|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1993 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1992 : ¥800,000 (Direct Cost : ¥800,000)
Constant creep tests in the stress range of 100 to 300 MPa were conducted at 1123 K using the full size specimens of Ti-50 at% Al heat treated at 1473 K for 6*10^5s. The stress dependence of the stress exponent of the minimum creep rate, called as n value, were investigated. The specimens crept at certain stress levels were interrupted at the time showing the minimum creep rate. The stress dependence of the dislocation substructures subjected to creep deformation were examined using the transmission electron microscopy. Following conclusions were reached.
1)The creep curves of TiAl exhibited no steady state stage. Thus, they consist of a transient stage and an accelerating creep stage. The latter occupied more than 90 pct of the rupture life.
2)The stress exponent of the minimum creep rate, n value, remains constant and equals to 3 less than 150MPa. In the stress range of 150 to 300 MPa, n value increase up to 8 with increasing the stress levels.
3)Under the stresses of less than 150 MPa, dynamically recrystalized grains can not be observed at the minimum creep rate stage. In the stress range of 150 to 300 MPa, however, dynamically recrystalized grains form along the grain boundaries.
4)linear increase of internal stress is obtained up to 150 MPa, so the ratio of the internal stress to the applied stress, sigma_i/sigma_a, remains constant value of 0.9. Under the stress of more than 150 MPa, sigma_i/sigma_a decreases with increasing the applied stress.