| The creep-rupture properties of a Ni-Cr-W-Al-Ti superalloy(KM 1557) have been investigated in the temperature range of 750℃ and 1000℃. In the stress and temperature ranges studied, the inverse of the rupture life(strain rate) exhibited power law dependence on the applied stress. The stress exponents for this alloy were between 5 and 12, and the activation energy for the creep was determined to be approximately 115 ㎉/mole. Precipitate free zones formed by grain boundary migration or sliding and the accommodation of sliding by the dislocation motion, were observed from the creep-ruptured specimens. Cracks were nucleated at the grain boundary or triple point, and propagated along the grain boundary containing PFZs. The shape of grains remained unchanged for the samples tested at low temperatures of 750 and 800℃. On the contrary, highly elongated grain shape was observed along the direction of applied stress when tested at high temperatures of 850, 900, 950, and 1,000℃. |
|
