Shear banding behaviour of a multifunctional titanium alloy during
high strain rate deformation
Xianghai An a, Emmanuel Flores Johnson b, Yulin Hao c, Luming Shen b and
Xiaozhou Liao a*
aSchool of Aerospace, Mechanical & Mechatronic Engineering, the University of
Sydney, NSW 2006, Australia
bSchool
of Civil Engineering, the University of Sydney, NSW 2006, Australia
cShenyang
National Laboratory for Materials Science, Institute of Metal Research,
Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
Contact's e-mail address: xianghai.an@sydney.edu.au
Abstract:
As an emerging class of multifunctional titanium alloys, Gum Metals with the single
body-centre cubic  phase possess superior mechanical properties, including the
combination of low Young’s modulus, large-scale non-linear elasticity and high
strength, which are not possible in conventional materials. These extraordinary
properties are attributed to their unique deformation through mechanisms that include
ideal shear deformation, nanodisturbance and conventional dislocation slip, twining,
and phase transformation. Details of the deformation mechanisms of Gum Metals
have not been fully understood. In this research, we explore the deformation
mechanisms of a Gum Metal under high strain rates, focusing more on its shear
banding behavior. A typical Gum Metal, Ti–24Nb–4Zr–7.9Sn (wt%) alloy was
selected and processed by hot rolling and annealing to acquire microstructures with a
bimodal grain size distribution and with large uniform grains, respectively. The two
types of samples were deformed under the strain rates of ~2700 s-1 and 5500 s-1
using a split Hopkinson compression bar. Microstructural characterisation was
conducted using electron backscatter diffraction and transmission electron
microscopy. It was found that the strength of the two types of samples is significantly
enhanced when the materials are deformed under high strain rates. Both materials
are susceptible to adiabatic shear banding. Different microstructures presented in the
shear bands in the two types of samples. Uniform equiaxed dynamic recrystallized
grains were seen in the annealed sample. The microstructures in the shear bands in
the hot rolled sample are highly sensitive to the shear band position: very fine
dynamic recrystallized grains elongated along the shear banding direction presented
in areas away from shear cracks, while both equiaxed grains and very fine elongated
grains co-existed in areas near shear cracks. The effects of original microstructures
on the microstructural evolution in shear bands will be discussed in details.