Mechanical and corrosion properties of graphene nanoplatelet-reinforced Mg-Zr and Mg-Zr-Zn matrix nanocomposites for biomedical applications

Magnesium (Mg)-based biomaterials have gained acceptability in fracture fixation due to their ability to naturally degrade in the body after fulfilling the desired functions. However, pure Mg not only degrades rapidly in the physiological environment, but also evolves hydrogen gas during degradation. In this study, Mg0.5Zr and Mg0.5ZrxZn (x = 1-5 wt.%) matrix nanocomposites (MNCs) reinforced with different contents (0.1-0.5 wt.%) of graphene nanoplatelets (GNP) were manufactured via a powder metallurgy technique and their mechanical and corrosion properties were evaluated. The increase in GNP concentration from 0.2 wt.% to 0.5 wt.% added to Mg0.5Zr matrices resulted in decreases in the compressive yield strength and corrosion resistance in Hanks' Balanced Salt Solution (HBSS). On the other hand, a higher concentration (4-5 wt.%) of Zn added to Mg0.5Zr0.1GNP resulted in an increase in ductility but a decrease in compressive yield strength. Overall, an addition of 0.1 wt.% GNPs to Mg0.5Zr3Zn matrices gave excellent ultimate compressive strength (387 MPa) and compressive yield strength (219 MPa). Mg0.5Zr1Zn0.1GNP and Mg0.5Zr3Zn0.1GNP nanocomposites exhibited 29% and 34% higher experimental yield strength, respectively, as compared to the theoretical yield strength of Mg0.5Zr0.1GNP calculated by synergistic strengthening mechanisms including the difference in thermal expansion, elastic modulus, and geometry of the particles, grain refinement, load transfer, and precipitation of GNPs in the Mg matrices. The corrosion rates of Mg0.5Zr1Zn0.1GNP, Mg0.5Zr3Zn0.1GNP, Mg0.5Zr4Zn0.1GNP, and Mg0.5Zr5Zn0.1GNP measured using potentiodynamic polarization were 7.5 mm/y, 4.1 mm/y, 6.1 mm/y, and 8.0 mm/y, respectively. Similarly, hydrogen gas evolution tests also demonstrated that Mg0.5Zr3Zn0.1GNP exhibited a lower corrosion rate (1.5 mm/y) than those of Mg0.5Zr1Zn0.1GNP (3.8 mm/y), Mg0.5Zr4Zn0.1GNP (1.9 mm/y), and Mg0.5Zr5Zn0.1GNP (2.2 mm/y). This study demonstrates the potential of GNPs as effective nano-reinforcement particulates for improving the mechanical and corrosion properties of Mg-Zr-Zn matrices. (C) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.