Advanced Materials Research Vol. 744

Abstract: The complex dielectric behaviors of ferroelectric barium titanate (BT) ceramics were investigated. The dielectric properties were studied as a function of temperature and frequency using broadband dielectric spectrometer. The results show that the maximum value of dielectric constant occurs at 500nm BT ceramics, which is approximately 7,500; the dielectric loss is lower than 0.03 with the temperature varying from 225 K to 450 K. Dielectric constant and dielectric loss experience three dielectric peaks corresponding to rhombohedral to orthorhombic, tetragonal and cubic transitions. With the frequency ranges from 1 MHz to 1 GHz, the dielectric relaxation is apparently present. The relaxation process obeys Cole-Cole relaxation model at high temperature and conforms to Debye relaxation model when the temperature far lower than Curie temperature. The relaxation time is the order magnitude of ~10^-9 s obtained by Havriliak-Negami function fitting, which is very consistent with theoretical calculation.

Abstract: The chemical composition of a 960 Mpa grade high strength steel with low carbon equivalent was designed. Effect of direct quenching and tempering process on the microstructure and mechanical properties of the experimental steel was studied. Results showed that fine lath martensite was obtained after controlled rolling and direct quenching. With tempering temperature increasing, the mechanical properties showed different trends for different tempering stages. And this had a direct relationship with the microstructure evolution. The matrix recovery softening, carbon desolution and precipitation of nanomicroalloy carbides influenced the strength change. With increase of tempering time, the strength decreased and toughness improved. Experimental steel tempered at 450 °C for 40min could obtain the best mechanical properties, which meet the requirement with a large impact energy margin.

Abstract: Mechanical adhesion method and precursor method were used to prepare Ti-B₄C-C and Ti-B₄C-Sucrose composite powders respectively with Ti, B₄C, graphite and sucrose (precursor of C) as raw materials. Ti (C,N)-TiB₂ composite ceramic preforms were prepared with the two kinds of powders by self-reactive spray forming technology. The compositions and microstructure were analyzed and observed by means of XRD and SEM. The porosity and fracture toughness of the preforms were tested. Then the influence of powder preparation technology on the microstructure and properties of the preforms were contrastively analyzed. It was shown that compared with Ti-B₄C-C composite powders, Ti-B₄C-Sucrose composite powders had lower interior adhesive strength, but the different composition among them mixed more uniformly and contacted tighter, which made the SHS reaction of them during the spray forming process take place more sufficiently. The two kinds of preforms were both composed of Ti (C,N)-TiB₂ main phases, titanium oxide by-product phases and some pores. Whereas there were less kinds and content of by-product phases in the preforms prepared with Ti-B₄C-Sucrose powders, and the materials were uniform and dense, with higher fracture toughness. The general properties of the preforms were obviously better than that of the preforms prepared with Ti-B₄C-C composite powders.

Abstract: By using some types of means such as Optical Microscope (OM), Scanning Electron Microscopy(SEM), the testing of tensile mechanical properties and the testing of friction and wear, the impacts of the Al-5Ti-1B and Al-20Sr modification on the Al-16Si-4Cu-0.5Mg-0.2Mn alloy microstructure, mechanical properties and friction properties are researched. The results turn out that the modification can significantly refine the primary silicon and the eutectic silicon in the alloy, the Al-5Ti-1B mainly refined the primary silicon in the alloy, the Al-20Sr refined the eutectic silicon; the alloy’s effect of refinement after compound modification is better than that in separate metamorphism. Modification can improve the tensile strength and elongation of the alloy: the tensile strength of the alloy has been increased by 65MPa after its compound modification; also the elongation by 0.4%. Modification can improve wear-resisting property of the alloy and also its effect of compound modification is better than that of separate metamorphism. The modification mechanism of Al-5Ti-1B is that Al3Ti and TiB2 belongs to heterogeneous nucleation; while the modification mechanism of Al-20Sr is that the strontium changes the growth pattern of Si phase.

Abstract: Ordered spin structure in two-dimensional materials is critical to the use of such materials in spintronics. Here, based on first-principles calculations, we demonstrated the existence of magnetic homogeneity in integrated two-dimensional structures. Our calculations show that hydrogenated MoS2 can be magnetized with a ferromagnetic character. The doped electrons in 4d orbitals of Mo atoms through hydrogenation lead to strong exchange splitting, which is the mechanism behind the transition of magnetic states. Given the recent progress in chemical control of two-dimensional materials, our results open a new way to produce two-dimensional spintronics.

Abstract: A kind of austempered boron alloyed high silicon cast alloy was developed though modification with Ti and controlling austempering temperature, the impact toughness of which increases to 20.7 J/cm², which is more than triple that of the previous work. The alloy with modification exhibits obvious grain refining both in matrix and boride, improved the morphology of boride into discontinuous network and small particles. The phenomenon and mechanism are discussed in the article, it proved TiC is possible to act as the nuclei of eutectic boride and Ti can be an effective modifier.

Abstract: Two new tetraphenylethene derivatives were designed and synthesized through Suzuki coupling reaction. The absorption, fluorescence properties, and application were studied. All compounds showed similar absorption pattern in pure THF, but exhibited significant red shifts with increasing the number of thienyl rings, indicating an extended π-electron delocalization from the TPE nucleus, brought about by the thienyl substituents. The new materials exhibit the novel feature of aggregation-induced emission, as a result of the twisted TPE units, which restrict the intramolecular rotation and reduce the ππ stacking. Photoluminescence of these chromophores ranges from 400 to 700 nm. The new materials can detect the volatile organic compounds with relatively high sensitivity in the aggregate state, which indicates the new materials can work as sensitive chemosensors.

Abstract: Effect of RE and V on microstructure and mechanical properties of high chromium cast iron were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, impact test and wear test. The results show that proper modification using RE combined with V makes the alloy present a more refined and homogenous austenite matrix, and makes the morphology of carbide changing from thick lath to thin lath, and rosette-like. Modification can also increase hardness, wear resistance and impact toughness of high chromium cast iron.

Abstract: This paper described the influence of different ageing treatments on bending performance of carbonized bamboo scrimber according to three ageing standards (ASTM D1037, BS EN1087-1 and WCAMA). The modulus of elasticity (MOE) and modulus of rupture (MOR) were tested and the fracture morphology of the samples after mechanical test was also analyzed by SEM before and after ageing. The results showed that the average reduction rates of MOE and MOR were respectively 47.48% and 34.98%. In addition, SEM micrographs revealed that the fracture morphology of ASTM and BS EN presented smoother surfaces than WCAMA. The fracture surface of WCAMA was similar to Control but smoother in some parts. This was mainly due to the brittle rupture playing a dominating role in different degrees based on three ageing treatments. In conclusion, the brittleness of material after ageing was intensified leading to the decline of the bending performance.

Abstract: In this paper, the bending properties of bamboo-wood container flooring and bamboo curtain-OSB container flooring were tested and the six-cycle artificial accelerated aging method of ASTM D1037 was conducted to evaluate the aging performance of two kinds of bamboo-wood container floorings. The modulus of rupture (MOR) and modulus of elasticity (MOE) were tested in the longitudinal and transverse directions before and after aging. The results showed that both the bending strength and MOE decreased after aging. The retention ratios of MOR of the bamboo-wood container flooring and bamboo curtain-OSB container flooring were respectively 43.5%, 72.0%, and the retention ratios of MOE were 54.6%, 76.3%. In general, the effect of aging on the bamboo-wood container flooring was larger than that on the bamboo curtain-OSB container flooring.