Previous studies have yielded conflicting results on how grain size affects the mechanical properties of nanomaterials, making it difficult to anticipate its effect for practical applications. Yang et al. sought to resolve this relationship for tungsten, a metal with a high melting point and other useful properties for certain nanotechnology applications.
The authors found that nanocrystalline tungsten, with an average grain size of 10 nm, is about 3.5 times stronger than coarse-grained tungsten, with an average grain size of 3 μm. These results are consistent with the Hall-Petch relationship, which predicts that a metal will get stronger as its grain size decreases. However, previous studies on various metals reported both softening and strengthening when grain size was decreased to the nanoscale.
X-ray diffraction was performed on the samples under nonhydrostatic compression in a diamond cell anvil cell. By analyzing the diffraction linewidth of the samples, the authors found that yield strength is higher for samples with the smaller grain size.
These results show that the Hall-Petch relationship is maintained at the nanoscale. The authors think that the quality of the bulk samples in previous similar experiments, such as their porosity, impurities, and grain-grain binding, may have contributed to the lack of consistency regarding the relationship between grain size and strength.
“This suggests that nanostructured bulk materials should have excellent mechanical properties, such as higher strength and hardness compared to common coarse-grained bulk materials,” said author Duanwei He. “However, we still need unremitting efforts to prepare bulk materials with nanostructures and make them practical.”
Next, the authors plan to use high pressure technology to ready high quality nanostructured bulk materials for potential applications in technology.
Source: “Strength enhancement of nanocrystalline tungsten under high pressure,” by Jing Yang, Wen Deng, Qiang Li, Xin Li, Akun Liang, Yuzhu Su, Shixue Guan, Junpu Wang, and Duanwei He, Matter and Radiation at Extremes (2020). The article can be accessed at https://doi.org/10.1063/5.0005395.
