Processing and characterization of a W–2Y material for fusion power reactors

A W-2Y material has been produced by powder metallurgy techniques including mechanical alloying of W and Y elemental powders in an argon atmosphere, followed by hot isostatic pressing of the milled powder at 1320 degrees C under a pressure of 200 MPa for 2 h. It was found that the mechanical alloying time should not exceed 40 h in order to achieve a homogeneous distribution of small powder particles and to limit air contamination and carbon/WC contamination by the jar and ball materials. The density of the ingots was found to be about 97% the theoretical one. It was observed that the microstructure of the compacted material is composed of grains having a bimodal size distribution, with mean sizes around 50 and 150 nm. In addition, the material contains an inhomogeneous distribution of oxide particles with a mean size ranging from 2 to 20 nm. In situ TEM chemical analyses revealed that the entire content of yttrium reacted with oxygen to form nanometric oxides whose composition corresponds to Y2O3. Charpy impact tests revealed that the material is brittle at the high temperature of about 1000 degrees C. Tensile tests confirmed that the material is brittle at 1000 degrees C but ductile at 1300 degrees C, indicating that the ductile-to-brittle transition temperature should lie between 1100 and 1200 degrees C. (C) 2011 EURATOM associated institution EPFL CRPP. Published by Elsevier B.V. All rights reserved.