【作者】 姜东梅；

【导师】 曹占义；

【作者基本信息】 吉林大学 ， 材料学， 2014， 博士

【摘要】 自从1878年第一次在人体中应用可降解生物镁合金开始，镁合金生物材料的开发设计及应用逐渐成为众多研究学者的热点。这是由于与高分子聚合物材料相比，镁合金材料具有一定的承载能力和良好的生物相容性；与传统金属硬组织植入材料相比，镁合金材料具有可降解吸收性能，不需要经过二次手术将植入材料摘除；但是与钛合金和钴-铬合金等金属材料相比，镁合金力学性能稍低，并且腐蚀速度过快，在使用过程中会因为承载能力不够和降解速度过快导致生物植入材料失效，影响镁合金生物材料在临床医学领域的应用。本工作为了改善可降解镁合金生物材料的力学性能和耐腐蚀性能，以少量多元原则对Mg-Zn-Ca系合金进行改性处理，并选择了生物相容性好，对合金强化效果好同时能够提高合金耐腐蚀性能的Zr、Nd、Y元素作为合金元素，设计熔炼出新型四元Mg-Zn-Ca-Nd/Zr/Y系生物镁合金。重点研究Zr、Nd、Y等元素及固溶处理对合金显微组织、相组成、力学性能和腐蚀行为的影响。研究结果表明：1.铸态Mg-4Zn-0.5Ca-xNd合金主要由-Mg基体和MgZn、Ca2Mg6Zn3、Mg41Nd5化合物组成，随着合金中Nd含量的增加，其显微组织逐渐细化，并且Mg41Nd5化合物的析出量逐渐增多，当Nd含量为2wt.%时，合金晶界上析出Ca2Mg6Zn3+Mg41Nd5共晶组织。当合金中Nd含量由1wt.%增至2wt.%时，晶内和晶界析出的化合物逐渐增多，强化了合金的基体和晶界；同时合金晶粒明显细化，合金力学性能提高。若继续增加Nd的含量，脆性相在合金晶界上聚集粗化，网状晶界的数量增多，降低了晶粒间结合力，合金力学性能下降。实验结果显示Mg-4Zn-0.5Ca-1Nd合金在37oC的SBF溶液中具有最佳的耐腐蚀性能，当Nd含量达到2wt.%以上时，尽管合金晶粒尺寸不断减小，但是在合金晶内和晶界上析出的化合物增多，导致合金腐蚀电流密度增加，合金耐腐蚀性能降低。2.铸态Mg-4Zn-0.5Ca-xZr合金主要由-Mg基体和Mg0.97Zn0.3、Ca2Mg6Zn3化合物组成，XRD图谱中没有出现Zr单质衍射峰。当Zr元素含量由0.1wt.%增至0.7wt.%时，合金的晶粒从65m降至30m，Zr元素细化晶粒作用明显，合金的强度和塑性变形能力提高，其中铸态Mg-4Zn-0.5Ca-0.7Zr具有最好的力学性能。析氢速率和电化学极化曲线结果表明，当Zr含量小于0.5wt.%时，合金的耐腐蚀性能随Zr含量的增加而增加。这是因为添加Zr元素改善了合金显微组织，使晶粒细化且组织均匀致密，有效降低合金的腐蚀电流密度，增加合金的耐腐蚀性能；但是当Zr含量大于0.5wt.%时，合金的耐腐蚀性能反而随着Zr含量的增加而降低，这是由于晶界上析出的Zr颗粒将晶界上连续分布的化合物截断，不能有效阻止腐蚀现象从一个晶粒向另一个晶粒的蔓延，提高了合金的腐蚀电流密度，降低了合金的耐腐蚀性能；铸态Mg-4Zn-0.5Ca-0.5Zr合金具有最好的耐腐蚀性能。固溶处理后合金的相组成不变，合金晶粒尺寸仍然随着Zr含量的增加而减小，部分合金元素固溶于合金基体中提高了合金的力学性能；同时合金中析出化合物的摩尔分数减少，合金的电化学性能提高。其中固溶态Mg-4Zn-0.5Ca-0.5Zr合金具有最好的综合性能，屈服强度达到153MPa，腐蚀速度仅为0.451mm/year。3.铸态Mg-6Zn-0.5Ca合金主要由-Mg固溶体和MgZn2、Ca2Mg6Zn3化合物组成。添加稀土元素Y后，颗粒状Mg12ZnY化合物弥散分布于基体上，并且Mg12ZnY化合物的摩尔分数随着Y元素含量的增加而增加。当Y元素的含量从0wt.%增至1.5wt.%时，合金晶粒的尺寸从118m降至79m。添加Y元素后，合金力学性能明显提高，这主要与Y元素的固溶强化，Y元素细化晶粒引起的晶界强化和Mg12ZnY化合物弥散析出强化有关。固溶处理后合金晶粒尺寸变大，但相组成未变。同样固溶处理能够提高合金的力学性能，其中固溶态Mg-6Zn-0.5Ca-1.0Y合金力学性能最好，其中抗拉强度、屈服强度和延伸率分别达到284MPa、166MPa、14.7%。4.铸态Mg-2Zn-0.5Ca合金主要有-Mg固溶体和CaZn3化合物组成，随着稀土元素Y的添加出现镁稀土强化相Mg24Y5。室温压缩实验显示，Mg-2Zn-0.5Ca合金断口比较平齐而光亮，断裂类型为脆性断裂；随着稀土元素Y的添加，以固溶形式和形成稀土强化相两种方式改善了合金的力学性能。将铸态和固溶态Mg-2Zn-0.5Ca-xY合金分别在SBF溶液中腐蚀浸泡30天发现，在本论文实验条件下，浸泡合金的腐蚀溶液pH值均随浸泡时间的增长而增大，其中铸态合金浸泡溶液的pH增加较快，最大极值为pH=10.4，而固溶态合金浸泡溶液的pH增加较慢，最大极值为pH=8.7。这一结果显示，与铸态合金相比，固溶态合金的腐蚀速率明显较小。对于Mg-2Zn-0.5Ca-1.5Y合金来讲，铸态合金的耐腐蚀性能较差，腐蚀速率达到最大值为9.748×10-4g/cm2/day，而固溶态合金的耐腐蚀性能较好，腐蚀速率达到最小值为0.2917×10-4g/cm2/day。更多还原

【Abstract】 Biodegradable magnesium implants were first applied to the human body in1878,many researchers had gradually focused on the design and application of biodegradablemagnesium alloys in recent years. It was due to magnesium alloys had more sufficientload-bearing ability and better biocompatibility than those of polymers; magnesium alloyshad degradation ability compared with traditional biological metal materials, then, it is notnecessary to be removed the implants through a second surgical operation; however,magnesium alloys had worse mechanical properties and faster corrosion degradable velocitythan those of titanium alloys and Co-based alloys, which restricts it from wide application inthe field of biological materials. For improving the mechanical properties and corrosionresistance of medical degradable magnesium alloys in this paper, based on a few amount andmulti-element principle, Mg-Zn-Ca alloys