Ti-Mo-Nb-Ta-Zr-Sn体系相图热力学、扩散动力学研究

Biomaterials research has attracted great attention due to increasing economic development, leading to improved living standards。β-Ti alloys are one of the important implant materials used to substitute hard tissue and form bone-implant coupling, due to their high mechanical and fatigue resistance, low density, high corrosion resistance, low elastic modulus and excellent bio compatibility properties. The lowering of elastic modulus can be achieved by specific chemical alloying and super-elasticity effects, associated with a stress-induced phase transformation from the BCC metastable beta phase to the orthorhombic α” martensite. In order to quantitatively description the influence of chemical composition to the martensite phase transformation, the phase transformation must be simulated with the phase field model which has integrated the CALPHAD approach. During simulation will get lattice stability parameters and instant chemical driving force from the thermodynamic database and get the instant atomic mobility parameters from the kinetic database. .In this project, the first principle calculation will been used to calculate the Gibbs energy of metastable phase; the phase diagrams and diffusion coefficients will be determined with both equilibrium alloy and diffusion couple methods. The Gibbs energy parameters and atomic mobility parameters will be optimized using the CALPHAD approach and the thermodynamic and kinetic database of the Ti-Nb-Ta-Zr-Sn system will be constructed. The results obtained from this study will provide fundamental knowledge and useful guidance to controlling the β--α” phase transformation and developing and designing low elastic modulus biomedical Ti alloys for medical applications.

随着经济发展，人民生活水平的提高，骨科植入材料的需求量不断增加。由于疲劳强度高、密度低、耐腐蚀、弹性模量低、具有良好的生物相容性，β-Ti合金已成为一种重要的骨科植入材料。调控β--α”热弹性马氏体相变是开发低模量β-Ti合金的关键。为定量描述成分对钛合金中马氏体相变的影响，必须采用集成CALPHAD技术的相场相变模型进行模拟，这一模拟需要从Ti合金热力学数据库中提取晶格稳定性参数和瞬间化学驱动力，还需要从Ti合金动力学数据库中提取瞬时原子移动性参数。本项目的目标是综合运用第一性原理计算、合金法、扩散偶法、和CALPHAD方法测量与计算Ti-Mo-Nb-Ta-Zr-Sn体系相图和互扩散系数；优化该体系各相的Gibbs参数与原子移动性参数，开发瞄准生物Ti合金设计与制备的多元相图热力学与扩散动力学数据库，为定量模拟与控制β--α”热弹性马氏体相变开发低模量生物钛合金打好坚实的基础。

由于具有高的强度、塑性、抗腐蚀性、生物相容性等一系列优点，β-Ti合金已成为一种重要的金属材料。为定量描述成分对钛合金中相变的影响，必须采用集成CALPHAD技术的相场相变模型进行模拟，这一模拟需要从Ti合金热力学数据库中提取晶格稳定性参数和瞬间化学驱动力，还需要从Ti合金动力学数据库中提取瞬时原子移动性参数。本项目基于扩散偶方法，结合Whittle-Green方法和Hall方法测定了Ti-Nb-Ta、Ti-Nb-Zr、Ti-Mo-Zr、Ti-Mo-Nb、Ti-Mo-Ta、Zr-Ti-Nb与Zr-Mo-Nb体系bcc相1373 K和1473 K下的互扩散系数和杂质扩散系数。利用CALPHAD方法建立了Ti-Al-Cr-Fe-Mo-Nb-Ta-V-Zr原子移动性参数数据库。并基于DICTRA软件的移动界面模型，对Ti-Al-(V，Cr，Mo，Fe，Nb，Ta)合金中的β/α相变过程进行了动力学模拟，研究了合金元素对析出与溶解过程的影响。通过平衡合金法，并结合SEM形貌观察、EPMA 相成分测定以及XRD 物相鉴定等实验，详细探究了Ti-Fe-Cr, Ti-Fe-Zr, Ti-Fe-Mo，Ti-Fe-Ta ，Ti-Al-Nb等多个Ti 基合金三元系在全成分范围和多个温度下的相平衡。初步建立了Ti-Al-B-Cr-Fe-Mn-Mo-Nb-Sn-Ta-V-Zr 合金热力学数据库，并将其用于多组钛合金热力学性质的计算。上述研究成果对进一步开发钛合金材料具有重要参考价值。此外，本项目还运用CALPHAD热力学、动力学计算的手段，根据相场模拟结果，设计制作了扩散偶，在一个试样内高通量地获取β稳定化元素含量连续变化的合金成分，研究了不同元素含量对合金组织、硬度的影响，在此基础上设计了多种未报道过的新型钛合金。研究表明,经过适当的固溶与时效处理，新合金的拉伸性能高于现有起落架用Ti5553高强韧钛合金。

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