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61.
Hiroyuki Kogawa Takashi Wakui Takashi Naoe Katsuhiro Haga Hiroshi Takada Masatoshi Futakawa 《Journal of Nuclear Science and Technology》2020,57(5):487-494
ABSTRACTNeutron flux per pulse reached world record at neutron source in Japan Proton Accelerator Research Complex (J-PARC). In the J-PARC, mercury target system is used as a spallation neutron source. A target vessel has a multi-walled protection system that comprises a mercury vessel enclosed with a double-walled water shroud. This is to prevent the leakage of the mercury outside the target vessel. The multi-walled structure needed to be complicated with a lot of welding lines. However, during the operation, we faced an unscheduled shutdown due to water leakage to the intermediate layer between the mercury vessel and water shroud. An investigation on the cause of the leakage was carried out. It is deduced that the leakage path was formed due to the crack propagation from welding defects that are caused by the complicated multi-walled structure. The crack propagation is attributed to the repeated stress by pressure waves generated in the mercury target. Based on the investigation results, the design was improved to remove the welding line on the complicated structure and to realize the stable operation with 1 MW proton beam, which is the final design value of the neutron source in J-PARC. 相似文献
62.
63.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided. 相似文献
64.
The study examines the corrosion fatigue behavior of friction stir welded Al2024 alloy in the corrosive medium. The fatigue tests are conducted at a stress ratio of -1 in the different corrosive medium. The decrease in the fatigue life of welded joints in the corrosive environment is attributed to an increase in the crack initiation susceptibility in the presence of corrosive media. The fractured surfaces are investigated using the scanning electron microscopy (SEM). The formation of the corrosive compounds was studied using x-ray diffractometry. 相似文献
65.
In this paper, microhardness and microstructural characteristics of dual phase DP590 steel resistance spot weld joint under two different welding conditions (i. e. single pulse and multi pulse) were studied. It was observed that applying multi pulse currents resulted in quasi-equiaxed grains of tempered martensite in fusion zone (FZ) of the weldment. The refinement of microstructure in fusion zone using multi pulse current treatment resulted in reduced hardness of the weld joint. 相似文献
66.
采用光学显微镜、扫描电镜、能谱仪及X射线衍射仪等微观分析手段,研究不同热处理工艺条件下2195铝锂合金电子束焊接头焊缝区的显微组织演变,探讨接头的焊后热处理强化机制。结果表明,焊后热处理可显著改善接头区域的显微组织,促进强化相的析出,有利于提高接头的力学性能。经过焊后固溶+双级时效热处理,焊态下接头熔合线附近存在的等轴细晶区消失,β′、θ′和T1等强化相在接头焊缝区析出,与单级时效处理工艺相比,双级时效处理的析出强化效果更为显著。力学性能测试表明,经过双级时效热处理后,接头的抗拉强度达到492.5 MPa,为母材强度的90.4%。接头拉伸断口表面存在许多小韧窝,并伴随出现解理面,接头呈韧-脆混合型断裂特征。 相似文献
67.
68.
S. H. Mousavi Anijdan H. R. Jafarian A. R. Khoshakhlagh 《Science & Technology of Welding & Joining》2018,23(5):387-393
Properties changes of an X52 microalloyed steel processed by a full-scale industrial electric resistant welding (ERW) equipment was studied. Lack of proper toughness level in the weld zone was investigated. Results show that the low toughness value could only be satisfactorily addressed after a two-stage annealing process. {100} pole figures for each processing step revealed a completely random texture for the initial plate. However, after the ERW process, a textured structure with the main components of brass, S and copper was obtained. Texture components were substantially weakened after the second stage of annealing and instead a cube texture was developed which could explain satisfactory level of toughness for the ERW pipe after conducting the two-step annealing process. 相似文献
69.
目前,影响海洋工程和船舶焊接结构质量的重要影响因素之一就是焊接变形,其产生的根本原因就是在焊接过程中因结构体受热不均、热梯度、残余应力等。基于此,本文对焊接变形预测的理论发展进程及其相关理论内涵进行详细阐述,并对基于神经网络的新型焊接变形预测理论的研究发展简单概述。 相似文献
70.
N. Chiker A. Haddad Y. Hadji M.E.A. Benammar M. Azzaz M. Yahi T. Sahraoui M. Hadji M.W. Barsoum 《Ceramics International》2018,44(3):3282-3290
Herein we study the infiltration behavior of Ti and Cu fillers into a Ti2AlC/Ti3AlC2MAX phase composites using a TIG-brazing process. The microstructures of the interfaces were investigated by scanning electron microscopy and energy dispersive spectrometry. When Ti2AlC/Ti3AlC2 comes into contact with molten Ti, it starts decomposing into TiCx, a Ti-richandTi3AlC; when in contact with molten Cu, the resulting phases are Ti2Al(Cu)C, Cu(Al), AlCu2Ti and TiC. In the presence of Cu at approximately 1630 °C, a defective Ti2Al(Cu)C phase was formed having a P63/mmc structure. Ti3AlC2 MAX phase was completely decomposed in presence of Cu or Ti filler-materials. The decomposition of Ti2AlC to Ti3AlC2 was observed in the heat-affected zone of the composite. Notably, no cracks were observed during TIG-brazing of Ti2AlC/Ti3AlC2 composite with Ti or Cu filler materials. 相似文献