Low-pressure arc plasma nitriding is a novel rapid plasma nitriding process which can significantly enhance wear and corrosion resistance of austenite stainless steels. In this study, low temperature (~ 400℃) nitriding was applied to AISI 316 austenitic stainless steel (316 SS). A nitriding layer of 15 μm thickness was obtained just after 1 h processing, which is composed of an outer thin sublayer of nanocrystalline expanded austenite (nano-γ_N) with a trace of Cr nitrides and an inner thick coarse-grained expanded austenite (γ_N) sublayer. The thin surface nanolayer plays the key role in corrosion resistance of the nitrided layer, which promotes the formation of passive film. And the thickness of the passive film formed on the surface of the nitrided steel is 27 nm, which is two times over that on the bare 316 stainless steel. The corrosion current of nitrided steel is 3.55×10^-8 A/cm² in 3.5% NaCl solution, c.a. one order of magnitude lower than that of the untreated 316 austenite stainless steel (1.99×10^-7 A/cm²), which indicated that the nitrided layer had a lower corrosion rate. The pitting corrosion potential was not detected via electrochemical polarization experiments, exhibiting a better pitting corrosion resistance of the nitrided steel.

The tensile-compressive properties of syntactic foams of fly ash cenospheres/epoxy resin were measured by universal testing machine, and the fracture surface were characterized by scanning electron microscopy (SEM). The effect of the content, particle size and gradation ratio of fly ash cenospheres on the tensile-compressive properties of the syntactic foam was investigated. The results show that the tensile strength and compressive strength of the syntactic foam increases first and then decreases with the increase of cenospheres content. The compressive strength of the syntactic foams reaches a maximum when the content of cenospheres is 15phr, while the tensile strength and compressive strength increase by 9.15% and 6.86% compared with pure epoxy resin respectively. For the same filling amount, the smaller the particle size of the cenospheres, the higher the tensile strength and compressive strength of the syntactic foam. The tensile strength and compressive strength of the syntactic foam filled with small size cenospheres (20 μm) increase 158.41% and 19.96% respectively over that of the syntactic foam filled with large size cenospheres (250 μm). The tensile strength and compressive strength of the syntactic foam filled with cenospheres of different grading ratios is mainly affected by the content of small size cenospheres. The more the content of small size cenospheres, the higher the tensile strength and compressive strength of the syntactic foam.

The effect of chemical treatment with HCl solution on the wetting properties, surface morphology, thermal properties, fineness and mechanical properties, chemical structure and microscopic state of aggregation structure was investigated for polyimide fiber-reinforcements The results show that after HCl treatment, the fiber surface exhibits characters of etching with increased surface roughness, higher surface free energy, and enhanced wetability, while certain reactive group is introduced onto the surface; With the increase of HCl concentration, the rise of temperature as well as the the increase of processing time, the wetability was sharply enhanced, the fineness and mechanical properties decrease slightly while the thermal property keeps preferably within a certain range. The existence of H⁺ in the treatment solution could result in that a few of imide rings on the fiber was broken and then hydrolyzed to polyamide acid, thereby its microscopic state of aggregation structure was changed and the ratio of amorphous region was enhanced, therewith its chemical structure does not change significantly. In general, HCl treatment is feasible for modifying the polyimide fiber surface.

BaTiO₃ nanoparticles were fabricated by gel method with polyacrylamide as raw material, and then Au nanoparticles were deposited on the surface of BaTiO₃ via a photocatalytic reduction method to yield Au/BaTiO₃ composite photocatalysts. The composite photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) and photoluminescence (PL) spectroscopy. The results show that the BaTiO₃ particles undergo no structural change after the deposition of gold; The Au particles with size of 5-20 nm were deposited on the surface of BaTiO₃ particles with an average size of ~55 nm; The composites present light absorbance centered around 560 nm due to the surface plasmon resonance (SPR) effect of Au nanoparticles; The Au/BaTiO₃ composites exhibit a reduction in recombination probability of photo-generated electrons and holes compared to bare BaTiO₃. In addition, the formation mechanism for Au nanoparticles on the surface of BaTiO₃ particles is proposed. The photocatalytic activity of the as-prepared composite photocatalyst was evaluated by the degradation of methylene blue (MB) under simulated sunlight irradiation, and the photocatalytic stability of the composites was also investigated. The results reveal that the photocatalytic activity of BaTiO₃ can be improved by the deposition of appropriate amount of gold, and moreover the composite photocatalyst exhibits good reusability. Finally, the promotion mechanism of Au particles on the simulated sunlight photocatalytic activity of BaTiO₃ is also discussed.

Nano particle modified composite geopolymers were prepared with waste brick powder (WBP) and class C fly ash (CFA) as raw material, and nano-particales SiO₂ and Al₂O₃ as modifier. Then their anti-permeability and anti-freezing-thawing as well as their pore structure were investigated. Results show that nano-SiO₂ is superior to nano-Al₂O₃ for enhancing the performance of geopolymers, and the combination of 2%(mass fraction) nano-SiO₂ and 1% nano-Al₂O₃ exhibits the best modification effect, so that the geopolymer possesses the highest anti-permeability and anti-freezing-thawing. It is found for the geopolymers after being freezing-thawing tested that the apparent porosity, true porosity, average pore size, the size of the most probable pores and the total porosity all enhanced, however the volume density decreased. Besides, the harmless and less-harmful holes with size smaller than 50 nm decreased, and in the contrast,the harmful and more-harmful holes increased.

