The hardness and microstructure evolution of a low carbon and high alloy martensite bearing steel after deep cryogenic treatment were studied by means of Rockwell hardness tester, X-ray diffractometer, and scanning electron microscope and transmission electron microscope. The results show that the deep cryogenic treatment promotes the transformation of retained austenite to martensite, which leads to an increase in the hardness after quenching. In addition, the hardness of the steel subjected to deep cryogenic treatment was higher than that of the non-cryogenically treated one during tempering. The deep cryogenic treatment causes the carbon atoms in the steel to segregate and precipitate as carbides during the tempering process. Compared with the steel without deep cryogenic treatment, the carbon content in the martensite matrix of the steel subjected to deep cryogenic treatment was lower after tempering, which indicated that more carbides were precipitated in the deep cryogenic treated steel during the tempering process. According to the results of transmission electron microscope images, a large number of nano-sized M₂C and M₆C carbides precipitated from the martensite matrix during tempering, which may be the main reason for the maintenance of high hardness of the steel after longtime tempering.

The TiVNbTa refractory high-entropy alloy (HEA) was fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The mechanically alloying process, phase composition and microstructure as well as the effect of sintering temperature, O- and N-content on the mechanical properties of the alloy were studied. The mechanically alloyed powders present a single BCC crystal structure, while the spark plasma sintered alloy composed of a FCC matrix with precipitated phases of TiN, TiC and TiO. The alloy sintered at 1100°C performed outstanding mechanical properties with compressive yield strength of 1506 MPa and plastic strain of 33.2%, respectively. As sintering temperature increased, the alloy fracture mechanism basically transformed from quasi-brittle fracture to ductile fracture, and finally to brittle fracture. The increase of O- and N-content had little effect on the strength of the alloy, but negative effect obviously on its plasticity.

The effect of Zn content on exfoliation corrosion resistance of extruded rods of Al-Zn-Mg-Cu alloy was investigated by standard exfoliation corrosion (EXCO) immersion test, and polarization curve measurement, optical microscopy (OM), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The results show that exfoliation corrosion resistance of the rods decreases with the increase of Zn content (mass fraction,%) from 7.93% to 9.85%, and the exfoliation corrosion rating changes from EA to EC with the maximum corrosion depth increasing from 334 μm to 579 μm. The lower EXCO resistance caused by higher Zn content is mainly attributed to the increased number of coarse second phase in alloys, the decreased size and spacing, as well as the higher Zn and Mg content of η-phase at grain boundaries after aging.

The microstructure and mechanical properties of Al-Si-Cu-Ni-Ce-Cr alloy after different heat treatment were investigated by optical microscope, scanning electron microscope, X-ray diffraction and universal tensile testing. Results show that the θ-Al₂Cu phase completely dissolved into the matrix and the γ-Al₇Cu₄Ni and most of the δ-Al₃CuNi phases dissolved into the matrix after two steps solution treatment. When the Al-Si-Cu-Ni-Ce-Cr alloy was treated by 490°C×2 h+520°C×2 h+185°C× 6 h, the ultimate tensile strength at room temperature and 300°C is 336.8 MPa and 153.3 MPa, respectively. Compare with the as-cast Al-Si-Cu-Ni-Ce-Cr alloy, the value of tensile strength at room temperature and 300°C increases 74% and 19.3%, respectively.

The effect of the prior martensite on the thermal stability of the nano-bainitic steel was investigated. The nano-bainitic steel composed of prior martensite, nano-sized bainitic ferrite and retained austenite was obtained by quenching and followed by bainite transformation at low temperature. The microstructure and hardness variation were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and hardness tester etc. for the nano-bainite steels after tempering at different temperatures. Results show that after tempering at 473~773 K the hardness of the nano-bainite steel containing prior martensite is higher than that of the untampered ones. However, after tempering at temperatures above 823 K, its hardness decreased rapidly and which down to 266.2HV at 923 K. The carbon was discharged from prior martensite to the retained austenite when the steel was tempered at 473~573 K. The carbon content of the later increased to a peak value, i.e. 1.52%, which improved the thermal stability of retained austenite, and further delayed the decomposition of the later, thus improved the thermal stability of the nano-bainitic steel at high temperature. The retained austenite decomposed into carbides, and the bainitic ferrite coarsened and recovered, formed new ferrite grain when the tempering temperature exceeded 723 K.

Corrosion behavior of zinc was field exposed to salt-rich arid atmosphere at Qinghai salt lake of Qinghai province at the Northwest China for 48 months was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), metalloscopy and EIS techniques.Results reveal that the corrosion kinetics of zinc in the atmosphere at a selected site followed the empirical equation m=Atⁿ. The corrosion of zinc on the skyward surface is heavier than that on the fieldward one, while spallation of the rust layer on the skyward surface did occur after exposure for 48 months. The corrosion products on the two surfaces were mainly composed of Zn₅(OH)₈Cl₂·H₂O, Zn₅(CO)₃(OH)₆, Zn₄SO₄(OH)₆·3H₂O, the rust layer contained also certain amount of SiO₂. The results of EIS analysis showed that the rust layer could suppress the corrosion of zinc substrate, the corrosion resistance of rust layers on the two surfaces increased with time, then the protectiveness of the rust layer on the skyward surface was weakened for 48 months exposure.

