Materials Science Forum Vols. 631-632

Abstract: Al-5mass%Zr FGMs fabricated by centrifugal casting method (CCM) have a very interesting microstructure. Since the intermetallics compounds of Al3Zr are plate in shape, Al3Zr platelet particles are almost oriented normal to the applied centrifugal-force direction. Considering this microstructure, the mechanical properties of Al/Al3Zr FGMs would vary for the same sample depending on the particles orientation and their volume fraction in the tested position. In this study, some mechanical properties of Al/Al3Zr FGMs were investigated. Al/Al3Zr FGMs rings were produced by CCM, under applied centrifugal force of 30, 60 and 120G (units of gravity). Microstructural observation along the centrifugal force direction was carried out. The platelet Al3Zr particles were almost oriented normal to the applied centrifugal force direction. The volume-fraction of Al3Zr particles increases close to the ring surface. Moreover, this distribution range of Al3Zr particles becomes broader with decreasing the applied centrifugal force. The same distribution trends were also observed for the hardness values. The Compression tests were also performed for further investigation of the mechanical properties. Samples under G=30 showed the lowest the 0.2%proof stress while those cast under G=120 had the highest 0.2% proof stress.

Abstract: Creep behavior of SUS304 stainless steel is studied by small punch creep (SP-C) test. Series of SP-C testing for SUS304 stainless steel are carried out at 600°C. The time dependence of the central deflection is obtained by the SP-C testing at different load level and the creep deflection curves are quantitatively similar to those observed in conventional uniaxial creep testing. In this paper, an analytic approach based on Chakrebarty’s membrane-stretch model is used to interpret the SP-C test method. The relationship between specimen central deflection and equivalent strain is deduced, and the relationship between load and equivalent stress are established. The creep stress exponent of SUS304 stainless steel is determined by the theory formula and the data obtained in the SP-C testing. Comparison of the creep stress exponent of the Norton equations in SP-C testing and conventional creep testing is performed. The results show that the creep stress exponent is well consistent with conventional experimental results.

Abstract: The small punch creep (SP-C) test technique is a new method which is applied to evaluate the high temperature creep properties of materials by using miniature specimen. In the present paper, the Finite Element Method (FEM) is employed to simulate the SP-C test in order to investigate the effects of test parameters on testing results of the SP-C test. In this attempt, we perform systematic numerical simulations of SP-C tests by changing friction coefficient, specimen thickness, the diameter of punch ball and the inner diameter of lower die, and discuss the effects of the variation of test parameters on test results in detail. The resulting regression equations for assessing the effects of testing parameters on test results are obtained. It is found that the test results are influenced significantly by the specimen thickness, the diameter of punch ball and the inner diameter of lower die. However, the effects of friction coefficient on the results of the SP-C test can be neglected.

Abstract: Multi-scale simulation of ordering process from electronic, atomistic scales to microstructural scale was carried out by hybridizing Phase Field Method (PFM) and Cluster Variation Method (CVM). The hybrid model was applied to disorder-L10 ordering process in Fe-Pd system. Furthermore, computation of relaxation constants in the PFM was attempted based on Path Probability Method (PPM) which is the time evolution version of the CVM, within a linearized analysis of order-order relaxation process.

Abstract: The effect of the heat-treatment on the calcium phosphate deposited on Ti-6Al-4V substrate by an electrolytic process has been investigated. The calcium phosphate were deposited in a 0.04M Ca(H2PO4)2･H2O (MCPM) solution on Ti-6Al-4V substrate at 60 °C, 10V and 80 Torr for 1h, and calcined at different temperature for 4h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterized the deposited samples. The XRD pattern of as-deposited sample contain the phase of dicalcium phosphate (DCPD) and HAP. When calcined at 400 °C for 4 h, the DCPD phase is vanished and HAP becomes the major phase. The XRD pattern reveals that the intensity of HAP and Ca2P2O7 (CPP) decreases, but the β-TCP, CaO and rutile TiO2 also shows up.

