Phase transformation and structure evolution of a Ti-45Al-7.5Nb alloy processed by high-pressure torsion

Xi Li, Rian J. Dippenaar, Jae Kyung Han, Megumi Kawasaki, Klaus Dieter Liss*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Intermetallic γ-based titanium aluminides of Ti-45Al-7.5Nb have been subjected to high-pressure torsion (HPT) processing. Significant grain refinement has been achieved from ∼10 μm to ∼30 nm, leading to the improvement in both physical and mechanical properties. Complementary studies correlated the microstructure, phase transformation behavior and the enhancement of mechanical properties. Neutron and X-ray diffraction revealed that an ongoing order-disorder transformation occurs by HPT processing, resulting in large heterogeneous behavior between the surface-near and the median layers of the disk. While the γ-phase almost disappeared underneath the surface region, such order/disorder phase transformation consistently decreases towards the middle-thickness section of the samples. A low bulk texture index is consistent with grain rolling and swirling rather than slip deformation. Vickers micro-hardness indentation confirms the improvement of hardness from 308 Hv to 605 Hv. For the first time, the present work demonstrates heterogeneity in structural transformation, such as displacive transformation and order/disorder transformation, which can be compared to earlier reported inhomogeneity in mechanical properties and microstructure within bulk nanostructured materials that were processed by HPT.

Original languageEnglish
Pages (from-to)1149-1157
Number of pages9
JournalJournal of Alloys and Compounds
StatePublished - 30 May 2019


  • Heterogeneity
  • High-pressure torsion
  • Neutron diffraction
  • Order-disorder transition
  • Ti-Al alloys


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