Papers by Author: Shi Ning Ma

Abstract: FeS solid lubrication duplex layer was prepared on the surface of 45 steel by ion nitrocarburizing-ion sulphurizing process. The sulphide grains and holes all in micron and nano scale and distributing equably in the sulphide surface layer with 10 μm thickness of the duplex layer. The duplex layer is composed of FeS, FeS₂ and Fe₃N. Under liquid paraffin oil with 0.1wt% n-Al₂O₃ lubrication, the synergistic effect between n-Al₂O₃ and the duplex layer is produced, and the chemical reaction films including sulphide, sulphate and nitride is formed, which makes the friction factor of the duplex layer keep being the lowest and about 0.07, and the volume loss is reduced by 97% than that of the plain surface(rubbing for 10 min), and reduced by 92% and 21% than that of the sulphurized surface and the nitrocarburized surface, respectively.

Abstract: Non-electric welding is a novel efficient technique for emergency maintenance, which utilizes the heat released by combustion reaction to join metals without needing any power supply or gas sources. Welding experiments were performed with 45 steel as the weld object, and results showed that the weld metal jointed the weld object in a metallurgic connection with the tensile strength above 280 MPa, which proved non-electric welding a fusion welding technique. Non-electric welding technology has advantages of simple operation and good mechanical performance, therefore possesses a promising application prospect.

Abstract: To improve its surface global performance, 7A52 aluminum alloy was treated by means of supersonic shot peening, then the structure of surface strengthening layer was characterized and its tribological properties were investigated, too. It was found that after having been peened, surface hardness of 7A52 aluminum alloy increased by 80%, surface crystalline grains were refined, a surface compression stress layer with thickness of 320μm was fabricated, which reached maximum 210MPa at the distance of 80~100μm from the top treated surface; The alloy performs superb tribological properties under both unlubrication friction and lubrication friction.

Abstract: Nanocrystalline surface layer was fabricated on a quenched and tempered Cr-Si alloy steel by using Surface mechanical treatment. The microstructure features of various sections in the surface layer were characterized by using transmission electron microscopy (TEM). By analyzing the microstructural characteristic at different depths in the treated surface, the effect of the initial microstructures on grain refinement process of quenched and tempered steel was investigated. Experimental evidence showed the initial subgrains with small angle boundary and lower dislocation density were firstly developed into Lamellar-type dislocation cells (DCs) with dense dislocation walls (DDWs). Some initial subboundaries were moved to DDWs by dislocation activities. The width of lamellar-type DCs was 2-3 times of that of initial lathy subgrains. The size of the DCs and subgrains formed in the interim of refinement process was not uniformity. On the top surface the cementite granules were decomposed or fragmented to hyperfine particles, and the size of the grains tended to uniformity. Experimental analysis indicated the configuration of microstructure was affect by the initial microstructure in the initial stage and the interim of the grain refinement process. Surface nanocrystallization of Cr-Si steel can be attributed to dislocation activities.

Abstract: Nano-Fe particles were selected as microwave-absorber, and added in the epoxy resin. Epoxy resin/nano-Fe composite materials were cured by microwave irradiation and heating. Vector network analysis, dynamic mechanical analysis(DMA) and scanning electron microscope(SEM) were used to study the curing behaviors of composite materials under the different curing ways. Results show that the dielectric constant(εr) and the dielectric loss factor(tanδ) of the epoxy resin increased obviously when nano-Fe particles were added, and microwave absorption properties of epoxy resin/nano-Fe composite materials improved greatly with increasing contents of nano-Fe particles. DMA results indicate that the storage modulus (E’) and glass transition temperature(Tg) of epoxy resin samples with nano-Fe particles were higher than those without nano-Fe particles. The microstructure and phase composition of the samples were studied by SEM and EDX. Results show that nano-Fe particles were homogeneously dispersed in the epoxy resin matrix under microwave irradiation, which implies improved strength and toughness of epoxy resin/nano-Fe composite materials.

