Dynamic deformation and failure of ultrafine-grained titanium

Abstract

Dynamic deformationand shear localization of ultrafine-grained (~120nm) pure titanium areexamined., The strain hardening can be considered as having two regimes: below and above a strain ~0.04; at this point there is a drastic decrease in the slope.The strain-rate sensitivity of ultrafine-grained titanium was found to be approximately the same as its coarse grained counterpart. Based on experimentally determined parameters, the Zerilli-Armstrong equation is modified to describe the mechanical response of the ultrafine-grained titanium over the strain rate range 10-5 to 10 3 s-1. Adiabatic shear banding was examined in a forced shear configuration where large strain is imposed in a narrow region. The microstructure inside the adiabatic shear band consists of a mixture of elongated grains and equiaxed nanograins (~40 nm) that aresignificantly smaller than the initial grains (~120 nm). The formation of equiaxed nanograins is modeled through a mechanism of rotational dynamic recrystallization. This further reduction in grain size from the one generated by ECAP is interpreted in terms of the Zener-Hollomon parameters for quasistatic and dynamic deformation. The adiabatic shear band eventually fractures by a combination of brittle and ductile failure.

Dynamic recrystallization in adiabatic shear banding: Effective-temperature model and comparison to experiments in ultrafine-grained titanium

“…the dislocation density A number of authors (e.g., [3,2,6]) observe DRX in conjunction with adiabatic shear banding; the DRX grains in the shear band apparently contain many fewer dislocations than the non-recrystallized grains. This observation is in contrast to the prediction of equations (25) and (27), which imply that as deformation proceeds and raises the effective temperature χ, grains progressively become smaller with increasing dislocation densities.…”

Strain localization and dynamic recrystallization in polycrystalline metals: Thermodynamic theory and simulation framework

“…There is growing evidence in the literature that dynamic recrystallization (DRX)the process by which fine, nano-sized grains with few or no dislocations form in the ASB -provides an additional softening mechanism and supplements the role of thermal softening in shear band initiation. DRX has been observed in conjunction with adiabatic shear localization in a broad range of metals and alloys, including titanium and titanium alloys (e.g., Rittel et al, 2008;Osovski et al, 2012Osovski et al, , 2013Li et al, 2017), magnesium (Rittel et al, 2006), copper (Rittel et al, 2002), and steel (e.g., Meyers et al, 2000Meyers et al, , 2001Meyers et al, , 2003.…”

Mechanical Behavior of Nanostructured and Ultrafine-Grained Metal Alloy under Intensive Dynamic Loading

“…A specific volume, which is occupied with UFG structure, influences on the HEL and the spall strength of alloys. Research of deformation localization and fracture mechanisms of NS and UFG alloys was investigated by a combination of structure-sensitive methods [1,2,[22][23][24][25][26][27]. The high sensitivity of modern infrared (IR) thermal vision systems in combination with the opportunity of noncontact continuous temperature and strain measurements gives us important information on processes of damage and fracture.…”

“…The increase of UFG material strength can be explained on the behavior of dislocation at submicrometer grain size. Laws of plastic deformation operating at room temperature for coarse-grained metals usually are based on dislocation mechanisms [1][2][3][4][5][6][7][8][9]. When grain size is decreased in nanometer range, dislocation activity becomes difficult.…”

“…During the last decade, the interest in research of mechanical behavior of ultrafine-grained (UFG) and nanostructured (NS) metal alloys has been risen sharply [1][2][3][4][5][6][7][8][9][10][11][12][13]. Compared to their coarse-grained counterparts, UFG and NS metals exhibit significantly higher static yield strength, hardness, but lower tensile elongation.…”