Nanostructuring is a commonly employed method of obtaining superior mechanical properties in metals and alloys. Compared to conventional polycrystalline counterparts, nanostructuring can provide remarkable improvements in yield strength, toughness, fatigue life, corrosion resistance, and hardness, which is attributed to the nano grain size. In this review paper, the current state-of-the-art of synthesis methods of nanocrystalline (NC) materials such as rapid solidification, chemical precipitation, chemical vapor deposition, and mechanical alloying, including high-energy ball milling (HEBM) and cryomilling was elucidated. More specifically, the effect of various process parameters on mechanical properties and microstructural features were explained for a broad range of engineering materials. This study also explains the mechanism of grain strengthening using the Hall-Petch relation and illustrates the effects of post-processing on the grain size and subsequently their properties. This review also reports the applications, challenges, and future scope for the NC materials.

Nanocrystalline Materials: Synthesis, Characterization, Properties, and Applications

The influences of Ag content on the friction and wear properties of TiCN–Ag films

Si-based supercapacitors have drawn much attention due to their compatibility with current Si-based microelectronics. However, complicated and expensive manufacturing technologies greatly restrict their practical applications. In this work, a supercapacitor electrode based on metal oxide and conductive polymers around silicon nanowire arrays (SiNWs) was first designed with a simple, facile, and low-cost method. The manganese dioxide (MnO2) and poly(3,4-ethylenedioxythiophene) (PEDOT) composite (PM) was coelectrodeposited on the SiNWs followed by spin-coating the high conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer doped with silver nanowires (PsAg). Thin reduced graphene oxide (rGO) sheets were inserted between the PM and PsAg for further enhancing the capacity of the electrode. Resulting from the large gaps caused by the tetramethylammonium hydroxide (TMAH) solution treatment, a three-dimensional (3D) hierarchical double-shelled structure of current collect layers (PsAg combined with rGO) and active material (PM) decorated SiNWs was formed (Si/PM/rGO-PsAg), which not only reduced the contact resistance between the active materials and current collector but also shortened the ion and electron diffusion paths. With the smart design, the prepared Si/PM/rGO-PsAg could be measured in an aqueous solution and exhibited outstanding electrochemical properties, including high areal capacitance (100.98 mF cm–2 at 1.5 mA cm–2) and excellent cycling stability (80.85% capacitance retention after 2000 cycles). Additionally, the practical applicability of the synthesized Si/PM/rGO-PsAg was investigated by fabricating a symmetric device, which displayed 85.91% retention over 5000 cycles and a maximum energy density of 0.0034 mWh cm–2. Our design concept opens up an avenue to prepare 3D silicon nanostructures based on metal oxide and conductive polymers for low-cost and high-performance supercapacitors. 

Chao Yang

Papers

Sputtered titanium nitride films on nanowires Si substrate as pseudocapacitive electrode for supercapacitors

Thermal stabilization of nanocrystalline promoting conductive corrosion resistance of TiN–Ag films for metal bipolar plates