厚板钛及钛合金电子束焊接头组织与性能的研究

发布时间：2018-04-10 16:03

  本文选题：电子束焊 + 厚板钛及钛合金　； 参考：《山东大学》2017年硕士论文

【摘要】：钛及钛合金因其密度小、比强度高、耐腐蚀性好及焊接性好等优异的综合性能,被广泛用于核潜艇耐压壳体、管路系统件等船用结构件的制造中。船用结构件多为大厚度焊接件,随着我国海洋强国战略规划的提出,船用大厚度焊接件的需求量不断增加,厚板钛合金的焊接问题引起了广泛关注。真空电子束焊具有热源功率密度高、能量集中、变形小及可焊厚度范围宽等一系列优点,可以避免传统的焊接方法在焊接厚板钛合金时所产生的缺陷,获得性能良好的接头。本课题分别对厚度30mm纯钛(TA1)及100mmTC4钛合金大厚板进行了电子束焊(EBW),并对接头进行了不同工艺的焊后热处理试验。研究了热处理前后厚度30mmTA1及100mmTC4电子束焊接接头横截面不同深度处显微组织、显微硬度的变化特点,测试了接头横截面不同深度处室温下的拉伸性能、冲击性能。采用扫描电子显微镜(SEM)对接头断口形貌进行了观察并分析显微组织对断裂机制的影响。厚度30mmTA1电子束焊接接头组织由母材区等轴α到焊缝区粗大α柱状晶+锯齿状α+针状α'组织过渡。焊缝区针状位α'使得接头硬度、强度变高,强度最高增幅为5.2%;韧塑性变差,降低幅度在10.7%～19.3%,接头上部和底部的强度优于中部。接头经过750℃×2h FC热处理焊缝区域α'马氏体数量增多;850℃×2h FC热处理焊缝的马氏体α'发生碎化生成大量无序、短小的针状组织。650℃×2h FC热处理后整体硬度降低,850℃×2h FC热处理后整体硬度升高,热影响区存在软化现象。TA1接头经过热处理后接头横截面不同深度处的组织性能更加均匀。厚度100mmTC4电子束焊接接头组织由母材区的等轴(α+β)相连续过渡到焊缝区的针状α'马氏体。接头横截面不同深度处的硬度和强度均高于母材、伸长率低于母材,接头伸长率最大降低幅度为30.2%,焊缝的冲击功低于母材的冲击功。TC4接头经600℃×2h FC处理焊缝α相得到粗化;850℃×2h FC热处理焊缝针状α'马氏体含量增多。(920℃×2h WC)+(500℃C×4h AC)热处理后焊缝组织为针状α'马氏体+原始β晶界;相比于焊件,接头最大平均抗拉强度增大141MPa,伸长率最多降低了 56.5%,焊缝硬度增大60HV,母材硬度增加40HV。不同热处理后100mm TC4电子束焊接接头各层性能更加均匀。TA1焊接件、650℃×2h FC及750℃ ×2hFC热处理后接头的拉伸、冲击断裂机制均为韧窝断裂。850℃×2hFC热处理后拉伸断裂机制为韧窝和准解离的混合型断裂,冲击断裂机制为准解离断裂。TC4焊件、600℃×2h FC和850℃×2h FC热处理后接头拉伸断裂机制均为韧窝断裂,(92℃×2h WC)+(500℃×4h AC)热处理态下拉伸试样断裂机制为解离断裂。TC4焊件焊缝冲击断裂机制为准解离断裂,60℃×2h FC和850℃×2h FC热处理后焊缝断裂机制为韧窝断裂;(920℃×2h WC)+(500℃×4h AC)热处理后焊缝冲击试样断裂机制为解离和韧窝的混合型断裂,解离断裂为主。
[Abstract]:Because of its low density, high specific strength, good corrosion resistance and good weldability, titanium and titanium alloys are widely used in the manufacture of marine structural parts such as nuclear submarine pressure shell, pipe system parts and so on.Marine structural parts are mostly welded parts with large thickness. With the strategic planning of our country, the demand for large thickness welded parts is increasing, and the welding problem of thick plate titanium alloy has attracted wide attention.Vacuum electron beam welding (VEBW) has a series of advantages such as high heat source power density, energy concentration, small deformation and wide weldable thickness range. It can avoid the defects of traditional welding method in welding thick plate titanium alloy and obtain good performance joint.In this paper, electron beam welding (EBW) was carried out on thick 30mm pure titanium (TA1) and 100mmTC4 titanium alloy thick plates, and different post-welding heat treatment tests were carried out on the joints.The microstructure and microhardness of 30mmTA1 and 100mmTC4 electron beam welded joints with thickness at different depths before and after heat treatment were studied. The tensile and impact properties at room temperature at different depths of cross section were tested.The fracture morphology of the joint was observed by scanning electron microscope (SEM) and the effect of microstructure on fracture mechanism was analyzed.The microstructure of thick 30mmTA1 electron beam welded joints is from the equiaxed 伪 in the base metal region to the coarse 伪 columnar zigzag 伪 'structure in the weld zone.The needle position 伪'in the weld zone makes the joint hardness, strength is higher, the maximum increase of strength is 5.2, the toughness and plasticity become worse, the decrease range is 10.7 and 19.3.The strength of the upper and bottom joint is better than that of the middle part.After 750 鈩，

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