► A bulk nanocrystalline Ni with a thickness of about 5.4
mm is made. ► The nc Ni holds an ultrahigh strength of 2920
MPa and an accepted ductility of 16%. ► The deformation-induced grain growth and ...triple-junction cracks are observed.
A bulk and dense nanocrystalline Ni with an average grain size of 19
nm and a thickness of 5.4
mm was fabricated by an electro-deposition technique. The nc Ni had a preferable (2
0
0) growth texture along the depositing direction. Under compression test, the nc Ni exhibited a high strength of 2920
MPa and an accepted good ductility of 16%. A novel fracture character, i.e., the triple-junction shaped micro-cracks with the size varying from few to several tens of micrometers which run through the holistic fracture body of the nc Ni, was observed. The reason for the formation of such cracks is attributed to GB activities, which leads to the formation of nano-sized void, and the subsequent formation of micro-crack.
The effect of Zn addition on the microstructures and mechanical behaviors of as-cast Mg-2.5Y-1Ce-0.5Mn alloy was investigated. Microstructure observation demonstrated that with the addition of 1wt%, ...3wt% and 5wt% Zn, the ternary phases of LPSO phase, LPSO phase +W-phase and W-phase +T-phase (Mg-Zn-Ce) are precipitated orderly, and the volume fraction of eutectic phases increases. The results of tensile tests demonstrated that with increasing Zn addition, the yield strength Y S of as-cast alloys increases continuously while the ultimate tensile strength UTS and elongation δ increase nonlinearly. Based on the analysis of microstructure, nanoindentation results and deformation surfaces, it found that the Y S is increased by the increased volume fraction of hard ternary phases. The largest δ in 1wt% Zn alloy is contributed from the LPSO phase with an excellent plastic accommodation while the insufficient accommodated role of LPSO phase and the easily broken W-phase deteriorate the ductility of 3wt% Zn alloy. The hard and brittle T-phase also damages the ductility, while the fine grains contribute to the moderate elongation in 5wt% Zn alloy. The UTS mainly arises from a sustainable increase of strain hardening ability after yielding that associated with both the high yielding point and excellent ductility.
Seeking efficient and inexpensive electrocatalysts for the oxygen evolution reaction (OER) is still the key to solving the electrochemical energy conversion process. In this work, Cu doped Ni3S2 ...nanosheet arrays grown on Ni foam have been synthesized using a two-step hydrothermal method. Doping Cu ion can effectively enhance the conductivity, accelerate charge transfer process and provide more catalytic active sites, thereby improving the OER performance of Ni3S2. In a series of Cu-doped Ni3S2 samples, Ni1.9Cu0.1-S (the chemical composition is Ni2.85Cu0.15S2) displays a small overpotential of 259 mV to reach a current density of 10 mA cm−2 and a Tafel slope of 54.9 mV dec−1, better than that of undoped Ni3S2 (with a overpotential of 274 mV). Also, the catalyst possesses pretty OER stability with the overpotential only rising by 1.9% after 12 h, which indicate the Ni1.9Cu0.1-S nanosheet arrays on Ni foam should be an effective OER catalyst in alkaline medium.
The optimized Ni1.9Cu0.1-S electrode showed better catalytic performances for OER in charge transfer, reaction kinetics and catalytic stability. Display omitted
•Porous Cu doped Ni3S2 nanosheet arrays were synthesized on Ni foam.•Doping Cu can reduce the contact resistance and accelerate charge transfer.•The optimized Ni1.9Cu0.1-S shows a high catalytic activity and stability for OER.
Tensile behavior of an electrodeposited Cu with ultrafine grain size of ∼200
nm was studied at different strain rates and room temperature. By increasing the strain rate the elongation to fracture ...increased noticeably. Analysis on the deformed and fracture surfaces suggested a shear localization process in the necking stage, which led to a different tendency of cracking. Strong strain rate dependences of work hardening and shear localization might be responsible for variation of the tensile ductility.
A ductile–brittle–ductile transition in the fracture mode of the Ni–8.6
wt.% Co alloy with an average grain size of 13
nm was observed through increasing the strain rates from 1.04
×
10
−5 to 1.04
s
...−1 at room temperature (RT). The Ni–Co alloy exhibited a limited plastic strain (about 1%) at the intermediate strain rates of 2.08
×
10
−3 to 4.17
×
10
−2
s
−1, which was attributed to that in this strain rate range less dislocations or GB atoms would be activated. However, a gradual brittle–ductile transition occurred with the strain rate decreasing from 2.08
×
10
−3 to 1.04
×
10
−5
s
−1. The lower strain rates allow the GB atoms diffuse easily, which would relax the stress concentration and hence enhance the ductility. Another brittle–ductile transition happened with increasing the strain rates from 4.17
×
10
−2 to 1.04
s
−1. The enhanced ductility at high strain rate can be explained by stress-assisted activation of GB atoms.
