| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1995: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1994: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
Particle strengthening is the most effective way for improving creep strength. This study aims at providing basic knowledge of alloy design for particle strengthened (PS) materials.
1. Many of PS materials are strengthened by thermally unstable precipitates. The coarsening of the precipitates strongly affects creep properties of PS materials. Creep data of PS materials have been analyzed by the following creep equation based on non-steady-state creep concept :
epsilon=A {1-exp(-alphat)} +beta {exp(alphat)-1} epsilon : strain, t : time (1)
This equation has three parameters, A,B and alpha, that characterize creep deformation. These parameters provide useful information about microstructural degradation, creep mechanism and alloy design.
2. PS materials often have an elongated grain shape made by hot extrusion. The grain shape has a significant effect on creep strength. Creep deformation is constrained at grain boundaries due to the compatibility requirement. Grain boundary sliding releases the constraint, and consequently enhances creep deformation. This is the cause of the grain shape dependent creep strength.
3. Creep of alpha_2-Ti_3Al/gamma-TiAl lamellar intermetallics has been studied as an example of composite materials. Coarsening of colony size and increase in gamma volume fraction result in higher creep resistance. Lamellar spacing, however, has no effect on creep strength.
4. In the alloy design, we must know creep properties under a service condition of the material. The long term properties are evaluated by extrapolation from short term data, and the extrapolation introduces an error. The cause of the extrapolation error has been discussed, and it has been proposed how to eliminate the extrapolation error.
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