高损伤容限块体金属玻璃在若干关键载荷模式下的断裂行为

Over the past three decades, mechanical behavior of bulk metallic glasses (BMGs) has been extensively investigated. With significant advantages of high yield strength, high elastic strain limit (~2%) and moderate fracture toughness, the BMGs are highly expected as a new class of structural materials. However, understanding of their mechanical behaviors under diverse loading conditions remmains very limited due to their restricted sample sizes and intrinsic brittleness. As noticed, fracture toughness of BMGs extends in a wide range, from the brittle as oxide glasses with near-zero damage tolerance and the highly-tough as conventional titanium alloys, even though the BMG failure is absent of tensile ductility. Recently, several damage-tolerant BMGs such as Zr61Ti2Cu25Al12 alloy were discovered, which are characterized in fracture toughness by crack-resistance curve (R-curve). Such a new unique BMG together with robust glass-forming ability provides an opportunity to promote the understanding for deformation and fracture behaviors of BMGs under more diverse loading conditions, including the cyclic, torsion and Charpy impact with high strain rate, rather than only under conventional quasi-static conditions, which have not been well understood yet so far. ..By this project, fracture behavior of the damage-tolerant Zr61Ti2Cu25Al12 BMG under several key loading conditions will be investigated. As such, several key scientific questions are expected to be addressed, as following. (i) What is the fatigue failure mechanism of the damage-tolerant BMG and its correlation with fracture toughness under monotonic loading? During crack growth under cyclic loading, what relationship between cracking and shear bands at crack tip is present? (ii) Deformation and fracture behavior of the damage-tolerant BMG under torsion loading. Determination of fracture toughness in anti-plane strain, or type III stress, KIIIC, for the damage-tolerant BMG and its correlation with fracture toughness in type I stress, KIC. (iii) For the damage-tolerant BMG, whether temperature-induced ductile-to-brittle transition (DBT) would happen under Charpy impact. What is a correlation between impact fracture energy and quasi-static fracture energy in the case of BMGs? Addressing these questions is significantly of interest not only for understanding the intrinsic properties in deformation and fracture of BMGs but also for their application as structural materials.

高损伤容限的块体金属玻璃（诸如Zr61Ti2Cu25Al12）具有“裂纹阻力曲线（R-curve）”的韧化特征，为进一步揭示块体金属玻璃（BMG）在循环、扭转、冲击等多种关键性载荷模式下的形变与断裂行为提供了机遇。本项目拟通过研究Zr61Ti2Cu25Al12等 BMG 在这些特殊载荷作用下的形变与断裂行为，澄清以下关键科学问题：（一）高损伤容限 BMG 的疲劳断裂机制及其与准静态断裂韧性之间的相关性。循环载荷作用下疲劳裂纹的生长机制及其与裂纹尖端处剪切带之间的交互作用。（二）高损伤容限 BMG 在扭转载荷作用下的形变与断裂；反平面应变载荷（III型应力）下的断裂韧性及其与I型断裂韧性之间的相关性。（三）在冲击载荷作用下高损伤容限 BMG 是否会发生因温度变化引起的“韧-脆转变”。 澄清这些问题对于深入理解 BMG 形变与断裂的本质及其作为结构材料的应用均具有重要意义。

在本项目资助下，开展可对高强韧Zr61Ti2Cu25Al12（ZT1）块体金属玻璃（BMG）在扭转载荷下的形变与断裂行为以及TiZrNbTaMo高熵合金（HEA）的研究，取得的代表性研究成果如下：.（一）揭示出Zr61Ti2Cu25Al12（ZT1）块体金属玻璃（BMG）的本征III型断裂韧性为KIIIC51 MPam，材料中的裂纹对反平面剪切载荷更加敏感。III型断裂韧性可作为金属玻璃构件的保守设计基准。在扭转载荷下，ZT1的断裂由单一主剪切带主导，没有发生明显的宏观塑性形变，其剪切屈服强度y=950 MPa。这些发现为金属玻璃作为构件工程应用的可靠性提供了依据。. （二）Zr-Ti-LTM-Al （LTM=Cu, Ni, Co）金属玻璃在含氯离子水溶液中的点蚀抗力取决于后过渡族元素的类型，含Ni和Co BMG的点蚀抗力优于含Cu的BMG；相对于Zr60Ni25Al15，Zr60Cu25Al15具有更快的点蚀生长速率和侵蚀性更强的坑内溶液环境，稳态点蚀更易于发展。这些发现为考虑环境腐蚀影响的BMG材料的工程应用提供了科学依据。.（三）将“高熵合金（HEA）”理念与生物医用材料的需求相结合，发展“生物医用高熵合金”。发现电弧熔炼态（TiZrNbTa）100-xMox （0 ≤ x ≤ 20）系列高熵合金呈现双相BCC结构，合金的硬度、杨氏模量、压缩屈服强度随着Mo含量线性增加，但压缩塑性应变和缺口断裂韧性（KQ）下降。 (TiZrNbTa)90Mo10高熵合金在腐蚀性生理介质中表现出优异的耐蚀性，其优异的自钝化能力和钝化膜的保护性源自于合金表面形成的复杂多种氧化物。.（四）TiHfNbTa等原子比中熵合金中的Hf元素对NbTa基质固溶体的固溶强化效力显著优于Ti元素，但损伤塑性。HfNbTa三元合金的强度与塑性可比肩TiZrHfNbTa五元合金。这些发现为进一步优化出强韧性兼顾、在人体生理环境下耐腐蚀、耐磨损的新型合金奠定了基础。

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