Etude par compression a hautes temperatures de la deformation plastique du bioxyde d'uranium polycristallin

Abstract

We have studied the compression of stoichiometric, sintered polycrystalline UO 2 as a function of strain rate ⋗e (7 × 10 −4/min < ⋗e < 7 × 10 −2/ min) , and temperature T (600 < T < 1700° C) . The brittle-to-ductile transition temperature is about 1000°C and we have studied by fractography the characteristics of the fracture at 600 and 800°C. In the plastic deformation range, two types of behaviour have been observed, (i) At low stress ( 5 < < 10 kg/mm 2 ), the dépendance of strain rate with flow stress σ is ⋗e = ( cte/T) σ 4,5 exp -(ΔH/RT) with ΔH = 96 kcal/mol . (The deformation is probably by dislocation climb.) (ii) At high stress ( σ > 10 kg/mm 2 ), the deformation is heterogeneous and one observes a compression yield point, the magnitude of which decreases with increasing temperature. In this range, the analysis of the activation parameters has not allowed us to establish a very satisfactory correlation with any of the available deformation schemes.