Microstructural and micro-mechanical analysis of 14YWT nanostructured Ferritic alloy after varying thermo-mechanical processing paths into tubing

Microstructural analyses and micro-pillar compression were conducted on 14YWT nanostructured ferritic alloy (NFA) to compare different processing pathways: hydrostatic extrusion and Pilger processing with varying annealing temperatures into thin walled tubing, and after hot extrusion and cross-rolling into a plate. Hydrostatic extrusion at 815 degrees C resulted in the smallest grain sizes and highest yield strength of 1.20 GPa. Pilger processing with annealing at 800 degrees C had fine grained regions and bands of coarse grains, leading to a large variation in yield strength of 0.9-1.40 GPa. Higher annealing temperatures of 1200 degrees C after pilger processing significantly increased the grain size and lowered the yield strength to 1.01 GPa. These tubes showed a stronger < 111 > crystallographic texture in the normal direction and elongated grains in the extrusion direction. Characterization of the nano-oxides using TEM reveals more numerous, smaller oxides present in tubing processed at lower temperatures. This work shows NFA tubing after hydrostatic extrusion and pilger processing can lead to fine grained microstructures and texturing leading to higher yield strengths at lower annealing temperatures (e.g. 800 degrees C).

Automated summary

Microstructural analyses and micro-pillar compression were conducted on 14YWT nanostructured ferritic alloy (NFA) to compare different processing pathways. Hydrostatic extrusion at 815 degrees C resulted in the smallest grain sizes and highest yield strength, while higher annealing temperatures of 1200 degrees C after pilger processing significantly increased the grain size and lowered the yield strength. Additionally, characterization of the nano-oxides using TEM revealed more numerous, smaller oxides present in tubing processed at lower temperatures.