Abstract
Hot compression tests were performed on cylinders of alpha zirconium at a temperature of 625°C and a strain rate of 10-3S-1. In the first series of tests, the specimens had polished ends and were tested without lubrication. Additional tests were carried out with glass lubricant applied to the specimen ends. In further tests the specimens had grooved ends and these were tested both with and without lubricant. The results indicated that the presence of both grooves and lubricant reduced the slope of the initial loading line, but had only a slight effect on the level of the high-temperature yield stress. Three different grain structures (equiaxed, coarse Widmanstätten, andftne Widmanstätten) resulted from the prior thermomechanical processing. The effect of these three initial microstructures on the subsequent high-temperature flow behaviour was determined. The flow stress of the fine Widmanstätten structure rose to apeak of ∼100MN/m2, which was about 40% greater than the steady-state flow stress for this and the other initial microstructures. Only a slight peak inflow stress was observed for the coarse Widmanstätten structure while the flow stress of the equiaxed alpha rose gradually to the steady-state level of ∼73MN/m2. All specimens were quenched immediately after removal of the load in order to preserve the dislocation substructure. Observations of the substructural changes occurring during de formation were made by post-test optical examination and thin-foil electron microscopy.
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