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Dislocation Pinning Effects Induced by Nano-Precipitates During Warm Laser Shock Peening: Dislocation Dynamic Simulation and Experiments" (2011)

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Dislocation Pinning Effects Induced by Nano-Precipitates During Warm Laser Shock Peening: Dislocation Dynamic Simulation and Experiments Purdue University Purdue e-Pubs Birck and NCN Publications Birck Nanotechnology Center 7-15-2011 Dislocation pinning effects induced by nano- precipitates during warm laser shock peening: Dislocation dynamic simulation and experiments Yiliang Liao Purdue University, [email protected] Chang Ye Purdue University, [email protected] Huang Gao Purdue University, [email protected] Bong-Joong Kim Purdue University Sergey Suslov Birck Nanotechnology Center, Purdue University, [email protected] See next page for additional authors Follow this and additional works at: http://docs.lib.purdue.edu/nanopub Part of the Nanoscience and Nanotechnology Commons Liao, Yiliang; Ye, Chang; Gao, Huang; Kim, Bong-Joong; Suslov, Sergey; Stach, Eric A.; and Cheng, Gary J., "Dislocation pinning effects induced by nano-precipitates during warm laser shock peening: Dislocation dynamic simulation and experiments" (2011). Birck and NCN Publications. Paper 975. http://dx.doi.org/10.1063/1.3609072 This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact [email protected] for additional information. Authors Yiliang Liao, Chang Ye, Huang Gao, Bong-Joong Kim, Sergey Suslov, Eric A. Stach, and Gary J. Cheng This article is available at Purdue e-Pubs: http://docs.lib.purdue.edu/nanopub/975 Dislocation pinning effects induced by nano-precipitates during warm laser shock peening: Dislocation dynamic simulation and experiments Yiliang Liao, Chang Ye, Huang Gao, Bong-Joong Kim, Sergey Suslov et al. Citation: J. Appl. Phys. 110, 023518 (2011); doi: 10.1063/1.3609072 View online: http://dx.doi.org/10.1063/1.3609072 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v110/i2 Published by the AIP Publishing LLC. Additional information on J. Appl. Phys. Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors Downloaded 23 Jul 2013 to 128.46.221.64. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions JOURNAL OF APPLIED PHYSICS 110, 023518 (2011) Dislocation pinning effects induced by nano-precipitates during warm laser shock peening: Dislocation dynamic simulation and experiments Yiliang Liao,1 Chang Ye,1 Huang Gao,1 Bong-Joong Kim,2 Sergey Suslov,2 Eric A. Stach,2,3 and Gary J. Cheng1,3,a) 1School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47906, USA 2School of Materials Science, Purdue University, West Lafayette, Indiana 47906, USA 3Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906, USA (Received 17 April 2011; accepted 8 June 2011; published online 26 July 2011) Warm laser shock peening (WLSP) is a new high strain rate surface strengthening process that has been demonstrated to significantly improve the fatigue performance of metallic components. This improvement is mainly due to the interaction of dislocations with highly dense nanoscale precipitates, which are generated by dynamic precipitation during the WLSP process. In this paper, the dislocation pinning effects induced by the nanoscale precipitates during WLSP are systematically studied. Aluminum alloy 6061 and AISI 4140 steel are selected as the materials with which to conduct WLSP experiments. Multiscale discrete dislocation dynamics (MDDD) simulation is conducted in order to investigate the interaction of dislocations and precipitates during the shock wave propagation. The evolution of dislocation structures during the shock wave propagation is studied. The dislocation structures after WLSP are characterized via transmission electron microscopy and are compared with the results of the MDDD simulation. The results show that nano-precipitates facilitate the generation of highly dense and uniformly distributed dislocation structures. The dislocation pinning effect is strongly affected by the density, size, and space distribution of nano-precipitates. VC 2011 American Institute of Physics. [doi:10.1063/1.3609072] I. INTRODUCTION precipitates also attracts great interest and has been quantita- tively studied using several proposed models.4–11 It is found Warm laser shock peening (WLSP) is an innovative that the strengthening effect greatly depends on the morphol- thermo-mechanical processing technique that has great poten- ogy and dispersion of precipitates. Nonetheless, none of this tial for improving the mechanical properties of metallic mate- research takes into account the ultra-highly diffused nano- rials, including surface hardening and fatigue life.1–3 One of scale precipitate