Effect of swaging on Young׳s modulus of β Ti–33.6Nb–4Sn alloy

The effect of swaging on the Youngʹs modulus of β Ti–33.6Nb–4Sn rods was investigated by X-ray diffraction, thermography, microstructural observations, deformation simulator analysis and cyclic tensile deformation. Stress-induced α″ martensite was stabilized by swaging, dependent on the diameter reduction rate during swaging. Thermography and deformation simulator analysis revealed that swaged rods were adiabatically heated, and consequently, stress-induced α″ underwent reverse transformation. Youngʹs modulus, which was measured by the slope of the initial portion of the stress–strain curve, decreased from 56 GPa in the hot-forged/quenched rod to 44 GPa in the rapidly swaged rod with a high reduction rate and to 45 GPa in the gradually swaged rod with a low reduction rate. The tangent modulus, which was measured by the slope of the tangent to any point on the stress–strain curve, decreased with strain even in the linear range of the stress–strain curve of the hot-forged/quenched rod and the rapidly swaged rod, while the tangent modulus remained unchanged for the gradually swaged rod. It was found that Youngʹs moduli in swaged β Ti–33.6Nb–4Sn rods were affected by stabilized α″ martensite. Low Youngʹs modulus of 45 GPa and high strength over 800 MPa were obtained when the reverse transformation by adiabatic heating was suppressed and the stress-induced α″ was sufficiently stabilized by gradual swaging to a 75% reduction in cross section area.