Features of the Deformation and Failure of Molybdenum-Tungsten Alloy with High-Temperature Repeated Static Loading

The low-cycle strength and cyclic creep, structural changes and the nature of failure for molybdenum-tungsten alloy of the system Mo – 30%W – NbC – C prepared by powder metallurgy at 1770, 2020, and 2270 K are studied. At these temperatures a single dependence for the steady-state cyclic creep rate on the ratio of the equivalent stress to the material yield point at the corresponding temperature and a generalized low-cycle strength curve for the alloy are obtained. It is shown that the cyclic nature of the applied load accelerates directional plastic deformation and failure of powder metallurgy alloy by a factor from 1.5 to 7 compared with prolonged static loading with retention of similarity for the cyclic and static creep curves. At these temperatures the alloy essentially fails as a result of the occurrence of a critical polygonization stage. The structural changes found are in complete conformity with previously predicted features of this mechanism. Under nonstationary loading conditions the incubation period of the critical polygonization stage is shorter, which results in acceleration of creep compared with testing under stationary conditions.