A novel symmetrical ruthenium complex (Ru-1) bearing pyrene groups was synthesized, and its molecular structure and purity were characterized by ¹H-NMR and ESI-MS. The ruthenium complex delivered ideal stability and performance over a wider range of temperature (below 400°C), which suggests that the stability of this material can satisfy the requirement of dye-sensitized solar cell. Thin films of Ru-1 complex can be prepared onto both graphene- and HOPG-electrode surface via self-assembly process, then their surface morphology and photoelectricity property were examined by means of AFM, Cyclic voltammetry and UV-vis spectroscopy. The results show that the growth of the film was uniform. A couple of sensitive and reversible redox peaks were acquired from the cyclic voltammograms of Ru-1 modified carbon electrodes, the Ru (II/III) oxidative peak was observed at 0.47 V. Uv-vis absorption spectra show that the membrane materials have intense and wide absorption peaks in a wider range, which is favorable for capture sunlight at longer wavelength. In sum, a carbon electrode of excellent photoelectric properties and stability can be obtained by modifying both graphene and HOPG electrodes with Ru-1complex.

Graphene oxide (GO) modified polyamide 6 nanocomposites (PA6/GO) were prepared by in-situ ring-opening polymerization with caprolactam (CL) and 6-aminocaproic acid (ACA) were used as polymerization monomers and GO as nano-filler. The structure and morphology of PA6/GO nanocomposites were characterized. The results shows that GO was uniformly dispersed in the PA6 matrix. The viscosity average molecular mass of PA6 reached 10⁴ orders of magnitude, but the excessive addition of GO would decrease the molecular mass of synthesized PA6. The addition of GO induced the transformation of crystallographic structure of the PA6 matrix from α-type to γ-type. At the same time, as a heterogeneous nucleating agent, GO promotes the crystallization of PA6 matrix in PA6/GO composites, and increases the crystallinity of PA6/GO composites.. Tensile strength of PA6/GO composites increased first and then decreased with the addition of GO. When the amount of GO was 0.4% (in mass fraction), the tensile strength of PA6/GO nanocomposites reached a maximum of 61.72 MPa, which was superior to that of pure PA6 (48.52 MPa) by 27.21%. When the GO content was 1.0% the thermal conductivity of PA6/GO nanocomposites reached 0.317 W/(m·K) and 0.280 W/(m·K) at 50℃ and 100℃, which were 33.19% and 33.23% higher than that of pure PA6, respectively.

The ratio (σ_s/σ_b) of ultimate tensile strength to yield strength for the 8.8-grade bolt were firstly obtained by tensile tests, and then its fatigue properties under the pre-applied stresses of 10%, 30% and 50% of the ultimate tensile strength were investigated, respectively. The results show that the fatigue limit of 8.8-grade bolt decreases from 370 MPa to 263 MPa with increasing the pre-applied stress from 10% to 50% of the ultimate tensile strength. In addition, the effective stress at fatigue limit was obtained as 562.75 MPa by handling the effect of pre-applied stress on the fatigue S-N curves of the 8.8-grade bolt with the effective stress parameter method. It means that the fatigue failure of 8.8-grade bolt will not happen when the effective stress is lower than 562.75 MPa. Finally, the maximum pre-applied stresses and pre-load torque curves corresponding to the 8.8-grade M6 and M27 bolts at different stress ratios were given.

The di-epoxy group-based N,N-diglycidyl-furfurlamine (DGFA) containing furan ring was synthesized via the reaction between epichlorohydrin and decylamine. Then a thermo-reversible epoxy resin (EP-DA) with self-healing performance is prepared by Diels-Alder (DA) reaction between the synthesized DGFA and bismaleimide. The structure and thermal reversibility of the prepared EP-DA were characterized by Fourier transform infrared spectroscopy (FT-IR). Results show that the as-prepared EP-DA exhibits excellent thermal reversibility, which is confirmed by the appearance observation and absence of the infrared absorption peak of DA bonds before and after heat treated at 130^oC. The as-prepared EP-DA has outstanding self-healing performance, which was approved via the qualitative observation of crack evolution and quantitative measurement of flexural load restoring by simulating crack repair. The width of cracks in EP-DA decreases gradually with the extending heat treatment time, while crack disappears completely when which is treated at 130^oC for 6 min, indicating that the self-healing rate is very high and cracks in EP-DA have been repaired apparently in 6 min. The EP-DA with cracks can be repaired completely upon heat treatment at 130^oC for 30 min and followed by 48 h at 70^oC; Moreover, the EP-DA has outstanding multiple damage/self-repair performance, and cracks within EP-DA can be repaired for more than three times. The repair efficiency of EP-DA after cut in half and then put together can reach 71.7%, 61.6%, and 54.5% after damage/heat treatment for three times in turn. Additionally, the as-prepared epoxy resin exhibits excellent reprocessing performance and which makes the recycling of waste epoxy resin possible.