【作者】 尹冬松；

【导师】 曾松岩； 张二林；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 针对医用可降解镁合金,本文选择具有生物相容性的Mn和Zn元素制备了Mg-Mn系和Mg-Zn-Mn系合金,用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、XRD、万能材料试验机、电化学测试系统和体外浸泡试验系统,研究了Mn和Zn对铸态合金微观组织、力学性能和腐蚀行为的影响规律、并对比研究了直接挤压和热处理后挤压对Mg-Zn-Mn系合金微观组织、力学性能和腐蚀行为的影响。最后对Mg-Zn-Mn合金进行动物体内植入试验,评价体内降解和力学性能衰退。得到如下结果:对铸态合金的微观组织和力学性能的研究发现:Mn能够细化镁合金的组织,并提高合金的拉伸强度,当Mn含量为1.48wt.%时,Mg-Mn合金的拉伸强度得到明显提高。Zn可以进一步细化铸态Mg-Mn合金的组织,并且在合金中形成Mg7Zn3相,铸态Mg-Zn-Mn系合金的拉伸强度、屈服强度和伸长率随Zn含量增加而增加,当Zn含量为3wt.%时,达到最高值,拉伸强度为218.6MPa,屈服强度为66.1MPa,伸长率为15.5%。挤压显著细化了Mg-Zn-Mn系合金的晶粒尺寸,显著提高了合金的拉伸强度和屈服强度。挤压后,Mg-1Zn-1Mn合金的拉伸强度为280.3MPa,屈服强度为246.5 MPa,伸长率为21.8%。随Zn含量增加,晶粒尺寸降低,当Zn含量增至3wt.%时,晶粒尺寸下降至3μm-5μm之间。合金的晶界处出现亚微米级的Mg7Zn3和MgZn相,拉伸强度和屈服强度进一步提高,但伸长率下降。挤压前均匀化热处理使挤压态合金的晶粒尺寸粗化,拉伸强度和屈服强度降低。腐蚀实验结果表明:Mn加入不会提高镁合金的耐蚀性能,但是当Mn含量达到1.48wt.%时,合金的耐蚀性能降低。Zn可以显著提高铸态Mg-Zn-Mn系合金的耐蚀性能,但当Zn含量达到3wt.%时,合金的耐蚀性能明显降低,挤压变形可以显著降低Mg-Zn-Mn系合金的腐蚀速率,使合金的自腐蚀电位正移,极化电阻提高;随着合金中的Zn含量增加,合金的耐蚀性能降低,腐蚀形式由点蚀转化为严重的晶界腐蚀。挤压前均匀化热处理可以降低高Zn含量(3wt.%)合金的腐蚀速率,使晶界处腐蚀得到减轻。通过对腐蚀机制的研究可知,由于凝固特性形成的Zn元素分布状态不同是造成铸态Mg-Zn-Mn系合金腐蚀形式不同的主要原因,而通过挤压的方法可以改变Zn元素的分布,减轻因Zn元素微观偏析所引起的腐蚀。动物体植入实验表明,镁合金植入3天后有较轻的炎症现象,两周后炎症现象消失。血液生化检测表明:植入3个月后,动物的肝功能和肾功能没有异常反应。在对镁合金植入体和骨结合界面的研究中发现:与骨组织接触的镁合金表面生成含有Ca和P的降解产物层。随着镁合金的降解,表面生成新生组织层,逐渐转化为新生骨组织,合金与骨组织结合良好。镁合金的抗弯强度随植入时间延长而降低,植入1个月后,抗弯强度为257.7MPa,约为原来的60%,植入3个月后,仍保持在113.6MPa,约为原来的30%,接近于人体骨皮质的抗弯强度。更多还原

【Abstract】 Aimed at bio-degradable magnesium alloys for medicine application, biocompatable Mn and Zn elements were selected to develop Mg-Mn and Mg-Zn-Mn alloys. Influences rule of Mn and Zn on the as-cast microstructure, mechanical properties and corrosion behaviour of the magnesium alloys were investigated by the use of optical microscope (OM), scanning electronic microscope (SEM), transmission electronic microscope (TEM), XRD, mechanical properties testing, electrochemical measurement and in-vitro evaluations. Influence of extrusion and homogenization on the microstructure, mechanical properties and corrosion behaviour of Mg-Zn-Mn alloys were also investigated. Implantation test was conducted to evaluate the in vivo degradation and mechanical properties reduction of magnesium implant. The results are summarized as follows:Microstructure observation and mechanical properties test showed that Mn can refine magnesium alloy, but also improve the tensile strength, and that significant increase in strength was found at 1.48wt.% Mn. Zn element can further refine the microstructure of the as-cast Mg-Mn alloy by forming Mg7Zn3 phase. The tensile strength, the elongation and the yield strength of the as-cast Mg-Zn-Mn alloys increased with increase in Zn content, and the highest properties was obtained at 3.0 wt% Zn, e.g. the ultimate tensile strength, yield strength and elongation were 218.6 MPa, 66.1MPa and 15.5%, respectively.The grain size of Mg-Zn-Mn alloys was refined remarkably and the tensile strength and the yield strength of the alloy were increased greatly after extrusion. The tensile strength, the yield strength and the elongation of the extruded Mg-1Zn-1Mn were 280.3 MPa, 246.5 MPa and 21.8%, respectively. With the increasing of Zn content, the grain size decreased, e.g. the grain size was 3-5μm at 3wt.% Zn. Sub micron Mg7Zn3 and MgZn phases appeared at grain boundary further increased the ultimate tensile strength and yield strength, but reduced the elongation. Homogenization treatment before the extrusion coarsened the grain size and reduced the tensile strength and yield strength. The corrosion testing showed that Mn could not improve the corrosion resistance. On the contrary, the corrosion resistance was reduced when Mn content exceeded 1.48 wt%. The corrosion resistance of the as-cast Mg-Zn-Mn alloys increased remarkably with Zn addition. However, the corrosion resistance decreased when Zn content was over 3wt.%. Extrusion treatment can significantly reduce the corrosion rate of Mg-Zn-Mn alloy, move the corrosion potential toward more noble and increase the corrosion resistance. With the increasing of Zn content the corrosion mode transformed from pitting corrosion to severe grain boundary corrosion. Homogenization heat treatment before extrusion can reduce the grain boundary corrosion and in turn reduce the corrosion rate of the alloy with high Zn content, such as 3wt.% Zn. The study on the corrosion mechanism showed that the segregation of Zn due to the different casting conditions contributed mainly to the different corrosion modes of the as-cast alloy. Extrusion treatment homogenized the distribution of Zn, therefore, reduced the corrosion rate.In vivo experiment showed the inflamma-tion appeared 3 days postimplantation, and disappeared 2 weeks postimplantation. Blood biochemistry analysis showed that no disorder was tested in the liver function and kidney function within 3 months implantation. Microstructure observation showed that a Ca-and P-containing degradation product layer was found at the interface between magnesium alloy implant and bone tissue. With the degradation of magnesium implant, newborn tissue layer formed on the surface of the magnesium implant and then transformed into newborn bone tissue gradually. The alloy and the newborn bone had good conjunction. The bending strength of the magnesium implant decreased with implantation time. The bending strength after 1 month implantation was 257.7 MPa, reduced by 40% in comparison with the original value, and 113.6 MPa after 3 months implantation, reduced by 70 %. However, the bending strength of the magnesium implant after 3 months postimplantation was still as high as the strength of natural bone.更多还原