are treated in modification, thus, Zr, Nd and Yelements which have good biocompatibility, improve the mechanical properties andcorrosion resistance of medical degradable magnesium alloys are selected as alloy elements,then, Mg-Zn-Ca-Zr/Nd/Y biological magnesium alloys are designed. It was investigated thatZr, Nd and Y elements and solid solution treatment influence on the microstructure,mechanical properties and corrosion behavior of the biodegradable magnesium alloys. Theresults are summarized as follows:1. The as-cast Mg-4Zn-0.5Ca-xNd alloys mainly consist of-Mg matrix, MgZn,Ca2Mg6Zn3and Mg41Nd5compounds. The microstructure is gradually refined and thenumber of Mg41Nd5compounds increases with the increasing of the content of Nd. When thecontent of Nd is2wt.%, eutectic structure of Ca2Mg6Zn3+Mg41Nd5can be found at grainboundaries. Compounds precipitated at grain boundaries and in grain interior graduallyincrease and strengthen the-Mg matrix and grain boundaries as the content of Nd increasesfrom1wt.%to2wt.%, meanwhile, the grains are obviously refined and alloys’mechanicalproperties are improved. If the content of Nd continues to be increased, brittle phases areaggregated at grain boundaries, forces among grains and alloys’mechanical properties areboth decreased. The experiment’s result indicates that Mg-4Zn-0.5Ca-1Nd alloy has thebest corrosion resistance of these alloys in SBF fluid at37oC. When the content of Nd is more than2wt.%, even if the sizes of grains are decreased, compounds precipitated at grainboundaries and in grain interior gradually increase, which lead to the increase corrosioncurrent density of alloys, the corrosion resistance properties of alloys decreases.2. The as-cast Mg-4Zn-0.5Ca-xZr alloys mainly consist of-Mg matrix, Mg0.97Zn0.3and Ca2Mg6Zn3compounds, The Ca2Mg6Zn3compound precipitates in grains interior andgrain boundaries, but XRD pattern of the Mg-4Zn-0.5Ca-xZr alloys has no diffraction peaksof Zr particles. The alloys’grains decrease from65m to30m as the content of Zrincreases from0.1wt.%to0.7wt.%, that is, the grains are obviously refined, the strength andplastic deformation are improved, especially, the as-cast Mg-4Zn-0.5Ca-0.7Zr alloy has thebest mechanical properties. The curves of the rate of the evolved hydrogen and polarizationrepresent that corrosion resistance of these alloys increases with the increasing of as thecontent of Zr is less than0.5wt%. The reason is that the grains are refined, the distribution ofthe grains are uniform, the corrosion current density of alloys are effectively decreased andthe corrosion resistance properties of alloys are increased after adding Zr element. If thecontent of Zr is more than0.5wt%, the corrosion resistance properties of alloys decreasewith the increasing of the content of Zr. It dues to the Zr particles congregate at the grainboundaries as impurities to dissever the continuity of the compounds, which can noteffectively stop corrosion spreading from one grain to another grain, therefore the corrosioncurrent density of alloys increases, the corrosion resistance properties of alloys decreases andthe as-cast