J. Mater. Sci. Technol. ›› 2018, Vol. 34 ›› Issue (5): 767-773.DOI: 10.1016/j.jmst.2017.09.004

• Orginal Article • Previous Articles     Next Articles

Formation of face-centered cubic titanium in laser surface re-melted commercially pure titanium plate

Zhuo Li, Xu Cheng, Jia Li*(), Huaming Wang   

  1. National Engineering Laboratory of Additive Manufacturing for Large Metallic Components, School of Materials Science and Engineering, Beihang University, Beijing 100191, China
  • Received:2017-02-27 Revised:2017-04-07 Accepted:2017-04-14 Online:2018-05-10 Published:2018-05-04
  • Contact: Li Jia

Abstract:

Micron-scale face-centered cubic titanium phase (named as δ phase) were noticed in the re-melted zone of laser surface re-melted commercially pure titanium plate. The morphology, sub-structure, orientation and distribution of δ phase were investigated by scanning electron microscopy, electron back-scattered diffraction and transmission electron microscopy. Three kind formation processes of δ phase were put forward based on the investigation. The first one is α′ → δ transformation which takes place in single α′ grains and leads to the orientation relationship {001}δ//{0001}α′ <110>δ//<11\(\overline{2}\)0>α′. The second one is β → α′ + δ transformation which takes place at α′/α′ interfaces and leads to the orientation relationship {001}δ//{1\(\overline{1}\)0}β 〈110〉δ//〈111〉β. The third one is another kind of β → α′ + δ transformation that takes place at α′/α′ interfaces and leads to the orientation relationship {1\(\overline{1}\)1}δ//{1\(\overline{1}\)0}β < 110 > δ// < 111 < β. It is believed that the transformations of δ phase are stress assistant ones and in the present investigation, the phase transformation stress of β → α′ transformation acts as the assistant driving force for the formation of δ phase.

Key words: Pure titanium, Laser surface re-melt, Martensitic phase transformation, Face centered cubic, Electron back-scattered diffraction