Investigations on the Microstructure and Degradation Behavior of Hollow Glass Microspheres/Mg Alloy Composites

Abstract

Degradable materials with low density exhibit unique applications in the petroleum equipment field. Herein, hollow glass microspheres (HGM)‐reinforced Mg alloy degradable composites are fabricated. The microstructure and degradation behavior of the composites are investigated using scanning electron microscopy, immersion tests, and electrochemical measurements. Then the influence mechanisms of the HGM on the degradation property of composites are further revealed. The results show that the addition of the HGM significantly reduces the density of the composites. Different degrees of chemical reaction between the Mg alloy melt and HGM wall happen during the fabrication of the composites, resulting in the formation of MgO and Mg2Si. From the corrosive morphologies of the composites, Mg2Si phase can serve as a microgalvanic cathode consequently inducing more galvanic corrosion. The interface between HGM and matrix alloy can serve as the initiation site for pitting corrosion and increase the exposed area of the matrix in the aggressive medium. The electrochemical measurements prove that the HGM can act a part in facilitating the exfoliation of degradation products. Consequently, the HGM greatly increases the degradation rate of the composites in the KCl solution. The current study provides a new insight for developing lightweight Mg‐based composites with quickly degradable performance.

Enhanced Mechanical and Degradation Properties of Hollow Glass Microspheres/Mg Matrix Composites by Incorporating Copper Power for Degradable Downhole Tool Applications

“…The pitting corrosions initiated preferentially on the α‐Mg matrix around the HGM particles and β phase, and this was mainly attributed to the thermal thermodynamic instability of the interface between HGM and Mg matrix and the galvanic corrosion between α‐Mg and β phase, which had been reported in previous research. [ 17 ] Meanwhile, more serious pitting corrosion was observed around Al 2 CuMg phase, and they occurred not only on the α‐Mg matrix but also on the β phase. It thus can be conjectured that Al 2 CuMg phase was cathodic relative to the α‐Mg and β phase and resulted in the microgalvanic corrosion of the latter two in the KCl solution.…”

“…The polygonal Mg 2 Si phase around the HGM particles was the reaction product. [ 9 ] It also can be seen that the semicontinuous network‐like β‐Mg 17 Al 12 phase precipitated along the grain boundaries, separating the α‐Mg phase into irregular block. With the increase in Cu content, some fine granular phases appeared in the β‐Mg 17 Al 12 phase in HGM/MA‐0.6Cu (Figure 3b) and a few fishbone‐like structures were observed in HGM/MA‐1Cu (Figure 3c).…”

“…Generally, the loop at the high‐frequency region (the smaller one) was related to the double‐electric layer of the substrate surface, and the loop at the low‐frequency region was related to the corrosion products layer. [ 17 ] The larger diameter of the capacitive loop means a better corrosion resistance (lower degradation rate). [ 18 ] With the increase in Cu content, the corrosion resistance of the composites first decreased and then increased, which was consistent with the results of polarization test.…”

“…Element alloying and introducing reinforcement particulates have been proved the effective methods to adjust the performances of the magnesium. Recently, some Mg-based alloys/composites that can be used for degradable downhole tools have been developed, such as Mg─Zn─Zr alloy, [6] Mg─Ni─Y alloy, [3] Mg─Al─Zn─Si alloy, [1] FAC/Mg alloy composites, [7] hollow glass microsphere (HGM)/ Mg alloy composites, [8,9] and so on. The addition of some hardening metal elements (such as Al, Zn, Zr, RE, et al) can significantly strengthen the Mg alloys.…”

“…[3,6,10] Among these elements, the effects of Al and Zn on the performances of Mg alloys have been reported by many researches, these studies indicated that Mg alloys containing high Al (10-20 wt%) and Zn (2-10 wt %) contents exhibited excellent compressive strengths and corrosion rates. [11] In our previous studies, [8,9] the Mg alloy with high Al and Zn contents (Mg─15Al─5Zn) was chosen as the matrix, a novel Mg-based composites was developed through adding HGM into the Mg alloy (denote as HGM/MA composites). Results showed that the HGM particles not only increased the compressive strength and degradation rate but also effectively reduced the density of the Mg alloy.…”