Materials Science Forum Vols. 561-565

Abstract: In this work the toughening mechanism and the microstructure of SPS-sintered Al2O3-ZrO2 nano-composite ceramics whose powder was prepared by mixed coagulative method, was studied. The study showed that the grain shape of Al2O3 was changed due to the additive ZrO2 and its density was improved in the Al2O3- ZrO2 ceramics. Meanwhile its grain was refined. The microstructure was the typical nano-composite ceramics mixed with intracrystalline and intercrystalline structure. The irregular aggregation of ZrO2 mostly existed on the grain boundary, where many grains of Al2O3 intersected. Some thin and dispersal globular nano grains (70nm-200nm) of ZrO2 were distributed in the Al2O3 crystal grains. That enhanced the mechanical performance of the matrix because of the refined grain and the intracrystalline nanometer structure. The study also showed that the changes of the mechanical performance of Al2O3-ZrO2(n) ceramic resulted from toughening mechanism introduced by nanometer grains, toughening mechanism introduced by ZrO2 phase transition and the intracrystalline structure.

Abstract: The composite accompanied with a function of thermoelectric conversion has been fabricated. It was a fiber metal laminate (FML) consisting of two aluminum alloy sheets of 0.5mm thickness and a central layer of glass fiber reinforced plastic (GFRP). The central layer with a thickness of 1mm included thermoelectric elements of Bi-Te based alloys between glass fibers. The mechanical properties of FML with and without the thermoelectric elements were evaluated by tensile and bending test. The thermomechanical properties were measured by a potentiometer for a module with heated and cooled sides, and plotted a potential as a function of difference in temperature between both sides.

Abstract: A novel two-step process was used to investigate the microstructure and properties of porous CMCs prepared by HIPing the pyrolyzed composites of commercially available ZrO2 (TZ- 3YS), silicon powders and phenolic resin. In the first step, preforms with 70, 80 and 90 mass % of ZrO2 powders were prepared by the pyrolysis of ZrO2 / Si / Phenol Resin composites at 850 oC in vacuum. And, then the pyrolyzed preforms were HIPed at 1400 oC for 30 minutes in Argon atmosphere under a pressure of 50 MPa to fabricate the porous CMCs, in the second step. XRD analyses suggested the formation of β-SiC in the composites below the melting point of silicon. SEM photographs showed that spherical pores of several μm in diameter were uniformly distributed in the matrices of composites and crystals of β-SiC with facets were observed in the pores. EDS analyses showed that the crystals were composed of Si and C with 1 : 1 atomic ratio suggesting that crystal are SiC. The maximum hardness (13.78 GPa) was achieved from the composite with 90 mass % ZrO2, which is more than that of bulk hardness of ZrO2 (10-12 GPa).

Abstract: In the present work, titanium matrix composites reinforced with TiB, TiC, and Re2O3 (Nd2O3 or Y2O3) were fabricated via common casting and hot-forging technology utilizing the chemical reaction between Ti, B4C (or C), rare earth (Re) and B2O3 through homogeneously melting in a non-consumable vacuum arc remelting furnace. In this work, Nd and Y were chosen as rare earth (Re) added in the in situ reaction. The thermodynamics of in situ synthesis reactions was studied. The results of X-ray diffraction (XRD) proved that no other phases appeared except for TiB, TiC and Re2O3. The microstructures of the composites were examined by optical microscopy (OM). The results showed that there were mainly three kinds of reinforcements: TiB whiskers, TiC particles and Re2O3 particles. The reinforcements were fine and were homogeneously distributed in the matrix. The interfaces of TiB-Ti and Y2O3-Ti have been examined by high-resolution transmission electron microscopy (HREM).Transmission electron microscopy (TEM) and selected area diffraction (SAD) were used to analyze the orientation relationships of TiB-Ti, Nd2O3-Ti, and Y2O3-Ti. The mechanical properties at room temperature improved with the addition of TiB whiskers and TiC particles although some reduction in ductility was observed. The (TiB+TiC)/Ti6242 composite with TiB:TiC=1:1 shows higher tensile strength and ductility.

