Microstructures and Properties of FeAl-Fe_3AlC_(0.5) Composites Prepared by SHS Casting

FeAl composites with 21, 37 and 50 wt pct Fe3AlC0.5 were fabricated by a self-propagating high temperature synthesis （SHS） casting. Phases and microstructures were analyzed by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Microhardness and bending strength of the composites were measured. The composites with 21 and 50 wt pct Fe3AlC0.5 mainly consisted of FeAl and FesAlC0.5 phases, whereas the composite with 37 wt pct Fe3AlC0.5 was composed of FeAl, Fe3AlC0.5 and graphite phases. The bonding of the reinforcement and the matrix was good. Hardness and bending strength of the composite with 37 wt pct Fe3AlC0.5 was lower than those of the 21 and 50 wt pct composites owing to the presence of the soft graphite phase.

Efficient prediction of corrosion behavior in ternary Ni-based alloy systems:Theoretical calculations and experimental verification

Pourbaix diagrams are calculated to describe electrochemical processes for alloys in aqueous solution.With the multi-component differentiation of alloy systems,the construction of Pourbaix diagrams is fac-ing challenges,especially for non-single-phase alloy systems.In this study,the simultaneous construction of phase diagrams and Pourbaix diagrams were implemented for predicting the evolution of the phases in the immune and passive regions.The CALPHAD(CALculation of PHAse Diagram)approach was used to quickly access the Gibbs free energies of various phases and the chemical potential of the elements in the phases from the thermodynamic database of the Ni-Si-Al-Y system.The corrosion behavior of two typical Ni-Al-Si and Ni-Al-Y systems was investigated.Si and Y were added to Ni-based alloys to produce the solid solutions L12-Ni_(3)(Al,Si)and L12-Ni_(3)Al+Ni_(5)Y,respectively.Calculations showed that NiO and Al_(2)O_(3)make up the passive area of the Ni_(3)Al 1 alloy.The introduction of SiO_(2)and Y(OH)3 in the passive region separately helped to minimize the alloys’susceptibility to corrosion.However,Si reduced the thermody-namical possibility of NiO for mation in the passive film,and the addition of Y caused extreme galvanic corrosion.Experiments on Ni-based alloys validated the results through electrochemical corrosion.It was also discovered that the presence of Ni_(5)Y produced galvanic corrosion and that Si reduced the oxide in the passive film,causing pitting corrosion.The corrosion prediction of the quaternary alloys indicates that the solid solution of Si in Ni_(5)Y reduces the galvanic corrosion effect and the dissolution of passive film.The current work demonstrates that phase diagrams and Pourbaix diagrams may be efficiently and accurately predicted using a well-constructed thermodynamic database,which has major implications for future studies on the corrosion behavior of multi-component alloys.

Carbon-based solid-liquid lubricating coatings for space applications-A review

Despite continuous improvements in machine elements over the past few decades,lubrication issues have impeded human exploration of the universe because single solid or liquid lubrication systems have been unable to satisfy the ever-increasing performance requirements of space tribology.In this study,we present an overview of the development of carbon-based films as protective coatings,with reference to their high hardness,low friction,and chemical inertness,and with a particular focus on diamond-like carbon(DLC)films.We also discuss the design of carbon-based solid-liquid synergy lubricating coatings with regards to their physicochemical properties and tribological performance.Solid-liquid composite coatings are fabricated via spinning liquid lubricants on solid lubricating films.Such duplex lubricating coatings are considered the most ideal lubrication choice for moving mechanical systems in space as they can overcome the drawback of adhesion and cold-welding associated with solid films under harsh space conditions and can minimize the crosslinking or chain scission of liquid lubricants under space irradiation.State of the art carbon-based solid-liquid synergy lubricating systems therefore holds great promise for space applications due to solid/liquid synergies resulting in superior qualities including excellent friction reduction and anti-wear properties as well as strong anti-irradiation capacities,thereby meeting the requirements of high reliability,high precision,high efficiency,and long lifetime for space drive mechanisms.

Fabrication of Bionic Superhydrophobic Manganese Oxide/Polystyrene Nanocomposite Coating

A superhydrophobic manganese oxide/polystyrene （MnO2/PS） nanocomposite coating was fabricated by a facile spraying process. The mixture solution of MnO2/PS was poured into a spray gun, and then sprayed onto the copper substrate using 0.2 MPa nitrogen gas to construct superhydrophobic coating. The wettability of the composite coating was measured by sessile drop method. When the weight ratio of MnO2 to PS is 0.5：1, the maximum of contact angle （CA） （140°） is obtained at drying temperature of 180 ℃. As the content of MnO2 increases, the maximum of CA （155°） is achieved at 100 ℃. Surface morphologies and chemical composition were analyzed to understand the effect of the content of MnO2 nanorods and the drying temperature on CA. The results show that the wettability of the coating can be controlled by the content of MnO2 nanorods and the drying temperature. Using the proposed method, the thickness of the coating can be controlled by the spraying times. If damaged, the coating can be repaired just by spraying the mixture solution again.

