Materials Science Forum Vols. 620-622

Abstract: The relationship between the processing technology and the dielectric property of the laminated AlN/h-BN ceramic composites has been studied. The results showed that the main polarization mechanism of laminated ceramic composites in low frequency range is space charge polarization at the interface of AlN layer and BN layer. Due to the affection of porosity, the permittivity increases and the dielectric loss decreases with increasing the hot pressing temperature. The permittivity increases and the dielectric loss decreases with increasing thickness ratio of different layer., Both permittivity and dielectric loss increase with increasing the content of AlN doping in BN layer.

Abstract: In order to obtain machinable ceramic with high hardness and strong mechanical properties, the SiC/Al/h-BN Composite Ceramics were fabricated by a new method which prepared the machinable pre-sintered body by Plasma Activated Sintering (PAS) and increased it's mechanical properties after hardening treatment. The results showed that the machinability and density of the pre-sintered h-BN/Al/SiC ceramic composites were excellent, and after hardening treatment, the mechanical properties (hardness, bending strength and density) increased obviously.

Abstract: High purity Ti3SiC2 ceramic was synthesized by mechanical alloying and vacuum sintering. The effect of aluminum (Al) content on the properties and processing of Ti3SiC2 was investigated. The results showed that proper addition of a definite amount of Al could obviously increase the purity of Ti3SiC2, and was favorable for reducing the sintering temperature of Ti3SiC2.

Abstract: C/C-SiC composites were rapidly fabricated using C/C with four different porosities in the range of 12.4%~45.7% and silicon by reactive-melt-infiltrated (RMI) method. The influence of the C/C porosity on the Si infiltration during the processing and on the microstructure and mechanical properties of the resulting C/C-SiC were investigated. The results show that β-SiC was formed by Si/C reaction and free Si remained in the composites. A higher porosity of C/C leads more Si infiltrating to the preform and produces higher density of C/C-SiC with lower porosity. The flexural strength of the composites was strong influenced by the matrix content and the interface between different phases. C/C-SiC derived from C/C with 24.8% porosity has the highest flexural strength (325.1MPa).

Abstract: In the present study, the fluid flow and the heat transfer with solidification analyses for the Cu thin wire production by OCC (Ohno Continuous Casting) process. The OCC process is widely used to produce cylindrical column castings continuously, a number of researches have been focused on the OCC process. However, few researches on the production of Cu thin wire by the OCC process have been reported, therefore it is necessary to investigate and optimize the process variables of the OCC process when producing the Cu thin wires. A commercial multiphysics software was used to analyse to the flow pattern and the temperature distribution in the OCC system proposed in the present study. Effect of the casting speed, the OCC mold temperature, the melt temperature on the castablility of the thin Cu wire and flow pattern and temperature distribution of the melt were discussed. It is expected that the present study is able to give the design parameters of the OCC system for production of Cu thin wire before the actual OCC system construction.

Abstract: With global climate becoming warmer more and more attention is being paid to cold materials. Lower surface temperature contributes to decrease the temperature of the ambient air as heat convection intensity from a cooler surface is lower. Such temperature reductions can have significant impacts on cooling energy consumption in urban areas, a fact of particular importance in hot climate cities. The black surface of asphalt pavement absorbs more heat from the sun, and higher temperature of pavement surface contributes to increase the effect of the urban heat island, but affects the performance and life span of a pavement. Asphalt pavements form an integral part of any transportation system and are typically engineered to last 15 years or more, but many have been failing early due to potholes, cracks, raveling and other problems. Cool pavement are mainly aimed to decrease the effect of asphalt pavement on the urban heat island, but the influence of cold materials on the high-temperature performance of asphalt concrete pavement is paid little attention relatively. In this paper, it’s discussed that the effect of asphalt-pavement high temperature and its improving measures. And the mechanism of cool pavements is introduced, and possible technologies applied to asphalt pavements are reviewed. The idea of asphalt concrete pavement with automatic temperature-control is put forward.

Abstract: The equiatomic multicomponent CoCrFeNiCuAl high-entropy alloy powder was synthesized by mechanical alloying. The effects of milling time and heat treatment on the structure and morphology of the ball milled alloy were investigated. Single BCC solid solution structure appears when the alloy is ball milled more than 30h. The 60h ball milled alloy powder shows a mean particle size of 3 μm, which is actually hard agglomerations of nanosized crystals with crystalline size less than 10nm. The 60h ball milled alloy exhibits good chemical homogeneity. The single BCC solid solution structure transforms to a BCC and a FCC phases when annealled at 600°C for 1h, which can be attributed to the supersaturatable solid solution formation during the mechanical alloying process.

Abstract: There is less study about the effect of magnesium on characteristics of bearing. In the paper, the bearing steel was modified by three types of Al-Mg alloys. Firstly, the total oxygen content value was measured, and then the inclusion size, shape and chemical composition were analyzed by optical microscopy, SEM and EDX. The results show that, after treated by Al-Mg alloy, the total oxygen content descends remarkably and the alumina inclusion with big size and different shapes transform into spinel with small size and spherical shape. The optimal effect of inclusion modification is acquired after treated by NO. 3 Al-Mg alloy containing 16.55 wt% Mg, most of the inclusions in steel are spinel and magnesia, and the size of 96.23 wt% inclusions is less than 3μm.

Abstract: The present study concerns the influence of aging parameters on the microstructure and corrosion behavior of duplex stainless steel S31803 and S32750. It has been found that the microstructural evolutions were extremely sensitive to sigma phase precipitation during aging treatment, and sigma phase was enhanced with the increase of aging time from 2 min to 120min at its precipitation peak temperature 850 °C for S31803 and 920°C for S32750 steels respectively. The precipitation of sigma phase in S32750 is ahead of that in S31803 steel, within 10min, the sigma phase precipitation rate of S32750 is much faster than that of S31803 steel. The precipitation amount of sigma phases in S32750 steel is noticeable higher than that in S31803 steel during any aging treatment. The corrosion resistance is directly influenced by the abundant sigma phases, especially for the S32750. This result is helpful for practical aging treatment establishment of the S31803 and S32750 duplex stainless steels.

Abstract: The densification behavior and mechanical properties of B4C by SPS at 1900°C for 2 min with additions of Al2O3 up to 10 wt.% were investigated. When the additional of 10 wt.%, the relative density was 99% and the hardness went to 33GPa. Sinterability was greatly improved by the addition of a small amount of Al2O3, and the SPS technology with high hearing rate is particularly attractive for prepare of poorly sinterable materials. The improvement was attributed to the enhanced mobility of elements through the Al2O3 near the melting temperature. As a result of this improvement in the density, mechanical properties, such as hardness, fracture toughness, increased remarkably.