Key Engineering Materials Vol. 351

Abstract: The bolt load retention (BLR) test fixtures and behaviors of Mg alloys by main research teams are reviewed. Parts of BLR test results are also presented. Since creep properties are relevant to BLR, an approach to predicting BLR behaviors from creep curves is briefly introduced. The BLR test fixtures and procedures in our study are also shown.

Abstract: This article deals with the influence of processing parameters on the microstructure of (AlN+Mg2Si)/Mg composites. Parameters such as stirring impeller shape and pouring temperature are shown to control the distribution and size of reinforcements and the amount of “Chinese script” type Mg2Si.

Abstract: Surface modification of activated carbon was performed using such chemical methods as nitric acid and H2O2.Oxidation of the ACs made samples with weakly acidic functional groups and the presence of other groups was confirmed by Fourier transform infra red (FTIR) spectroscopy. With different time for modification, the amount of elements of carbon and oxygen will change a lot and the results of these experiments show a stronger ability of HNO3 solution in oxidization. Furthermore the differences of face morphology between ACs and oxidized ACs can be observed clearly

Abstract: Well-dispersed SiO2 slurry with high solid content for aqueous tape casting was obtained by selecting the appropriate dispersant, binder, plasticizer and other additives. However, it is difficult to prepare well-dispersed CNTs/SiO2 slurry because CNTs tend to aggregation and the bulk density disparity of CNTs and SiO2 is obvious. In addition, the contradiction between removing organic additives and retaining the properties of CNTs should be considered. Some methods are provided to solve the as-mentioned difficulties.

Abstract: The main problems for multiphase materials are the even mixing and the bonding or reacting among two or more phases, as well as the states of their grain boundaries. The mixing of two phases is usually effective by using liquid medium. The technology of second phase coating for the original particles or so call nucleo-shell structure is a well approach for the even mixing. For ceramic matrix multiphase materials low sintering temperature is the effective way to avoid the occurring of reaction between different phases. The design of grain boundary and its stress is important for their bonding states. The thinking for above problems would be described briefly in this paper. The purpose of multiphase materials design is expected that every phase will be playing its role, combining together and then given out a comprehensive performances. So it is necessary to consider the following problems. 1. Even mixing Even mixing between each other material is important for multiphase materials. It’s the better when the processing is carrying on in the liquid state for the even mixing of two phase materials. Using physical or chemical method could be formed the fine solid particles with even dispersion of two or more phases materials. Usually it could be obtained nano-scale particles. The application of nano-technology is necessary. The nano-scale mixing of two phases materials would be greatly increased the contacting surface of each other particles without agglomeration. Of course, if one phase of material is fine solid particle which disperses in another phase of material solution, the even mixing of two phases is obtained similarly. Making a coating to other phase particle is a very good approach for the two phases even mixing. Coating process is attracting more and more attention in the preparation of composite materials mainly due to its predominance in the improvement of the uniformity for different phases [1]. The thickness of coating material determines the amount proportion of two phases which is able to be control. Two examples of so-called “nucleo-shell structure” will be introduced in the following parts. Cermet composites have been widely studied due to their potential for achieving higher toughness and reasonable strength compared with ceramic matrix. But except for numbered systems, such as Co/WC and Ni/TiN, few systems have reached the people’s expectation mainly for the poor wettability between metal and ceramic. Al/Al2O3 cermet is a low density and high strength material, and it has many potential and actual applications in military, industrial and consumer regions. To improve the dispersive uniformity of the two phases, coating aluminum with alumina may be a good candidate since such coatings not only stabilize aluminum dispersions but also make it possible to control inter-particle and particle-matrix interactions [2]. Figure1a-c shows the images

Abstract: The porous ceramic support was prepared from cordierite by adjusting the phase composition, grain size of aggregate, additions of pore-forming material and binder. The porous ceramic support had excellent chemical stability and relative high strength with a porosity of 48％and pore size of 128μm. Factors that affected the properties of the support material were analyzed. The pore size of the porous ceramic support was directly proportional to the grain size of the aggregate around firing temperature. The strength of the support material increases with a rise in amount of the binder and firing temperature. The porosity of the support material increases while the strength decreases with a rise in amount of the pore-forming agent.

Abstract: We developed a new titanium alloy with high strength, low elastic modulus, high elasticity and plasticity after cold working. Thermo mechanical processing, ageing, recrystallization after cold working was conducted to change the mechanical properties. The release of the elastic deformation energy after cold working is help to get the low modulus, however, the precipitation of α phase hamper the formation and propagation of the fatigue crack. Recrystallization after cold working could refine the grain size from 100μm to 1～5μm. Cold working after recrystallization absolutely restricts the propagation of the fatigue crack. As a result, the fatigue strength was increased, and the same time, it keeps the low elastic modulus.

Abstract: This work studied the possibility of the application for Metal Matrix Composites (MMCs) in extendible exit cone nozzles (EECNs), through analyzing the stress distribution on the solid rocket motor’s EECNs. The result shows that the MMCs can be used on the EECNs. With replacing the traditional steel by light MMCs to serve as the key supporting components, the strength and stiffness can satisfying the application request. The mass of the components are drastically decreased. This technique has promising applications.

Abstract: In the present study, the BaTiO3/Ni composites were prepared by using the pressureless sintering technique. The ferroelectric and ferromagnetic properties of the composites are measured. The composites exhibit ferroelectric properties only when the Ni content is as low as 1 vol.%. Nevertheless, the saturated magnetization of the BaTiO3/Ni composites increases with the increase of Ni content. The BaTiO3/Ni composites exhibit multiferroic characteristics.