Thermal creep behavior in heat-treated and modified textured Zr-Excel pressure tube material

Thermal creep properties of Zr-Excel alloy (Zr-3.5 wt% Sn-0.8 wt% Nb-0.8 wt% Mo) have been investigated in this study. The limits of existing experimental data on the current material and the search for more isotropic properties in Pressure Tube (PT) material motivates the current study. Heat-treatment on Excel PT materials leads to significant microstructural changes, where a strong texture of the As-Received (ASR) PT materials has been altered to a different degree of randomness at various solution temperatures. Microstructural alteration through heat-treatments should have an influence on the thermal creep behavior of the current material. It is observed that at a relatively high creep test temperature (>300 °C), steady-state creep rate of both ASR and heat-treated materials depends on the applied stress in a power law fashion and approaches stress exponent value of ~3. However, at a relatively low test temperature, n showed a high value in all treatments. The activation energy (Q) for the creep mechanism has been found to be microstructure-dependent. The ASR material has a Q value of ~73 to ~114 kJ/mol at the applied test temperature range (150-350 °C). However, martensitic structure formation and other microscopic changes (dislocation structures and elemental segregation) caused significant increase in Q values up to ~325 kJ/mol in the heat-treated materials. A significant decrease has been observed in creep anisotropy in the WQ-895 treatment for which texture has been moderately randomized.