Materials Science Forum Vol. 984

Abstract: The fatigue life and fatigue stress of 30CrMnSiA material are studied by fracture retro estimation under experimental conditions. With the help of Scanning electron microscopy (SEM), fatigue crack can be observed. By Paris law, the fatigue life and fatigue stress of 30CrMnSiA material can be estimated by fatigue striation under the experimental environment. The method is simple and feasible, and the relative error is lower.

Abstract: In the paper, the microstructure and mechanical properties of ZYK530 Mg alloy with different aging heat treatment processes were analyzed and studied by OM, SEM, EDS and XRD. The results show that after heat treatment at different temperatures and aging times, the hardness of the alloy first decreases, then increases in a wave-like manner, and then decreases in a wave-like manner after reaching its peak value. The optimum aging process of ZYK530 alloy is T5-220°C×5h, and the maximum hardness is 88.34HRE, which tensile strength, yield strength and elongation are 335MPa, 305MPa and 13.5% respectively. Compared with the untreated forged alloy, the mechanical properties are increased by 6.3%, 4.8% and 35%, which its fracture mechanism is mainly ductile-brittle mixed fracture.

Abstract: Conventional and nanometer aggregate ZrO₂-7wt.%Y₂O₃ ceramic powders taken as raw materials, plasma spraying and plasma spraying-laser remelting compound technology was used to prepare conventional and nanostructured thermal barrier coatings on the TiAl alloy surface. Effects of powder structure (feedstock) and laser remelting on organizational structure and phase of the coatings were analyzed using scanning electron microscope (SEM) and X-ray diffractometer (XRD). Results indicate that: conventional plasma sprayed ceramic coating presents typical lamellar stacking features; plasma sprayed nanostructured coating consists of fully melted region and partially melted region, presenting a two-phase structure. Under the comprehensive impacts of laser power, energy density, temperature field distribution in the laser action region, ceramic heat conductivity coefficient and coating thickness and other factors, the coating presents obvious lamellar structural features after laser remelting; the upper part is compact columnar crystal remelting region and the lower part is residual plasma spraying region. Due to toughening effect of residual nanoparticles in the remelting region of laser remelted nanostructured coating, grain-boundary strength is high and there are a considerable number of transgranular fractures, but the fractures in the remelting region of laser remelted conventional coating are basically intergranular fractures. Conventional plasma sprayed ceramic coating is mainly of tetragonal phase together with a small quantity of monoclinic phases, but nanometer plasma sprayed ceramic coating only has non-equilibrium tetragonal phases. After laser remelting, both conventional coating and nanometer coating mainly have non-equilibrium tetragonal phases with a small quantity of cubic phases.

Abstract: Basing on the study of adsorption behavior of glycidoxypropyl-trimethoxy-silane (GTMS), pretreatment method of AA2024-T3 aluminum alloy for sol-gel films was optimized. The morphology, composition and corrosion protective performance of alloy coated with the films were investigated by using FE-SEM, EDS, AFM and EIS. The results showed that the Al matrix exhibited better ability to adsorb GTMS molecules than the second phase particles, especially at lower concentration of GTMS. Further, the 5% GTMS films cover the whole surface, but the selective adsorption behaviors still exist. It was concluded that less second phase particles and smoother surface were benefit to the sol-gel films on aluminum alloy. Depending on this conclusion, the pretreatment method for sol-gel films was optimized. The optimized surface condition conducted with 50 g•L^-1 sodium hydroxide and ultrasound at 60 oC for 30 s was obtained. These samples coated with the sol-gel films revealed good anti-corrosion performance. The coverage degree of the films was up to 97.95 %.

