过时效软化区组成。疲劳裂纹在焊缝中的扩展速率最高;热影响区内,应力值范围较低时,疲劳裂纹扩展速率低于母材,随着应力值范围的增加,其扩展速率高于母材。疲劳断口分析表明,裂纹在焊缝中以不规则和粗糙的脆性疲劳条纹形式扩展,而在热影响区则以塑性的疲劳条纹扩展,扩展抗力较高。     

AA6082铝合金搅拌摩擦焊接头疲劳扩展速率

研究了6082-T6铝合金搅拌摩擦焊接头不同位置的疲劳裂纹扩展速率,并分析了接头的组织及疲劳断口形貌。试验结果表明,疲劳裂纹扩展速率最快的区域为接头焊核细晶区;当裂纹在热影响区扩展时,在较小的应力强度因子范围(ΔK)条件下,裂纹的扩展速率低于其在母材中的扩展速率,伴随着ΔK的逐渐增加,裂纹的扩展速率明显加快并高于其在母材中的扩展速率。断口形貌表明,疲劳裂纹在焊核区扩展主要由脆性的准解理断裂形貌组成,扩展速率较快;而热影响区及母材区的断口形貌主要由光滑的疲劳条纹组成。     

含稀土相高温钛合金焊接接头的疲劳断裂特性

研究了Ti-60合金电子束焊接接头的显微组织及稀土相的分布特征;对焊接接头高温旋转弯曲疲劳性能进行了试验研究,讨论了影响接头疲劳性能的主要因素.焊后状态下焊缝区中存在大量的α′马氏体组织,焊缝区中的稀土相颗粒弥散分布于晶界及晶内,尺寸在100～200 nm.焊接接头具有较好的高温旋转弯曲疲劳性能,无焊接缺陷的接头均断裂在母材区,稀土相颗粒对裂纹的扩展具有阻碍作用.     

桥梁钢Q345焊接接头疲劳裂纹扩展速率研究

对桥梁用钢Q345焊接接头疲劳裂纹扩展性能进行了试验研究。测得对接接头的硬度分布,结果表明,焊接接头焊缝中心处的硬度值较低,在热影响区的重结晶区存在硬度最高点,而在部分重结晶区存在硬度最低点,硬度最低点为对接接头的薄弱区。通过疲劳裂纹扩展速率测试,得到其对接接头不同区域的疲劳裂纹扩展a-N曲线以及lg(da/dN)-lgΔK曲线。分析对比对接接头各区域的疲劳裂纹扩展速率lg(da/dN)-lgΔK曲线可知,在同一应力水平下,对接接头不同部位的疲劳裂纹扩展速率不同,热影响区的扩展速率较快,母材次之,焊缝金属最慢。并通过疲劳断口和焊接接头的显微组织,分析了其疲劳裂纹扩展速率不同的原因。     

高速列车用高强铝合金焊接接头疲劳裂纹的扩展特性

使用疲劳试验机测试A7N01铝合金焊接接头的疲劳裂纹扩展速率,采用光学显微镜对焊接接头的显微组织进行分析,使用扫描电镜对疲劳断口形貌进行研究。结果表明:母材的显微组织为时效状态的α(Al)基体与粗大一次相、弥散二次强化相以及少量的夹杂物构成的轧制状态组织;热影响区的显微组织为α(Al)基体以及少量未固溶的一次相组织,焊缝的显微组织为α(Al)基体与离异共晶组织。焊接接头的显微组织以及第二相粒子尺度不同导致了疲劳裂纹扩展特性不同。随着应力比的增加,疲劳裂纹扩展速率均呈增大趋势。裂纹尖端塑性区内的第二相粒子与基体的不协调塑性变形可促进疲劳裂纹的扩展,影响疲劳裂纹的扩展速率。     

16Mn钢埋弧焊接头疲劳裂纹扩展速率的研究

对16Mn钢双面埋弧焊CT试样的焊缝、热影响区、母材及垂直焊缝方向的疲劳裂纹扩展速率进行了研究。结果表明,焊接接头的不同部位疲劳裂纹扩展速率不同,平均应力、焊接残余应力、金相组织对疲劳裂纹的扩展速率都有一定的影响。     

