Silver Hardening via Hypersonic Impacts
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.173
Silver Hardening via Hypersonic Impacts Eliezer Fernando Oliveira1,2, Pedro Alves da Silva Autreto1,3 and Douglas Soares Galvão1,2 1
Gleb Wataghin Institute of Physics, Universidade Estadual de Campinas, Campinas, SP, Brazil.
2 Center for Computational Engineering & Sciences (CCES), University of Campinas - UNICAMP, Campinas, SP, Brazil.
3
Federal University of ABC, Center of Natural Human Science, Santo Andre, SP, Brazil.
ABSTRACT
The search for new ultra strong materials has been a very active research area. With relation to metals, a successful way to improve their strength is by the creation of a gradient of nanograins (GNG) inside the material. Recently, R. Thevamaran et al. [Science v354, 312316 (2016)] propose a single step method based on high velocity impact of silver nanocubes to produce high-quality GNG. This method consists of producing high impact collisions of silver cubes at hypersonic velocity (~400 m/s) against a rigid wall. Although they observed an improvement in the mechanical properties of the silver after the impact, the GNG creation and the strengthening mechanism at nanoscale remain unclear. In order to gain further insights about these mechanisms, we carried out fully atomistic molecular dynamics simulations (MD) to investigate the atomic conformations/rearrangements during and after high impact collisions of silver nanocubes at ultrasonic velocity. Our results indicate the coexistence of polycrystalline arrangements after the impact formed by core HCP domains surrounded by FCC ones, which could also contribute to explain the structural hardening.
INTRODUCTION Ultra-strong materials have been used in several technological applications, such as protective materials industry and armors for vehicles, aircraft, etc [1]. In the case of metals, one of the most successful methods to create ultra-strong metallic structure is through gradient creation of nanograins (GNG) [2,3]. However, in general GNC require a multi-step process and can result in large number of grains with micro instead of nanosize domains [4]. Recently, R. Thevamaran et al. [5] developed a new method in which using a single-step process it was possible to produce almost perfect nanoscale silver GNG. This method consists of shooting silver microcubes at hypersonic velocity (~400 m/s) against solid targets. This process is very efficient to enhance their mechanical (especially hardening) properties. But, the stored elastic energy in the deformed silver nanostructures promotes a recrystallization and they undergo to a transition from nanopolycrystalline to monocrystalline one, leading to structures quite similar to the ones before
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impacts [5]. About 40 days after the impacts, no GNG is observed in the structure,
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