表面改性后AZ31B镁合金在不同模拟体液中的降解性能研究

采用化学沉积法在AZ31B镁合金表面制备了钙磷陶瓷涂层,通过浸泡试验和电化学试验研究了其在3种不同模拟体液(生理盐水、PBS、Hank′s)中的降解性能。结果表明,沉积处理改变了AZ31B镁合金在模拟体液中的降解性能,明显抑制了其降解速度;浸泡后溶液的pH值变化结果和电化学实验结果均表明,在3种不同模拟体液中,表面处理后AZ31B镁合金显示出不同的降解速度,顺序依次为:生理盐水>PBS溶液>Hank′s溶液。     

In vitro corrosion of magnesium alloy AZ31 --- a synergetic influence of glucose and Tris

Biodegradable Mg alloys have generated great interest for biomedical applications. Accurate predictions of in vivo degradation of Mg alloys through cost-effective in vitro evaluations require the latter to be conducted in an environment close to that of physiological scenarios. However, the roles of glucose and buffering agents in regulating the in vitro degradation performance of Mg alloys has not been elucidated. Herein, degradation behavior of AZ31 alloy is investigated by hydrogen evolution measurements, pH monitoring and electrochemical tests. Results indicate that glucose plays a content-dependent role in degradation of AZ31 alloy in buffer-free saline solution. The presence of a low concentration of glucose, i.e. 1.0 g/L, decreases the corrosion rate of Mg alloy AZ31, whereas the presence of 2.0 and 3.0 g/L glucose accelerates the corrosion rate during long term immersion in saline solution. In terms of Tris-buffered saline solution, the addition of glucose increases pH value and promotes pitting corrosion or general corrosion of AZ31 alloy. This study provides a novel perspective to understand the bio-corrosion of Mg alloys in buffering agents and glucose containing solutions.     

<Emphasis Type="Italic">In vitro</Emphasis> corrosion of magnesium alloy AZ31 — a synergetic influence of glucose and Tris

Biodegradable Mg alloys have generated great interest for biomedical applications. Accurate predictions of in vivo degradation of Mg alloys through cost-effective in vivo evaluations require the latter to be conducted in an environment close to that of physiological scenarios. However, the roles of glucose and buffering agents in regulating the in vivo degradation performance of Mg alloys has not been elucidated. Herein, degradation behavior of AZ31 alloy is investigated by hydrogen evolution measurements, pH monitoring and electrochemical tests. Results indicate that glucose plays a content-dependent role in degradation of AZ31 alloy in buffer-free saline solution. The presence of a low concentration of glucose, i.e. 1.0 g/L, decreases the corrosion rate of Mg alloy AZ31, whereas the presence of 2.0 and 3.0 g/L glucose accelerates the corrosion rate during long term immersion in saline solution. In terms of Tris-buffered saline solution, the addition of glucose increases pH value and promotes pitting corrosion or general corrosion of AZ31 alloy. This study provides a novel perspective to understand the bio-corrosion of Mg alloys in buffering agents and glucose containing solutions.     

电轧AZ31镁合金在模拟海水中腐蚀行为研究

为对比研究高能电脉冲轧制工艺和冷轧工艺对AZ31镁合金腐蚀性能的影响,采用腐蚀形貌观察、动电位极化测试、电化学阻抗谱与腐蚀速度测试等方法系统地研究了高能电脉冲轧制和冷轧AZ31镁合金带材在模拟海水(3.5%NaCl)中的腐蚀行为.结果表明:在同样变形量下,与冷轧AZ31镁合金相比,电轧AZ31镁合金的耐腐蚀性略有提高.这与电轧AZ31镁合金再结晶比例大,位错密度小,具有较低能态的位错组态及能形成较稳定的腐蚀产物膜有关.     

New insights into the effect of Tris-HCl and Tris on corrosion of magnesium alloy in presence of bicarbonate,sulfate,hydrogen phosphate and dihydrogen phosphate ions