Abstract: In this paper, an amendment method for stress and strain of double-curved laminated composite is proposed and studied. According to finite element analysis results of the same model with two different mesh size (coarse mesh size 120mm× 300mm and refined mesh size 30mm× 30mm ), stress and strain have been amended with modified formula in user material subroutine (UMAT) subprogram so that the corrected results of model with coarse mesh is similar to the results of model with refined mesh. Using this method, with coarse mesh, a satisfied accuracy results still can be obtained without refining mesh. It’s efficient for design and analysis of complex structures.

Abstract: The tensile behaviour of nanometric SiC particulate (SiCp) reinforced aluminium matrix composites (AMCs) was examined at room temperature, 215°C and 350°C. These AMCs were produced via powder metallurgy (P/M) using Al 7075 powder reinforced with different volume fractions (1 vol.%, 3 vol.% and 5 vol.%) of nano-SiCp. The experimental results exhibit that at room temperature un-reinforced Al has both maximum strength and ductility whereas the 5 vol.% SiCp/Al composite has only maximum stiffness. Similar trends were obtained for tests performed at 215°C. However at 350°C, the 1 vol.% SiCp/Al composite has the highest stiffness. Optical microscopy and scanning electron microscopy were performed for microstructure study, examination of the SiCp distribution in the Al matrix and fractography.

Abstract: In this studies, Mg(Al)-50 vol.% SiC particle composites were fabricated by pressure infiltration with the two different matrix base materials of Mg and Mg-6Al alloy. Thermal conductivities of the two composites were compared and the effect of addition was studied using X-ray diffraction and scanning electron microscopy (SEM). The analysis of the X-ray diffraction shows that the Al-addition to the Mg causes a contraction of the Mg lattice parameters, which brings a better matching between the matrix and SiC particle. The microstructure and the fracture surface of the composite were characterized by using SEM. The alloying element Al exists mainly in the form of α solid solution, which has a uniform distribution in matrix. From calculation, the interfacial thermal barrier resistance of the Mg-6Al/SiCp composite is about one order of magnitude lower than that of the Mg/SiCp composite.

Abstract: When mixtures of Fe, Al, Ti and B powders were heated, the combustion synthesis, or SHS, reaction occurred and produced a TiB2 particle dispersed FeAl-based composite. The TiB2 particle size increased with increasing TiB2 volume fraction from 0.3 to 0.8, which was considered to be due to the fact that the adiabatic temperature of the reaction increases with the increase in TiB2 concentration in the composite due to the large formation enthalpy of TiB2. The TiB2 particle size decreased with increasing preheating time, temperature and pressure before the SHS reaction. It was suggested that partial reaction between elemental powders before the SHS reaction reduced the adiabatic temperature and hence the TiB2 particle size. The Vickers hardness of the composite varied from 500 to 2000 depending on the microstructure. This method was applied to the production of TiC-FeAl, TiC-Fe, TiB2-Fe composites.

Abstract: The wear behavior of CFRP laminates with nano-particles dispersed surfaces of Al2O3 or carbon has been investigated and compared with that of conventional CFRP which is without particles dispersed surfaces. As a result of comparison, it is shown that the CFRP laminate with Al2O3 nano-particles dispersed surfaces inherently had low coefficient of friction and high sliding wear resistance. The measured value of specific wear rate was 3.5x10-7mm3/Nm, independently of sliding time. The wear behavior of CFRP laminates with carbon nano-particles dispersed surfaces has been more effectively improved. The measured specific wear rate of this material was in the range of 10－ 7mm3/Nm in spite of comparatively small amount of nano-particles dispersion, which is relatively good as tribomaterial. For the successful application of this method, it is essential to explore the optimum amount of Al2O3 or carbon nano-particles to be dispersed onto prepreg surfaces. The deflocculation of the agglomerated particles and their homogeneous dispersion and good impregnation are the key points in this technology.

Abstract: The flexural/twist anisotropy, present in most balanced, symmetric laminates with angle play layers, have an important influence on elastic instability of plate composite. The maximal compression load can be reduced up to 13% in comparison with the orthotropic plate. The anisotropy changes also the deformation mode form. Based on the finite element studies, we developed an empirical law – the relation between the knockdown factor, the anisotropy factor and the plate geometry. The knockdown factor is defined as the ratio between the maximum loads of the anisotropic plate and of the orthotropic one. In this way, the semi-analytic instability calculation approach is based on analytical linear bifurcation theory with orthotropic properties and on empirical consideration of the flexural/twist anisotropy effect by the knockdown factor.