基于喷丸强化的生物医用镁合金腐蚀和摩擦学特性研究

发布时间：2019-05-24 09:07

【摘要】：为了解决生物医用镁及镁合金在生物体内腐蚀过快的问题,并且保持良好的生物相容性,本文以医用WE43镁合金为研究对象,以高能喷丸表面处理技术为强化手段,对喷丸强化前后WE43镁合金试样的腐蚀和摩擦磨损行为进行了深入的研究。(1)对不同喷丸参数下强化的试样进行残余应力场数值模拟分析发现,弹丸直径、入射速度对试样表面的残余应力场分布及等效应变的影响最大,弹丸入射角度的影响次之,直径为0.8mm和1.0mm、入射速度为90m/s、入射角度为90o的试样表面喷丸效果最优。对试样分别进行了60s、90s和120s的喷丸强化处理,试样表面的微观组织分析结果发现,喷丸强化使WE43镁合金表面产生了约120~150μm的晶粒细化层,晶粒细化机制为孪晶-位错堆积-亚晶形成-动态再结晶。试样的硬度从处理表面至心部呈梯度分布,表面硬度达基体硬度的两倍。残余压应力测试结果与数值模拟分析结果一致性良好,喷丸强化120s试样表面的综合特征良好。(2)对喷丸强化前后的WE43镁合金试样分别进行了模拟体液(简称SBF)浸泡实验和盐雾腐蚀实验,研究了试样的腐蚀降解行为。腐蚀速率结果显示,SBF浸泡中,未喷丸强化试样的腐蚀速率最大,3组喷丸试样的腐蚀速率相仿,在腐蚀后期由于强化层逐渐失效导致腐蚀速率上升;盐雾腐蚀过程中,4组试样的腐蚀速率相差不大,腐蚀速率逐渐减小直到稳定,喷丸强化对试样耐盐雾腐蚀性能的提高较小。溶液的PH值变化结果显示,喷丸试样的溶液PH值均小于未喷丸处理试样的溶液,喷丸强化能够有效减小试样在SBF中的腐蚀速率,并且喷丸强化时间越长,强化效果越好。试样腐蚀后的形貌分析得出,喷丸处理试样的表面状态较未喷丸试样好,表面均有磷酸盐的沉积。综合而言,喷丸强化对WE43镁合金的SBF浸泡腐蚀性能提高较明显,耐盐雾腐蚀性能次之,且喷丸强化120s的试样耐腐蚀性能最好。(3)分别对喷丸前后的WE43镁合金试样进行了SBF和质量分数为3.5%NaCl溶液中的电化学测试,结果显示,试样在两种电解液中的自腐蚀电位均正移,自腐蚀电流密度均减小,试样的电化学腐蚀特性增强。未喷丸试样的开路电位曲线较喷丸试样的波动更加剧烈,喷丸试样能够有效改善试样表面的缺陷。但试样在NaCl溶液中的电化学曲线均比在SBF中的曲线变化小,试样在SBF中电化学行为优于NaCl溶液中的试样。(4)开展了生物医用镁合金的摩擦磨损实验。在定载荷、定转速的条件下,喷丸处理试样的干摩擦系数和磨损量较未喷丸试样的明显减小,干摩擦下的磨损机理为磨粒磨损为主;在SBF润滑条件下,喷丸120s试样的润滑摩擦系数明显降低,且所有试样的质量损失均大于干摩擦下的试样,润滑条件下试样表面的磨损是磨粒磨损、腐蚀磨损和剥落磨损共存。对于喷丸120s试样,定转速、动载荷条件下,镁合金试样的干摩擦系数随载荷的增加而增加,润滑摩擦系数先减小后增加,试样的润滑摩擦系数始终小于干摩擦系数;定载荷、动转速的条件下,镁合金试样在低速下的摩擦系数比高速下的大,这是由于低速下试样表面的微凸体未被完全磨掉的原因;所有试样的磨损量随着载荷和速度的增加而增加,且SBF润滑条件下的磨损量明显大于干摩擦条件下的磨损量。
[Abstract]:In order to solve the problem of fast corrosion of the biological medical magnesium and the magnesium alloy in the living body, and maintain good biocompatibility, the medical WE43 magnesium alloy is used as the research object, and the high-energy shot blasting surface treatment technology is used as the strengthening means. The corrosion and friction wear behavior of WE43 magnesium alloy samples before and after shot peening is studied. (1) The numerical simulation of the residual stress field of the specimen under different shot-peening parameters shows that the effect of the diameter of the projectile and the incident velocity on the distribution of the residual stress field and the equivalent effect of the surface of the specimen is the most, the effect of the angle of incidence of the projectile is the second, the diameter is 0.8 mm and 1.0 mm, The incident velocity is 90 m/ s, and the surface shot peening effect of the sample with the incident angle of 90 o is the best. The test samples were shot-peened for 60 s,90 s and 120 s, respectively. The results of the microstructure analysis of the surface of the sample show that the surface of the WE43 magnesium alloy has a grain refining layer of about 120-150. m u.m on the surface of the WE43 magnesium alloy, and the grain refining mechanism is the twin-dislocation accumulation-subcrystal formation-dynamic recrystallization. The hardness of the sample is distributed in a gradient from the treatment surface to the core part, and the surface hardness of the sample is twice the hardness of the base body. The results of the residual compressive stress test and the numerical simulation analysis result in good agreement, and the comprehensive characteristics of the surface of the shot-shot reinforced 120s test sample are good. (2) The simulated body fluid (SBF) soaking experiment and salt spray corrosion test were carried out on the WE43 magnesium alloy samples before and after shot peening, and the corrosion and degradation behavior of the sample was studied. The corrosion rate results show that, in the SBF immersion, the corrosion rate of the non-shot-shot