In vitro degradation is an important approach to screening appropriate biomedical magnesium(Mg) alloys at low cost. However, corrosion products deposited on Mg alloys exert a critical impact on corrosion resistance. There are no acceptable criteria on the evaluation on degradation rate of Mg alloys. Understanding the degradation behavior of Mg alloys in presence of Tris buffer is necessary. An investigation was made to compare the influence of Tris-HCl and Tris on the corrosion behavior of Mg alloy AZ31 in the presence of various anions of simulated body fluids via hydrogen evolution, p H value and electrochemical tests.The results demonstrated that the Tris-HCl buffer resulted in general corrosion due to the inhibition of the formation of corrosion products and thus increased the corrosion rate of the AZ31 alloy. Whereas Tris gave rise to pitting corrosion or general corrosion due to the fact that the hydrolysis of the amino-group of Tris led to an increase in solution p H value, and promoted the formation of corrosion products and thus a significant reduction in corrosion rate. In addition, the corrosion mechanisms in the presence of Tris-HCl and Tris were proposed. Tris-HCl as a buffer prevented the formation of precipitates of HCO_3~-, SO_4~(2-),HPO_4~(2-) and H_2PO_4~- ions during the corrosion of the AZ31 alloy due to its lower buffering p H value(x.x).Thus, both the hydrogen evolution rate and corrosion current density of the alloy were approximately one order of magnitude higher in presence of Tris-HCl than Tris and Tris-free saline solutions.     

Corrosion fatigue behavior of extruded magnesium alloy AZ31 in sodium chloride solution

In the present study, corrosion fatigue experiments were done using the extruded magnesium alloy AZ31 in the 3% sodium chloride solution to clarify the corrosion fatigue characteristics of the material. Corrosion fatigue lives greatly decreased as compared with those in laboratory air. It was also clarified that most of the corrosion fatigue life (70–80%) at the lower stress amplitude is occupied with the period of the corrosion pit growth. Corrosion fatigue lives were evaluated quantitatively by dividing the corrosion fatigue process into the following two periods, i.e. (1) the corrosion pit growth period preceding the crack initiation from the pit and (2) the crack growth period before the specimen failure. In the analysis, the law of the corrosion pit growth proposed by authors was used to deal with the above first period. The evaluated results corresponded well to the experimental results.     

Povidone–iodine as a corrosion inhibitor towards a low modulus beta Ti-45Nb implant alloy in a simulated body fluid

Povidone-iodine and various bactericidal agents used in dental procedures may affect the corrosion response of an implant/prosthesis in the oral environment. The effect of various concentrations of povidone–iodine (PI) on the corrosion behavior of a low modulus beta titanium alloy, Ti-45Nb, has been investigated in normal saline solution. The open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements have been used to assess the electrochemical response of the alloy surface on PI addition so as to effectively predict the prosthetic treatment outcome. As the concentration of PI is increased, the corrosion rate decreases, suggested by decreased R_p values. Povidone–iodine acts as an anodic inhibitor by adsorbing on the anodic sites of the alloy. Addition of PI to a simulated body fluid such as normal saline leads to a decrease in corrosion rate of Ti-45Nb alloy.     

The electrochemical corrosion behavior of K38G nanocrystalline thin film in 3.5% NaCl solution

The electrochemical corrosion behavior of a K38G nanocrystalline (NC) thin film fabricated by magnetron sputtering technique has been investigated in comparison with cast K38G alloy in 3.5% NaCl solution. The results indicated that compared with the cast K38G alloy, the NC thin film had a higher occurring frequency of metastable pits and lower rates of stable pitting nucleation and growth. The influence of nanocrystallization on the pit initiation and pit growth processes has been discussed, respectively.     

Effect of chloride ion level on the corrosion performance of MAO modified AZ31 alloy in NaCl solutions

Microarc oxidation coatings were fabricated on AZ31 magnesium alloy in the electrolyte of sodium phosphate. Potentiodynamic polarization and electrochemical impedance spectroscopy tests were employed to investigate the electrochemical corrosion behavior. The corroded surface was characterized by an optical microscope and X-ray diffraction. The influence of chloride ion concentration on the corrosion resistance of microarc oxidation coated AZ31 alloy is discussed. The corrosion current density enlarged ratio and the charge transfer resistance reduced ratio indicated that the extent of the corrosion damage of microarc oxidation coated AZ31 alloy is much higher when chloride ion concentration is greater than 5%. A corrosion mechanism related to the effect of chloride ion concentrations on the corrosion behavior is proposed.     

Fluoride Conversion Coating on Biodegradable AZ31B Magnesium Alloy

A fluoride conversion coating was successfully prepared on AZ31B magnesium alloy by chemical reaction in hydrofluoric acid. Morphologies, composition, bonding strength, corrosion properties, in vitro cytotoxicity and antibacterial properties of the coating were investigated, respectively. The scanning electron microscopy observations revealed a dense coating with some irregular pores. The thin-film X-ray diffraction analysis indicated that the coating was mainly composed of MgO and MgF2. The electrochemical impedance spectroscopy results showed that the fluoride conversion coating significantly improved the corrosion resistance of AZ31B. The hydroxyapatite formed on the surface of the fluoride coated AZ31 B after being immersed in the simulated blood plasma indicated the good bioactivity of the material. The in vitro cytotoxicity test showed that the fluoride coated AZ31B alloy was not toxic to BMMSCs （human bone marrow-derived mesenchymal stem cells）. It was also found that the fluoride coated AZ31 B alloy had antibacterial capability.     