Strain-hardening and warm deformation behaviors of extruded Mg–2Sn–0.5Yb alloy (at.%) sheet were investigated in uniaxial tensile test at temperatures of 25–250 °C and strain rates of ...1 × 10−3 s−1–0.1 s−1. The data fit with the Kocks–Mecking type plots were used to show different stages of strain hardening. Besides III-stage and IV-stage, the absence of the II-stage strain hardening at room temperature should be related to the sufficient dynamic recrystallization during extrusion. The decrease of strain hardening ability of the alloy after yielding was attributed to the reduction of dislocation density with increasing testing temperature. Strain rate sensitivity (SRS) was significantly enhanced with increasing temperature, and the corresponding m-value was calculated as 0.07–0.12, which indicated that the deformation mechanism was dominated by the climb-controlled dislocation creep at 200 °C. Furthermore, the grain boundary sliding (GBS) was activated at 250 °C, which contributed to the higher SRS. The activation energy was calculated as 213.67 kJ mol−1, which was higher than that of lattice diffusion or grain boundary self-diffusion. In addition, the alloy exhibited a quasi superplasticity at 250 °C with a strain rate of 1 × 10−3 s−1, which was mainly related to the fine microstructure and the presence of the Mg2Sn and Mg2(Sn,Yb) particles.
Display omitted
•A superhydrophobic brass surface was fabricated by laser ablation and heat treatment without using chemical modification.•Corrosion resistance of fabricated surface was studied by ...performing electrochemistry tests.•Hierarchical structure and adsorption of organic compounds from air are responsible for observed superhydrophobicity.•Superhydrophobic surface has over 13 times lower corrosion current density than polished brass surface.•Better corrosion resistance of superhydrophobic surface arises from air pockets trapped in roughness grooves.
In this work, a superhydrophobic brass surface was fabricated by laser ablation followed by heating treatment, and corrosion resistance of this surface was studied by performing electrochemistry tests. The observed superhydrophobicity arises from the synergistic effect of the micro/nano hierarchical structure produced by the laser ablation and the adsorption of organic compounds from ambient air (mainly the nonpolar C−C/C−H groups) during the heating treatment. The superhydrophobic surface shows better corrosion resistance than polished brass surface because of the additional air film resistance and the decrease in the solid-electrolyte contact area caused by the air pockets trapped in the roughness grooves.
The CuS/MnS composite hexagonal nanosheet clusters were fabricated through a one-step facile hydrothermal method without any surfactant. The adding of CuS plays a role of template for the growth of ...CuS/MnS composite, as CuS can induce the growth of MnS, forming a stable three-dimensional cluster structure composed by hexagonal nanosheets, which provides easy access of electrolyte, effective electronic transmission and stable circulation structure. The as synthesized CuS/MnS composite electrode (3 h) shows a high specific capacitance (1144 F g-1 at 1 A g−1), which is five times higher than that of either CuS or MnS electrode under the same conditions, excellent rate property (567 F g-1 at 50 A g−1 and 40.8% rate retention even at 100 A g−1), and good cycling stability (85.9% of the initial capacity after 10000 cycles). So, the CuS/MnS nano-composite should be a promising candidate electrode material for supercapacitors.
Display omitted
•The CuS/MnS composite with a stable three-dimensional cluster structure composed of small hexagonal nanosheets in different directions were fabricated.•The prepared CuS/MnS composite-3h electrode shows high specific capacitance of 1144 F g-1 at 1 A g−1.•The composite electrode exhibits a high rate capability and an excellent cycling stability for 10000 cycles.
Determining the equilibrium wetting states and exploring the conditions and mechanisms of the wetting state transition from the Cassie-Baxter (CB) state to the Wenzel (W) state (CB-W transition) have ...been a central topic in the study of superhydrophobic behavior on rough or textured surfaces. Although considerable progress has been made, some issues regarding this topic are still not completely understood. In this study, a systematic thermodynamic analysis has been performed to address several key issues related to this topic. Generalized theoretical expressions for determining the equilibrium wetting states (the threshold Young contact angle of the CB region) and evaluating the stability of the CB state (the energy barrier separating the CB and W states and the critical pressure for the CB-W transition) have been derived. Applying these expressions to four types of surfaces built with protrusions in paraboloid, truncated cone, inverted truncated cone and flat-top pillar shapes, the wetting equilibrium and resultant wetting states have been studied. The physical meanings of the threshold Young contact angle, the roles and mechanisms of the energy barrier and critical pressure in stabilizing the CB state have been discussed. Finally, a general guidance for achieving robust superhydrophobicity on the studied surfaces has been given.
Display omitted
•Research background about wetting state transitions on rough surfaces are reviewed.•Expressions of threshold Young angle, energy barrier and critical pressure are derived.•Equilibrium wetting state can be determined by threshold Young angle.•Stability of Cassie-Baxter state should be evaluated by critical pressure.•Guidance for achieving robust superhydrophobicity is given.
A black phosphate coating for C1008 steel Li, Guangyu; Niu, Liyuan; Lian, Jianshe ...
Surface & coatings technology,
2004, 2004-1-00, 20040101, Letnik:
176, Številka:
2
Journal Article
Recenzirano
This paper describes an effective metal finishing technology for obtaining black phosphate coatings on steel. The black conversion coating obtained on steel (C1008, AISI) and cast iron (No.35, ASTM) ...was dense and uniform with a thickness up to 18 μm. The coating shows better corrosion resistance; lubricating ability and higher efficiency of light-absorption than the traditional phosphate coatings. The black phosphate-forming mechanism was investigated. It is shown that sodium molybdate added to the black phosphate treatment bath can refine the microstructure. Corrosion tests showed that the corrosion rate was lower than that of traditional phosphating. The black phosphate coating, when employed as the pretreatment layer before laser heat-treatment, can remarkably improve the efficiency of light-absorption during laser heat-treatment. This phosphate technology had been employed successfully on the production line in the automobile industry.
PDF
