Abstract
The effect of the Ca2Mg6Zn3 phase on the corrosion behavior of biodegradable Mg-4.0Zn-0.2Mn-xCa (ZM-xCa, x = 0.1, 0.3, 0.5 and 1.0 wt.%) alloys in Hank’s solution was investigated with respect to phase spacing, morphology, distribution and volume fraction. With the increase in Ca addition, the volume fraction of the Ca2Mg6Zn3 phase increased from 2.5% to 7.6%, while its spacing declined monotonically from 43 μm to 30 μm. The Volta potentials of secondary phases relative to the Mg matrix were measured by using scanning kelvin probe force microscopy (SKPFM). The results show that the Volta potential of the intragranular spherical Ca2Mg6Zn3 phase (+109 mV) was higher than that of the dendritic Ca2Mg6Zn3 phase (+80 mV). It is suggested that the Ca2Mg6Zn3 acted as a cathode to accelerate the corrosion process due to the micro-galvanic effect. The corrosion preferred to occur around the spherical Ca2Mg6Zn3 phase at the early stage and developed into the intragranular region. The corrosion rate increased slightly with increasing Ca content from 0.1 wt.% to 0.5 wt.% because of the enhanced micro-galvanic corrosion effect. The decrease in the phase spacing and sharp increase in the secondary phase content resulted in a dramatic increase in the corrosion rate of the ZM-1.0Ca alloy.
Highlights
Magnesium (Mg) alloys have attracted great attention as promising biodegradable materials for orthopedic implants and cardiovascular interventional devices [1–5]
We have focused on the effects of the Ca2Mg6Zn3 phase with respect to its morphology, distribution and volume fractions on the corrosion behavior of Mg-4.0Zn-0.2Mn-xCa alloys in Hank’s simulate solution, a solution similar to human body fluid, which is generally used for in vitro corrosion experiments
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Summary
Magnesium (Mg) alloys have attracted great attention as promising biodegradable materials for orthopedic implants and cardiovascular interventional devices [1–5]. Compared with traditional metallic biomaterials, such as stainless steels and titanium alloys, Mg alloys reduce the stress-shielding risk [6]. Mg alloys usually degrade within a few weeks, and the produced Mg2+ ions can be advantageous for bone healing without toxicity [7]. The uncontrolled corrosion of Mg alloys may lead to unexpected mechanical failure before tissue recovery. This is a major problem for Mg alloys being used as clinical implants in a physiological environment with a high chloride and/or pH of 7.4–7.6 [7]. Controlling the corrosion of Mg alloys is becoming an urgent problem
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