AZ镁合金用于干电池负极材料的电化学性能研究

采用失重法、线性电位扫描、扣式电池放电测试等方法,研究AZ21和AZ31镁合金作为镁锰干电池负极材料时的电化学性能以及电解质添加剂Li2CrO4对其电化学性能的影响。结果表明,作为干电池的负极材料,在Mg(ClO4)2作电解质时,AZ21与AZ31相比,其自腐蚀速率大,开路电压稍高,电池容量和正极材料利用率低;添加少量的Li2CrO4能大大降低AZ21和AZ31合金的自放电速率,其缓蚀作用随Li2CrO4浓度的增加而增加,但当超过0.3%(质量分数)后反而降低;Li2CrO4的添加可提高电池的工作电压、电池容量和正极材料利用率。     

Biodegradable behaviors of AZ31 magnesium alloy in simulated body fluid

Magnesium alloys have unique advantages to act as biodegradable implants for clinical application. The biodegradable behaviors of AZ31 in simulated body fluid (SBF) for various immersion time intervals were investigated by electrochemical impedance spectroscopy (EIS) tests and scanning electron microscope (SEM) observation, and then the biodegradable mechanisms were discussed. It was found that a protective film layer was formed on the surface of AZ31 in SBF. With increasing of immersion time, the film layer became more compact. If the immersion time was more than 24 h, the film layer began to degenerate and emerge corrosion pits. In the meantime, there was hydroxyapatite particles deposited on the film layer. The hydroxyapatite is the essential component of human bone, which indicates the perfect biocompatibility of AZ31 magnesium alloy.     

AZ31镁合金在Hank’s模拟体液中的腐蚀行为研究

研究了AZ31镁合金在Hank's模拟体液中的腐蚀行为,包括腐蚀形貌、腐蚀速度和腐蚀电化学特征参数.通过扫描电子显微镜(SEM)比较了不同腐蚀环境中镁合金样品的腐蚀形貌特征.利用失重法测量了镁合金的腐蚀速度,并依此分析了Hank's模拟体液中各成分对镁合金腐蚀速度的影响.测量并分析了不同pH值下的动电位动态极化曲线.结果表明,镁合金在Hank's模拟体液中的腐蚀主要为氯离子引起的点蚀;H_2PO_4~-和HPO_4~(2-)具有缓蚀作用;pH值的升高可以提高镁合金腐蚀反应的自腐蚀电位,降低腐蚀反应的热力学倾向,稳定腐蚀过程中形成的钝化膜,从而降低了腐蚀速度.     

Effect of D-fructose on the in-vitro corrosion behavior of AZ31 magnesium alloy in simulated body fluid

The effect of addingd-fructose to simulated body fluid(SBF) on the corrosion behavior of AZ31 magnesium(Mg) alloy at 37.C and at a pH of 7.4 was studied by potentiodynamic polarization(PDP), electrochemical impedance spectroscopy(EIS), potentiostatic polarization and hydrogen(H2) collecting techniques,Raman spectroscopy technique, scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), X-ray photoelectron spectroscopy analysis(XPS) and Fourier transformed infrared(FTIR). The results demonstrated that the addition of fructose enhanced the deposition of phosphates forming thick and compact corrosion products, which inhibited the transmission of aggressive ions into the Mg substrate. As a result, both the anodic dissolution of Mg and negative difference effect(NDE) were suppressed. Thus, the corrosion resistance of AZ31 Mgalloy in SBF was significantly improved.     

In vitro degradation behaviour of a friction stir processed magnesium alloy

In this study, the in vitro degradation behaviour of a friction stir processed AZ31 magnesium alloy was investigated. Electrochemical experiments in simulated body fluid suggest that friction stir processing marginally enhances the degradation resistance of the alloy, which could be attributed to the dissolution of secondary phase particles. Homogenisation of the microstructure reduces galvanic corrosion. It is envisaged that the beneficial effect would be more pronounced for magnesium alloys which contain high volume fraction of galvanic corrosion inducing secondary phase particles.     

