Influence of processing on the microstructure and mechanical properties of 14YWT

The investigation of the mechanical alloying (MA) conditions for producing the advanced oxide dispersion strengthened (ODS) 14YWT ferritic alloy led to significant improvements in balancing the strength, ductility and fracture toughness properties while still maintaining the salient microstructural features consisting of ultra-fine grains and high concentration of Y-, Ti- and O-enriched nanoclusters. The implemented changes to the processing conditions included reducing the contamination of the powder during ball milling, applying a pre-extrusion annealing treatment on the ball milled powder and exploring different extrusion temperatures at 850 degrees C (SM170 heat), 1000 degrees C (SM185) and 1150 degrees C (SM200). The microstructural studies of the three 14YWT heats showed similarities in the dispersion of nanoclusters and sub-micron size grains, indicating the microstructure was insensitive to the different extrusion conditions. Compared to past 14YWT heats, the three new heats showed lower strength, but higher ductility levels between 25 and 800 degrees C and significantly higher fracture toughness values between 25 degrees C and 700 degrees C. The lower contamination levels of O, C and N achieved with improved ball milling conditions plus the slightly larger grain size were identified as important factors for improving the balance in mechanical properties of the three heats of 14YWT. (C) 2015 Elsevier B.V. All rights reserved.