The influence of C- and B-content on the solidification and high temperature stress rupture behavior of K417G nickel-based superalloy have been investigated by means of DTA analysis, optical microscope, scanning electron microscope, isothermal quenching and stress rupture tests at 950℃/235 MPa. Results show that the precipitation temperature and the amounts of the primary carbide are mainly affected by the C-content, which are both increased with the rise of C-content in the alloy. During stress rupture deformation at 950℃/235 MPa, the fracture mechanism of the alloy can be described as that cracks initiate on and then propagate along grain boundaries. Wherein, the MC-type carbides on the grain boundary could decompose into M₂₃C₆-type carbide enriched in Cr, which will reduce the stability of the boundary. Within the composition range of the tested alloys, raising the B-content could increase the grain boundary strength of the alloy during deformation at high temperature. As a result, the proper decrease C-content, while increase B-content can improve the high temperature stress rupture property of the alloy.

The influence of the particle size ratio of the ceramic shell for directional solidification of superalloy and the Cr₂O₃ additive on the surface quality of castings was investigated by means of multi-index orthogonal experiment and the range analysis while taking the sand-burning on the surface quality and roughness of the resulted castings as the calibration. The results show that the main components of the sand-burning layer on the casting surface includes Al₂O₃ and elements Cr, Ni of the alloy. Adjusting the particle size gradation can reduce the porosity of the ceramic shell surface layer and then yield a dense shell surface layer, thereby reducing the penetration of the molten alloy into the ceramic shell surface layer during the directional solidification process and reducing the physical adhering sand on the surface of the casting. The addition of Cr₂O₃ additive can induce the reaction of Cr₂O₃ with Al₂O₃ in the shell resulting in the formation of the binary compound Al₂O₃-Cr₂O₃ or ternary compound Al₂O₃-SiO₂-Cr₂O₃, which can inhibit the active elements (Ni, Ti, Al, etc.) in the casting react with free SiO₂ in the ceramic shell to reduce the formation of Al₂O₃ on the casting surface, thereby reducing the chemical adhering sand on the casting surface and improving the casting surface quality.

The bacterial cellulose (BC) cultured and purified in the laboratory were oven-dried and freeze-dried respectively and then was carbonized at high temperature. The results show that the oven-dried BC lost the nanofiber structure, and the freeze-drying technology could prevents the nanofibers from stacking and keeps the BC three-dimensional structure. The physicochemical properties such as micromorphology, elemental composition, crystal structure of the carbonized bacterial cellulose (CBC) and thier evolution process with carbonization temperature were systematically investigated. Through Pt-deposition on the conductive carrier of CBC carbon nanofibers, thus an electrode of composite materials could be acquired, which then were used for methanol electrocatalysis. Finally the relationship between the electrochemical performance of CBC-based composite materials and its micro-nano structure and chemical composition was highlighted.

6005A-T6 Al-alloy profiles were subjected to friction stir welding (FSW) at a high welding speed of 1000 mm/min, while the effect of mechanical grinding of the butt face on the microstructure and mechanical properties of the butt joints was investigated. The results show that the microstructure of “S” line is more obvious in the FSW joint with unpolished surface, compared to that of the traditional FSW joint with polished surface. Both FSW joints exhibited similar microhardness distribution and tensile properties, and all the samples failed at the lowest hardness zones, i.e., the heat affected zone (HAZ), during tensile tests. The fatigue properties are almost the same for both FSW joints with unpolished and polished surfaces, while the fatigue strength was 105 MPa and 110 MPa, respectively. At high stress amplitudes the samples fractured at the base material, but the sample failed at the HAZ at a low stress amplitude of 120 MPa, and two crack initiation zones were found. All of the fracture surfaces exhibited typical three zones, namely crack source zone, propagation zone and final fracture zone. The results indicate that the static tensile and dynamic fatigue properties of FSW joints were not affected by the surface mechanical polishing.

Novel TiC reinforced Ti-based composites were synthesized via in situ microwave sintering with nanotubes (MWCNTs) and pure Ti as raw materials. The properties of the composites were investigated, and the formation mechanism of TiC reinforced phase of the composites was discussed. The results show that TiC reinforced phase could be generated in-situ in the Ti-matrix during microwave sintering. When the addition amount of MWCNTs <1% (in mass fraction), the formed TiC was granular-like and distributed uniformly in the dense Ti matrix of fine grains. When the addition amount of MWCNTs >1.5%, the formed TiC turns to be of dendritic morphology, while the Ti matrix is coarsened and the composite becomes porous. Sequentially, the wear mechanism of the composites will change from adhesive wear to abrasive wear due to the addition of MWCNTs. With the increasing addition amount of MWCNTs the microhardness of the composite increases firstly and then decreases. When the addition amount of MWCNTs is 1%, the acquired composite presents a higher microhardness of about 527HV and better wear resistance with the friction coefficient of about 0.35, which are 1.2 times more and 0.4 less than the corresponding terms of the pure Ti respectively.

