Rapid In Vitro Corrosion Induced by Crack-Like Pathway in Biodegradable Mg–10% Ca Alloy

Abstract

Abstract:The in vitro corrosion mechanism of the biodegradable cast Mg-10% Ca binary alloy in Hanks' solution was evaluated through transmission electron microscopy observations. The corrosion behavior depends strongly on the microstructural peculiarity of Mg 2 Ca phase surrounding the island-like primary Mg phase and the fast corrosion induced by the interdiffusion of O and Ca via the Mg 2 Ca phase of lamellar structure. At the corrosion front, we found that a nanosized crack-like pathway was formed along the interface between the Mg 2 Ca phase and the primary Mg phase. Through the crack-like pathway, O and Ca are atomically exchanged each other and then the corroded Mg 2 Ca phase was transformed to Mg oxides. The in vitro corrosion by the exchange of Ca and O at the nanosized pathway led to the rapid bulk corrosion in the Mg-Ca alloys.

Localized Corrosion of Binary Mg–Ca Alloy in 0.9 wt% Sodium Chloride Solution

“…6 SEM micrographs of the sample surface after the SRET measurement a, high-magnification images of the area with an active spot before b and after c the removal of corrosion products by ultrasound and SEM image of a corroded defect on the Mg-1.0Ca alloy surface d Although the etching solution used is much more aggressive than the 0.9 wt% NaCl solution, there is a same mechanism of the localized dissolution for Mg-Ca alloy. This fact is also supported by the work of Jung et al [28,51], in which it was reported that the fast corrosion of the Mg 2 Ca phase in Mg-Ca alloy is induced by the atomically exchange of O and Ca and then the corroded Mg 2 Ca phase is transformed to Mg oxides. Previous studies [15,52] showed that the fast corrosion of Mg 2 Ca phase leads to the rapid increase in Ca 2?…”

“…1a of the polished surface reveals precipitate particles distributed like discontinuous network in the alloy matrix. It has been reported that the discontinuous precipitate is a eutectic micro-constituent of white color, which consists of gray a-Mg and light b-Mg 2 Ca, and the eutectic Mg has a gray color very similar to the primary a-Mg phase [28].…”

“…9c). With the deepening of corroding pits, the galvanic corrosion transfers into the interior of alloy [28] and the corrosion product deposits accumulate gradually around the pits, which eventually leads to the formation of the volcanic-like structure as the opened cap covering the pit. The permeation of chloride ion into some defects on matrix substrate also results in corroded defects on matrix phase during exposure [55,56].…”