Shear band widening mechanism in Ti–6Al–4V under high strain rate deformation (original) (raw)
2020, Journal of Materials Research
In this study, mechanical properties and microstructural investigation of Ti64 at high strain rate are studied using a split-Hopkinson pressure bar method under compression for temperatures up to 800°C. Flow softening in the mechanical response of material to such loading conditions hints at instability in compression, which increases with an increase in temperature. Microstructural characterization of the deformed material is characterized using the electron-backscattered diffraction technique. It reveals the presence of instabilities in Ti64 in the form of a fine network of shear bands. The shear band width grows with an increase in temperature along with the area fraction of shear band in the material, displaying its improved capacity to contain microstructural instabilities at higher temperature. After a detailed microstructural investigation, a mechanism for shear band widening is proposed. Based on this mechanism, a path generating nuclei within shear bands is discussed. The microstructure within adiabatic shear bands in titanium is characterized by fine equiaxed grains formed at a high temperature via rotational dynamic recrystallization under dynamic impact/explosive loading conditions [9, 10, 11]. Peirs et al. [12] reported elongated equiaxed grains at the outer edge of shear bands, which became narrower toward the center and eventually breaking down into nanocrystalline grains at their core. Also, Ramesh et al. [13] showed the microstructural evolution caused by a planar dislocation motion and twinning, grouping of dislocations into cells, formation of elongated subgrains along a shear direction, and development of equiaxed nanocrystalline grains. Rittel et al. [14] observed that dynamic recrystallization preceded the shear failure and thus suggested that such failure was an outcome of microstructural evolution leading to localized softening of the material before thermal softening. Shear band formation was also reported to depend on experimental conditions and material parameters. A material with Widmanstätten microstructure was observed to fail at smaller strain than that with the equiaxial microstructure as the crack could easily grow within the laths [4]. An initiation strain for shear band formation showed strain rate dependence, with a lower onset strain at higher strain rates [15]. Shear bands
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