厚壁TC4-DT钛合金电子束焊接接头的微观组织特征

Microstructure Characteristics of Electron Beam Welded Thick-Wall TC4-DT Joint

对50mm厚壁TC4-DT钛合金进行焊接试验,通过对接头横截面进行光学显微组织分析和显微硬度测试,研究电子束焊接对该合金微观组织特征的影响。结果表明:TC4-DT钛合金母材显微组织为等轴状初生α相和层片状(α+β)所构成的典型双态组织。焊缝区的显微组织为网篮状马氏体组织α,,焊缝上部粗大的原始β柱状晶界明显,下部原始β晶粒尺寸较小且晶界不明显。热影响区显微组织可分为2个区域,近焊缝热影响区显微组织为少量等轴初生α+针状马氏体α,,近母材热影响区显微组织为等轴初生α+含针状α的转变β组织。2个区域的分界取决于焊接冷却过程的β转变温度。接头焊缝区和热影响区显微硬度偏高,近焊缝热影响区显微硬度达到峰值。另外,不同焊缝深度处显微硬度有差别:随着熔深位置增加,焊缝区的显微硬度呈递增趋势。

Experiments of electron beam welding was carried out for a 50 mm thick TC4-DT titanium alloy. The effect of electron beam welding on the microstructure characteristics was investigated using optical microscope observation and microhardness measurement for the cross-section of the welded joints. The results show that the microstructure of base metal was typical bimodal structure composed of primary a phase and lamellar （a＋β）. The microstructure of weld metal was basket-like martensite a＇. Coursed primary β grain boundaries were clear in upper and middle parts of weld metal, while the size of the β grains was small and the grain boundaries were not obvious in the bottom. The microstructure of heat affected zone （HAZ） may be divided into two regions. The microstructure of HAZ near fusion zone was consisted of little primary a phase and needle martensite a＇, while the microstructure near base metal was constituted of primary a phase and transferred β containing aciculate a. The boundary of the two regions was dependent on the β phase transfer temperature during weld cooling. The microhardness of the weld metal and HAZ was higher than that of base metal, and there was a peak value of microhardness in the HAZ near fusion zone. In addition, the microhardness of the fusion zone had an increased tendency with the measured weld depth increasing.