Influence of modification, refinement and heat treatment on the microstructure and mechanical properties of A356 Al-alloy components prepared by squeeze casting was investigated. The results show that with increase of Al-10Sr modification agent, the morphology of eutectic Si changed from lamellar, rod-like shape to granular and wormlike shape, and the grain size of α-Al increased first and then decreased. When 0.3% Al-10Sr modification agent was added, the optimal mechanical properties of squeeze casting components including ultimate tensile strength of 221.3 MPa, yield strength of 104.5 MPa and elongation of 10.3% were achieved. The improvement of mechanical properties can be attributed to the increase of nucleation rate, the decrease of α-Al grain size and the change of eutectic Si morphology by adding 0.3% Al-10Sr modification agent. With the increase of A-5Ti-B refiner, the α-Al grain size first decreased and then increased, but the changing trend of mechanical properties is inverse. When 0.6% Al-5Ti-B refiner was added, the optimal ultimate tensile strength, yield strength and elongation were 215.6 MPa, 106.6 MPa and 9.0%, respectively. T6 heat treatment including solid solution at 540℃ for 4 h and artificial aging at 190℃ for 4 h led to the improvement of yield strength and ultimate tensile strength, but it led to the decrease of elongation. The optimal mechanical properties such as yield strength of 239.3 MPa, ultimate tensile strength of 297.5 MPa and elongation of 8.0% were obtained for the squeeze casting component with T6 treatment and an addition of 0.6% A-5Ti-B refiner. The globularization of eutectic Si, the refinement of eutectic Si, the homogenization of composition for the prepared component and the precipitation of Mg2Si phase in α-Al matrix all lead to the improvement of mechanical properties of squeeze casting component with T6 treatment.
The high temperature deformation behavior of TC2 Ti-alloy was investigated by means of finite element simulations and isothermal hot compression tests parallelly. Firstly, the characteristic stress-strain curves of TC2 were analyzed, and the high temperature constitutive equation and activation energy were acquired . Secondly, the microstructure evolution was observed with optical microscope. It was found that the globularization of α-phase is obvious at high temperature and low strain rate. Thirdly, the power dissipation and thermal processing map of TC2 Ti-alloy were drawn. And the deformation mechanism was characterized by strain rate sensitivity exponent m. Lastly, and the optimized processing window of TC2 Ti-alloy was determined as: (I) 760~825℃, 0.007~0.024 s-1; (II) 850~900℃, 0.018~0.37 s-1; and (III) 900~950℃, 1~10 s-1. Within these ranges the power dissipation rate of TC2 Ti-alloy is significant and sufficient dynamic recrystallization occurs in the process of deformation.
Nano-porous Co was prepared by electrochemically dealloying of Zr56Al16Co28 amorphous alloy in 0.5%(mass fraction) NH4F and 1 mol/L (NH4)2SO4 mixed solution. Nano-porous Co has the bicontinuous porous structure with large specific surface area and fast charge transfer ability. The prepared nano-porous Co exhibits good performance in many aspects: firstly, it delivers a high specific capacitance of 318 F/g at 2 A/g, suggesting its good performance as supercapacitor electrode; secondly, it exhibits degradation efficiencies under square wave potential as high as 96% for Direct Blue 6 and Acid Orange II respectively. The degradation ability of nano-porous Co electrode per unit mass is 3.5 times higher than that of Zr56Al16Co28 amorphous alloy electrode.
Fe2W-type ferrite BaFe2-x2+CoxFe163+O27(x=0.0~0.8) was prepared by solid phase method, and of which the microstructure and magnetic properties were characterized by means of X-ray diffractometer (XRD), scanning electron microscope (SEM), infrared spectrometer (FT-IR) and vibrating sample magnetometer (PPMS-VSM), as well as Reitveld fitting method. The results show that all samples are single phase BaFe2-x2+CoxFe163+O27 without residual α-Fe2O3. The grain has a good hexagonal structure and the particle size distribution is uniform. Last but not least, the partial substitution of Co2+ forFe2+can significantly improve the saturation magnetization (Ms) at 300 K for Fe2W-type ferrite BaFe2-x2+CoxFe163+O27.
Bi2O3 particles were fabricated by polyacrylamide gel method, after that the as-prepared Bi2O3 particles were decorated by the AuAg alloy nanoparticles (6~18 nm) to obtain AuAg/Bi2O3 composite. The composite exhibits obvious light absorbance centered around ~577 nm owing to the surface plasmon resonance (SPR) effect of AuAg alloy, which extends the light response range of Bi2O3. More importantly, the separation of photogenerated charges in bare Bi2O3 can be improved by the decoration of AuAg alloy nanoparticles. The rhodamine B (RhB), methyl orange (MO) and Cr(VI) are employed as target reactant to evaluate the photocatalytic degradation and reduction activity of AuAg/Bi2O3 composite under simulated sunlight and visible light irradiation. Results indicate that the composite exhibits obviously enhanced photocatalytic activity compared with the bare Bi2O3. After simulated sunlight irradiation for 2 h the degradation percentage of RhB and MO as well as reduction percentage of Cr(VI) increase by ~34.2%, ~38.0% and ~56.7%, respectively. Furthermore, it is worth noting that the AuAg/Bi2O3 composite has excellent photocatalytic and structure stability. According to above experimental results a possible photocatalytic mechanism of AuAg/Bi2O3 composite was proposed.
The combustion characteristics of carbon fiber/epoxy laminates were investigated by means of cone calorimeter at 35 kW/m2 heat flux in terms of ignition time, mass loss rate, heat release rate etc. The mathematical model of thermal penetration depth was established in order to acquire the relation of thermal penetration depth of materials with their thickness, which was a reference to differentiate the carbon designed fiber/epoxy laminate either as ‘thermally thin’ or ‘thermally thick’-type, and analyze the combustion process of laminates. The results show that with the increase of thickness of carbon fiber/epoxy resin laminate the ignition time increases, the average mass loss rate and the mass loss rate peak decrease, the total heat release increases, and the peak heat release rate increases first and then decreases. It follows that the carbon fiber/epoxy resin laminates present burning behavior as either ‘thermally thin’ or ‘thermally thick’-type may be depend upon its own physical thickness when it is ignited, and ‘thermally thick’ material has a changing thermal response process from ‘thermally thick’ to ‘thermally thin’-type during the combustion process.
The microstructure and toughness of the simulated coarse grain heat affected zone (CGHAZ) of the normalized microalloying offshore steels V-N-Ti and Nb-V-Ti were investigated by means of a welding thermal simulator. The results show that the perculiar microstructure led to better CGHAZ toughness for the V-N-Ti steel. For V-N-Ti steel, the high N content increases the precipitation temperature of Ti-rich (Ti, V)(C, N) particles and the ferrite nucleation ability, so that refines the original austenite grain and decreases the effective grain size with high boundary tolerance angle 15o, hence, the fine polygonal ferrite could efficiently deflect or even arrest the propagation of cleavage microcracks, so it had good low temperature CGAHZ toughness. While there exist chain-like M-A on original austenite grain boundaries, coarse original austenite grains and larger amount of fine grains with high boundary tolerance angle 15o that may be responsible to the lower simulated CGHAZ toughness of Nb-V-Ti steel.
