块体非晶合金层裂微损伤演化行为表征

Spallation is one of the most important dynamic failure modes for amorphous alloys. Though the process of nucleation, growth and coalescence of nano- and micro-voids within hundreds of nanoseconds is known to be the principle mechanism in spallation of the material under shock loading, studies on quantitatively characterization of the evolution behavior of microvoids were rarely reported. As the fact that spallation is a rate- and microstructure- dependent microdamage evolution process, this work will focus on several areas about spallation in Zr-based bulk amorphous alloys as follows: based on the physical observation on the process of nucleation, growth of microvoids, and the intrinsic response of unique microstructures in amorphous alloys, the mechanism of nucleation and growth of microvoids will be revealed, and proper models will be developed to characterize the microvoids' nucleation and growth processes; numerical simulations will be carried out to studied the effects of microstructures and micro defects during the microvoids evolution process in nanoscale and atomic scale. Via quantitatively characterization on microvoids evolution process in spallation of Zr-based bulk amorphous alloys, the physical mechanism will be revealed for understanding the material's failure process under shock loading. Finally, the spallation behavior and tensile fracture mechanism at ambient temperature will be comprehensively addressed.

非晶合金层裂特性是其重要冲击拉伸性能之一。尽管已经获知Zr基块体非晶合金冲击载荷下层裂是在百纳秒内纳微米量级微孔洞成核、长大和连接所致，但是定量表征非晶合金层裂微孔洞演化行为研究少见报道。考虑到层裂行为依赖微结构效应而且率相关，演化过程中微孔洞成核、长大、连接与材料的微结构效应及变形机制密切相关，本工作拟基于层裂微孔洞成核、长大演化的物理过程，基于非晶合金特有的纳微结构本征响应，探索Zr基块体非晶合金层裂微孔洞成核、长大演化机制，建立适宜描述非晶合金层裂微孔洞成核、长大演化模型并获得微孔洞成核、长大规律；对非晶合金层裂涉及到原子分子层面、与非晶合金特有微结构以及微结构缺陷直接关联的微孔洞演化行为进行数值模拟表征。 通过对非晶合金层裂微孔洞演化行为的定量表征揭示冲击载荷下非晶合金层裂微孔洞演化诱致材料破坏的物理内涵、全面理解认识非晶合金层裂特性以及非晶合金室温下拉伸断裂机理。

本项目基于非晶合金层裂微损伤演化行为分别从实验、机制、数值模拟三大方面进行了研究。发展“多脉宽-短脉宽-层裂微损伤实验技术”，在控制撞击应力幅值条件下将应力脉宽控制在100ns量级，有效捕捉非晶合金层裂微损伤演化初期信息。基于短脉宽层裂演化实验结果，进行非晶合金层裂微损伤微孔洞微观实验观测，并对所获得的非晶合金层裂样品中微孔洞演化行为进行微观表征。结果表明在一维应变加载条件下非晶合金层裂微损伤初期源于纳微米孔洞成核，随着演化进程发展，纳微孔洞发展成微裂纹。在实验表征基础上研究非晶合金层裂微孔洞长大微观机制以认知非晶合金微孔洞成核长大行为。鉴于其独特的微结构、微缺陷及其微变形机制， 基于非晶合金层裂实验观测结果和现象，研究非晶合金层裂微孔洞长大现象，探讨其长大机制，研究微孔洞失稳的临界条件，微孔洞的动态长大规律。基于对“冻结”在样品中的100-1000nm的微裂纹进行高倍显微形貌观测，对Zr基非晶合金样品中币形微裂纹进行了研究。采用分子动力学方法模拟非晶合金材料本征微缺陷与微孔洞成核长大行为，实现了在纳米微米尺度下材料微损伤演化行为的模拟表征。模拟研究了非晶合金微孔洞成核演化初期的韧脆转变机，进行了静水拉伸应力作用下原子局域无序度的表征，解释了微孔边邻域中原子团簇演化与微孔洞成核演化关联。