脉冲荷能粒子束瞬态热驱动靶材表层微裂纹的机制研究

By means of the diagnostic platform which based on the ultrafast infrared detector and piezoelectric materials shock wave detection technique, proceeding from the energy driving essence of crack formation, this project aims at the forming mechanism of micro-cracks in the target surface layer under the transient heat caused by pulsed energy beam, which served by intense pulsed ion beam(IPIB) with nanosecond pulse width and compressed plasma flow(CPF) with microsecond pulse width. Monocrystalline and polycrystalline materials such as silicon, germanium and tungsten are selected as target material in experiment. The forming characteristic and relative characteristic with beam parameters of micro-cracks in the surface layer can be acquired though rapid online dynamic diagnosis and offline characterization analysis. The elastic and elastoplastic thermomechanical model will be established to obtain the distributions of stress and strain of target material. And then, the dynamic response of material internal energy and strain energy can also be acquired. Introducing the J integration method from fracture mechanics, the crack propagation models which dominated by type I fracture mode will be established. Through connecting the change of strain energy and inherent strength of material, the forming criterion of micro-crack in the target surface layer under the loading of pulsed energetic particle beam will be proposed. Using the molecular dynamics method, the microfracture physical mechanism of material will be revealed atomically. This project will not only enhance the understanding of formation and propagation of micro-cracks in the target surface layer under the dynamic loading with nanosecond scale pulse width, but also play a significant role in application of pulsed energetic particle beam technique on the material surface processing.

本项目借助基于超快红外探测器和压电材料冲击波测试技术的诊断平台，以纳秒脉宽的强脉冲离子束（IPIB）和微秒脉宽的压缩等离子体流（CPF）为脉冲能量束，从裂纹产生的能量驱动本质出发，研究瞬态热加载下靶材表层微裂纹的形成机制。实验上以硅、锗、钨等单晶/多晶材料为靶材，通过快速在线动态诊断和线下表征分析获得表层微裂纹的形成特征，以及与束流参数的相关性特征；建立弹性和弹塑性热力耦合模型，获得材料表面的应力应变场分布，进而得出束流能量馈入后材料内能和应变能的动态响应；引入断裂力学的J积分方法，建立I型断裂模式主导的裂纹发展模型，通过关联材料的应变能变化和固有强度，提出脉冲荷能粒子束加载下靶材表层微裂纹产生的判据；采用分子动力学方法，从原子层面上揭示材料微观断裂的物理机制。这将加深人们对纳秒尺度的动态加载下靶材表层微裂纹形成和发展认识，对脉冲荷能粒子束技术在材料表面加工的应用具有重要意义。

为研究材料在强脉冲离子束（IPIB）和压缩等离子体流（CPF）瞬态热加载下的表层微裂纹的产生与发展问题，结合对材料热应力、应变状态的分析，建立了与材料特性和束流特征相关的表层微裂纹生成的物理判据。课题基于铌镁酸铅-钛酸铅(PMN-PT)单晶铁电材料制备了温度-应力双参数探测器，搭建了冲击波造成的温度和热应力的在线测试平台。为超快红外探测器搭建了电磁屏蔽装置，标定了超快红外探测器输出信号与温度之间的对应关系，建立了纳秒尺度的测温测试平台。以纳秒脉宽的IPIB和微秒脉宽的CPF为脉冲能量束，辐照了硅、钨等单晶/多晶材料靶材，通过多种表征分析手段，观察了辐照后靶材表层微裂纹的形状与特征。结合束流参数的测定，分析了瞬态热负载下材料表层应变能变化引起的微裂纹定向生长的原理，并建立与材料特性和束流特征相关的层间微裂纹生成判据。利用断裂力学的J积分参数，与材料微观的断裂强度因子进行比对，建立对热应力加载下裂纹可扩展性的判定。分析了由于材料表面第二相夹杂物的存在，导致的局域热喷发形成熔坑的物理过程，解释了部分裂纹沿熔坑开裂的产生机制。此外，结合层间微裂纹的能量驱动本质，基于分子动力学的方法，建立束流能量与由微观原子势和晶面取向所决定的材料强度之间的联系，并分析了不同加载条件时拉伸作用对裂纹产生的影响。