How the fluorographene replaced graphene as nanoadditive for improving tribological performances of GTL-8 based lubricant oil

Fluorographene,a new alternative to graphene,it not only inherits the 2-dimensional(2D)layered structure and outstanding mechanical properties,but also possesses controllable C-F bonds.It is meaningful to reveal the evolution processes of the tribological behaviors from graphene to fluorographene.In this work,fluorinated reduced graphene oxide nanosheets(F-rGO)with different degree of fluorination were prepared using direct gas-fluorination and they were added into gas to liquid-8(GTL-8)base oil as lubricant additive to improve the tribological performance.According to the results,the coefficient of friction(COF)reduced by 21%,notably,the wear rate reduced by 87%with the addition of highly fluorinated reduced graphene oxide(HF-rGO)compared with rGO.It was confirmed that more covalent C-F bonds which improved the chemical stability of HF-rGO resisted the detachment of fluorine so the HF-rGO nanosheets showed less damage,as demonstrated via X-ray photoelectron spectroscopy(XPS),Raman spectra,and transmission electron microscopy(TEM).Meanwhile,the ionic liquid(IL)adsorbed on HF-rGO successfully improved the dispersibility of F-rGO in GTL-8 base oil.The investigation of tribofilm by TEM and focused ion beam(FIB)illustrated that IL displayed a synergy to participate in the tribochemical reaction and increased the thickness of tribofilm during the friction process.

Recent advances in single-crystalline two-dimensional polymers:Synthesis,characterization and challenges

Two-dimensional polymers(2DPs)are emerging crystalline 2D organic material comprising free-standing,single-atom/monomer-thick,planar,and covalent networks with long-ranging structural order.Benefiting from their intrinsic porosity,crystallinity,and electrical properties,2DPs have displayed great potential for separation,energy conversion and electronic fields.In this mini review,we aim to provide the recent progress in crystalline 2DPs films form synthesis strategies to characterization methods,as well as the future trends.We first present the synthesis strategy of single-crystalline 2DPs films including crystal engineering approaches and surface science.Also,we summarize the characterization methods of 2DPs films and highlight the advantages and limitations of different methods focusing on chemical bonding,morphology,and crystal structure.Finally,we will present the current challenges and trends regarding the future developments of crystallinity,monomer design,synthesis strategy and characterization.

Effect of surface roughness on the angular acceleration for a droplet on a super-hydrophobic surface

The motion of droplets on a super‐hydrophobic surface,whether by sliding or rolling,is a hot research topic.It affects the performance of super‐hydrophobic materials in many industrial applications.In this study,a super‐hydrophobic surface with a varied roughness is prepared by chemical‐etching.The adhesive force of the advancing and receding contact angles for a droplet on a super‐hydrophobic surface is characterized.The adhesive force increases with a decreased contact angle,and the minimum value is 0.0169 mN when the contact angle is 151.47°.At the same time,the motion of a droplet on the superhydrophobic surface is investigated by using a high‐speed camera and fluid software.The results show that the droplet rolls instead of sliding and the angular acceleration increases with an increased contact angle.The maximum value of the angular acceleration is 1,203.19 rad/s^(2) and this occurs when the contact angle is 151.47°.The relationship between the etching time,roughness,angular acceleration,and the adhesion force of the forward and backward contact angle are discussed.

Visible-Light Photocatalytic and Photo-bactericidal Activity of Ni-CuWO_(4)/OTiO_(2) Composite

A series of nickel-doped copper tungstate/oxygen-rich TiO_(2) heterojunction-constructed composites of xNi-CuWO_(4)/OTiO_(2) were successfully prepared to demonstrate the enhancement of the visible-light photoactivity through promoting the photogenerated charge carrier separation efficiency.Of all these composites,0.2Ni-CuWO_(4)/OTiO_(2) exhibits excellent and stable visible light photoactivity for the photooxidative coupling of benzylamine to the corresponding N-benzyl-1-phenymethanimine(BPMI)in air atmosphere.The conversion of benzylamine and the selectivity to BPMI reach 97%and 99%,respectively.The catalyst shows good cyclability with the conversion of benzylamine decreasing just by 22%after being repeated six times with the well-maintained selectivity of BPMI.The composite also exhibits excellent photo-bactericidal ability,which greatly inhibits the reproducing of both the Gram-positive bacteria(e.g.,S.epidermidis)and Gram-negative bacteria(e.g.,E.coli).