Effects of β treatments on microstructures and mechanical properties of TC4-DT titanium alloy

beta Processing (deformation in beta phase field followed by heat treatment in alpha + beta phase field) and beta annealing (deformation in alpha + eta phase field followed by annealing in beta phase field) were carried out to research their influence on microstructures and mechanical properties including fracture toughness of TC4-DT titanium alloy. The tensile properties at room and high temperature as well as fracture toughness were tested for all the experiment conditions. The microstructure evolution and fracture surfaces were researched by optical microscope and scanning electronic microscope (SEM) and the microstructure features were measured by means of image analysis software. Results showed that the microstructures were lamellar in beta processing and acicular Widmanstatten in beta annealing respectively. Spheroidization of a lamellar was found in the microstructures of beta processing. SEM observation showed that the fracture mechanism changed from transcrystalline in the beta processing conditions to a mixture of intercrystalline and transcrystalline at the beta annealing conditions. The tensile strength and plasticity did not change much under the beta processing conditions. While at beta annealing conditions, the strength and plasticity varied with the temperature in a reverse trend. The biggest fracture toughness was obtained at beta annealing conditions. It was found that beta annealing was preferable to beta processing with regard to obtaining high fracture toughness and tensile properties with a little sacrifice of plasticity which does not affect its practice use. (C) 2011 Elsevier B.V. All rights reserved.