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Strengthening mechanisms, creep, and fatigue processes in dispersion-hardened niobium alloy. Final scientific report, 1 Feb 89-31 Jan 92
Summary
This three-year study investigated the creep and fatigue properties of pure niobium and Nb-1%Zr alloy, developing a model for primary creep transients based on subgrain boundary migration and finding that cyclic hardening and a microplastic plateau characterize fatigue behavior in niobium. The results support the use of these refractory alloys in nuclear and aerospace high-temperature applications.
The creep and fatigue properties of pure Nb and Nb-l%Zr alloy were investigated. A model was developed based on the migration of subgrain boundary that can explain the anomalous primary creep transients found in Nb-l%Zr alloy, due to coarsening of subgrain structure. TEM investigations confirmed that such subgrain coarsening occurs during primary creep of Nb-l%Zr. Baseline low cycle fatigue studies of Nb and Nb-l%Zr were completed. Cyclic hardening is observed and there is a microplastic plateau in Nb. The Nb-1%Zr is stronger in cyclic deformation than Nb, with little influence of strain rate. The deformation in the alloy at both high and low strain rates is controlled by the interaction between gliding edge dislocation and solute atoms.