Abstract: To improve the corrosion resistance on Q235 low carbon steel, in this paper, tetraethyl orthosilicate (TEOS), N-dodecyl trimethoxysilane and γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) were used to make organic-inorganic hybrid sol-gel film. Cross cut test adhesion method, neutral salt spray test, electrochemical test and film protective efficiency were taken to value the corrosion resistance property. The corrosion topography was studied by optical microscope. In addition, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) curves and equivalent electric circuit fitting were used to analyze the corrosion mechanism. The cross cut adhesion of sol-gel film can reach 1 class and the protection class can attain 5 class after 72 hours neutral salt spray test. According to the potentiodynamic polarization curve analysis, the corrosion potential of sol-gel film coating sample after 0.5 hours immersion was -0.46 V (vs. SCE) on the 0.1 Hz, and its corrosion current density was 4.74×10^-7 A·cm^-2. The corrosion potential of bare Q235 low carbon steel plate after 0.5 hours immersion was -0.78 V (vs. SCE) on the 0.1 Hz, and its corrosion current density was 4.75×10^-6 A·cm^-2. The impedance value on 0.1 Hz (|Z|_0.1Hz) (1.27×10⁶ Ω·cm²) of sol-gel film coating sample was more than three orders of magnitude higher than the value of the low carbon steel plate. Even dipping in 3.5 wt. % NaCl for 72 hours, the |Z|_0.1Hz value of sol-gel coating sample was still one order of magnitude higher than the low carbon steel plate with 0.5 hours immersion. Sol-gel film with excellent adhesion can significantly improve the corrosion resistance of low carbon steel plate. Sol-gel film can increase the protection efficiency of low carbon steel plate by 90%.

Abstract: BK7 optical glass has been widely used in modern high-tech fields such as aerospace, automotive, optical precision instruments, electronic information, etc. due to its excellent performance, but its gap between plasticity and hardness is huge, making traditional machining easy to appear sub-surface. Damage and other phenomena, surface quality is difficult to meet the requirements. In this paper, the ultrasonic milling dynamics model was firstly established, and then the multi-factor method was used to detect the longitudinal torsional composite ultrasonic milling and ordinary milling of BK7 optical glass, and the surface roughness and surface topography of different spindle speed, milling speed and milling depth were analyzed. Finally, the laws and mechanisms affecting the quality of the machined surface were obtained. It is found that the surface quality is best when the spindle speed is 3000r/min and the milling depth is 0.2mm; the surface quality of BK7 optical glass decreases with the increase of milling speed. The surface quality and processing efficiency of BK7 optical glass are improved by longitudinal torsional composite ultrasonic vibration milling, and the optimal process parameters for BK7 optical glass longitudinal torsional ultrasonic milling are provided.

Abstract: The determination of the migration of 11 organotin compounds in food contact materials by GC-MS was established. The gastric acid was simulated with 0.07 mol/L hydrochloric acid solution, and the sample was soaked and extracted, and then derivatized with sodium tetraethylborate, extracted with n-hexane liquid solution, detected by GC-MS, and quantified by internal standard method. The linear range of the method is 5~600 μg/L, the correlation coefficient is greater than 0.997, and the method detection limit is 0.014 mg/kg. The recoveries of the three concentration levels ranged from 83.6% to 105.6% with a relative standard deviation of less than 11.4%. The method is simple and sensitive, and can be used for detecting the migration of organotin compounds in food contact materials.

Abstract: Here we synthesized a high-density single crystal anatase phase TiO₂/ITO nanorods array composite by one-step hydrothermal method. TiCl₄, H₂O, and HCl were used as the titanium precu-rsor, oxygen source, and inhibitors, respectively. The TiO₂ nanorods array were analyzed using X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), optical contact angle tester and ultraviolet-fluorescence spectrophotometer, separately. The nanorods in the composite grew along the [101] crystal plane, with a diameter of about 500 nm and a length of about 3 μm. The effect of PVP addition on the crystal phase and morphology of TiO₂ na-norod arrays was investigated. When the amount of PVP added was 0.5g, the diameter of nanorods was about 77-120nm, and a neat array structure appeared. In the photocatalytic experiment, methyl orange and acid red were used as degraded materials, the photocatalytic degradation rate was up to about 100%. When the hydrophilicity was the best, the optical contact angle of the sample after ultr-aviolet light irradiation was 7.2°. These results indicated that TiO₂ after doping experiments got better photocatalytic properties.

Abstract: The present study involves preparation of Ag nanoparticles (Ag NPs) deposited on non-woven fabrics by a two-step method including the chemical precipitation of Ag₂O nanoparticles on the fabrics followed by in situ reducing of the precursor into Ag NPs by different reductive processes including chemical reduction, photo-reduction and dielectric barrier discharge (DBD) cold plasma treatment. The morphology as well as the antibacterial efficiency of the Ag NPs deposited on non-woven fabrics are also evaluated. The Ag NPs-modified fabrics prepared by DBD plasma treatment exhibit significant antibacterial properties against both Escherichia coli and Staphylococcus aureus, and accordingly have potential applications in the healthcare and medicine fields.