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Transition of Dislocation Glide to Shear Transformation in Shocked Tantalum

Published online by Cambridge University Press:  28 February 2017

Luke L. Hsiung  and
Geoffrey H. Campbell
Luke L. Hsiung*
Affiliation:
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550-9900, U.S.A.
Geoffrey H. Campbell
Affiliation:
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550-9900, U.S.A.
*
*(Email: [email protected])
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Abstract

A TEM study of pure tantalum and tantalum-tungsten alloys explosively shocked at a peak pressure of 30 GPa (strain rate: ∼1 x 104 sec-1) is presented. While no ω (hexagonal) phase was found in shock-recovered pure Ta and Ta-5W that contain mainly a low-energy cellular dislocation structure, shock-induced ω phase was found to form in Ta-10W that contains evenly distributed dislocations with a stored dislocation density higher than 1 x 1012 cm-2. The TEM results clearly reveal that shock-induced α (bcc) → ω (hexagonal) shear transformation occurs when dynamic recovery reactions which lead the formation low-energy cellular dislocation structure become largely suppressed in Ta-10W shocked under dynamic (i.e., high strain-rate and high-pressure) conditions. A novel dislocation-based mechanism is proposed to rationalize the transition of dislocation glide to twinning and/or shear transformation in shock-deformed tantalum. Twinning and/or shear transformation take place as an alternative deformation mechanism to accommodate high-strain-rate straining when the shear stress required for dislocation multiplication exceeds the threshold shear stresses for twinning and/or shear transformation.

Keywords

dislocationsphase transformationshock loading
Type
Articles
Information
MRS Advances , Volume 2 , Issue 27: Mechanical Behavior and Failure Mechanisms of Materials , 2017 , pp. 1417 - 1428
Copyright
Copyright © Materials Research Society 2017 

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References

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