Electron Beam Welding of IN792 DS: Effects of Pass Speed and PWHT on Microstructure and Hardness.
Electron Beam Welding of IN792 DS: Effects of Pass Speed and PWHT on Microstructure and Hardness.
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DOI：
10.3390/ma10091033
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发表时间：
2017-09-05
期刊：
影响因子：
--
通讯作者：
Varone A
中科院分区：
文献类型：
--
作者：
Angella G;Barbieri G;Donnini R;Montanari R;Richetta M;Varone A
采用电子束（EB）焊接方法在2 mm厚的定向凝固IN 792高温合金板上实现了焊缝成形。这项工作的第一部分证明了预热工件以避免在焊缝中形成长裂纹的重要性。通过比较不同的预热温度（PHT）和通过速度（v），可以确定最佳工艺参数，即PHT = 300 °C和v = 2.5 m/min。采用光学显微镜（OM）、扫描电子显微镜（SEM）能量色散谱（EDS）、电子背散射衍射（EBSD）、X射线衍射（XRD）和显微硬度测试。在焊态条件下，定向取向晶粒的结构在MZ中完全丧失。MZ中的γ'相由小的圆形颗粒（20-40 nm）组成，其总量取决于PHT和焊接道次速度，而HAZ中的γ'相与BM相同。即使MZ中的γ'相的量低于原始材料的量，纳米尺寸的颗粒也引起硬度的增加。EDS检查未显示γ'和γ相中的相关成分变化。在最佳样品上进行700和750 °C下两小时的焊后热处理（PWHT）。PWHTs后，有序相的数量增加，且在750 °C时效果更明显，而MZ中γ'颗粒的尺寸几乎保持不变。在整个关节测量的硬度曲线显示向上移动，但峰谷高度是一个小的低，表明在不同的区域更均匀的功能。
Electron Beam (EB) welding has been used to realize seams on 2 mm-thick plates of directionally solidified (DS) IN792 superalloy. The first part of this work evidenced the importance of pre-heating the workpiece to avoid the formation of long cracks in the seam. The comparison of different pre-heating temperatures (PHT) and pass speeds (v) allowed the identification of optimal process parameters, namely PHT = 300 °C and v = 2.5 m/min. The microstructural features of the melted zone (MZ); the heat affected zone (HAZ), and base material (BM) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD), and micro-hardness tests. In the as-welded condition; the structure of directionally oriented grains was completely lost in MZ. The γ’ phase in MZ consisted of small (20–40 nm) round shaped particles and its total amount depended on both PHT and welding pass speed, whereas in HAZ, it was the same BM. Even if the amount of γ’ phase in MZ was lower than that of the as-received material, the nanometric size of the particles induced an increase in hardness. EDS examinations did not show relevant composition changes in the γ’ and γ phases. Post-welding heat treatments (PWHT) at 700 and 750 °C for two hours were performed on the best samples. After PWHTs, the amount of the ordered phase increased, and the effect was more pronounced at 750 °C, while the size of γ’ particles in MZ remained almost the same. The hardness profiles measured across the joints showed an upward shift, but peak-valley height was a little lower, indicating more homogeneous features in the different zones.
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