Slip transmission behavior across α/β interface and strength prediction with a modified rule of mixtures in TC21 titanium alloy

Slip transmission behavior across α/β interface has been investigated in an α/β titanium alloy, TC21 alloy (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si). Scanning electron microscopy (SEM) was used to observe slip lines morphology and transmission across the interface in samples which undergo a certain tensile strain. Details of slip traces in α and β lamellae have been observed in detail by Transmission electron microscope (TEM). Atomic Force Microscopy (AFM) technique was used to observe and measure height of a single slip step at the surface of α lamellae. Two processes of slip transmission, direct transmission and a deviation of 10° angle from α to β lamellae, are observed at α/β interface corresponding to basal slip and prismatic slip in α phase, respectively. Slip transmission is not observed across α/βtrans interface when β phase is strengthened by fine α laths. A modified rule of mixtures is developed to predict yield strength of TC21 alloy by introducing an interaction term. Based on experimental data and slip transmission behavior from α to β lamellae, interaction term is calculated by multiplication of barrier stress and a coefficient. The coefficient is closely related to slip transmission behavior. Easy slip transmission across the interface leads to high absolute value of the coefficient, which indicates that the interaction term has an apparent effect on prediction of strength. The low absolute value means that interaction term from interface has less effect on prediction of strength than the high one.