Ratcheting behavior of ZEK100 magnesium alloy with various loading conditions and different immersing time
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Lilan Gaoa) School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People’s Republic of China; and School of Mechanical Engineering, Tianjin University of Technology, Tianjin 300191, People’s Republic of China (Received 14 December 2016; accepted 10 March 2017)
It is desirable to evaluate the ratcheting behavior of biomedical magnesium under cyclic loading with and without precorrosion, due to the promising future in biomedical implant field. This study focuses on the investigation of the uniaxial ratcheting strain evolutions of ZEK100 magnesium alloy sheet under various loading conditions and different corrosion time. To illustrate the ratcheting response in detail, the effects of several factors on the ratcheting strain evolution were discussed, including mean stress, stress amplitude, specimen orientations, loading history, and precorroded duration. A series of asymmetrical multistep stress-controlled ratcheting tests were conducted. The mean stress, stress amplitude, and precorrosion duration have significant influence on the ratcheting response of material. ZEK100 magnesium alloy is sensitive to loading history. ZEK100 magnesium alloy exhibits anisotropic behavior, and it is found that the final ratcheting strain of transverse direction (TD) specimens is always larger than that of rolling direction (RD) specimens. The corrosion behavior of ZEK100 magnesium alloy in phosphate buffered solution (PBS) simulated physiological environment was also studied. The corrosion process is characterized by pitting corrosion, and the corrosion rate of material stabilizes at about 2.4 g/(m2 d) after an exponentially decrease at initial stage.
I. INTRODUCTION
In recent years, new innovative magnesium alloys have attracted a lot of attentions as potential load-bearing bioimplant materials due to their excellent mechanical properties, biocompatibility as well as biodegradability.1,2 Magnesium alloys have relatively low elastic modulus that is much closer to that of natural bones than currently traditional metallic materials, which could minimize or even avoid stress shielding effect.3 With all of these special properties, magnesium and its alloys become promising candidates and are widely studied for biomedical implant applications. However, magnesium alloys could be degraded in physiological environment, which makes the secondary surgery as well as the problems caused by the surgery avoidable. Considering magnesium alloys are biodegradable in the body, the corrosion products are expected to be not deleterious to the surrounding tissues. Nevertheless, the problems impeding magnesium alloys’ application in biomedical field still exist, the most Contributing Editor: Michele Manuel a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.104
prominent one is that magnesium alloys corrode so fast in physiological environment that they lose the required mechanical integrity before the damaged tissues have healed.4 The rapid corrosion of magnesium alloys in physiologic
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