Atsuyuki Mitani

Microstructure and High Temperature Strength Characteristics of Unidirectionally Solidified Al2 O3 /GdAlO3 Eutectic Composite

Enploying unidirectional solidification, Al2O3/GdAlO3(Gadolinium Aluminum Perovskite:GAP) eutectic composite was fabricated. The Al2O3/GAP eutectic composite obtained has a flexural strength of over 600Mpa above 1500C. The composite also showed plastic deformation above 1550C on the flexural test. The effect of microstructure on mechanical strength at high temperature was investigated. Al2O3/GAP eutectic composites having different microstructure were fabricated by controlling the temperature gradient on unidirectional solidification. It was found that the flexural strength at high temperature of the composite became higher with refining the microstructure.

High Temperature Stability of MGC’s Gas Turbine Components in Combustion Gas Flow Environments

Melt growth composites (MGCs) have a unique microstructure, in which continuous networks of single-crystal phases interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, oxidation resistance and thermal stability in an air atmosphere at very high temperature. In order to investigate the recession behavior of MGCs in combustion gas flow environment, we have just started the exposure tests to evaluate the influence of combustion gas flow environment on MGCs. The MGCs have about 95% of the initial flexural strengths after the exposure test for 10 hours at T = 1500 °C, P = 0.1–0.3 MPa, V = 150–250 m/s, PH2O = 15–45 kPa in the combustion gas flow environment. MGCs have excellent thermal stability and water vapor resistance in comparison with conventional ceramic materials such as Si3 N4 and Al2 O3 under the high temperature combustion gas flow environment.© 2005 ASME

An Image-Based Microscale Simulation of Thermal Residual Stresses in DSE Oxide Ceramic Composite

An image-based microscale analysis was conducted by using finite element method (FEM) to simulate the thermal residual stresses in directionally solidified eutectic (DSE) oxide ceramic composites from the thermal expansion and elastic properties and the microstructure features of the constituent phases. This microscale analysis allows a real simulation of morphologies of constituent phases such as size, array and shape. Meanwhile, this model can be applied not only for the calculation of thermal residual stresses, but also for the calculation of mechanical properties. In this work, simulations focus on the distribution of thermal residual stresses in the directionally solidified eutectic (DSE) Al2O3/ Y3Al5O12 (YAG) ceramic composite. A good agreement between simulated and measured thermal residual stresses was observed.

Tensile and bending behavior of melt growth Al2O3/YAG composite at ultra high temperatures (1773-2023K)

The deformation and fracture behavior at 1773-2023K of the unidirectionally solidified eutectic Al2O3/YAG (Yttrium-Aluminum Garnet with the composition of Y3Al5O13) ceramic composite was investigated. The stress-stain curve and strength of unnotched and notched specimens, measured by bending and tensile tests, showed that (a) both unnotched and notched specimens fractured in a brittle manner at low temperatures and at high displacement speeds, but in a ductile manner at high temperatures and at low displacement speeds, and (b) the notched strength increased, reaching maximum, and decreased with increasing temperature and decreasing displacement speed. The increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum value was accounted for by the increase in plastic zone size ahead of the notch, and the decrease with further increasing temperature and decreasing displacement speed by the loss of the stress carrying capacity of the yielded ligament, based on the finite element analysis.

Strain measurement of a ductile composite Al2O3/Y3Al5O12 (YAG) by neutron diffraction

Strain measurement of an unidirectionally solidified single-crystal Al 2 O 3 / single-crystal Y 3 Al 5 O 12 (YAG) eutectic composite was performed by neutron diffraction technique using two-axis crystal diffractometer with one-dimensional position sensitive detector. Microstructure of this composite shows a formation of a compatible interface with no amorphous phase region among the two-phase grain boundaries. This fact causes excellent characteristics on high-temperature tensile and flexural strengths in the range of 350 ∼ 400 MPa from the room temperature up to 2073 K (just below its melting point of about 2100 K) with no apparent temperature dependence. The neutron diffraction measurements were carried out to measure residual strains of the two phases in the composite, together with the sintered specimens of Al 2 O 3 and YAG as the reference materials, respectively. The YAG phase strains for three crystal lattice planes were successfully evaluated from the full set of the diffraction data. But the corresponding strains for Al 2 O 3 phase were not determined because the data set of Al 2 O 3 phase was not unambiously obtained due to overlapping of the diffraction profiles from the two phases and/or no clear observation of the corresponding set of the peaks. It is shortly discussed that the overlapped profile results from the compatible interfaces with almost equal lattice spacings of the two phases. Contrary to the case of polycrystalline composites, the strains in this composite indicate a strong anisotropy because of the dual phase single crystal constituents.