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 γ or near lamellar structure depending on the HIPping or heat treatment temperature. For the near γ 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 Bf to B27. The tensile strengths of both near γ and near lamellar samples were about 600 MPa, but the near lamellar microstructure gave rise to above 0.5% ductility while the near γ microstructure always had zero ductility. The factors affecting the evolution of microstructures and tensile properties are discussed.

► As-HIPped microstructure of Ti4522XD powders depended on HIPping temperature.
► Near lamellar microstructure had the best tensile properties.
► Starting powder size had no significant influence on tensile properties.
► Post-HIP ageing had no significant influence on tensile properties.
► The evolution of borides during HIPping or heat treatment was investigated.