Effects of Thermo-Mechanical Processing on the Microstructure and Mechanical Properties of β -Type Titanium Alloys

This study investigates the microstructural evolution and mechanical behavior of severe cold-rolled β-type Ti-29Nb-13Ta-4.6Zr (TNTZ) alloys under systematic solution heat treatments (ST) at 1063 K for durations ranging from 5 to 60 minutes. This comprehensive analysis provides valuable insights into the microstructural and mechanical characteristics of TNTZ alloys under varying solution heat treatment durations, offering a foundational understanding for optimizing their application in engineering contexts. Microstructural analysis reveals that both solution-treated (ST) and cold-rolled (CR) samples exhibit a predominant single body-centered cubic (BCC) β phase, while cold-rolled and solution-treated (CST-Q) samples display a combination of β and martensite orthorhombic α'' phases. ST samples demonstrate equiaxed grains with an average diameter of ~72 μm, albeit with limited clarity. In contrast, CST-Q samples treated for over 10 minutes exhibit finer equiaxed grains within the 7-14 μm range. Hardness values increase with prolonged solution heat treatment, reaching approximately ~183 HV for ST and ~234 HV for CR. Moreover, hardness continues to rise with increasing treatment duration, reaching ~204 HV for CST10Q, ~229 HV for CST30Q, and ~242 HV for CST60Q. Mechanical properties, including tensile strength, yield strength, and elongation, vary across samples. ST shows values of ~710 MPa, ~610 MPa, and ~25%, CR with ~1305 MPa, ~395 MPa, and ~17.5%, CST5Q with ~1042 MPa, ~440 MPa, and 17.5%, CST10Q with ~1010 MPa, ~650 MPa, and 21%, and CST60Q with ~930 MPa, ~660 MPa, and ~21%. Fracture surfaces of all samples exhibit dimple structures and microvoid nucleation, indicative of ductile failure.