reinforced sample is the highest, the corrosion rate of the three-group shot-shot test sample is similar, and the corrosion rate is increased due to the gradual failure of the reinforcing layer in the later stage of corrosion. In the process of salt spray corrosion, the corrosion rate of the four samples is not much different. And the corrosion rate is gradually reduced until the corrosion rate of the salt fog resistance of the sample is small. The change of the PH value of the solution shows that the PH value of the solution of the shot-shot test sample is less than that of the non-shot-shot test sample, and the shot-peening strengthening can effectively reduce the corrosion rate of the sample in the SBF, and the longer the shot-shot strengthening time, the better the strengthening effect. The morphology of the sample after the corrosion of the sample shows that the surface state of the shot-shot test specimen is better than that of the non-shot-shot sample, and the surface has the deposit of phosphate. In general, the corrosion resistance of the SBF of the WE43 magnesium alloy can be improved obviously, and the corrosion resistance of the salt-resistant fog can be the second, and the corrosion resistance of the test piece of the shot-shot strengthening 120s is the best. (3) The electrochemical measurements of the SBF and the mass fraction of 3.5% NaCl solution were carried out on the WE43 magnesium alloy samples before and after the shot peening. The results show that the self-corrosion potential of the sample in the two electrolytes is positive, the self-corrosion current density is reduced, and the electrochemical corrosion characteristic of the sample is enhanced. The open-circuit potential curve of the un-peened sample is more severe than that of the shot-peened sample, and the shot-peened sample can effectively improve the defect of the sample surface. However, the electrochemical behavior of the sample in the NaCl solution is smaller than that in the SBF, and the electrochemical behavior of the sample in the SBF is better than that in the NaCl solution. (4) The friction and wear experiment of biomedical magnesium alloy was carried out. Under the condition of constant load and fixed speed, the dry friction coefficient and the wear amount of the shot-peened specimen are less than that of the un-peened sample, and the wear mechanism under dry friction is the abrasive wear. Under the condition of SBF lubrication, the lubrication friction coefficient of the shot-peened 120s sample is obviously reduced. And the wear of the surface of the sample under the condition of lubrication is the coexistence of abrasive wear, corrosion wear and peeling and abrasion. the dry friction coefficient of the magnesium alloy sample is increased with the increase of the load, the lubricating coefficient of friction is increased firstly, the lubricating coefficient of friction of the sample is always less than the dry friction coefficient, the friction coefficient of the magnesium alloy sample at low speed is higher than that at high speed due to the fact that the micro-convex body on the surface of the sample at low speed is not completely worn off; the wear amount of all the samples is increased with the increase of the load and the speed, And the wear amount under the condition of the SBF lubrication is obviously higher than that of the dry friction condition.
【学位授予单位】：济南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG668;TG146.22

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