Ni-based bimetallic films with 20 at.% and 45 at.% Cu and mesostructured surfaces were prepared by electrodeposition from an aqueous solution containing micelles of P123 triblock copolymer serving as a structure-directing agent. The pH value of the electrolytic solution had a key effect on both the resulting Cu/Ni ratio and the surface topology. The catalytic activity of the CuNi films toward hydrogen evolution reaction was investigated by cyclic voltammetry (CV) in 1 M KOH electrolyte at room temperature. The Cu₄₅Ni₅₅ film showed the highest activity (even higher than that of a non-mesostructured pure Ni film), which was attributed to the Ni content at the utmost surface, as demonstrated by CV studies, as well as the presence of a highly corrugated surface.

Purpose: This paper aims to study the friction layer and tribological property of polyimide (PI)–matrix composites under different friction speeds. Design/methodology/approach: Friction tests were conducted under friction speeds ranging from 20-120 km/h and pressure of 0.57 MPa by a pin-on-disk tribometer. Findings: The results indicate that the friction coefficient decreases with the increasing of the friction speed. Under different friction speeds, the structure of the friction layer and debris are different, which affects the actual tribological performance of the composites. At low friction speed, the morphology of the friction layer is mainly particulate. The higher level of clenching action between the friction pair leads to a high friction coefficient, and the morphology of the particles in the particulate zone and the wear debris are mostly equiaxial particles. At high friction speed, the morphology of the friction layer is mainly a compact zone. The reduction of the surface roughness leads to a low friction coefficient. The debris collected on the counter surface at high friction speeds are mostly big sheets, and the morphology of the particles in the particulate zone is mostly rod-like. Controlling the conditions of the disk and the pin can reveal the influence of friction speed on the friction layer. The wear mechanisms at different friction speeds are also discussed. Originality/value: By controlling the conditions of the disk and the pin to reveal the influence of friction speed on the friction layer, and the evolutions of the friction layer, wear debris were carefully inspected with the aim of demonstrating the relationship between friction speed and wear mechanism of PI–matrix composites.

In this work, Al–Mg alloys fabricated by combining continuous rheo-extrusion (CRE) and Sc modification were proposed for producing Al–Mg alloys with high efficiency and superior mechanical performance. The microstructural evolution and mechanical property response of the CREed Al–5Mg alloy with Sc modification were investigated. The grain refinement and strengthening mechanisms induced by nanoscale Al₃Sc-phase particles in the alloy were discussed. The results showed that an obvious grain refinement effect was achieved in the CREed Al–5Mg alloy as the Sc content increased from 0 to 0.5 wt%, and the average grain size decreased from 52.6 μm to 2.4 μm, respectively. The primary Al₃Sc-phase particles formed during solidification behaved as heterogeneous nucleation sites for the α-Al matrix, while the nanoscale Al₃Sc-phase particles achieved during CRE enhanced the driving force of continuous dynamic recrystallization and the Zener drag force. As a result, a superior grain refinement effect was observed. The ultimate tensile strength, yield strength, and hardness of the alloy were enhanced as the Sc content increased from 0 to 0.5 wt%. Grain boundary strengthening, second-phase strengthening, and dislocation strengthening were the main strengthening mechanisms of the CREed Al–Mg–Sc alloys.