A influência do tamanho de grão na resistência à corrosão do magnésio puro processado por HPT e recozido

Abstract

Pure magnesium has been studied for bone implants, but its low corrosion resistance in physiological environments is a limiting factor for many applications. The study of significant parameters such as grain size and surface homogeneity is important in order to better understanding of how to improve the metal's corrosion resistance. HPT (High Pressure Torsion) processing of metal allows the reduction of the grain size of the material surface in micrometric scales. Also, the application of annealing heat treatment, after the HPT processing, in different temperatures, can gradually increase the material grain size. The aim of this work is to evaluate the grain size influence on the corrosion resistance of pure magnesium processed by HPT and anneal. For this, 99.7% pure magnesium samples were processed by HPT at a 6 GPa applied pressure, with number of turns equal to 10 and rotation speed of 2 rpm, at room temperature, and submitted to annealing treatments at temperatures of 100 ° C, 150 ° C, 200 ° C, 300 ° C and 400 ° C to obtain samples with different grain sizes. To evaluate the effect of grain size on the corrosion resistance of pure magnesium samples, electrochemical corrosion tests were performed, such as electrochemical impedance spectroscopy (EIS) and hydrogen evolution, both in a Hank's solution. Samples surface morphology characterization was carried out by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) analysis. It was found that the pure magnesium processed by HPT showed higher resistance to corrosion when annealed at 200° C, suggesting that a grain size treatment on a more homogeneous surface under the studied conditions is significant