Through studies and discussions on mechanical properties of ultra-high strength hull structural (UHSHS) steels and their weld joints, the problem concerning weldability of UHSHS steels was concluded as poor low temperature toughness in coarse-grained heat affected zone (CGHAZ) under large heat input welding procedure. The root causes of this problem were analyzed on two aspects: the formations of martensite-austenite (M-A) constituents and granular bainite. Current three approaches of oxide metallurgy technology application, Cu precipitation introduction and high Ni content design to improve the weldability of UHSHS steels were summarized. Under comprehensive analyses on the current status of UHSHS steels, it is considered that the design of ultra-low C and high Ni content can further improve the weldability of ultra-high strength hull structural steels.

The effect of irradiation with swift heavy ion beam of 350 MeV ⁵⁶Fe²¹⁺ on the internal structure characteristics of single crystal ZnO was investigated by means of Raman spectroscopy and transmission electron microscopy (TEM). It follows that two new vibration absorption peaks appeared in Raman spectra for the ZnO after irradiation. The results of characterization with different coaxial Raman incident lights proves that the vibration absorption peak at 576 cm^-1 is closely related to the oxygen vacancy (V₀). TEM images show that there exist many defects such as interstitial, vacancy and dislocation in the irradiated ZnO single crystal, but the electron diffraction patterns of which did not reveal any obvious amorphous wherein. It illustrates that the higher energy and irradiation dose will hardly impact the structure and properties of the entire ZnO. This has fully proved that ZnO single crystal with good resistance to swift heavy ion beam irradiation.

Two kinds of microstructure, namely the microbands refined microstructure and the martensite-ferrite two phase microstructure, were obtained for a low Cr alloy steel by using different rolling technologies, then the fracture behavior of the steel under different tensile conditions was investigated. Analysis of the strain-stress curves and the microstructures after deformation show that the increase of rolling temperature and the decrease of strain rate could reduce the tensile strength, meanwhile, the enhancing recrystallization process can release the constraint of interior slip systems on the motion of subboundaries. Abnormal increase of tensile strength at 650℃ for the two phase microstructure can be attributed to the numerous precipitation of M₇C₃ in the ferritic matrix, which balances the mechanical properties between ferrite and annealed martensite, therefore improves the tensile strength at 650℃.

Artificial defects of different size were introduced on rotary bending fatigue test samples of Al-7Si-0.6Mg Al-alloy, which is the desired material for the high-speed railway contact net support and positioning device. The influence of defect sizes on the fatigue strength of the alloy was examined via rotating bending fatigue machine, while the quantitative relationship between fatigue strength and defect size was established. The results show that the larger the artificial defect size, the greater the decrease of the high cycle fatigue strength of the sample. The artificial defect size of less than 370 μm has no effect on the high cycle fatigue strength of the alloy; The modified Murakami formula can be applied for more accurate evaluation of the high cycle fatigue strength and stress intensity factor threshold of Al-7Si-0.6Mg Al-alloy within the range of applicability conditions.

The combined process of vacuum low-pressure carburizing heat treatment for aviation gear steel 16Cr3NiWMoVNbE was investigated, with the emphasis on the effect of carburizing, quenching, cryogenic treatment and tempering process on the microstructure and mechanical properties of the steel. The results show that after carburizing and quenching, the cross sectional microstructure of the steel, can be differentiated as carbide region, mixed region of carbide and acicular martensite, acicular martensite region and lath martensite region from the surface to the center. A large number of blocky Cr carbides precipitated at grain boundaries in the carbide region, where very little Ni can be detected. The fine precipitates in the acicular martensite and the lath martensite matrix are carbides of the microalloying elements Nb, V, and Mo. After the carburization, the carbon concentration of the carburized steel decreases gradually from the surface to the center, correspondingly, the hardness increased first and then decreased, and the depth of carburized layer was 0.95 mm. The subzero treatment at -70^oC promotes the transformation of retained austenite to martensite, which greatly improves the overall hardness of the carburized steel.

4,4'-diamino-2,2'-bistrifluoromethylbiphenyl (TFMB), 4,4'-(hexafluoroisopropene) diacetic anhydride (6FDA) and 3,3',4 4'-biphenyltetracarboxylic dianhydride (BPDA) were used as the reactive monomer, a series of fluorinated copolyimide films were prepared by changing the proportion and feeding method of non -fluorinated monomer BPDA. The properties of the films were characterized and analyzed. The results show that both the feeding method and the proportion of BPDA in the dianhydride monomer can affect the properties of the films. The prepared fluorinated copolyimide films are soluble in the aprotic polar solvent at room temperature, and the film have a high light transmittance in the visible light range. As the content of non-fluorinated dianhydride monomer BPDA increased the optical properties of the film decrease slightly, while the thermal properties and mechanical tensile properties were improved. When the proportion of non-fluorinated dianhydride monomer is 68.97%, the transmittance of the prepared copolyimide film still maintains in 96.01% at 500 nm; When the non-fluorinated dianhydride monomer account for 35.71% of the dianhydride monomer, the thermal decomposition temperature at a weight loss of 10% of the prepared copolyimide film is 595.23℃, correspondingly the tensile strength is 100.98 MPa. The change of feeding mode of BPDA have different effect on the optical properties, mechanical properties and mechanical tensile properties of the copolyimide film.

