Microstructures and tensile properties of hot isostatic pressed Ti4522XD powders

The effect of heat treatment and of particle size on the microstructures and tensile properties of gas atomised and hot isostatically pressed (HIPped) Ti4522XD powders have been investigated. The dendritic microstructures of as-atomised powders transformed to a fine near gamma or near lamellar structure depending on the HIpping or heat treatment temperature. For the near gamma microstructure, the prior particle boundaries (PPBs) were enriched in Ti or Ti3Al. For samples which transformed to a near lamellar microstructure, smaller particle size powders produced smaller lamellar colony sizes, but also smaller lamellar volume fractions. Some of the very fine TiB borides present in the as-atomised powders grew very significantly during HIPping or heat treatment, meanwhile, their structure changed from B-f to B27. The tensile strengths of both near gamma and near lamellar samples were about 600 MPa, but the near lamellar microstructure gave rise to above 0.5% ductility while the near gamma microstructure always had zero ductility. The factors affecting the evolution of gamma microstructures and tensile properties are discussed. (C) 2011 Elsevier B.V. All rights reserved.