Mg-4Zn-0.5Ca-0.5Zr alloy has the best corrosion resistance properties. The phasecomposition of alloys is unchanged after solid solution treatment. The mechanical propertiesof alloys are improved since the sizes of the grains are still decreased with the increasing ofcontent of Zr and some of solute atoms solubilize in the-Mg matrix; Meanwhile, the molefraction of compounds is decreased, then the electrochemical properties are improved. Thesolution-treated Mg-4Zn-0.5Ca-0.5Zr alloy has the best comprehensive properties, the yieldstrength is153MPa, the rate of corrosion is only0.451mm/year.3. The as-cast Mg-6Zn-0.5Ca alloys mainly consist of-Mg matrix, MgZn2andCa2Mg6Zn3compounds. After adding the rare earth element Y, the granular compoundMg12ZnY dispersive distributes in the matrix， and as the increase of the content of elementY, the sizes of grains decrease and the mole fraction of the Mg12ZnY compound increasegradually. The sizes of grains of the as-cast alloys are decreased from118m to79m withthe increasing of Y content from0wt.%up to1.5wt.%. The mechanical properties are greatlyimproved after adding Y, which has relationship with solid solution strengthening resulting from element Y, grain size refinement strengthening and the precipitation strengtheningresulting from compound Mg12ZnY. The phase composition of alloys is unchanged aftersolid solution treatment, but the sizes of grains become increase. In the same way, solidsolution treatment could improve the mechanical properties of alloys, namely, thesolution-treated Mg-6Zn-0.5Ca-1.0Y alloy has the best mechanical properties, the ultimatetensile strength, yield strength and elongation whose values are284MPa,166MPa,14.7%,respectively.4. The as-cast Mg-2Zn-0.5Ca alloy mainly consist of-Mg matrix and CaZn3compounds. After adding the rare earth element Y, the rare earth compound Mg24Y5distributes in the matrix. The compression test at room temperature indicates that thecompression fracture of solution-treated Mg-2Zn-0.5Ca alloy is relatively flat and bright, thefracture surface exhibits brittle fracture pattern. Because solid solution is strengthenedresulting from element Y and precipitation is strengthened resulting from compound Mg24Y5,the mechanical properties of alloys improve. It indicates that the pH value of the corrosionliquor increases with the increasing of the immersion time, the pH value of the corrosionliquor immersed with the as-cast alloys reaches the maximum of10.4, and the pH value ofthe corrosion liquor immersed with the solution-treated alloys reaches the maximum of8.7under the condition of experiment after the as-cast and solution-treated Mg-2Zn-0.5Ca-xYalloys of immerse in SBF fluid for30days. Compared with the as-cast alloys, the corrosionrate of solution-treated is obviously smaller. As for the Mg-2Zn-0.5Ca-1.5Y alloy, the seriesof as-cast Mg-2Zn-0.5Ca-хY alloys have worse corrosion resistance abilities than those ofthe solution-treated alloys, the maximum corrosion rate of as-cast Mg-2Zn-0.5Ca-1.5Yalloys is9.748×10-4g/cm2/day, the minimum corrosion rate of solution-treatedMg-2Zn-0.5Ca-1.5Y alloys is0.2917×10-4g/cm2/day.更多还原