Abstract: TZP-3Y20A/HA composites with addition of different volume fraction of hydroxyapatite (HA) were fabricated successfully using spark plasma sintering (SPS). The densification behavior and mechanical properties of composites are investigated as a function of sintering temperature and HA content respectively. The density of TZP-3Y20A composite increases steadily with temperature and a maximum value of 97.8% is obtained after sintering at 1400°C. Sintering the TZP-3Y20A/HA composites at 1400°C led to the decomposition of HA in the samples. Flexural strength, fracture toughness and Vickers hardness values increase with increasing sintering temperature, show decrease trend with increasing of HA content at the same temperature. They compared well with densities obtained at different sintering temperature. The maximum flexural strength, fracture toughness and Vickers hardness of 967.1 MPa, 5.27 MPam1/2 and 13.26 GPa were achieved for TZP-3Y20A composite respectively. Flexural strength, fracture toughness and Vickers hardness values of TZP-3Y20A/HA composite fell within the value range of dense HA and of TZP-3Y20A composite.

Abstract: Several diamond coatings were performed on -TiAl substrates by a microwave-plasma assisted CVD, which were made directly to the substrate and indirectly to the TiC, Ti5Si3, Al2O3+TiO2 and Si layers on the substrate. The direct coatings suffered from severe delamination and cracks. The deposited layers on TiC and Ti5Si3 layers partially delaminated, while those on Al2O3+TiO2 and Si layers adhered well without delamination. All the diamond films deposited were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectra showed that poly- and nano-crystalline diamond films were obtained for the coatings of -TiAl.

Abstract: A W/Cu system functionally graded material (FGM), which may be used as plasma facing component for fusion reactors, was prepared by inserting W-Cu layers with gradient composition between tungsten and copper alloy plates. W-Cu gradient layers were hot-press sintered from W-Cu powder mixtures added with zinc powder as the sintering aid, whose relative density increased with sintering temperature, reaching a value higher than 96% at 850°C. XRD and SEM measurements showed that the sintered W-Cu gradient layers were the mechanical mixtures of W and Cu. A wholly dense W/Cu system FGM was then obtained at 850°C by hot-press, whose composition and structure changed gradually. The finite element method (FEM) calculation showed that the residual stresses in the W/Cu FGM were effectively reduced as compared with the directly-bonded W/Cu joint.

Abstract: Porous calcia stabilized zirconia ceramics (CSZC) with closed pores were presurelessly sintered by adding different contents of zirconia hollow balls. CSZC FGM with porosity gradient structure was then fabricated by laminating five layers with designed contents of zirconia hollow balls. The porosity, microstructure, and bending strength of the obtained CSZC samples were characterized. The results show that the hollow balls distribute uniformly and are well bonded with the matrix, and the porous structure is mainly composed of closed pores. The porosity of the CSZC increases linearly from 5.7 % to 31.6 % when the content of zirconia hollow balls increases from 0 % to 30 %, and the bending strength decreases rapidly from 297 MPa to 30 MPa. The thermal shock behavior of the CSZC and FGM was evaluated using air-quenching technique. It is shown that the residual bending strength of the quenched samples increases after several quenching cycles, and the samples are damaged by thermal shock after eight thermal cycles because of the production of monoclinic zirconia. FGM samples with porosity gradient structure can endure above twelve thermal shock cycles and exhibits better thermal shock resistance.

Abstract: Centrifugal method is often applied as the fabrication process of Functionally Graded Materials (FGMs). This is because that this processing method can fabricate FGMs with large size, easily. However, this processing method has a serious problem, namely it is difficult to disperse particles with small size and low wet ability with matrix. Many of powders with nano or very fine particle size often have attractive attention as functional materials. Therefore the above problem of the centrifugal method should be improved. In this study, we proposed a centrifugal mixed-powder method as novel processing technique for the fabrication of FGM containing nano-particle. On first of this processing, powder mixture of functional nano-particle and matrix material is inserted into rotating mold. After that, matrix ingot is melted in crucible and then the molten matrix is poured into the rotating mold with powder mixture, and then, powder of matrix material will be melted by the heat from molten matrix poured from crucible. Finally, an FGM ring with functional nano-particles distributed on its surface can be obtained. Using this processing method, Al-based FGM containing TiO2 nano-particles on its surface could be fabricated. TiO2 particle has approximately 500nm in diameter. From microstructural observation, it was found that TiO2 particles were successfully distributed on surface of FGM ring. Also, hardness on the surface of the FGM ring was higher than that on inner part due to the dispersion hardening.