Dislocation behavior in nickel and iron during laser shock-induced plastic deformation
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ORIGINAL ARTICLE
Dislocation behavior in nickel and iron during laser shock-induced plastic deformation Wangfan Zhou 1 & Xudong Ren 1 & Yu Yang 1 & Zhaopeng Tong 1 & Lan Chen 1 Received: 4 May 2019 / Accepted: 10 December 2019 # Springer-Verlag London Ltd., part of Springer Nature 2019
Abstract Laser shock peening is one of the most effective surface strengthening techniques, which uses laser shock-induced plastic deformation to optimize surface stress state and microstructures of target material. In this paper, dislocation dynamics simulation was used to investigate laser shock induced ultra-high strain rate plastic deformation of face-centered cubic (FCC) nickel and body-centered cubic (BCC) iron. Molecular dynamics was employed to calculate dislocation mobility. Based on the obtained dislocation mobility coefficient, dislocation dynamics models of nickel and iron were established. Results show that the velocity of dislocation motion increases as temperature decreases. Under ultra-high strain rate deformation, dislocation density of nickel increases while dislocation density of iron decreases as temperature rises. Moreover, iron exhibits thermal softening while nickel exhibits thermal hardening under laser shock loading. Plastic deformation dominated by dislocations is sensitive to loading direction, depending on the Schmidt factor of the slip system. The ultra-high strain rate induced by laser shock can effectively increase dislocation density by promoting dislocation multiplication and suppressing dislocation annihilation. Keywords Laser shock peening . Surface strengthening . Plastic deformation . Dislocation dynamics
1 Introduction Laser shock peening (LSP) is an advanced manufacturing technology used to strengthen surface properties of metallic components. As illustrated in Fig. 1, a laser beam with ultrashort pulse width is used to irradiate target surface coated by an ablative layer during LSP. The ablative layer vaporizes by absorbing laser energy and further develops to high pressure shock wave. Due to the shock wave-induced nanosecond or femtosecond laser, the target surface layer plastically deforms at ultra-high strain rate (106 s−1). The enhanced surface properties after LSP are mainly ascribed to LSP-induced workhardened layer and compressive residual stresses in target material [1–3]. The work hardening effect introduces high density of dislocations and dislocation evolution further induces grain refinement in the surface layer. Since work hardening occurs in
* Xudong Ren [email protected] 1
School of Mechanical Engineering, Jiangsu University, 212013 Zhenjiang, People’s Republic of China
a very short time, it is impossible to directly observe dislocation evolution using experimental methods. Molecular dynamics (MD) method is commonly used to investigate the microscopic mechanism of plastic deformation. However, a large number of atoms need to be calculated while simulating plastic deformation of a large system, which is computationally expensive [4, 5]. Since dislocations are carriers of
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