J. Mater. Sci. Technol. ›› 2019, Vol. 35 ›› Issue (8): 1681-1690.DOI: 10.1016/j.jmst.2019.04.004
• Orginal Article • Previous Articles Next Articles
Shilin Zhangab, Yingjie Maab*(
), Sensen Huangac, Sabry S. Youssefab, Min Qiab, Hao Wangab, Jianke Qiuab, Jiafeng Leiab*(), Rui Yangab
Received:2019-01-04
Revised:2019-03-18
Accepted:2019-03-19
Online:2019-08-05
Published:2019-06-19
Contact:
Ma Yingjie,Lei Jiafeng
About author:1Authors contributed equally to this work.
Shilin Zhang, Yingjie Ma, Sensen Huang, Sabry S. Youssef, Min Qi, Hao Wang, Jianke Qiu, Jiafeng Lei, Rui Yang. Temperature-gradient induced microstructure evolution in heat-affected zone of electron beam welded Ti-6Al-4V titanium alloy[J]. J. Mater. Sci. Technol., 2019, 35(8): 1681-1690.
Fig. 1. SEM morphology of the as-received Ti-6Al-4V alloy showing the equiaxed microstructure consisting of αp and intergranular β.
Fig. 2. Scheme of the as-received Ti-6Al-4V plate weldment.
Fig. 3. Macrostructure of Ti-6Al-4V alloy EBW weldment (a) and SEM image of FZ (b).
Fig. 4. SEM images of HAZ of Ti-6Al-4V EBW weldment at different positions: (a) near-BM, (b) mid-HAZ, (c) local magnification of mid-HAZ, (d) near-FZ, showing various α structures (including αp, rim-α, dendritic α, αs colony, abnormal αs and “ghost” structure) indicated by the arrows.
Fig. 5. Constituent distribution of alloying elements of near-BM (a), mid-HAZ (b) and near-FZ (c) in Ti-6Al-4V EBW weldment, the left, middle and right column showing the morphology, element Al and V distribution respectively.
Fig. 6. Line scanning consequences of Al and V distributions of near-BM (a,b), mid-HAZ (c,d) and near-FZ (e,f) position in Ti-6Al-4V EBW weldment, the blue arrows showing the scanning routes.
Fig. 7. EBSD analysis of BM in Ti-6Al-4V EBW weldment: (a) the morphology of corresponding scanning region, (b) IPF map, (c) pole figures of α phase, (d) grain boundary distribution of αp and (e) misorientation statistics of αp grains.
Fig. 8. EBSD analysis of near-BM and mid-HAZ in Ti-6Al-4V EBW weldment: (a) the morphology of corresponding scanning region, (b) IPF map, (c) pole figures of α phase, (d) grain boundary distribution of α and (e) misorientation statistics of α grains.
Fig. 9. Cumulative misorientation in rim-α (a) and dendritic α (b) in the mid-HAZ.
Fig. 10. EBSD analysis of abnormal αs in mid-HAZ: (a) morphology of the scanning region, (b) IPF map and (c) pole figures of the corresponding region.
Fig. 11. EBSD analysis of near-FZ in Ti-6Al-4V EBW weldment: (a) the morphology of corresponding scanning region, (b) IPF map, (c) pole figures, (d) grain boundary distribution of α and (e) misorientation statistics of α grains.
Fig. 12. EBSD analysis of “ghost” structure in near-FZ: (a) scanning region, (b) misorientation of α phase (2°<red<10°, 10°<blue<75°, 75°<black<90°), (c) IPF map and (d) misorientations along the green arrow in (b).
| Type | Position | V distribution (rich: +) | Orientation relationship | Formation mechanism |
|---|---|---|---|---|
| αp grains | Near-BM Mid-HAZ | -- | {1010}<0001> texture | Rolling |
| Rim-α | Mid-HAZ | + | To be identical with αp grain | Elements distribution |
| Dendritic α | Mid-HAZ | + | Protuberances evolution | |
| αs colony | Mid-HAZ Near-FZ | +++ | BOR with β phase and independent to αp grain | β→αs |
| Abnormal αs | Mid-HAZ | + | ||
| “Ghost” structures | Near-FZ | - |
Table 1 The summary of microstructure characterization of different α phase in HAZ of Ti-6Al-4V EBW weldment.
| Type | Position | V distribution (rich: +) | Orientation relationship | Formation mechanism |
|---|---|---|---|---|
| αp grains | Near-BM Mid-HAZ | -- | {1010}<0001> texture | Rolling |
| Rim-α | Mid-HAZ | + | To be identical with αp grain | Elements distribution |
| Dendritic α | Mid-HAZ | + | Protuberances evolution | |
| αs colony | Mid-HAZ Near-FZ | +++ | BOR with β phase and independent to αp grain | β→αs |
| Abnormal αs | Mid-HAZ | + | ||
| “Ghost” structures | Near-FZ | - |
Fig. 13. Variations of nanoindentation hardness with the declination angle of the loading direction relative to the c-axis of HCP crystal in the Near-FZ zone.
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