Effects of tempering temperature on impact wear of 30Cr3Mo2WNi hot-working die steel are investigated by SEM, TEM, hardness, and impact wear tests. From 300 to 680°C, the hardness of the steel ...decreases and the impact toughness increases with increasing tempering temperature, while a secondary hardening with maximum hardness, 48.6 HRC, is achieved at 550°C. Fatigue delamination wear is the main mechanism during the impact wear, and three typical damage features are identified with different tempering temperatures. Brittle fatigue cracks are easy to occur in the steels tempered at 300°C. Ductile fatigue cracks occur at medium temperatures. Surfaces of steel tempered are extruded at 680°C.
The review summarizes the typical synthetic strategies, morphologies, catalytic performances, mechanisms, application conditions and scope of various metallic matrices, such as Au, Mo, Ni, and Ti, ...for supporting TMCs catalysts. The development directions and outlook of self-supporting TMCs@Metal electrodes for large-scale preparation and catalytic water splitting in industrial applications are discussed in detail.
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•The self-supporting catalytic electrodes for water splitting are studied.•The electrodes classified according to different substrates are summarized.•The loaded TMC materials and preparation strategies are discussed in detail.•The prospects of TMCs@Metal electrodes for industrial applications are suggested.
Transition metal chalcogenides (TMCs) are the fascinating replacement of noble catalysts in catalytic water splitting due to their unique physical and chemical properties and low cost. However, their industrial application is substantially restricted by their poor conductivity. Decorating TMCs on metal substrates to fabricate self-supporting electrodes could be an efficient strategy for solving this problem. In this review, typical synthetic strategies for self-supporting TMCs on metal substrates are introduced in detail, while all types of metallic matrices, such as Au, Mo, Ni, Ti, Cu, etc., for supporting TMC catalysts are comprehensively summarized. By comparing the matrix types, types of loaded TMC materials, preparation strategies, application conditions, and scope, we attempt to establish rules of various metals as substrates, which may provide suggestions for material design. Finally, we briefly discuss the development directions of self-supporting TMCs@Metal electrodes for large-scale preparation and catalytic water splitting in industrial applications.
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•The synthetic methods and electrochemical performances of Nb/Ta-based materials have been discussed, respectively.•The connection between different morphologies and electrochemical ...performances of Nb/Ta-based materials has been given.•The reasons for enhanced rate capability and cycling stability of Nb/Ta-based materials have been summarized.•The bottlenecks and challenges of Nb/Ta-based materials are given.
As transition metals, Nb and Ta share similar physical and chemical properties, exhibiting high melting and boiling points. Materials coexisting with Nb and Ta have attracted much attention in electrochemical energy storage, which are attributed to their unique crystal structures. However, Nb2O5 has the drawback of having a low electronic conductivity, which results in poor rate capability. Thus, Nb-based materials, including Nb-based oxides, Nb-based oxides/carbon and Nb-based carbides/nitrides, have been explored. This review discusses the use of Nb/Ta-based materials in electrochemical energy storage applications, including rechargeable batteries (e.g., lithium-ion batteries and sodium-ion batteries), supercapacitors and hybrid supercapacitors. In addition, the bottlenecks and challenges of using these materials are briefly discussed.