The flow stress behavior during hot compression of 37CrS4 at 950~1100℃, by strain rate in the range of 0.01 s^-1~10 s^-1 was investigated by means of single pass hot compression test with Gleeble-1500D thermal simulation machine. The results show that the true stress-strain curve of 37CrS4 special steel presents the occurrence of obvious dynamic recrystallization during high-temperature plastic deformation. The microstructure after hot deformation is typical lath martensite. The ratio of critical strain to peak strain of dynamic recrystallization behavior is 0.77162, and the fitting correlation is 0.9576. The softening mechanism of the material is the synergistic effect of dynamic recovery and dynamic recrystallization. The zener-Hollomon parameter (Z parameter) was introduced to establish the recrystallization kinetic model, and then the segmented flow stress constitutive model of 37CrS4 special steel based on dynamic recovery and dynamic recrystallization was obtained. The average correlation of the constitutive model is 0.9756. The predicted stress of the segmented constitutive model was consistent with the experimental stress, in fact, which could accurately predict the high temperature plasticity of 37CrS4 and the variation of flow stress during deformation.

One-dimensional SnO₂ nanorod arrays (1D-SnO₂ NRAs) have been synthesized through hydrothermal method. The influence of hydrothermal parameters such as precursor concentration, reaction time, temperature, number of reaction and NaCl addition on the growth and morphology of 1D-SnO₂ NRAs were investigated by means of scanning electron microscopy with energy dispersive spectroscopy and X-ray diffractometer . The results show that the low precursor concentration is conducive to the preparation of nanorods with large aspect ratio, while the reaction time can selectively change the length of the nanorods. Interestingly, the growth of the nanorod array has apparent temperature sensitivity, that is, the rod length, diameter and substrate coverage all increase significantly as the reaction temperature increases. Furthermore, the NaCl additives in the precursor can favor the oriented growth, whilst restrain the substrate coverage of nanorods.

CoFe₂O₄-Co₃Fe₇ nanoparticles were successfully prepared by reducing CoFe₂O₄ nanoparticles in 5% H₂ + 95% N₂. Meanwhile, CoFe₂O₄ nanoparticles were successfully loaded onto the porous carbon by hydrothermal method with the porous carbon fiber calcined from jute fiber as precursor. The prepared two composites were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectrometer, and simultaneous thermal analyzer (STA). Their electromagnetic parameters and microwave absorption performances were measured by vector network analyzer (VNA). The results show that the microwave absorption performances of CoFe₂O₄-Co₃Fe₇ nanoparticles and CoFe₂O₄/porous carbon are obviously better than that of the plain CoFe₂O₄ nanoparticles. The effective bandwidth (frequency width of reflection loss <-10 dB) of CoFe₂O₄-Co₃Fe₇ nanoparticles is 4.8 GHz, while that of CoFe₂O₄/porous carbon can reach 6 GHz, covering the entire Ku band (12~18 GHz). The excellent microwave absorption performance can be attributed to the appropriate dielectric constant, large dielectric loss, porous structure, and the synergistic effect of dielectric loss and magnetic loss. Owing to the characteristics of low cost, low density and good microwave absorption performance, the CoFe₂O₄/porous carbon has broad application prospect for Ku band as an economic, lightweight and broadband microwave absorbent.

A thermal barrier coating (TBC) of MCrAlY/8YSZ with hybrid microstructure was prepared on 15CrMo stainless steel by means of HVOF spraying technique, namely the coating consists of a hybrid structured YSZ top-coat made of mixture of agglomerated and fused and crushed YSZ powder and a bond coat of NiCoCrAlTaY, while an intermediate layer of NiCoCrAlTaY/YSZ composite was inserted in between the above two coats. The bonding strength and fracture toughness of the YSZ coating can be improved by these two strategies to enhance the spallation resistance of the TBC. Two individual powder feeders were used to feed the NiCoCrAlY and YSZ powder independently into the plasma plume so that the feeding rate and heating experience of both powders can be controlled independently. SEM was used to characterize the coating microstructure. Adhesion of the TBC coating was examined according to ASTM C633 Standard. Elastic modulus, fracture toughness and thermal conductivity of the YSZ layer were measured. Spallation resistance of the coating was assessed by water quenching test from 750°C. The results show that the desired coating microstructure was achieved by HVOF and APS, and all the three layers bond well each other without any interfacial cracks. The adhesion strength of the YSZ coat increases from 25.8 MPa to 38.6 MPa. Evident changes in elastic modulus and thermal conductivity were not detected. A great improvement of 100% in fracture toughness of the YSZ coating was achieved. As a result of all the above measures, the occurrence of 30% area spallation for the top coat could be rose to 72.1 cycles during water quenching test, in comparison, only 19.7 for the TBC made of the same material with conventionally desired structure.