Effect of annealing temperature on as-cast Ti6Al4V-5Cu alloy microstructure, tensile properties, and fracture toughness

The effects of annealing temperature on the microstructure, tensile properties, hardness, and fracture toughness of an as-cast Ti6Al4V-5Cu alloy with a lamellar microstructure were investigated. Following annealing treatment in the range of 740-940 degrees C, the phase thicknesses in the alloy are changed. The alpha lamellar thickness was found in a range of 1.28-7 mu m and beta-phase thickness in a range of 0.35-2.3 mu m. For higher ductility and good fracture toughness, higher annealing temperatures were desirable. The alpha-lamellar thickness was an important microstructural feature influencing the fracture toughness. Lowering the thickening of alpha platelet/ lamellar structure could enhance the fracture toughness of the as-cast Ti6Al4V-5Cu alloy. At various annealing temperatures, the Ti6Al4V-5Cu alloy exhibited varying degrees of deformation resistance. The elongation percentage of the alloy increased with annealing temperature. The effect of the change in annealing temperature on the hardness (HV) of the alloy exhibited a zig-zag profile. The hardness of the alloy was not related to the phase thickness. The crack path tortuosity and nature of plastic deformation, particularly on the alpha/beta interface structure, were also important influencing factors in fracture toughness. Good plasticity and a regularly tortuous crack propagation path were both favorable for the fracture toughness of the alloy.