As part of our work in nanomechanical testing, we regularly come across great research articles. Members of our Nanomechanical Testing Journal Club receive brief reviews of select papers, collected below. Sign up to automatically receive the Journal Club via email:
HIGH-THROUGHPUT NANOINDENTATION FOR STATISTICAL AND SPATIAL PROPERTY DETERMINATION
Eric Hintsala, Ude Hangen, Douglas D. Stauffer
Journal of Materials, 2018, 70 (4), 494-503
(view article: https://link.springer.com/article/10.1007%2Fs11837-018-2752-0)
Standard nanoindentation tests are “high throughput” compared to nearly all other mechanical tests, such as tension or compression. However, the typical rates of tens of tests per hour can be significantly improved. These higher testing rates enable otherwise impractical studies requiring several thousands of indents, such as high-resolution property mapping and detailed statistical studies. However, care must be taken to avoid systematic errors in the measurement, including choosing of the indentation depth/spacing to avoid overlap of plastic zones, pileup, and influence of neighboring microstructural features in the material being tested. Furthermore, since fast loading rates are required, the strain rate sensitivity must also be considered. A review of these effects is given, with the emphasis placed on making complimentary standard nanoindentation measurements to address these issues. Experimental applications of the technique, including mapping of welds, microstructures, and composites with varying length scales, along with studying the effect of surface roughness on nominally homogeneous specimens, will be presented.
BIOINSPIRED NACRE-LIKE ALUMINA WITH A BULK-METALLIC GLASS-FORMING ALLOY AS A COMPLIANT PHASE
Amy Wat, Je In Lee, Chae Woo Ryu, Bernd Gludovatz, Jinyeon Kim, Antoni P. Tomsia, Takehiko Ishikawa, Julianna Schmitz, Andreas Meyer, Markus Alfreider, Daniel Kiener, Eun Soo Park, Robert O'Ritchie
Nature Communications, 2019, 10 (961)
(view article: https://www.nature.com/articles/s41467-019-08753-6)
Bioinspired ceramics with micron-scale ceramic “bricks” bonded by a metallic “mortar” are projected to result in higher strength and toughness ceramics, but their processing is challenging as metals do not typically wet ceramics. To resolve this issue, we made alumina structures using rapid pressureless infiltration of a zirconium-based bulk-metallic glass mortar that reactively wets the surface of freeze-cast alumina preforms. The mechanical properties of the resulting Al2O3 with a glass-forming compliant-phase change with infiltration temperature and ceramic content, leading to a trade-off between flexural strength (varying from 89 to 800 MPa) and fracture toughness (varying from 4 to more than 9 MPa·m½). The high toughness levels are attributed to brick pull-out and crack deflection along the ceramic/metal interfaces. Since these mechanisms are enabled by interfacial failure rather than failure within the metallic mortar, the potential for optimizing these bioinspired materials for damage tolerance has still not been fully realized.
IN SITU TEM OBSERVATION OF REBONDING ON FRACTURED SILICON CARBIDE
Zhenyu Zhang, Junfeng Cui, Bo Wang, Haiyue Jiang, Guoxin Chen, Jinhong Yu, Chengte Lin, Chun Tang, Alexander Hartmaier, Junjie Zhang, Jun Luo, Andreas Rosenkranz, Nan Jiang, Dongming, Guo
Nanoscale, 2018, 10, 6261-69
(view article: https://pubs.rsc.org/en/content/articlelanding/2018/nr/c8nr00341f#!divAbstract)
BioSilicon carbide (SiC) is widely used in harsh environments and under extreme conditions, including at high-power, high-temperature, high-current, high-voltage and high-frequency. The rebonding and self-matching of stack faults (SFs) is highly desirable to avoid catastrophic failure for SiC devices, especially for specific applications in the aerospace and nuclear power industries. In this study, a novel approach was developed using an eyebrow hair to pick up and transfer nanowires (NWs), in order to obtain in situ transmission electron microscope (TEM) images of the rebonding and self-matching of SFs at atomic resolution. During rebonding and healing, the electron beam was shut off. Rebonding on the fractured surfaces of monocrystalline and amorphous SiC NWs was observed by in situ TEM at room temperature. The fracture strength was 1.7 GPa after crack-healing, restoring 12.9% of that of a single crystal NW. Partial recrystallization along the <111> orientation and the self-matching of SFs are responsible for the rebonding of the monocrystalline NW. In comparison, the fracture strengths were 6.7 and 5.5 GPa for the first and second rebonding, respectively recovering 67% and 55% of that of an amorphous NW. Atomic diffusion contributed enormously to the rebonding on fractured surfaces of an amorphous NW, resulting in a healed surface consisting of an amorphous phase and crystallites. This rebonding function provides new insight into the fabrication of high-performance SiC devices for the aerospace, optoelectronic and semiconductor industries.