Key Engineering Materials Vols. 531-532

Abstract: Aimed at improving mechanical properties of high strength low alloy steel welds, oxides with high melting point and high stability were added into steel liquid. By thermodynamics calculation and thermal simulating technology, phase transformation characteristics of low alloy steel weld with TiO₂ addition were investigated. The results showed that TiO₂ added in welds led to the decrease of phase transformation temperature and the wideness of γ→α transformation temperature range. The starting and finishing transformation temperature of ferrite respectively dropped about 311K and 486K on the cooling condition of 373K/s. Moreover, the complex inclusions of TiOx-MnO-SiO₂-MnS with spherical shape and 0.67μm mean size formed in weld metal. In addition, only acicular ferrite existed in the titanium oxide added welds. So it was concluded that titanium oxide can effectively be used to control phase transformation and then achieve fine and favorable microstructure.

Abstract: The precipitation behaviors were investigated during isothermally aging at 700°C and 800°C after cold compressed by 30% in thickness in Fe-18Cr-12Mn-0.48N high-nitrogen austenitic stainless steel by using optical microscopy (OM), laser scanning confocal microscopy (LSCM) and transmission electron microscopy (TEM). The results show that precipitation morphology in cold-deformed sample is the same as non-cold-deformed sample, which also displays discontinuous cellular way. Cold deformation accelerates the precipitation of M2N phase. The precipitation occurs at not only grain boundaries but also twin grain boundaries in the experimental steel. In cold-deformed sample, besides the long-strip M2N precipitates, intermetallic phase-σ phase owning bct structure and lattice parameters of a=0.8800nm and c=0.4544nm were observed along grain boundaries and inside the grain.

Abstract: Hydrophobic silica aerogels were prepared from industrial microsilica via ambient pressure drying. The process consists of two stages, synthesis of sodium silicate solution from microsilica by hydrothermal reaction with sodium hydroxide, and preparation of silica aqueous gel and porous silica aerogels from the obtained sodium silicate solution. The mixed solution of hexane/ethanol/trimethylchlorosilane was used to modify the sol-gel derived silica aqueous gel so as to obtain porous structure by ambient pressure drying. The microstructure, pore properties of the silica aerogels were analyzed by FTIR and N₂ adsorption-desorption methods, and the oil adsorption of the synthesized silica aerogels was investigated. The results indicate that the obtained silica aerogels are light-weight and hydrophobic porous materials, with the specific surface area of 767~828 m²•g^-1, porosity of 91.5~95.1% and the average pore diameter of 5.22~8.02 nm. The synthesized silica aerogels have good oil adsorption capacity and the highest saturated oil adsorption rate can achieve 1105%.

Abstract: Multi-component ceramic coating (Ti, Al)C was prepared on the 45 carbon steel by electrical discharge coating (EDC) in kerosene. The (Ti, Al)C coating was analyzed by different methods including X-ray diffraction (XRD), scanning electron spectroscopy (SEM) and energy disperse spectroscopy (EDS).The thermo gravimetric technique was used to approximate the kinetics of oxidation of the (Ti, Al)C coating and the carbon steel and the tribological performance is tested too. The results indicated the thickness of the coating was about 20μm, and the composition of the ceramic coating mainly consisted of (Ti, Al) C and Fe. An oxide film with compact structure formed after 600°C oxidation for 200h, and it was mainly composed of Al2O3 and TiO2, which inhibited further oxygen diffusion into the coating. The (Ti, Al) C coating possessed slow oxidation rate and high temperature oxidation resistance. The coefficient of the coating was lower than that of carbon steel and it had excellent abrasion resistance performance at the load of 100N. Carbon steel lose weight tremendously with an increase at the load of 100, but for the (Ti, Al) C coating the weight loss was very slow.

Abstract: Mesoporous carbon material CMK-3 was successfully prepared by using mesoporous silica material SBA-15 as hard template and sucrose as carbon source through a nanocasting method. In order to improve the hydrophilic properties of the carbon materials, a large amount of carboxylic functional groups have been introduced upon the surface of carbon materials by oxidative treatment. Transmission electron microscopy (TEM) exhibit highly ordered mesostructure with 2-D hexagonal symmetry of our sample. An absorption assigned to the -COOH groups is clearly visible in Infrared spectra, suggesting the presence of carboxylic functional groups. Rhodamine B (Rh B) was selected as a model for determining the adsorption activity of the obtained material. This material exhibited a high adsorption capacity, and an extremely rapid adsorption rate.

