Twinning anisotropy of tantalum during nanoindentation.

Goel, Saurav; Beake, Ben; Chan, Chi-Wai; Faisal, Nadimul Haque; Dunne, Nicholas

Abstract

Unlike other BCC metals, the plastic deformation of nanocrystalline Tantalum (Ta) during compression is regulated by deformation twinning. Whether or not this twinning exhibits anisotropy was investigated through simulation of displacement-controlled nanoindentation test using molecular dynamics (MD) simulation. MD data was found to correlate well with the experimental data in terms of surface topography and hardness measurements. The mechanism of the transport of material was identified due to the formation and motion of prismatic dislocations loops (edge dislocations) belonging to the 1/2 (111) type and (100) type Burgers vector family. Further analysis of crystal defects using a fully automated dislocation extraction algorithm (DXA) illuminated formation and migration of twin boundaries on the (110) and (111) orientation but not on the (010) orientation and most importantly after retraction all the dislocations disappeared on the (110) orientation suggesting twinning to dominate dislocation nucleation in driving plasticity in tantalum. A significant finding was that the maximum shear stress (critical Tresca stress) in the deformation zone exceeded the theoretical shear strength of Ta (Shear modulus/2. π~10.03. GPa) on the (010) orientation but was lower than it on the (110) and the (111) orientations. In light of this, the conventional lore of assuming the maximum shear stress being 0.465 times the mean contact pressure was found to break down at atomic scale.

Citation

GOEL, S., BEAKE, B., CHAN, C.-W., FAISAL, N.H. and DUNNE, N. 2015. Twinning anisotropy of tantalum during nanoindentation. Materials science and engineering: A [online], 627, pages 249-261. Available from: https://doi.org/10.1016/j.msea.2014.12.075

• Journal Article Type: Article
• Acceptance Date: Dec 18, 2014
• Online Publication Date: Dec 26, 2014
• Publication Date: Mar 11, 2015
• Deposit Date: Nov 12, 2015
• Publicly Available Date: Dec 27, 2015
• Journal: Materials science and engineering: A
• Print ISSN: 0921-5093
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 627
• Pages: 249-261
• DOI: https://doi.org/10.1016/j.msea.2014.12.075
• Keywords: MD simulation; Nanoindentation; Tantalum; Anisotropy
• Public URL: http://hdl.handle.net/10059/1345
• Contract Date: Nov 12, 2015