Aiming at overcoming the strength-ductility trade-off in structural Ti-alloys,a new family of TRIP/TWIP Ti-alloys was developed in the past decade (TWIP: twinning-induced plasticity;TRIP: transformationinduced plasticity).Herein,we study the tunable nature of deformation mechanisms with various TWIP and TRIP contributions by fine adjustment of the Zr content on ternary Ti-12Mo-xZr (x =3,6,10) alloys.The microstructure and deformation mechanisms of the Ti-Mo-Zr alloys are explored by using in-situ electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).The results show that a transition of the dominant deformation mode occurred,going from TRIP to TWIP major mechanism with increasing Zr content.In the Ti-12Mo-3Zr alloy,the stress-induced martensitic transformation (SIM) is the major deformation mode which accommodates the plastic flow.Regarding the Ti-12Mo-6Zr alloy,the combined deformation twinning (DT) and SIM modes both contribute to the overall plasticity with enhanced strain-hardening rate and subsequent large uniform ductility.Further increase of the Zr content in Ti-12Mo-10Zr alloy leads to an improved yield stress involving single DT mode as a dominant deformation mechanism throughout the plastic regime.In the present work,a set of comprehensive in-situ and ex-situ microstructural investigations clarify the evolution of deformation microstructures during tensile loading and unloading processes.