Background Airway remodelling is the major pathological feature of chronic obstructive pulmonary disease (COPD), and leads to poorly reversible airway obstruction. Current pharmacological ...interventions are ineffective in controlling airway remodelling. In the present study, we investigated the potential role of artesunate in preventing and treating airway remodelling and the underlying molecular mechanisms in vitro and in vivo. Methods A COPD rat model was established by cigarette smoke (CS) exposure. After 12 weeks of artesunate treatment, pathological changes in the lung tissues of COPD rats were examined by ELISA and histochemical and immunohistochemical staining. A lung functional experiment was also carried out to elucidate the effects of artesunate. Human bronchial smooth muscle (HBSM) cells were used to clarify the underlying molecular mechanisms. Results Artesunate treatment inhibited CS-induced airway inflammation and oxidative stress in a dose-dependent manner and significantly reduced airway remodelling by inhibiting alpha-smooth muscle actin (alpha-SMA) and cyclin D1 expression. PPAR-gamma was upregulated and TGF-beta1/Smad2/3 signalling was inactivated by artesunate treatment in vivo and in vitro. Furthermore, PPAR-gamma knockdown by siRNA transfection abolished artesunate-mediated inhibition of HBSM cell proliferation by activiting the TGF-beta1/Smad2/3 signalling pathway and downregulating the expression of alpha-SMA and cyclin D1 in HBSM cells. Conclusions These findings suggest that artesunate could be used to treat airway remodelling by regulating PPAR-gamma/TGF-beta1/Smad signalling in the context of COPD. Keywords: Artesunate, COPD, Airway remodelling, Cigarette smoke, PPAR-gamma
The article studies on the effect of slippage rate on frictional wear behaviors of high-tungsten high-speed steel (HTHSS) under high-pressure contact by using a self-made ring-on-ring wear machine. ...The microstructure of HTHSS is characterized by dual-scale tungsten carbides, including microscale eutectic M6C carbide (Fe0.55W0.30Cr0.08Mo0.07)6C and nanoscale secondary M6C carbide. Slippage rate has a significant effect on frictional wear behaviors. The peak value of friction coefficient occurs at the slippage rate of 5.5%. The friction coefficient will reduce whether the slippage rate increases or decreases. However, the increase in slippage rate makes wear failure mechanism change from fatigue to scratch, causing continuously significant increase in wear weight loss. The roles of different scale M6C carbides in resisting wear were also discussed.
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•Sliding-rolling frictional wear behaviors of HSS with micro-nano scales M6C were studied.•Slippage rate decides wear failure mode and therefore affects wear property of HSS.•High stress contact caused martensite transformation, contributing in delaying wear failure.•Micro-nano scales M6C play a different role under different slippage rate.
A new hatted 1T/2H‐phase MoS2 on Ni3S2 nanorods, as a bifunctional electrocatalyst for overall water splitting in alkaline media, is prepared through a simple one‐pot hydrothermal synthesis. The ...hat‐rod structure is composed mainly of Ni3S2, with 1T/2H‐MoS2 adhered to the top of the growth. Aqueous ammonia plays an important role in forming the 1T‐phase MoS2 by twisting the 2H‐phase transition and expanding the interlayer spacing through the intercalation of NH3/NH4+. Owing to the special “hat‐like” structure, the electrons conduct easily from Ni foam along Ni3S2 to MoS2, and the catalyst particles maintain sufficient contact with the electrolyte, with gaseous molecules produced by water splitting easily removed from the surface of the catalyst. Thus, the electrocatalytic performance is enhanced, with an overpotential of 73 mV, a Tafel slope of 79 mV dec−1, and excellent stability, and the OER demonstrates an overpotential of 190 mV and Tafel slope of 166 mV dec−1.
A hatted‐rod MoS2‐Ni3S2@NF heterostructure is a promising electrocatalyst for water splitting. The facile one‐pot hydrothermal synthesis strategy, high electrocatalytic activity, and robust stability for HER and OER are prominent features of this work. The phase transformation and electrocatalytic activity of the hatted nanorod materials can be adjusted by controlling the addition of aqueous ammonia (see scheme).
Tungsten disulfide (WS2) is well known to have great potential as an electrocatalyst, but the practical application is hampered by its intrinsic inert plane and semiconductor properties. In this ...work, owing to a Co-based zeolite imidazole framework (ZIF-67) that effectively inhibited WS2 growth, few-layered WS2 was confined to the surface of Co, N-doped carbon polyhedron (WS2@Co9S8), with more marginal active sites and higher conductivity, which promoted efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). For the first time, WS2@Co9S8 was prepared by mixing in one pot of a liquid phase and calcination, and WS2 realized uniform distribution on the polyhedron surface by electrostatic adsorption in the liquid phase. The obtained hybrid catalyst exhibited excellent OER and HER catalytic activity, and the OER potential was only 15 mV at 10 mA cm–2 higher than that of noble metal oxide (RuO2). The improvement of catalytic activity can be attributed to the enhanced exposure of sulfur edge sites by WS2, the unique synergistic effect between WS2 and Co9S8 on the metal–organic framework (MOF) surface, and the effective shortening of the diffusion path by the hollow multi-channel structure. Therefore, the robust catalyst (WS2@Co9S8) prepared by a simple and efficient synthesis method in this work will serve as a highly promising bifunctional catalyst for OER and HER.
