From single phase to dual-phase TRIP-TWIP alloys: design approach and properties

International audienceAiming at increasing the yield strength of transformation and twinning induced plasticity (TRIP and TWIP) titanium alloys while maintaining a good work-hardening, a dual-phase α/β alloy is designed and studied. The composition Ti-7 Cr-1.5 Sn (wt.%) is proposed, based on an approach coupling Calphad calculations and classical Bo-Md design tool used in Ti-alloys. Its microstructure is made of 20% of α precipitates in a β matrix, the matrix having optimal Bo and Md parameters for deformation twinning and martensitic transformation. The alloy indeed displays a yield strength of 760 MPa, about 200 MPa above that of a Ti-8.5Cr-1.5Sn (wt.%) single β phase TRIP/TWIP alloy, combined with good work-hardening and ductility. In situ synchrotron X ray diffraction and post-mortem electron back-scattered analyses are performed to characterize the deformation mechanisms. They 2 evidence that the TRIP and TWIP mechanisms are successfully obtained in the material, validating the design strategy. The interaction of the precipitates with the {332} β twins is analyzed, evidencing that the precipitates are sheared when hit by a twin, and therefore do not hinder the propagation of the twins. The nature of the interaction is discussed, as well as the impact of the precipitates on the mechanical properties