Martensite zirconium alloys: effect of chemical composition on creep characteristics

The results of an extensive investigation of creep and creep fracture characteristics of martensitic zirconium alloys are summarized and briefly discussed. It is shown that at the temperature 773 K and the applied stress 100 MPa alloying with a properly chosen combination of tin and molybdenum makes it possible to reduce the steady state creep rate of alpha zirconium by seven orders of magnitude. The fracture in creep of martensitic zirconium alloys hardly has features typical of an intercrystalline creep fracture. Most probably, the creep fracture of martensitic zirconium alloys is controlled by the same deformation mechanism as the creep itself. From the point of view of application of martensitic zirconium alloys at temperatures 720 to 770 K their considerable disadvantage consists in that that at creep rates considered for engineering practice the steady state creep rate depends on the applied stress linearly. This suggests the Nabarro-Herring creep as the rate controlling mechanism. Consequently, any further significant reduction in the creep rate and/or increase in the time till fracture requires a considerable reduction in the applied stress. (author)