| Conventionally cast equiaxed, directionally cast columnar and perpendicular to the solidified direction of columnar(transverse) Rene 80 specimens were creep rupture tested at 760° 657㎫, 871℃ 353㎫ and 982℃ 157㎫. Due to the difference of the arrays of grain boundaries among the specimens, different creep crack initiation and propagation mechanisms operated. The columnar specimens showed good creep rupture properties. To investigate effect of section size on the creep rupture properties of Rene 80, the equiaxed, columnar and transverse specimens having two different section sizes were creep rupture tested at the same conditions as the above. The transverse and columnar specimens have evident section size effects but the equiaxed specimens were different. This may be explained as follows : if the cracks initiated, the relative section size effect of the specimen will reduce. So the initiated cracks increase the applied stress under constant toad conditions. But due to the irregular arrays of grain boundaries and coarse grains, the section size effect was not clear in the equiaxed specimens. |
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