Correlation Between Microstructure and Tensile Properties in TC18 Alloy with Lamella Structure

The microstructure evolution of TC18 titanium alloy (Ti-5Al-5Mo-5V-1Cr-1Fe) after β solid solution plus aging (β-STA) and β annealing slow cooling plus aging (BASCA) heat treatments were investigated in this paper. The effects of microstructure on tensile properties and plastic deformation behavior were studied. The results suggested that α lamellar structures are formed after both STA and BASCA heat treatment. A multi-scale lamellar structure consisting of micro- and nano-scaled α platelets is formed during BASCA treatment, whereas β-STA treatment mainly generated conventional lamellar structure. In addition, the alloy after β-STA treatment displayed high strength but limited elongation, while the alloy after BASCA treatment exhibited good strength-ductility combination. A model considering α/β phase boundary strengthening, solid solution strengthening and dislocation strengthening is applied to analyze the strength of the alloy. Finally, the plastic strain partition and deformation behavior of the lamellar structure are discussed.