Microstructural evolution of adiabatic shear bands in steel by impact
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Date
2014
Authors
Boakye-Yiadom, Solomon
Journal Title
Journal ISSN
Volume Title
Publisher
Materials Science And Engineering A
Materials Science And Engineering A
Philosophical Magazine
Materials Science And Engineering A
Metallurgical And Materials Transaction A
Materials Science And Engineering A
Materials Science And Engineering A
Philosophical Magazine
Materials Science And Engineering A
Metallurgical And Materials Transaction A
Materials Science And Engineering A
Abstract
This research, is initiated to systematically study the microstructure of AISI 4340 steel prior to impact, after impact and after post-impact annealing to determine the effect of the pre-deformation microstructure on the nucleation and initiation of ASBs, and the mechanism of evolution of ASBs during impact. This study used state-of-the-art microstructural characterization techniques such as the FIB and STEM/HRTEM to reveal that initial microstructural inhomogeneity produces nucleation sites for the initiation of ASBs during impact. It was observed that double misfit interfaces and boundary layers, formed around precipitated carbides (interface between reinforcements and matrix), increased the volume fraction of dislocation sources within the pre-impact specimens. It is demonstrated that the intersection of an activated dislocation source with the direction of maximum shear (regions of stress concentrations) within the specimens during impact, is a necessary condition for the points of intersection to act as possible sites for the nucleation and initiation of ASB depending on the rate of dislocation generation, local strain and strain rate. In addition, the structure that evolves after strain localization starts out with elongation of the grains in the shear direction with the initiation of random and transverse dislocation boundaries along the elongated grains. The elongated grains break along the initiated dislocation boundaries as strain/strain rate increases resulting in the creation of smaller elongated-broken grains and nanograins. Boundary refinement of the broken grains occurring through grain rotation and adiabatic heating results in the evolution of refined grains, subgrains and nanograins. The presence of elongated grains, broken grains, refined grains, subgrains and nanograins within the evolved shear band structures demonstrate that the local deformation is dependent on the imposed local strain and strain rate and that these mechanisms occur concurrently during impact. The results obtained, which are specific to the behavior of BCC ferritic Pearlitic hardenable steels, lead to the conclusion that the evolution of ASBs is a simultaneous layering of microstructures initially driven by dislocations which produce the final structures observed in the shear bands at the end of passage of the stress wave.
Description
Keywords
Microscopy, Dislocations, Adiabatic Shear Bands, X-ray Diffraction, Impact, Focused Ion Beam
Citation
S. Boakye-Yiadom And M. N. Bassim, Effect Of Prior Heat Treatment On The Dynamic Impact Behavior Of 4340 Steel And Formation Of Adiabatic Shear Bands, Materials Science And Engineering A (2011) 8700-8708
S. Boakye-Yiadom And M. N. Bassim, Effect Of Heat Treatment On Stability Of Impact-Induced Adiabatic Shear Bands In 4340 Steel, Materials Science And Engineering A 546 (2012) 223-232
S. Boakye-Yiadom, N. Bassim And A. K. Khan, Microscopical Study Of The Formation Of Adiabatic Shear Bands In 4340 Steel During Dynamic Loading, Philosophical Magazine 93 (2013) 4544-4568
S. Boakye-Yiadom, A. K. Khan And N. Bassim, A Systematic Study Of Grain Refinement During Impact Of 4340 Steel, Materials Science And Engineering A 605 (2014) 270–285
S. Boakye-Yiadom, A. K. Khan And N. Bassim, Deformation Mapping and the Role of Carbides on the Microstructure and Properties of Evolved Adiabatic Shear Bands, Metallurgical And Materials Transaction A 45 (2014) 5379-5396
S. Boakye-Yiadom, A. K. Khan And N. Bassim, Effect of Pre-impact Microstructure on the nucleation and initiation of Adiabatic Shear Bands (ASBs) During Impact, Materials Science And Engineering A (2014) 373-394
S. Boakye-Yiadom And M. N. Bassim, Effect Of Heat Treatment On Stability Of Impact-Induced Adiabatic Shear Bands In 4340 Steel, Materials Science And Engineering A 546 (2012) 223-232
S. Boakye-Yiadom, N. Bassim And A. K. Khan, Microscopical Study Of The Formation Of Adiabatic Shear Bands In 4340 Steel During Dynamic Loading, Philosophical Magazine 93 (2013) 4544-4568
S. Boakye-Yiadom, A. K. Khan And N. Bassim, A Systematic Study Of Grain Refinement During Impact Of 4340 Steel, Materials Science And Engineering A 605 (2014) 270–285
S. Boakye-Yiadom, A. K. Khan And N. Bassim, Deformation Mapping and the Role of Carbides on the Microstructure and Properties of Evolved Adiabatic Shear Bands, Metallurgical And Materials Transaction A 45 (2014) 5379-5396
S. Boakye-Yiadom, A. K. Khan And N. Bassim, Effect of Pre-impact Microstructure on the nucleation and initiation of Adiabatic Shear Bands (ASBs) During Impact, Materials Science And Engineering A (2014) 373-394