采用纳米尺度堆垛层错突破单晶强度研究

Microstructural design of materials with high strength promotes development of fields such as engineering, civilian and military industries and especially the strategic and emerging industries. However, conventional strengthening methods still cannot follow the urgent requirement of these fields. In recent years microstructural design at the nanoscale has become a significant direction to further strengthen materials. Strength of a single crystal is commonly regarded as the limit to strengthen a material. However, recent research shows nanoscale twins help to exceed this limit. Our preliminary investigation also reveals that strength of materials with nanoscale stacking faults can overcome this limit. As the characteristic size of microstructures (the distance between twin boundaries or neighboring stacking faults) increases beyond a critical value, stacking faults are prior to twins. Stacking faults are, therefore, more optimal microstructures to strengthen a material. This project thus focuses on face-centered-cubic metals which have broad applications in high-tech industries. Adopting molecular statistical thermodynamics combining in situ transmission electron microscopy experiments, we aim to achieve a preferred microstructure having strength beyond that of a single crystal with physical mechanisms of critical characteristic size to be revealed and a more practical mechanical model to be established. It is expected that the outcome of this project will provide a novel strategy for the microstructural design to strengthen materials and potential applications in the fields of national strategic and emerging industries.

高强度材料的微结构设计对工业、国防，尤其是航空航天等国家战略性新兴产业的发展起推动作用，但传统增强方法已无法满足这些产业的迫切需求。近年来，纳米尺度的微结构设计成为进一步提高材料强度的一个重要方向。通常认为单晶的强度是材料强度的极限，然而近期的研究指出纳米尺度孪晶是突破该极限的一个途径，申请人的预研表明纳米尺度堆垛层错不但突破该极限，且在特征微结构间距（孪晶界间距及堆垛层错间距）超过其临界值时，较孪晶增强有更大的优越性，从而有望成为另一种甚至更优化的微结构设计。因此，申请项目以在高新技术中有广泛应用的面心立方金属为切入点，采用申请人所在课题组的白以龙院士提出的分子统计热力学方法结合原位实验，拟深入揭示特征微结构间距的临界值的物理涵义，建立堆垛层错增强的力学模型，实现突破单晶强度的择优增强的目标。该研究对新的高强度材料的研发具有重要的科学意义，在国家规划的战略性新兴产业将有广泛的应用前景。

高强度材料的微结构设计对工业、国防，尤其是航空航天等国家战略性新兴产业的发展起推动作用，但传统增强方法已无法满足这些产业的迫切需求。近年来，纳米尺度的微结构设计成为进一步提高材料强度的一个重要方向。通常认为单晶的屈服强度是材料强度的极限，然而近期的研究指出纳米尺度孪晶是突破该极限的一个途径。我们主要以镍基超合金为研究对象，系统研究了合金中的复杂堆垛层错、超晶格内禀堆垛层错、孪晶界、反相界以及异质界面结构对其屈服强度、硬度和韧性的影响。结果表明纳米尺度堆垛层错不但突破单晶的屈服强度极限，且在特征微结构间距小于临界值时，较孪晶增强有更大的优越性，从而有望成为另一种甚至更优化的微结构设计。该项目建立了位错与界面碰撞的力学模型，揭示了位错与界面相互作用的规律。强韧机制包括界面对位错行为的阻碍、钉扎。弱化机制包括界面的褪去、去孪晶、界面及孪晶界迁移。该项目的成果对镍基超合金的发展及材料的界面结构强韧化设计具有重要科学意义。