Comparison of biodegradable behaviors of AZ31 and Mg–Nd–Zn–Zr alloys in Hank's physiological solution

The main challenge for the application of magnesium and its alloy as degradable biomaterials lies in their high degradation rates in physiological environment. In the present work, the biodegradable behavior of a patent magnesium alloy Mg–Nd–Zn–Zr (JDBM) and a reference alloy AZ31 was systematically investigated in Hank's physiological solution. The corrosion rate of JDBM (0.28 mm/year) was much slower than that of AZ31 (1.02 mm/year) in Hank's solution for 240 h. After corrosion products were removed, smooth surface of the JDBM was observed by SEM observation compared to many deep pits on the surface of AZ31. Open-circuit potential and potentiodynamic polarization results manifested that pitting corrosion did not occurred on the surface of JDBM at the early period of immersion time due to the formation of a more protective and compact film layer suggested by electrochemical impedance spectroscopy study. The corrosion rate of magnesium alloys was found to slow down in dynamic corrosion in comparison with that in the static corrosion. This provided the basis for scientific evaluation of in vitro and in vivo corrosion behavior for degradable biomagnesium alloy. The present results suggest that the new patent magnesium alloy JDBM is a promising candidate as degradable biomaterials and is worthwhile for further investigation in vivo corrosive environment.     

微波辅助法制备镁合金的植酸镁/羟基磷灰石复合涂层及其耐蚀性能

采用微波辅助法在AZ31镁合金表面制备了植酸镁/羟基磷灰石(PA/HA)复合涂层。利用FESEM、EDS、XRD和电化学性能测试等方法表征涂层的表面形貌、物相组成以及耐蚀性能,探究了植酸溶液的pH值对PA/HA复合涂层形貌及耐蚀性能的影响,并通过浸泡实验研究了镁合金及PA/HA复合涂层在模拟体液(SBF)中的降解矿化行为。结果表明:在植酸预处理中,植酸溶液的pH=5.0时制备得到的PA/HA复合涂层表面均匀、无裂纹,与镁合金基底的界面结合良好;并且在此pH值下PA/HA复合涂层包覆镁合金样品的交流阻抗最大,自腐蚀电流密度最小,说明其耐蚀性最好。在SBF中,PA/HA复合涂层能够快速诱导磷灰石的生成,并显著提高镁合金基底的耐蚀性能。     

Effects of High Magnetic Field on Solidification and Corrosion Behaviors of Magnesium Alloy

The solidification behaviors of AZ61 magnesium alloy under a high magnetic field were studied. The corrosion property of AZ61 alloy was investigated in a solution of 3.5 mol/L NaCI by measuring electrochemical p.olarization. The results show that the high magnetic field can refine microstructure and benefit aluminum transfer. The crystal of α-Mg is induced to orient with their c-axis parallel to the magnetic field. The corrosion studies indicate that different crystal plane of magnesium has different corrosion property. The passivating films on the α- and b-planes have higher corrosion resistance than that on the c-plane. Aligned structure affects the corrosion property of AZ61 magnesium alloy.     

Electrochemical behavior of biocompatible AZ31 magnesium alloy in simulated body fluid

Dense oxidation coatings have been successfully developed on biocompatible AZ31 magnesium alloy, using microarc oxidation technique, to improve the corrosion resistance. Three different deposition voltages of 250, 300, and 350 V have been employed. The effect of voltage on the coating corrosion resistance has been evaluated through electrochemical experiments in a simulated body fluid (SBF) up to 7 days. Potentiodynamic polarization and electrochemical impedance spectroscopy scans were performed in the SBF solution, followed by optical microscopy surface inspection. The results indicate that the corrosion rates of the coatings are in the order of 250 < 300 < 350 V after immersion for 7 days, and the charge transfer resistance (R _ct) of the three samples is in the order of 250 > 300 > 350 V. Both the electrochemical tests and the surface inspection suggest that the 250 V coating has the highest corrosion resistance, with lowest corrosion current density, highest R _ct, and the best surface quality.     

高能喷丸对AZ31镁合金耐腐蚀性及硬度的影响

采用高能喷丸对AZ31镁合金棒材端面进行表面自纳米化处理,利用失重法研究了AZ31镁合金喷丸试样和未喷丸试样在中性5%NaCl溶液中的腐蚀行为。利用扫描电子显微镜(SEM)、能量色谱仪(EDS)对塑性变形层腐蚀后的表面形貌、元素分布进行了表征,利用微观硬度计测试了由喷丸表面到基体的硬度变化。结果表明,喷完后AZ31镁合金试样的腐蚀速率明显大于未喷丸的试样,随着腐蚀时间的延长,喷丸试样的腐蚀率急剧减小,然后缓慢降低,在喷丸表面形成了1层厚度约150μm的塑性变形区,在喷丸表面有裂纹存在。晶粒细化显著提高了母材表面的微观硬度,喷丸表面的微观硬度最高达到135HV,是母材的2倍多。