Abstract: Good dispersing stability is required for nano-SiO2 which, however, tends easily to conglomerate, to be widely applied as an important functional material of high toughness, high resistance to corrosion and good high-temperature performance. Through ultrasonic treatment, the suspension of SiO2 nano-powder in water was prepared utilizing sodium dodecylbenzenesulfonate (SDBS) as the dispersant. The effect of SDBS content and ultrasonic treatment time on the suspension stability was investigated by way of testing the particle size of SiO2 nano-powder, the Zeta potential and transmittance of the suspension. The results show that with increasing SDBS content, the particle size of SiO2 nano- powder decreases and then increases, which is similar to the case of increasing the ultrasonic treatment time. With optimum SDBS content, the suspension of SiO2 nano-powder possesses a good dispersing stability due to the existence of electrostatic and steric effects resulting from the particular structure of SDBS. The optimum dispersing condition is SDBS of 1.6 wt% with the ultrasonic time of 18 min.

Abstract: Micro-arc oxidation (MAO) is an effective approach to improve the properties of aluminium and its alloys by forming ceramic coatings on the surface. However, the oxide layers often have a porous surface structure, which limits their mechanical properties. In order to enhance the properties of the layers produced by micro-arc oxidation, SiO2 nanoparticles reinforced Al2O3 composite coatings were produced on 7A52 aluminium alloy by adding SiO2 nanoparticles into the electrolyte. With the addition of SiO2 nanoparticles in the electrolyte, the formation rate of Al2O3 coating enhanced considerably and the current density through the sample surface became much higher than that without SiO2 at the same voltage. The coatings were investigated with X-ray fluorescence spectrometry (XRF), Scanning electron microscopy (SEM), Vickers hardness test, and reciprocating friction and wear test. Compared with the Al2O3 coatings without SiO2 nanoparticles, the n-SiO2 reinforced Al2O3 composite coatings are much denser and harder, and the wear resistance is also improved significantly. The improvement can be attributed to the enhancement of the surface structure and morphology of the n- SiO2 reinforced Al2O3 composite coatings.

Abstract: The nanostructured surface layers were fabricated on a hardened and tempered chrome-silicon alloy steel and a normalized medium carbon steel by mean of Supersonic Fine Particles Bombarding (SFPB). The microstructure features in the treated surface layer were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Experimental results show the nanostructured surface layer is fabricated on both samples after SFPB treatment. The microstructure of the top surface is characterized by uniformly distributed nano-scale grains with equiaxed shape and random crystallographic orientations. The mean size of equiaxed nanocrystallites on the top surface layer is approximately 15-20nm for the SFPB treated medium carbon steel and Chrome-silicon alloy steel. During severe deformation the grain refinement in ferrite and cementite phases is observed, the cementite phases are exposed to breaking and dissolution due to mechanical alloying resulting in the formation of a supersaturated solid solution of carbon in α-Fe matrix. In the ferrite phase, the grains are refined by the process of dislocation actives and forming cell structures separated by dense dislocation walls (DDWs), as well as evolution of dislocation to subboundaries and grain boundaries.

Abstract: Supersonic fine particles bombarding (SFPB) is an important way to perform surface nanocrystallization. Harder the material is, higher the bombarding particles speed is needed. The gun with excellent features is premise to obtain the nano-structured layer.This paper analysed the advantages of rectangle Laval nozzle compared to annular-shape one and calculated critical structured parameters of the nozzle.Numerical simulation analysis of flow field of the nozzle at inlet temperature 300K and inlet pressure 0.25 MP, 1.0 MP, 1.7 MP and 2.5MP and velocity field of the gun with divergent-angle extended-barrel conduced by a commercial finite volume code FLUENT software of CFD; Consequently, the overall structure of the gun was optimized and determined finally. The sample of 38CrSi steel was treated by this gun. And the nano-structure layer on the surface was observed by TEM.

Abstract: A room temperature fast curing epoxy resin nano-adhesive was prepared and modified by nano-SiO2 and liquid rubber CTBN. It shows good shear strength value and heat-durability and also meets the conditions of room temperature and short solidified time. Compared with conventional resin mixing method, adhesive modified by nanomaterial can achieve better heat-durability. Compound cation/nonionic surfactants were used for modifying nano-SiO2 and solution mix method was used for preparation of nano-SiO2 epoxy resin adhesive. The effects of nano-SiO2 to adhesive’s mechanical property and heat-durability were investigated. Adhesive with 2wt% nano-SiO2 shows improved properties which shear strength value is 17.9 MPa and vitrification point is 216.5°C. Micropores and grains of nano-SiO2/liquid rubber CTBN modifying system were observed using scanning electron microscope. Adhesives were investigated using infrared spectroscopy analysis. Nano-SiO2 modified using compound surfactant has higher reacting activity and accelerates the reaction of adhesive. It can be used as catalyst.