Ball-studs with coarse grained WC were prepared on Q345 steel plateby in-situ plasma metallurgy method with powder mixtures of Ni/W/C as raw material on. The microstructure, composition, phase constituent and microhardness of the ball-studs were characterized by means of SEM, EMPA, XRD and microhardness tester. The results show that among others, the powder mixture with 40% Ni could produce the most desirable ball-studs with brighter surface, higher compactness and stronger adhe sive to the substrate; coarse granules of WC with an average size ca 80μm evenly distributed in the inner portion of the ball-stud matrix of (Fe,Ni); meanwhile, the network-pattern eutectic structure of Ni₁₇W₃ and (Fe, Ni) can be detected. The average microhardness of ball-stud is 1183.517HV_0.1, while the microhardness of the coarse grain of WC is 2078HV_0.1.

The thin-film thermocouple of NiCr-NiSi without and with protective coatings of SiO₂ and SiO_xN_y were respectively manufactured by magnetron sputtering method. Then their oxidation performance was examined at 100~800℃ for 90 mim in air. The results show that the anti-oxidation capacity of the thermocouple with SiO_xN_y coating is 3~5 times higher than that with SiO₂ coating at 800℃ according to the intensities of the diffraction peaks of NiO in XRD spectra of the above two thermocouples. Meanwhile, the slightly oxidization of SiO_xN_y coating during high temperature process can effectively enhance its protectiveness as well.

A 1200 MPa grade high-strength low-alloy (HSLA) steel was welded by metal active gas(MAG) welding method with filler material of GHS50NS welding wire by three different heat inputs. And then the effect of heat input on microstructure and property of the weld joints was investigated by means of optical microscopy, scanning electronmicroscopy, transmission electron microscopy and mechanical tests. The results indicate that the microstructure of weld joints consists mainly of acicular ferrite, a granular bainite and small amount of M-A by different heat inputs. With the increasing heat input, the amount of acicular ferrite was increased and its lath width was coarsened while the amount of granular bainite decreased, and the type of non metallic inclusions which promote the nucleation of acicular ferrite in weld joints was a complex oxide-sulfide Ti-Mn-Al-O-S. The strength and hardness of the welded joint decreases with the increase of heat input, but it has a good combination of strength and toughness. Along with the increase of heat input, the morphology of the impact fracture of the weld joint changed from fracture with mixed mode to brittle fracture. When the heat input is 20 kJ/cm, the comprehensive performance of the welded joint is the best.

Hybrid materials LGC were prepared with the L-aspartic acid connected graphene oxide and the acidified MWCNT (WMCNT-COOH) as raw materials. Then nanocomposites of LGC/HDPE-g-MAH with different amount of LGC were prepared by melt blending method with maleic anhydride grafted high density polyethylene (HDPE-g-MAH) as raw material and LGC as nano-fillers. The LGC hybrids and LGC/HDPE-g-MAH nanocomposites were characterized by using Fourier transform infrared spectroscopy (FTIR), Raman spectrum (Raman), X-ray diffraction (XRD), Scanning electron microscope (SEM), Differential scanning calorimetric analysis (DSC), Thermogravimetric analysis (TGA), Dynamic mechanical analysis (DMA) and mechanical properties characterizations. Results show that L-aspartic linked effectively GO and WMCNT-COOH, while the LGC formed via an amide bond. Functional groups (amino or carboxyl group, etc.) in LGC may interact with the carboxyl groups of polymer matrix, which improved the interface between the matrix and the filler; the changes of dissipation factor verified that strong interactions exist between LGC and HDPE-g-MAH matrix chains; therewith the crystallization temperature, melting temperature and thermal stability of nanocomposites were enhanced; while with the increasing amount of LGC, the tensile strength and impact strength of the nanocomposites increased first and then decreased, by addition of 0.5%and 0.75%(mass fraction) LGC, the impact strength and tensile strength of the nanocomposites were enhanced by 95.9% and 62.4% respectively in comparison , with the blank HDPE-g-MAH.

Fullycompatibleblend cured resins DDM/AHEP were prepared by incorporating different among of aliphaticand epoxide-functional hyperbranched polymer (AHEP) into an aromatic-diamine typebenzoxazine(DDM) network without cure-induced phase separation. Then their structure and thermo-mechanical property were investigated by means of FTIR,DSC and DMA. The results show that the Young's modulus and impact toughness of DDM could be simultaneously enhanced by the incorporating AHEP.Flexural strength and impact strength of the cured DDM/AHEP blend approach a maximum for5% incorporationof AHEP, representing an increase of over 11.5% and 167% respectively in comparison to that of the original DDM. The fracture surface morphology of the cured blend has the characteristic of in-situ toughness enhancement.

The effect of different flash allowances on the microstructure and mechanical properties of flash butt welded joint for 510CL wheel steel was investigated. The results indicate that the heat affected zone consists of interfacial zone, coarse grain zone, annealed zone and incomplete annealed zone. The Vickers hardness of interface area is the highest, and the peak hardness range is 201 ~ 219 HV. When flash allowance is lower, interface area mainly consists of blocky ferrite and granular bainite. When flash allowance is moderate, the interface area consists of acicular ferrite with excellent mechanical performance. Excessive flash allowance generates too much heat, and the interface area will mainly consist of widmanstatten structure and granular bainite with poor mechanical properties. The welded joint fracture may be ascribed to the existence of too much widmentstatten structure with high density of mismatch. In order to obtain flash butt joint with good performance, the reasonable range design of flash allowance is 3.5 ~ 5.5 mm.