医用Zr-Nb合金塑性变形应力诱发ω相变可控机理研究

In this study, mechanical compatibility and settability are simultaneously considered to solve the problem in biomedical applications; the springback is lowered by increasing the local elastic modulus via stress-induced ω phase transformation. The effects of Nb concentration on the stability and elastic stiffness of β matrix with bcc structure are investigated by measuring the elastic stiffness, elastic modulus and Poisson’s ratio of Zr-Nb alloys with different Nb contents quantitatively. The deformation behaviors of the Zr-Nb single crystal alloy with different orientation under uniaxial tensile and uniaxial compression tests are comprehensively studied, the morphology and volume fraction of the stress-induced ω phase are observed by TEM and HRTEM, furthermore, the relationship of orientation (stress direction)-stress-induced ω phase-unloading elastic modulus (elastic recovery strain) is established. The reversible behavior of the stress-induced ω phase is clarified by investigating the morphology and volume fraction of stress-induced ω phase, the dislocation state, and the fault stacking properties in the alloys with different orientation and different deformation strain under uniaxial tensile and compression tests. The achievements of the project will enrich the acquaintance of the stress-induced ω phase transformation and establish a theoretical basic for increasing local elastic modulus via stress-induced ω phase transformation, further offer new method and provide technical support on development of novel “Elastic modulus-tunable” biomedical metallic materials for spinal fixation applications.

本项目利用应力诱发ω相变提高局部弹性模量，进而降低回弹幅度来同时满足力学兼容性及定形性，从而解决临床应用中遇到的瓶颈问题。以Zr-Nb合金为研究对象，通过实验研究和理论分析相结合的方式，定量分析Nb含量对合金β相稳定性、弹性常数、弹性模量及泊松比的影响规律；阐述Nb元素对bcc结构β相相稳定性和弹性常数的作用机制；考察Zr-Nb单晶合金不同晶体取向拉伸及压缩作用下的变形行为，利用TEM及HRTEM观察应力诱发ω相的形貌、体积分数，建立晶体取向（受力方向）-应力诱发ω相微观结构-卸载弹性模量（弹性回弹幅度）之间的本构关系；研究不同晶体取向变形中不同形变量对应的应力诱发ω相形貌、数量及位错形态等微观组织特征，明确应力诱发ω相变是否可逆，并阐明其可逆条件及机制。研究成果将丰富应力诱发ω相变内涵，为利用应力诱发相变提高局部弹性模量奠定理论基础，为新型脊柱固定用合金的研制提供新思路和技术支撑。

本项目旨在利用应力诱发ω相变提高局部弹性模量，进而降低回弹幅度来同时满足力学兼容性及定形性，从而解决临床应用中遇到的瓶颈问题。以Zr-Nb合金为研究对象，定量分析Nb含量对合金β相稳定性、弹性模量等力学性能的影响规律；考察Zr-Nb合金的变形行为，研究不同形变量对应的应力诱发ω相数量等微观组织特征，明确应力诱发ω相变是否可逆。.通过合金设计，利用悬浮熔炼法制备出成分均匀的不同Nb含量的小合金锭。研究不同Nb含量对合金微观组织、弹性模量及变形行为的影响规律。实验结果表明，固溶态合金主要由基体β相与淬火ω相组成，淬火ω相对应衍射斑点的强度随着Nb含量的增加而减弱，证明Nb元素会增加β基体的稳定性。固溶态所有合金的弹性模量低于70 GPa，15Nb和17Nb合金更是低于60 GPa，弹性模量更接近于人骨的弹性模量，可以保证其力学兼容性。冷轧变形后合金弹性模量均得以提高，且15Nb和17Nb的提高幅度更是达到了34.3%和26.5%。TEM观察结果证实了冷轧变形态15Nb和17Nb中应力诱发ω相的存在。同时EBSD结果表明，随着Nb含量的增加，冷轧变形带由15Nb中的{332}<113>变形孪晶变为17Nb中的扭折带，即Nb含量改变了合金的变形模式。拉伸/弯曲加载-卸载实验结果证明17Nb具有最低的回弹幅度，验证了利用形变诱发ω相降低回弹幅度的有效性。.利用高能X射线技术原位观察了Zr-17Nb合金变形过程中的结构演化规律。结果显示，合金在拉伸过程中存在形变诱发ω相变，且该形变诱发ω相变行为的起始阶段发生在合金变形的宏观弹性变形阶段，即Zr-17Nb合金中形变诱发ω相变为应力诱发相变，且随着应力的增加，ω相的体积分数增加。在卸载过程中ω相的峰减弱乃至消失，说明形变诱发ω相变具有可逆性。淬火速度会影响Zr-17Nb合金中的应力诱发相变，淬火速度的增加可以使应力诱发相变临界应力降低，同时还会对应力诱发ω相变起促进作用。研究成果将丰富应力诱发ω相变内涵，为利用应力诱发相变提高局部弹性模量奠定理论基础，为新型脊柱固定用合金的研制提供新思路和技术支撑。