Abstract
The Mg–Zn–Zr–Gd alloys belong to a group of biometallic alloys suitable for bone substitution. While biocompatibility arises from the harmlessness of the metals, the biocorrosion behavior and its origins remain elusive. Here, aiming for the tailored biodegradability, we prepared the Mg–2.0Zn–0.5Zr–xGd (wt %) alloys with different Gd percentages (x = 0, 1, 2, 3, 4, 5), and studied their microstructures and biocorrosion behavior. Results showed that adding a moderate amount of Gd into Mg–2.0Zn–0.5Zr alloys will refine and homogenize α-Mg grains, change the morphology and distribution of (Mg, Zn)3Gd, and lead to enhancement of mechanical properties and anticorrosive performance. At the optimized content of 3.0%, the fishbone-shaped network, ellipsoidal, and rod-like (Mg, Zn)3Gd phase turns up, along with the 14H-type long period stacking ordered (14H-LPSO) structures decorated with nanoscale rod-like (Mg, Zn)3Gd phases. The 14H-LPSO structure only exists when x ≥ 3.0, and its content increases with the Gd content. The Mg–2.0Zn–0.5Zr–3.0Gd alloy possesses a better ultimate tensile strength of 204 ± 3 MPa, yield strength of 155 ± 3 MPa, and elongation of 10.6 ± 0.6%. Corrosion tests verified that the Mg–2.0Zn–0.5Zr–3.0Gd alloy possesses the best corrosion resistance and uniform corrosion mode. The microstructure impacts on the corrosion resistance were also studied.
Highlights
The magnesium alloys have attracted considerable attentions in biomaterial applications, due to their outstanding mechanical properties and unique biodegradability in the physiological environments [1,2]
Thin foils for Transmission electron microscopy (TEM) observation were punched into discs of 3 mm in diameter, mechanically polished to approximately 70 μm, and twin-jet electropolished in a solution of 97% ethyl alcohol and 3% perchloric acid at −45 ◦ C and 0.1 A
Gd element tends to accumulate at the front of the solid–liquid interface, which increases the supercooling phenomenon in the solid–liquid interface area, leading to the increase of nucleation rate
Summary
The magnesium alloys have attracted considerable attentions in biomaterial applications, due to their outstanding mechanical properties and unique biodegradability in the physiological environments [1,2]. To improve the corrosion resistance and mechanical properties, element alloying has been widely applied [8]. As an essential but harmless element in the human body, zinc provides strength for Mg alloy, due to solid solution strengthening [10]. Alloying the Zr with Mg will effectively refine the grain size and improve mechanical property and corrosion resistance [11]. Though with certain toxicity in living body, the Gd can be released below the harmful rates subjected to proper controls [12] Following these progresses, several Mg–Zn–Zr–Gd alloys were developed [13]. In contrast to dedicated studies of mechanical properties after Gd addition [14], the corrosion behaviors are rather scarcely reported for the Mg–Zn–Zr–Gd alloys. An optimized percentage was figured out, and impacts of microstructural evolution on mechanical properties and anticorrosion were studied
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