Deformation twinning in Ti48.9Zr32.0Nb12.6Ta6.5 medium entropy alloy

The {112}_β deformation twinning has never been confirmed in refractory high or medium entropy alloys (HEAs or MEAs) at room temperature. Here a Ti_48.9Zr_32.0Nb_12.6Ta_6.5 MEA shows {112}_β twins was designed based on the d-electron alloy design method learned from β Ti alloys. The solution-treated (ST) samples show equiaxed grains, single β phase, homogenous chemical composition and good tensile properties. Transmission electron microscopy (TEM) investigation shows that the ST samples is free of athermal ω phase. Following TEM results revealed abundant dislocations and their structures such as jogs, loops, cross-slips and slip bands in the deformed samples. The {112}_β twins were observed in the fractured samples, with interfacial ω phase on the twin boundary. Elemental segregation has not been detected in the twinned region by scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) mapping. The interaction between dislocations and twins was revealed by low-angle annular dark field (LAADF), thus twins in addition to the dislocation jogs, loops, cross-slips and slip bands, contribute to the work hardening in the present MEA. Deformation twinning in HEAs and MEAs has been discussed and twins can be expected in these alloys when the effects of their constituent elements were carefully considered. In particular, the present strategy of starting from β Ti alloys can be applied to design refractory HEAs and MEAs with desirable deformation microstructures.