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18. On the damage tolerance of 3-D printed Mg-Ti interpenetrating-phase composites with bioinspired architectures

Author

Zhang, Mingyang, Zhao, Ning, Yu, Qin, Liu, Zengqian, Qu, Ruitao, Zhang, Jian, Li, Shujun, Ren, Dechun, Berto, Filippo, Zhang, Zhefeng, and Ritchie, Robert O

Subjects
Printing, Three-Dimensional, Titanium
Abstract

Bioinspired architectures are effective in enhancing the mechanical properties of materials, yet are difficult to construct in metallic systems. The structure-property relationships of bioinspired metallic composites also remain unclear. Here, Mg-Ti composites were fabricated by pressureless infiltrating pure Mg melt into three-dimensional (3-D) printed Ti-6Al-4V scaffolds. The result was composite materials where the constituents are continuous, mutually interpenetrated in 3-D space and exhibit specific spatial arrangements with bioinspired brick-and-mortar, Bouligand, and crossed-lamellar architectures. These architectures promote effective stress transfer, delocalize damage and arrest cracking, thereby bestowing improved strength and ductility than composites with discrete reinforcements. Additionally, they activate a series of extrinsic toughening mechanisms, including crack deflection/twist and uncracked-ligament bridging, which enable crack-tip shielding from the applied stress and lead to "Γ"-shaped rising fracture resistance R-curves. Quantitative relationships were established for the stiffness and strengths of the composites by adapting classical laminate theory to incorporate their architectural characteristics.

Published
2022

20. Flaw-insensitive fracture of a micrometer-sized brittle metallic glass

Author

Qu, Ruitao, Maaß, Robert, Liu, Zengqian, Tönnies, Dominik, Tian, Lin, Ritchie, Robert O, Zhang, Zhefeng, and Volkert, Cynthia A

Subjects
Engineering, Materials Engineering, Metallic glass, Fracture toughness, Size effect, Small-scale, Bulk metallic glass, fracture toughness, size effect, small-scale, Condensed Matter Physics, Mechanical Engineering, Materials, Materials engineering, Mechanical engineering, Condensed matter physics
Abstract

Brittle materials, such as oxide glasses, are usually very sensitive to flaws, giving rise to a macroscopic fracture strength that is much lower than that predicted by theory. The same applies to metallic glasses (MGs), with the important difference that these glasses can exhibit certain plastic strain prior to catastrophic failure. Here we consider the strongest metallic alloy known, a ternary Co55Ta10B35 MG. We show that this macroscopically brittle glass is flaw-insensitive at the micrometer scale. This discovery emerges when testing pre-cracked specimens with self-similar geometries, where the fracture stress does not decrease with increasing pre-crack size. The fracture toughness of this ultra-strong glassy alloy is further shown to increase with increasing sample size. Both these findings deviate from our classical understanding of fracture mechanics, and are attributed to a transition from toughness-controlled to strength-controlled fracture below a critical sample size.

Published
2021

32. 3D printed Mg-NiTi interpenetrating-phase composites with high strength, damping capacity, and energy absorption efficiency

Author

Zhang, Mingyang, Yu, Qin, Liu, Zengqian, Zhang, Jian, Tan, Guoqi, Jiao, Da, Zhu, Wenjun, Li, Shujun, Zhang, Zhefeng, Yang, Rui, and Ritchie, Robert O

Subjects
Engineering, Materials Engineering, Chemical Sciences, Affordable and Clean Energy
Abstract

It is of significance, but still remains a key challenge, to simultaneously enhance the strength and damping capacities in metals, as these two properties are often mutually exclusive. Here, we provide a multidesign strategy for defeating such a conflict by developing a Mg-NiTi composite with a bicontinuous interpenetrating-phase architecture through infiltration of magnesium melt into three-dimensionally printed Nitinol scaffold. The composite exhibits a unique combination of mechanical properties with improved strengths at ambient to elevated temperatures, remarkable damage tolerance, good damping capacities at differing amplitudes, and exceptional energy absorption efficiency, which is unprecedented for magnesium materials. The shape and strength after deformation can even be largely recovered by heat treatment. This study offers a new perspective for the structural and biomedical applications of magnesium.

Published
2020

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