A6N01-T5合金FSW和MIG焊接头疲劳裂纹扩展行为的对比

研究了6N01-T5铝合金搅拌摩擦焊(FSW)和氩弧焊(MIG)接头不同部位的疲劳裂纹扩展性能, 并对疲劳断口和接头组织进行了分析. 结果表明,对于FSW和MIG焊接头, 其裂纹扩展速率从高到低的部位依次为焊缝(核)区、热影响区和母材. 裂纹在FSW和MIG焊接头相同区域的扩展速率无明显差别, 然而裂纹在FSW接头细晶组织中开始扩展所需的门槛值ΔK要比对应的MIG焊接头高, 总体上其裂纹在FSW焊核区的抗疲劳裂纹扩展性能要优于对应的MIG焊缝区. 裂纹在FSW和MIG焊接头焊核(缝)区扩展的疲劳断口表现为脆性断裂, 而在热影响区则以规则和光滑的疲劳条纹形式扩展.     

ON FATIGUE CRACK PATH DEVIATION AT ELEVATED TEMPERATURE IN ELECTRON BEAM REPAIRED WELDMENTS OF TURBINE DISK

Fatigue crack growth behaviors in electron beam weldments of a nickel-base superalloy are. studied. The objective of this paper is to discuss effects of the inhomogeneity of mechanical performance on fatigue crack growth (FCG) rate and crack path deviation (CPD). The base metal served in a turbine disk of aerospace engine was selected to fabricate bead-on-plate weldments by using electron beam welding. Some wedge-type opening loading specimens, notched in three different zone of weld metal, HAZ and base metal, were employed and performed fatigue crack growth tests at 650℃. The results show that the fatigue crack growth of electron beam welded joints is instable due to the influence of mechanical heterogeneities. Owing to the crack deviation at the weld metal and heat-affected-zone (HAZ), the effective growth driving force at the tip of fatigue crack was reduced with the reduction of the effective stress intensity factor (SIF) which finally causes fatigue crack rate decrease. Fatigue crack was strongly affected by size and the symmetrical characteristics of the plastic zone at the crack tip, which means that the integrity of the welded structure containing the fatigue crack mainly depended on the toughness of the low strenqth zone.     

Corrosion fatigue crack propagation behavior of A7N01P-T4 aluminum alloy welded joints from high-speed train underframe after 1.8 million km operation

Using the potentiodynamic polarization analysis, the fatigue crack propagation behavior of A7N01P-T4 aluminum alloy metal inert gas welded joints cut from a high-speed train underframe after 1.8 million km operation was studied in air and in a 3.5 wt% NaCl solution. The fracture surface and crack growth path were analyzed using optical microscopy, scanning electron microscopy, and electron backscattered diffraction. The results reveal that the corrosion fatigue crack growth rate of an A7N01P-T4 welded joint in a 3.5 wt% NaCl solution is higher than that in air. Furthermore, the corrosion fatigue crack growth rate is noted to be the fastest in the heat-affected zone, followed by the base metal, whereas it is the slowest in the weld metal, which is consistent with the corrosion resistance of the A7N01P-T4 joints. The second phase is observed to exhibit a significant influence on the corrosion fatigue crack propagation path. The cracks are noted to grow toward the soft orientation and have obvious plastic deformation during the propagation process, which indicates that the anodic dissolution is the main cause of the corrosion fatigue crack growth.     

