Surface Nanostructuring of a CuAlBe Shape Memory Alloy Produces a 10.3 ± 0.6 GPa Nanohardness Martensite Microstructure
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Centro Tecnológico Aragón, Facultad de Estudios Superiores Aragón, Universidad Nacional Autónoma de México. Av. Rancho Seco s/n, Col. Impulsora, Cd. Nezahualcóyotl, 57130 Estado de México, Mexico
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Departamento de Materiales y Manufactura, Facultad de Ingeniería, Universidad Nacional Autónoma de México, PIIT, Vía de la Innovación 410, Apodaca, 66629 Nuevo León, Mexico
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Departamento de Materiales y Manufactura, Facultad de Ingeniería, Edificio O, Universidad Nacional Autónoma de México. Avenida Universidad 3000, Coyoacán, 04510 Ciudad de México, Mexico
*
Author to whom correspondence should be addressed.
Materials 2020, 13(24), 5702; https://doi.org/10.3390/ma13245702
Received: 24 October 2020
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Revised: 3 December 2020
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Accepted: 8 December 2020
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Published: 14 December 2020
(This article belongs to the Special Issue Shape Memory Materials: New Design Concepts and Novel Materials)
Severe plastic deformation (SPD) has led to the discovery of ever stronger materials, either by bulk modification or by surface deformation under sliding contact. These processes increase the strength of an alloy through the transformation of the deformation substructure into submicrometric grains or twins. Here, surface SPD was induced by plastic deformation under frictional contact with a spherical tool in a hot rolled CuAlBe-shape memory alloy. This created a microstructure consisting of a few course martensite variants and ultrafine intersecting bands of secondary martensite and/or austenite, increasing the nanohardness of hot-rolled material from 2.6 to 10.3 GPa. In as-cast material the increase was from 2.4 to 5 GPa. The friction coefficient and surface damage were significantly higher in the hot rolled condition. Metallographic evidence showed that hot rolling was not followed by recrystallisation. This means that a remaining dislocation substructure can lock the martensite and impedes back-transformation to austenite. In the as-cast material, a very fine but softer austenite microstructure was found. The observed difference in properties provides an opportunity to fine-tune the process either for optimal wear resistance or for maximum surface hardness. The modified hot-rolled material possesses the highest hardness obtained to date in nanostructured non-ferrous alloys.
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Keywords:
advanced alloy materials; materials synthesis and characterisation; shape memory alloy; surface modification; severe plastic deformation; martensite; nanohardness
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Description: Dark-field microscopy (crossed polarisers) of the hot-rolled CuAlBe-alloy. The cubic austenite phase is optically isotropic and should appear black; a thin oxide film on the surface produces a slight rotation of the optical axis which produces a blue colour. Additionally, the internal stresses generate an opto-elastic effect which allow for the observation of dark fringes revealing the stress patterns. The monoclinic martensite phase is optically anisotropic and appears as fine brightly coloured needles.
MDPI and ACS Style
Figueroa, C.G.; Jacobo, V.H.; Cortés-Pérez, J.; Schouwenaars, R. Surface Nanostructuring of a CuAlBe Shape Memory Alloy Produces a 10.3 ± 0.6 GPa Nanohardness Martensite Microstructure. Materials 2020, 13, 5702. https://doi.org/10.3390/ma13245702
AMA Style
Figueroa CG, Jacobo VH, Cortés-Pérez J, Schouwenaars R. Surface Nanostructuring of a CuAlBe Shape Memory Alloy Produces a 10.3 ± 0.6 GPa Nanohardness Martensite Microstructure. Materials. 2020; 13(24):5702. https://doi.org/10.3390/ma13245702
Chicago/Turabian StyleFigueroa, Carlos G., Víctor H. Jacobo, Jacinto Cortés-Pérez, and Rafael Schouwenaars. 2020. "Surface Nanostructuring of a CuAlBe Shape Memory Alloy Produces a 10.3 ± 0.6 GPa Nanohardness Martensite Microstructure" Materials 13, no. 24: 5702. https://doi.org/10.3390/ma13245702
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