Jingui Yu

Low-cost and large-scale fabrication of a superhydrophobic 5052 aluminum alloy surface with enhanced corrosion resistance

Superhydrophobic 5052 aluminum alloy substrates with excellent corrosion resistance have been fabricated by a simple and low-cost method of acid treatment and modification of fluoroalkyl-silane combined with surface passivation. Via an etching process with hydrochloric acid, hierarchical convex–concave micro/nano-structures have been formed on 5052 aluminum alloy surfaces. Then they were covered with a flocculent layer after passivation with potassium permanganate. The wettability and corrosion resistance of the as-prepared substrates have been systematically investigated. The results indicate that aluminum alloy substrates with an etching time of 5 min and passivation time of 180 min exhibit good superhydrophobicity with a water contact angle of 153 ± 0.7°. In addition, corrosion resistance was also explored by potentiodynamic polarization curves and electrochemical impedance spectroscopy. Clearly, the corrosion resistance of the as-prepared aluminum alloy substrates has been greatly enhanced, which will be positive to extend further the applications of Al alloys in engineering fields, such as shipbuilding and oceanographic engineering.

Molecular dynamics simulation of crack propagation behaviors at the Ni/Ni3Al grain boundary

The primary purpose of this paper is to study intergranular and transgranular crack propagation behavior at the grain boundary (GB) of Ni/Ni3Al by Molecular Dynamics (MD) simulation. Cracks are loaded in tension mode I. The stress–strain curves, the changes of dislocation network, the crack propagation speeds and the changes of interfacial energy are compared with those of two models. The results show that the yield stress of the intergranular crack model is greater than that of the transgranular crack model. It is found that the intergranular crack propagation does not extend along the GB, but the crack extends into the γ′ phase. In addition, the transgranular crack extends at an angle of 45° and the dislocation moves on the slip system {11} [01]. The transgranular crack model breaks completely under a small strain. Moreover, the tranagranular crack propagation results from deformation damage of the model, and its propagation mechanism is shear rupture along the slip plane. The intergranular crack initiates propagation at the most dense position of the slip bands.

A universal laser marking approach for treating aluminum alloy surfaces with enhanced anticorrosion, hardness and reduced friction

Lined and grating grooves have been fabricated on a large scale engineering Al alloy plate via a simple, convenient, efficient, and low cost laser marking method. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize and analyze the microstructure and composition of the as-prepared samples. The results demonstrate that regular and tailored roughness structures were successfully constructed on the surface. In addition, the roughness of the structures could be easily modulated. Furthermore, the corrosion resistances to seawater and tribological properties have been investigated. The corrosion resistance, hardness and friction resistance of Al alloy surfaces treated by the laser marking approach were remarkably enhanced, which presents a great opportunity for applications in the field of engineering.

Atomistic view of thin Ni/Ni3Al (0 0 1) under uniaxial tension of twist grain boundaries

Atomic motion and the structure response of grain boundaries (GBs) are essential to the plastic deformation of small-volume polycrystal systems, especially for thin materials that exhibit some dramatic characteristics. Here, the microstructure and properties of thin Ni/Ni3Al (0 0 1) with the uniaxial tension of twist GBs are investigated using molecular dynamics (MD) simulations with an embedded atom (EAM) potential. We find that low angle twist GB dislocations propagate mainly from the corners to the center of the interface, and for high angle twist GBs they originate from the edge of the interface but do not extend to the center. In the process of plastic deformation, both low angle and high angle twist GB fractures occur in the center of the interface, which is completely different from the situation of thick materials reported by other references. More interestingly, the fracture patterns between low angle and high angle twist GBs exhibit extremely different performance due to the different characteristics of the initial dislocation structures in the interfaces.

Tensile mechanical properties of Ni3Al nanowires at intermediate temperature

Molecular dynamics (MD) methods are employed to study the mechanical properties of Ni3Al nanowires (NWs) along the [001], [110] and [111] crystal orientations under tensile loading at intermediate temperatures. The stress–strain responses, Youngs modulus, elongations and crystal defects of NWs are compared at different temperatures and different crystal orientations. The simulation results indicate that the yield stress decreases linearly with an increase in temperature, which is the same as the trend for Youngs modulus. In addition, tensile tests exhibit that Ni3Al NWs have an obvious intermediate temperature brittleness (ITB) behavior at about 900–1100 K. The crystal structure is less stable at intermediate temperatures. Furthermore, we find that the different crystal defects formed are mainly point dislocations and stacking faults. The higher the stacking fault energy (SFE) of Ni3Al NWs, the easier are the dislocation slips. The glide dislocation expands within the {111} glide plane. In general, studying the relation between the incipient plastic deformation and the temperature of Ni3Al NWs at different crystal orientations can help us further understand the mechanical properties accurately and completely.

Simulation study and experiment verification of the creep mechanism of a nickel-based single crystal superalloy obtained from microstructural evolution

Molecular dynamics (MD) simulations and experiments were used to understand the creep properties and microstructural evolution of a nickel-based single crystal superalloy. By observing the microstructural evolution using MD simulations, we have found a P-type rafting in the [001] crystal orientation owing to dislocations cutting into the γ′ phase. The deflected γ phases lead to an L-type rafting, indicating it is an inferior creep property in the [011] crystal orientation. Unlike the [001] and [011] crystal orientations, dislocations climb over to the γ′ phase without rafting in the [111] crystal orientation, which manifests a superior creep property. In addition, by comparing the effect between temperature and stress on the creep properties, the results suggest that the creep of the [111] crystal orientation was strongly influenced by stress, whereas the creep properties of the [001] and [011] crystal orientations were significantly affected by temperature. Furthermore, the experimental results are consistent with the MD simulations. This study provides fundamental guidance for the rational design and testing of nickel base single crystal superalloy for structural applications.

The Effect of Textured Surfaces with Different Roughness Structures on the Tribological Properties of Al Alloy

Abstract In this study, four kinds of roughness structures were constructed on the Al alloy surface using laser marking technology. The tribological properties of the surfaces under the condition of dry friction were carefully investigated. The results indicate that the fabricated surfaces have similar compositions. The hardness of surfaces can be improved after the laser surface treatment. Besides, the texturing of surfaces can efficiently reduce friction and improve friction resistance. However, the friction-reducing mechanisms are not the same. The surfaces with lined and grating grooves can remove wear debris away from the interfaces between steel balls and surfaces, while those with irregular protrusions and micro-orifices array would be able to trap wear debris in the microstructure. Furthermore, due to the different friction mechanisms of distinct roughness structures, their friction-reducing performances are greatly affected by the actual friction conditions (sliding speed and load), which offers a guide for constructing a specific roughness structure on the Al alloy surface to improve its friction resistance efficiently.