Based on the concept of modification of molecular skeleton structure, a series of (acceptor-π-donor-π-acceptor) A-π-D-π-A type indole-based metal-free organic dye sensitizers were designed, and their photoelectric conversion behavior and the relevant electronic transmission mechanisms were theoretically investigated by using density functional theory and the time-dependent density functional theory. Results show that compared with the traditional D-π-A molecular skeleton structure the overall performance of A-π-D-π-A type indole-based organic dye sensitizers was significantly improved in terms of the appropriate energy level structure and orbital electron distribution, broadened spectral absorption coverage range, improved light-harvesting efficiency and enhanced IET performance. At the same time, it should be noted that the enhancement of electron-deficient properties of the π-bridge could further enhance the properties of A-π-D-π-A type indole-based metal-free organic dye sensitizers.

The optical fiber preform waste, an industrial by-product, was successively dried, crushed and grinded to produce fine particles, and then which are modified with coupling agents KH-570 and A-151 respectively to prepare KH-570/SiO₂ and A-151/SiO₂. Further, the prepared two powders were blended respectively with epoxy resin (EP) to prepare EP based composites. The results of hydrophobicity test, FT-IR and SEM show that the two coupling agents present significant modification effect on the waste particles, however the modification effect of A-151 is better. The overall tensile properties of the composites can be ranked as the following order: A-151/SiO₂/EP>KH-570/SiO₂/EP> unmodified powder/EP, and the tensile properties are the best when the powder mass fraction was 20%. The maximum tensile strength of the above three particles modified EPs is 49.37 MPa, 45.57 MPa, and 44.36 MPa, which are 19.9%, 10.7% and 7.8% higher than that of the plain EP, respectively. Correspondingly the maximum elongations at break of the three composites are 0.92%, 0.82% and 0.46% higher than that of the plain EP, respectively. Besides the composite material prepared by filling the powder with good modification effect show better heat resistance performance.

A multi-layered electromagnetic absorbing composite was proposed to have the structure composed alternately of absorbing prepreg layer and absorbing damping layer, thus the embedded co-curing composite with excellent electromagnetic absorbing property and high damping property as well as other excellent static and dynamic properties was developed. The theoretical expression of the electromagnetic reflection loss of the structure was deduced, and the absorbing performance of the structure was theoretically analyzed by using MATLAB program based on the theoretical expression. The electromagnetic absorbing test verified the validity of the theoretical results. Modal test, free decay test and interlinear shear test obtained the variation curve of modal parameters, damping performance and interlamellar shear performance with the content of electromagnetic absorbing material. The experimental data show that with the increase of the content of electromagnetic absorbing materials in the composite, of which the reflection loss and the modal natural frequency decrease, the electromagnetic absorption bandwidth, the modal damping ratio and the damping loss factor increase, whereas, the interlamellar shear stress enhances.

A series of double perovskite oxide Pr_(2-x)Tb_xCoMnO₆ (x=0, 0.05, 0.1, 0.15) was prepared by high temperature solid state reaction. The effect of Tb-doping on the Curie temperature, magnetic entropy change and magnetic phase transition of double perovskite oxide Pr₂CoMnO₆ was investigated by analyzing the relevant data. The results show that the series of double perovskite oxides Pr_(2-x)Tb_xCoMnO₆ (x=0,0.05,0.1,0.15) all is good single-phase with crystallographic structure of monoclinic P2₁/n; they all have two magnetic transition points (T_C1 and T_C2); T_C1 and T_C2 decrease with the increasing Tb-content; within the desired temperature region, as the temperature decreases the state of the prepared four double perovskite oxides underwent the following transition: paramagnetic state, paramagnetic-ferromagnetic and coexistence state; by a given external magnetic field of 7 T, the maximum magnetic entropy change ΔS_{Mof the prepared four double perovskite oxides is -1.862, -1.779, -1.768 and -1.766 J/(kg·K) respectively. In other word, Tb-doping makes the maximum magnetic entropy change smaller, but increases its half-height wide temperature range. It can be judged that among others, Pr1.9Tb0.1CoMnO6 is the most potential candidate as a high-temperature magnetic refrigeration material especially, regarding to its RCP value; Based on the analysis of the Arrott curve, the recalibration curve and the Loop curve, the four double perovskite oxides underwent a first-order phase transition during the process.}