A series of the second generation bi-crystal superalloys with specific misorientation grain boundaries (GBs) were prepared by the twin crystal seed method, and then their microstructure of GBs was characterized by means of scanning electron microscopy (SEM), meanwhile their tensile properties were examined comparatively at ambient temperature and 760 ^oC. Therewith, the effect of GBs misorientation on the tensile properties of single crystal superalloy can be elucidated clearly. Results show that, the tensile properties decrease with the increase of misorientation, but there is a difference in the decreasing trend for tensile properties at different temperature. At ambient temperature, the tensile strength continuously decreases and the elongation is unchanged with the increase of GBs misorientation. However, at 760 ^oC, the tensile strength is almost unchanged within misorientation below 8°, and decreases rapidly between 8° and 12°, but the elongation decreases rapidly in misorientation ranges of 0°~4° and 8°~12°. With the increase of GBs misorientation, the tensile fracture mechanism changes from cleavage-like fracture to intergranular fracture at 760 ^oC, but the tensile fracture mechanism is always cleavage fracture at ambient temperature. Finally, an energy model was proposed to qualitatively explain the competitive relationship between the two fracture mechanisms during the tensile fracture process at 760 ^oC.

Herein, the effect of compression rate on the hydrogen embrittlement (HE) sensitivity of X65 pipeline steel was studied viain-situ small punch test (SPT). Compared with the samples exposed to 4 MPa nitrogen on one side, those exposed to 4 MPa hydrogen show significant HE sensitivity with features of obvious quasi-cleavage fracture as well as a significant decrease in small punch (SP) energy. When exposed to hydrogen, as the compression rate decreases, the HE sensitivity of samples increases significantly, while the SP energy value decreases accordingly. This indicates that within this range of compression rates, the HE sensitivity of X65 pipeline steel exhibits an upward trend with decreasing compression rate. At low compression rates, hydrogen diffusion can keep up with dislocation motion. Dislocations can carry hydrogen clusters along to the crack tip, thereby triggering significant hydrogen embrittlement phenomena. Additionally, based on the segmental compression test results of the load-displacement curves and the morphology analysis of the sample in each stage of the fracture process, the mechanism of hydrogen effect on the compression process of X65 pipeline steel by the applied stress was revealed.

A novel oligomeric polyimide (SPI) incorporated with Cardo structures, flexible siloxane bonds, and phenylethynyl terminations was designed and synthesized. Then, the prepared SPI was blended with polyimide (PI) matrix in different proportions to produced SPI modified PI polymer. Upon curing, the SPI modified PI polymer exhibited significant improvements in thermal and mechanical properties. The glass transition temperature (T_g) of the cured blends increased from 382 ^oC for the PI matrix to 459 ^oC. Correspondingly, the tensile strength and tensile modulus were improved from 96.25 MPa and 1.83 GPa to 128.96 MPa and 2.41 GPa respectively. The enhanced thermal stability and mechanical performance of the modified PI may be attributed to the synergistic effects between the siloxane structures with the semi-interpenetrating polymer network (semi-IPNs) formed during the thermal crosslinking process.

Herein, the effect of long term thermal exposure at 900 and 1000 ^oC on the microstructure variation of the interface MCrAlY thermal barrier coating/DZ411 Ni-based directionally solidified superalloy (IC/S)was studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicate that with the extension of thermal exposure time, the substrate beneath the IC/S undergoes recrystallization, the orientation of σ-phase precipitates is 45° respect to the IC/S. Significant differences were observed in the evolution of secondary reaction zone (SRZ) and topologically close-packed (TCP) phases during heating process at 900 ^oC and 1000 ^oC. After being exposed at 900 ^oC for 100 h the granular Cr-rich phase precipitated in the interdiffusion zone (IDZ) composed of chaotically distributed γ'-phase; In contrast, IDZ and SRZ were formed after being exposed at 1000 ^oC for 100 h, and the precipitates of Cr-rich phase were not significant. After being exposed at 900 ^oC for 500 h to 2000 h, IDZ and SRZ gradually grow, and the orientation of Cr-rich phase precipitates nearby the recrystallized grain boundary with an angle 45°; However, at 1000 ^oC the Cr-rich phase precipitates and aggregates below the recrystallized grain boundary, and SRZ gradually degenerates into IDZ. The evolution of interface structure is closely related to the diffusion of elements after long-term heat exposure.

Nanocomposites NiCo@C(N)/NC were fabricated by a two-step method, that is, NiCo@C(N) nanocapsules were first prepared by arc-discharge technique, next dopamine (DA) was self-polymerized on NiCo@C(N) surface, which then were subjected to post-heat treatment. The study focuses on the effect of the dopamine content on the microwave absorption performance of the nanocomposites. The acquired nanocomposites NiCo@C(N)/NC were characterized by means of X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and vector network analyzer in terms of their phase composition, microstructure, and electromagnetic properties etc. The results show that the NiCo@C(N)/NC nanocomposites possess excellent wave-absorbing properties when the mass ratio of NiCo@C(N) to DA is 1∶2. Accordingly, the optimal reflection loss is -38.87 dB at a thickness of 3.17 mm and a frequency of 6.61 GHz. It achieves an effective absorption bandwidth of 4.93 GHz when the coating is matched to a thickness of 1.67 mm. The NiCo@C(N)/NC nanocomposites exhibit excellent wave absorbing performance due to the heterogeneous structure of N-doped carbon, defective induced dipole polarization, and the formation of a conductive network, all of which contribute to its high dielectric loss capability. Also, the appropriate amount of N-doped graphitic carbon can effectively improve the electromagnetic synergy effect between the NiCo core and the nitrogen-doped carbon double-shell, thus optimize the impedance matching of the nanocomposites.