Preparation and characterization of Mo/Al2O3 composites Zhou, Yucheng; Gao, Yimin; Wei, Shizhong ...
International journal of refractory metals & hard materials,
January 2016, 2016-01-00, 20160101, Letnik:
54
Journal Article
Recenzirano
In order to improve the performance of molybdenum, the Mo/Al2O3 composites were prepared by using a hydrothermal method for the synthesis of the precursor powders and subsequent powder metallurgical ...processing. The morphologies of the composite powders and the microstructures and properties of the composites were investigated. Compared with the pure Mo powder, the grains of composite powders are smaller because of the existence of the fine Al2O3 particles. The results from the sintered composites show that the fine Al2O3 particles are evenly distributed in the Mo matrix and well bonded with the Mo matrix. With increasing Al2O3 content, all the values of the micro-hardness, compressive strength and flow stress at 0.08 strain are increased. The strengthening effect is more remarkable at elevated temperatures. At room temperature, the compressive strength and the flow stress at 0.08 strain of the composite with 40vol.% Al2O3 are 1.67 and 2.01 times greater than those of pure molybdenum, respectively, while the values are up to 2.02 and 2.52 at 1100°C.
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•Preparation of the Mo/Al2O3 composites by using the hydrothermal method and a subsequent powder metallurgy process.•The effects of Al2O3 addition on the morphology of the mixed powder were investigated.•The microstructures of the composites were studied.•The compressive properties at room-temperature and at 1100°C were examined.
The sintered Al2O3-reinforced tungsten alloys were fabricated via hydrothermal process and powder metallurgy method. Subsequently, the compression tests of sintered W-0.25 wt% Al2O3 alloy with ...Gleeble 1500D thermal simulator were conducted in the temperature range of 1300–1600 °C and strain rate range of 0.01–10 s−1. The processing map of the sintered W-0.25 wt% Al2O3 alloy was established and the swaged W-0.25 wt% Al2O3 alloy was obtained by hot working on the basis of the data analysis from the processing map. For the swaged W-0.25 wt% Al2O3 alloys annealed at various temperature, the mechanical properties are obviously reduced, and recrystallization temperature of the swaged W-0.25 wt% Al2O3 alloys is above 1600 °C, at least 200 °C higher than of the swaged pure tungsten. The Al2O3 particle is well combined with the W matrix. In addition, there is a transition layer between the Al2O3 particles and W matrix. The swaged W-0.25 wt% Al2O3 alloys possess high strength of 611 MPa with a total elongation of 45% at 800 °C. The ultimate tensile strength of the swaged W-0.25 wt% Al2O3 alloys are always higher than that of the swaged pure W alloys at different temperatures, indicating that the addition of Al2O3 particles can effectively pin dislocations and grain boundaries, thus improving the high-temperature strength of alloys.
•The processing map of the sintered W-0.25 wt% Al2O3 alloy was established.•The addition of Al2O3 can effectively increase the recrystallization temperature of tungsten alloy.•There is a transition layer between the Al2O3 particles and W matrix.
Al2O3-dispersion-strengthened tungsten matrix alloys were fabricated by hydrothermal synthesis and powder metallurgy. The Al2O3 content was varied from 0 to 1 wt%, and sintering was conducted for 8 h ...at 2350 °C. The addition of Al2O3 was found to significantly affect the grain size and compressive strength of the sintered alloys. The grain size of the sintered samples ranged from approximately 10 to 3 µm with increasing Al2O3 content. When the Al2O3 content was increased to 0.25 wt%, the microhardness and compressive strength reached the maximum values of 386 HV and 1628 MPa, respectively. Subsequently, the deformation behavior of the W–0.25 wt% Al2O3 alloy at high temperature was studied. The constitutive equation relating the flow stress and deformation parameters of the W–0.25 wt% Al2O3 alloy was established, and the hot deformation activation energy (Q) of the W–0.25 wt% Al2O3 alloy was found to be 321.79 kJ/mol.
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