Abstract
In order to obtain the optimum conditions for micro-hardness measurements of sintered UO2, two kinds of hardness tests (Vickers and Knoop) were examined with non-irradiated UO2 of 2.5 and 5μm in grain size. The hardness values were obtained as a function of the applied load in the load range of 25-1, 000g.
In the Vickers test, cracks were generated around the periphery of an indentation even at lower load of 50g, which means the Vickers hardness is not suitable for UO2 specimens.
In the Knoop test, three stages of load dependence were observed for sintered pellet as well as for a single crystal by Bates. Load dependence of Knoop hardness and crack formation were discussed. In the range of applied load around 70-100g there were plateau region where hardness values were nearly unchanged and did not contain any cracks in the indentation. The plateau region represents a hardness of a specimen. From a comparison between the hardness values of 2.5μm and those of 5μm UO2, it was approved that the degree of sintering controls the hardness in the plateau region.