Spinel ferrite Ni _x Co_{1 - x} Fe₂O₄ was prepared by sol-gel method, and the effect of different ion ratios Ni²⁺∶Co²⁺ on its structure and wave-absorbing properties were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and vector network analyzer (VNA). Focus on its following features: crystallographic structure, particle size, micromorphology, electromagnetic loss and wave-absorbing performance. The results showed that the average particle size of ferrite wave-absorbers prepared with a molar ratio of citric acid to metal ions of 1∶1 by pH = 7 and followed by being crystalized 950 ^oC for 3 h, is 66.00~70.00 nm. When Ni²⁺∶Co²⁺ = 5∶5, Ni_0.5Co_0.5Fe₂O₄ has the best wave-absorbing performancewith the minimum reflection loss value is -16.15 dB at the absorption layer thickness of 3.00 mm and the frequency is 17.32 GHz, and the effective frequency band width is 2.21 GHz (15.79~18.00 GHz), which is in the Ku band, and the excellent wave-absorbing performance of Ni_0.5Co_0.5Fe₂O₄ is attributed to the combined effect of exchange resonance and eddy current loss.

The effect of sulfate-reducing bacteria (SRB) on the corrosion behavior of N80 steel in SRB containing solution at 20, 37 and 50 ^oC, and for this case the effectiveness of a compound bactericidal corrosion inhibitor in the bactericidal effect and corrosion inhibition performance of N80 steel were comparatively investigated via biological culture technique, weightlessness measurement electrochemical testing, and surface analysis etc. The results showed that the corrosion rate of N80 steel was proportional to the SRB activity at different temperatures. The SRB activity was the highest at 37 ^oC, the polarization resistance R_p of N80 steel was the smallest, and the corrosion rate (0.03553 mm/a) was the largest, which was 1.53 times of that at 20 ^oC and 1.16 times of that at 50 ^oC, thus the corrosion was the most serious. However, after adding the compoundbactericidal corrosion inhibitor, the R_p value of N80 steel at 20 and 37 ^oC were increased significantly, and the corrosion of the steel was effectively inhibitedwith corrosion inhibitionefficiency of 65.45% and 64.79%, respectively. This is mainly due to that the lipophilic group hydroxymethyl of the bactericide tetrahydroxymethyl phosphate sulfate (THPS), as one of the components of the compound bactericide corrosion inhibitor, enters the bacterial cell membrane, changes its protein properties, then resulting in bacteria death; Meanwhile the dimethyl sulfoxide promotes the hydroxymethyl of THPS to enter the bacterial cell membrane and enhances the bactericidal effect. As a signal molecule, D-tyrosine, a bactericidal enhancer, promotes the decomposition of biofilm, destroys the surrounding concentration difference, thus slows down the corrosion. The Chitosan in the corrosion inhibitor combined with Fe²⁺ to produce a protective film to protect the substrate, thereby, reducing the corrosion rate. However, at 50 ^oC, the corrosion inhibition efficiency for N80 steel was only 0.26%, which is due to that the excessive temperature intensifies the movement of corrosion inhibitor molecular, increase in the molecular desorption rate adsorbed on the surface of N80 steel and the dissociates the adsorption film, resulting in a very low corrosion inhibition efficiency.

Composites of SiC_P/6092 Al-alloy with 0%, 17% and 30% SiC (volume fraction) were prepared by powder metallurgy, and then micro-arc oxidation films were made on the composites in sodium silicate electrolyte via micro-arc oxidation facility with an adjustable double pulse power supplier, and then the microstructure and composition, as well as the corrosion resistance of the micro-arc oxidation films were characterized by XRD, SEM, and Auto-Lab methods. The results show that the prepared films composed of an inner dense layer and an external loose layer, which are mainly composed of α-Al₂O₃, γ-Al₂O₃ and Mullite. There are many tiny pores on the film surface, and the pore diameter and surface roughness decrease with the increase of SiC content in the matrix. The SiC particles in the matrix have an inhibitory effect during the micro arc oxidation process, thus the growth of the oxide films slows down with the increase of SiC content, but the SiC particles do not decompose to participate in the oxidation reaction. The thickness of the loose layer decreases first and then increases with the increase of SiC content, and the thickness of the dense layer increases first and then decreases with the increase of SiC content. Among others, the oxide film on the composite of SiC_P/6092 Al-alloy with 17% SiC (volume fraction) particles had the best corrosion resistance with free corrosion potential of -0.466 V, corrosion current density of 3.82 × 10^-9 A·cm^-2 and polarization resistance of 1.0 × 10⁵ Ω·cm².