Abstract
In this study, we have investigated the effect of oxygen contents on strain rate senstivitiy (SRS) within Gr. 1 and 4 commercially pure titanium (CP-Ti). The SRS was evaluated in multi-scales using macro-scopic tensile test with constant strain rate (CSR) method and strain rate jump (SRJ) method, and nanoindentation test with SRJ method. Electron backscatter diffraction (EBSD) has been used to characterise crystallographic texture and individual grain orientation of samples. Slip and twin activities of each CP-Ti were compared by EBSD measurements and the associated Schmid factor (SF) analysis. The active slip system is anticipated to be different in each relation between loading directions and textures, but twin activity is much similar. The texture dependent global SRS is thus thought to be resulted from the different slip activity. Local SRS was dependent not only on the grain orientation but also on the oxygen contents, leading to the fact that the impact of oxygen contents is closely correlated in macro- and micro-scopic level.
Highlights
Titanium alloys are attractive material in aerospace industry [1] due to their high strength-to-weight ratio, corrosion resistance and excellent mechanical properties
We have examined the effect of oxygen contents on strain rate sensitivity (SRS) in comparative Gr. 1 and 4 commercially pure titanium (CP-Ti), and in macro- and micro-scopic level by conducting the tensile test with continuous stiffness measurement (CSM) method and nanoindentation test with strain rate jump (SRJ) method
The slip activity anticipated by Schmid factor (SF) analysis is significantly different along the RD and transverse directions (TD) loading directions, whereas the twin activity characterised by Electron backscatter diffraction (EBSD) measurement is much similar
Summary
Titanium alloys are attractive material in aerospace industry [1] due to their high strength-to-weight ratio, corrosion resistance and excellent mechanical properties These alloys often undergo a significant cyclic loading condition during flight, and these regimes appartently have time sensitive load-hold. This cyclic loading system combined with load-hold stage is related to the fatigue life of structural components, and has shown the reduction of the number of cycles to failure by an order of magnitude or more than simple fatigue test without the holding stage [2]. As the significant decrease of elogation in titanium is observed [10,11,12] with the oxygen cencentration, it is needed to carefully control the optimal balance between strength and ductility
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