cluster (5 nm to 10 nm in radius and 103 to the most promising characteristics of WLSP is that highly 104/lm3 in volume density) generated by DP, although most dense and uniformly distributed dislocation structures can be of them consider precipitates introduced by static aging with formed due to the interaction between gliding dislocation a much larger size and lower volume density. The disloca- structures and dense nanoscale precipitates generated during tion pinning effects and the resulting dislocation structures WLSP by dynamic precipitation (DP). The pinning effect of under extremely high strain rate processing (>106/s) have nano-precipitates on the dislocation motion provides the key been seldom studied experimentally. contribution to mechanical improvements such as enhancing To investigate the interaction of dislocation and precipi- surface hardness, stabilizing residual stress, and preventing tatation, not only transmission electron microscopy12–15 crack initiation, thus improving fatigue life and strength. (TEM) but also several simulation methods have been uti- Therefore, it is worthwhile to study the interaction of disloca- lized, such as molecular dynamic (MD) simulation,16–20 tion and nano-precipitates during the shock wave propagation Monte Carlo (MC) simulation,21,22 and dislocation dynamic and its effects on the dislocation evolution and mechanical (DD) simulation.9,23–25 Both MD and MC simulations are enhancement. usually restricted by the limited size (nanoscale) and the There have been lots of efforts at investigating the pin- short duration (picoseconds) due to the prohibitive computa- ning effects on dislocation evolution. It is generally accepted tional cost, whereas DD simulation can be applied for much that dislocation structures overcome obstacles with a small larger sizes (more than 10000b, with b being the Burgers characteristic radius and a low volume density via the shear- vector) and longer times (more than 100 ns). Therefore, DD ing mechanism, whereas the dislocation motion in the matrix simulation is more suitable for investigating the effects of containing unshearable obstacles is governed by the Orowan the highly diffused nanoscale precipitate cluster on disloca- process, which leaves the obstacles surrounded by pinned tion behaviors. Multiscale discrete dislocation dynamics dislocation loops. In addition, the strengthening effect of (MDDD), proposed by Zbib et al.,26,27 is one of the most advanced DD models, particularly for studying the dis- a)Author to whom correspondence should be addressed. Electronic mail: location evolution, dislocation/particle interaction, and parti- 28 [email protected]. cle strengthening. For instance, Yashiro et al. studied 0021-8979/2011/110(2)/023518/8/$30.00 110, 023518-1 VC 2011 American Institute of Physics Downloaded 23 Jul 2013 to 128.46.221.64. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions 023518-2 Liao et al. J. Appl. Phys. 110, 023518 (2011) dislocation behaviors at the matrix–precipitate interface by TABLE I. Experimental conditions of WLSP. proposing a back force model associated with the anti-phase boundary energy. Khraishi et al.23,25 reported a fundamental Laser wavelength 1064 nm Laser beam overlap 75% understanding of the particle strengthening in metal-matrix Sample thickness 2.38 mm composites with a particle size of around 1000b and the WLSP temperature for steel 4140 250 C hardening effect of a spatial distribution of defect clusters Laser beam diameter 2 mm with a radius of 2b to 10b. However, the dislocation evolu- Pulse duration 5 ns tion and strengthening effect predicted by these studies have WLSP temperature for AA6061 160 C not been compared with experimental results. In this study, aluminum alloy 6061 (AA6061) and AISI 4140 steel are chosen for use in the WLSP experiments. The sample is then polished to a thickness of 30 microns. The dislocation structures after WLSP processing are character- final thinning is carried out via the H-Bar method using a ized using TEM and are compared with the results of focused ion beam (Nova-200). Before TEM observations, MDDD simulation. The strengthening effect due to the dislo- the samples are cleaned with acetone in order to get a better cation pinning is investigated by the hardness test after image quality. In addition, the FWHM value of the 2h angle WLSP experiments and stress/strain curves during the shock as measured via x-ray diffraction (Bruker D8-Discover loading by MDDD simulation. The effects of the density, XRD) is utilized to compare the relative defect density after size, and space distribution of nano-precipitates are studied. processing. Furthermore, the surface hardness after WLSP is measured by the
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