高温高压极端条件下剪切诱导锆钛合金相变机理和力学性质的理论研究

Zirconium-Titanium (Zr-Ti) alloy is widely used in the aerospace, medical and nuclear industries due to its high melting-point, superior hardness and excellent strength-to-weight ratio, corrosion resistance as well as low thermal neutron absorption cross section. Its phase transition and melting processes under extreme high temperature and pressure are very complex and are one of the hot topics in experimental and theoretical mechanics studies. Experimental measurements on the dynamic phase transformation and mechanical properties of Zr-Ti alloy under high pressure and temperature are difficult and expensive, and experimental techniques cannot directly observe the nucleation process of phase transformation in the micro electronic and atomic level. This proposal focuses on the Zr-Ti alloy, which is a representative of transition metal. We will first investigate the solid state phase transition process by using the first principle calculations, and then employ the controllability of molecular dynamics simulations to study the moving direction of the phase boundary of solid-solid and solid-liquid under shear field. In particular, we will reveal the effects of shear field on the phase transformation and the mechanical properties by using the equilibrium and non-equilibrium molecular dynamic simulations under high temperature and pressure. Our studies could clarify the sliding atomic lays and dislocation path information of Zr-Ti alloys. The purpose of this proposal is to reveal the mechanism of shear induced phase transformation in electronic and atomic motions level. The research work in this proposal can provide theoretical supports for the experimental manufactures of high performance Zr-Ti alloy and provide insights into the researches of melting, phase change and heat equation of state of the other transition metal alloys.

锆钛合金具有高熔点、超高硬度和比强度、耐腐蚀及热中子吸收截面小等优异性能，在航空航天、医学和核工业等领域有着广泛的应用。它在极端高温高压下的相变和熔化的物理过程极其复杂，是实验和理论力学关注的热点之一。用实验手段测量高压及高低温交变环境下的锆钛合金动态相变和力学性能往往费用昂贵，且难以从原子层次对相变形核的微观过程进行直接观察。本项目拟以过渡金属的典型代表锆钛合金为研究对象，在运用第一性原理计算获得各固态相变数据的基础上，利用经典分子动力学模拟的可操控性深入研究剪切场存在时固-固、固-液相界的移动方向；采用平衡和非平衡分子动力学动态模拟高温高压下剪切场对相变和力学性能的影响，阐明锆钛合金中原子层的滑移和位错路径信息，从电子、原子运动角度揭示剪切应力对其相变的诱导机制。本项目研究成果可为实验制备性能优异的锆钛合金提供理论支撑，也可为其它过渡金属合金的熔化、相变和热状态方程等问题提供研究思路。

锆钛合金具有高熔点、超高硬度和比强度、耐腐蚀及热中子吸收截面小等优异性能，在航空航天、医学和核工业等领域有着广泛的应用。它在极端高温高压下的相变和熔化的物理过程极其复杂，是实验和理论力学关注的热点之一。本项目以过渡金属的典型代表锆钛合金为研究对象，运用第一性原理计算获得Zr-Ti合金各固态相变范围和相变次序，通过弹性常数计算得出力学变化规律，并判断出Zr-Ti合金不同相在零温零压下材料软硬度不同，并且随着压力的增加不同相的材料延展性变化不同；通过马利肯布居（Mulliken population）、态密度以及能带结构给出来Zr-Ti合金可能发生相变的微观机理，从电子、原子运动角度揭示剪切应力对其相变的诱导机制。通过虚晶近似方法对于不同成分的Zr-Ti合金研究发现：在压强为0 GPa时，Zr0.75Ti0.25组分总态密度强度最大，而且分波态密度中d电子贡献较大；在压强为20 GPa时，总态密度强度增加，且费米面下移，金属性增强；通过准谐德拜模型研究了Zr-Ti热力学性质，包括而热容、德拜温度参数以及热膨胀系数,它们都是随着压强的增加而呈不同程度的减少。温度对它们的影响也不同，越高的温度可以产生越小的德拜温度，越大的热容和热膨胀系数。但当温度较高时，热膨胀系数几乎不随温度改变，即不受温度影响; 本项目研究成果可为实验制备性能优异的锆钛合金提供理论支撑，也可为 其它过渡金属合金的熔化、相变和热状态方程等问题提供研究思路。