Harmonic structures of Ti-6Al-4V: a synchrotron X-Ray diffraction study of in situ uniaxial deformationThursday (29.09.2016) 11:45 - 12:00 Part of:
For structural applications and concerning the global mechanical behavior, the compromise between ductility and mechanical resistance is a dilemma in materials science. The Ti-6Al-4V alloy studied in this work combined contradictory characteristics mentioned above. To achieve this, this titanium alloy was developed from a new process of powder metallurgy in order to obtain a microstructure, called harmonic, which has a bimodal size distribution consisting of fine grains, named "shell", and coarse grains, named "core" (cf. Fig. 1), evenly distributed, interconnected and forming a 3D network. This alloy is composed by two main crystallographic phases (hexagonal close-packed Ti-α and body-centered cubic Ti-β). This unique microstructure is heterogeneous on a microscopic scale but homogeneous on a macroscopic scale [1-2]. This elaboration allows achieving mechanical properties combining ductility and high mechanical strength.
The main objective of this work, carried out as part of an ANR HighS-Ti (ANR-14-CE07-0003) project, is to understand and explain the mechanical behavior of this unusual microstructure. In this presentation, the first results of an uniaxial tensile test under in situ Synchrotron Radiation (X-Ray Diffraction) will be presented. Quantitative analysis of the displacement of the Bragg peaks leads to the fact that the various grains families require different value of stress to initiate plastic deformation. The intrinsic phase selectivity of X-ray diffraction allowed monitoring the elastic strain of the β-phase and the α-phase independently during the macroscopic deformation. Finally, qualitative analysis of the evolution of the diffraction pattern suggests a destruction of the harmonic structure from a value of strain of about 7%, probably induced by twinning deformation.
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 S.K. Vajpai, M. Ota, et al., Metallurgica and Materials Transactions A, A 46 (2015) 903-914.
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