Abstract: In the aerospace and auto industries, the residual tensile stresses will cause the structures broke and damaged. Hence, different methods were considered to optimize the machining processes. In this article, a residual stresses calculation model using AdvantEdge 2D turning was integrated with 2D milling physical model in order to analyze high-speed milling thin-walled workpiece. Through optimizing the processing parameters (improving the cutting speed and decreasing the cutting depth) during high-speed milling, not only we can get a high removal rate and receive a distribution of equably surface residual stresses, but also a slowing down trend of in-depth residual stress can be obtained. In addition, we evaluate this method using a typical part at the sensitive area, and the machining quality can be improved obviously.

Abstract: Wood is being used extensively in timber construction in China. In fire-resistant design for timber construction, the main goal is to ensure that enough structural integrity is maintained during a fire to prevent structure collapse. It is important to understand its structural performance when exposed to elevated temperatures and loaded by stress levels. To study the interaction effect of Chinese larch wood, a total of 72 small clear wood samples were observed under constant stress levels when the wood temperature was elevated. The results indicated that Chinese larch wood was more susceptible to the coupling effect of temperature and stress. The interaction promoted a temporary stable flexural structure to collapse during a short exposure time.

Abstract: Pr0.5Ca0.5Mn0.99Al0.01O3 compound was prepared by standard solid state reaction to study its ac susceptibility at low temperatures. The X-ray powder diffraction patterns show that the compound is single-phase orthorhombic structure. The cusps of charge ordering and the long range AFM order of the “pseudo”-CE type are suppressed with Al dopping in Pr0.5Ca0.5MnO3 compound. ZFC and FC magnetization of this compound bifurcate at Tf. The behavior of ac susceptibility at low temperatures is investigated. The intensity of the real component ' at the freezing temperature Tf is suppressed with the increase of frequency. Tf is linear with the logarithm of the frequency. The normalized slope P = ΔTf/TfΔlog10ω, which is much lower than canonical insulating spin glass systems in which 0.06 ≤ P ≤ 0.08. The intensity of '' at Tf increases with the increase of frequency. The ground state of this sample is cluster glass.

Abstract: The balance melting point and compatibility of Polypropylene/Syndiotactic1,2 polybutadiene (PP/s-PB) blends and neat PP were studied by using DSC, the results showed that the presence of s-PB in PP would have a strong impact on balance melting point of PP. The presence of s-PB in PP could effectively decrease balance melting point of PP. Balanced melting point depression proves that there are strong interactions between two macromolecular chains in compatible part of blend. According to Nishi-Wang theory, PP and s-PB are incompatible in thermodynamics, but compatible in dynamics. Namely, PP/s-PB are partial compatible. The structure is heterogeneous in microscopy, but homogeneous in macroscopic, this also proves that there are strong interactions between two macromolecular chains in blend. The strong interactions is a kind of useful toughness effect on PP.

Abstract: C/SiC composites have widely application prospects in the field of aeronautic and aerospace for their excellent properties. The joining of C/SiC composites is a key to fabricate large and complex components. In this paper, 1D C/SiC pins were prepared by precursor infiltration and pyrolysis (PIP) process and used to join C/SiC composites by Slurry react (SR) and PIP process. The shear strength of the C/SiC pins with different carbon fiber volumes was investigated with the maximum shear strength as high as 339.46MPa. Influences of C/SiC pins on the joining properties of C/SiC composites were studied. The shear strength and flexural strength of C/SiC-C/SiC joining are improved from 9.17MPa and 30.41MPa without pins to 20.06MPa and 75.03MPa with one C/SiC pin (diameter 2mm), respectively. The reliability of C/SiC-C/SiC joining is also improved with C/SiC pins in that the fracture mode changes from catastrophic without pins to non-catastrophic. The SEM photos show a strong bond between joining layer and C/SiC composites without obvious interface.