Dynamic deformation and failure of ultrafine-grained titanium

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• 作者：Zezhou Li^a ; Bingfeng Wang^b ; Shiteng Zhao^a ; Ruslan Z. Valiev^c ; Kenneth S. Vecchio^a ; Marc A. Meyers^a ; ^{mameyers@eng.ucsd.edu}
• 关键词：Ultrafine-grained titanium ; Constitutive response ; Adiabatic shear band formation and failure mechanism
• 刊名：Acta Materialia
• 出版年：2017
• 出版时间：15 February 2017
• 年：2017
• 卷：125
• 期：Complete
• 页码：210-218
• 全文大小：2179 K
• 卷排序：125

文摘

Dynamic deformation and shear localization of ultrafine-grained (∼120 nm) pure titanium are examined. 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 is 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 103 s−1. Adiabatic shear banding is 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 are significantly 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 parameter for quasistatic and dynamic deformation. The adiabatic shear band eventually fractures by a combination of brittle and ductile failure.