Microstructural evolution and intermetallic formation in Zn-Mg hybrids processed by High-Pressure Torsion

ABSTRACT

High-pressure torsion (HPT) was used to investigate the synthesis of Zn-Mg hybrids by direct bonding of separate disks of Zn and Mg at room temperature under an applied pressure of 6.0 GPa after 1, 5, 15 and 30 turns. Microstructural characterisation of the HPT-processed disks showed the formation of a sub-micron multilayered structure embedded in a Zn-rich matrix with an average grain size of ∼ 600 nm at the disk periphery after 30 turns. XRD and TEM analysis revealed the presence of MgZn₂ and Mg₂Zn₁₁ intermetallic compounds, which increased in volume fractions with increasing number of turns. The formation of these intermetallics, together with Hall-Petch strengthening, led to an exceptional increase of the hardness values after 15 turns. Electrochemical testing in simulated body fluid showed that the degree of plastic deformation had an impact on the corrosion resistance of the Zn-Mg hybrids, which would affect their implementation in the biomedical field for absorbable applications. This study confirmed that there is significant potential for using HPT in the joining of dissimilar metals at room temperature to form Zn-Mg hybrids containing ultrafine-grained metal-matrix heterostructures with enhanced hardness.

KEYWORDS:

• Heterostructure
• high-pressure torsion
• intermetallic compound
• severe plastic deformation
• ultrafine-grained
• Zn-Mg

Disclosure statement

The authors declare that there is no conflict of interests regarding the publication of this article.

ORCID

David Hernández-Escobar http://orcid.org/0000-0001-6133-5259

Zia Ur Rahman http://orcid.org/0000-0003-0629-5287

Hakan Yilmazer http://orcid.org/0000-0001-5602-4966

Megumi Kawasaki http://orcid.org/0000-0003-0028-3007

Carl J. Boehlert http://orcid.org/0000-0001-8051-1051

Additional information

Funding

The funding for this research was supported by National Science Foundation Division of Material Research (Grant No. DMR1607942) through the Metals and Metallic Nanostructures (MMN) program.