Incoloy 825镍基高温合金电子束焊工艺及接头组织与力学性能分析

采用电子束焊,对空冷器管箱Incoloy 825镍基高温合金进行对接焊试验. 通过对焊接接头的组织观察,并结合拉伸力学性能以及接头的冲击韧性等试验,分析镍基高温合金电子束焊接头的组织和力学性能. 结果表明, 采用电子束焊焊接镍基高温合金可以得到良好的焊接接头,焊缝区组织由大片等轴晶和少量柱状晶组成;焊缝区没有出现明显的元素烧损现象;焊缝、热影响区硬度达到母材硬度值;焊缝接头抗拉强度达到600 MPa,接近母材抗拉强度,接头断裂形式为韧性断裂;焊缝和热影响区的冲击吸收能量高于母材区,其中焊缝区的冲击吸收能量达到了262 J,冲击断口形貌为韧窝状.     

Fatigue properties of ferrite/bainite dual-phase X80 pipeline steel welded joints

Fatigue properties are important parameters for the safety design and security evaluation of pipelines. In this work, fatigue life and fatigue crack propagation of full-thickness X80 pipeline steel joints compared with the base metal (BM) was investigated. Full-thickness BM specimens showed superior fatigue life compared with that of welded joints. The fatigue crack initiation of full-thickness X80 welded joint specimens occurred at the outside weld toe and then grew inward until a fracture was formed. During fatigue crack growth in the heat-affected zone (HAZ), crack growth rate linearly increased with increased ΔK in each HAZ subregion. However, the change rate of fatigue crack growth rate (da/dN) differed among HAZ subregions. This difference was related to the variation in crack path and fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behaviour.     

电子束焊接对调质15CrMnMoVA高强钢组织及性能的影响

为实现高淬火倾向的航空高强钢材料的高质量接头,以15CrMnMoVA高强钢为研究对象,进行了电子束焊接工艺试验研究;针对不同结构的电子束焊接接头,分析了焊缝显微组织特征、焊接接头的显微硬度分布和力学性能,探讨了电子束焊接工艺对接头组织性能的影响。结果表明,15CrMnMoVA钢的焊缝中心形成了网篮状马氏体组织,其显微硬度为典型的马鞍形分布。不同锁底结构的电子束焊接接头的拉伸性能基本都与母材相当,但其疲劳性能差异明显,锁底长度为1.5 mm时焊接接头的疲劳性能较好。     

搅拌摩擦焊和熔化极气体保护焊6082铝合金疲劳性能分析

对10 mm厚6082-T6铝合金进行搅拌摩擦焊(FSW)和熔化极气体保护焊(MIG焊)焊接,利用疲劳性能试验机、光学显微镜、扫描电子显微镜等手段对6082铝合金FSW和MIG焊接头的疲劳力学性能、微观组织、裂纹扩展特征、疲劳断口进行了分析. 结果表明,在疲劳寿命为2×106周次时,6082铝合金母材及其FSW和MIG焊接头的名义应力分别为126.3,110.2,84.2 MPa;在高应力水平下(Δσ=160 MPa),FSW接头疲劳寿命明显大于MIG焊接头、与母材的疲劳寿命相当. MIG焊疲劳断口均位于焊趾处,焊缝内的气孔缺陷为其主要裂纹源;FSW疲劳断口大多发生在轴肩边缘. 接头的微观断口具有准解理特征,断口中存在疲劳条纹和韧窝.     

Microstructure and fatigue crack growth behaviour of electron beam welding in 30CrMnSiNi2A steel

The effects of two post-weld heat treatment processes on the microstructure and fatigue properties of the electron beam welded joints of 30CrMnSiNi2A steel were studied. Electron beam local post-weld heat treatment ( EBLPWHT) , in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were accepted. The experimental results show that, after EBLPWHT, the main microstructure of weld is changed from coarse acicular martensite into lath martensite, and base metal is changed from ferrite and perlite into upper bainite and residual austenite, however the microstructures of different zones of joints in FWPWHT conditions are tempered sorbite. The fatigue crack growth rate da/dN of welds and base metal are not obviously changed among EBLPWHT, FWPWHT test and as-welded (AW) test, as the mechanical properties of materials have a certain but not large effect on the da/dN of welded joints. The resistance to near threshold fatigue crack growth data of welded joints can be largely improved by EBLPWHT and it is related to microstructure and crack closure effect.