Microstructural study of Ti45Nb alloy before and after HPT processing using experimental and ab initio data mining approach

• Published in: Materials characterization 2020-11, Vol.169, Article 110635
• Main Authors: Cvijović-Alagić, I., Rakin, M., Laketić, S., Zagorac, D.
• Format: Article
• Language: English
• Subjects: Ab initio calculations; Electron microscopy; High-pressure torsion; Ti[sbnd]45Nb alloy; XRD
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2020.110635

Potential application of the Ti45Nb (mass%) alloy in biomedicine as a hard-tissue replacement material puts the improvement of the alloy mechanical and biological compatibility in the research focus. Selection of the appropriate alloy production and post-production parameters influence the appearance of the favorable alloy microstructural characteristics and in turn, increase the possibility of its successful biomedical application. The high-pressure torsion (HPT) is one of the post-processing methods which enables the severe plastic deformation of the difficult-to-deform materials resulting in the higher material compatibility with biological systems. The scope of the present research was to investigate the microstructural characteristics of the Ti45Nb alloy before and after the HPT deformation using the experimental and theoretical methods. The electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to analyze the Ti45Nb alloy microstructure. Significant grain refinement induced by HPT processing was confirmed. Possible appearance and coexistence of multiple metastable phases in the Ti45Nb alloy microstructure reported in the literature led to the additional alloy microstructural characterization using the X-ray diffraction (XRD) technique. Additional XRD investigations revealed that along with the β-Ti phase in the alloy microstructure the supplementary Ti4Nb phase is present before and after the HPT process application. The appearance of the Ti4Nb phase in the alloy microstructure was confirmed by ab initio modeling. Furthermore, additional structures were predicted and studied using a combination of data mining and first-principles calculations in the Ti4Nb compound. The five most relevant structure candidates are fully structurally determined and the proposed SrSn4 modification with orthorhombic symmetry which crystallizes in space group Cmcm (no. 63) is found to be in the best agreement with the obtained XRD results. [Display omitted] •HPT processing resulted in significant grain refinement in Ti45Nb microstructure.•EBSD and TEM showed presence of β-Ti, while XRD revealed additional Ti4Nb phase.•Quantum mechanics and data mining were successfully used to explore Ti45Nb system.•Experimental observations are in a very good agreement with ab initio calculations.•The structure of the Ti4Nb compound is successfully characterized and calculated.