Tensile deformation behavior of Ti-Nb graded alloy fabricated by direct laser deposition

Compositional gradient titanium alloys are one of the research directions for novel biomedical materials. In this work, Ti-30Nb/Ti-40Nb gradient titanium alloy was fabricated using direct laser deposition (DLD) additive manufacturing technology. The room-temperature tensile deformation behavior of this gradient structure was investigated using in-situ electron backscatter diffraction (EBSD). The as-solution-treated structure consists of β phase and α″ martensite, with the gradual increase in volume fraction of α″ martensite from the Ti-30Nb region to the Ti-40Nb region. The Nb content regulates the thermal and mechanical stability of the β phase, resulting in different deformation behavior in the Ti-30Nb region, Ti-30Nb/Ti-40Nb transition zone and Ti-40Nb region. In the Ti-30Nb region, the β phase exhibits the weakest stability, with deformation mechanism primarily driven by dislocation slip, stress-induced αʺ martensitic (SIM α″) transformation, and {011}α″ compound twinning. In the Ti-30Nb/Ti-40Nb transition zone, the β phase exhibits moderate stability, with multiple deformation mechanisms working synergistically during tensile deformation. The αʺ martensite still deforms via {011}αʺ compound twinning and dislocation slip, while the β matrix deforms via dislocation slip, SIM α″ transformation, and {332}β twinning. In the Ti-40Nb region the high stability of the β phase fundamentally suppresses the the SIM α″ transformation, making dislocation slip, shearing and limited {332}β twinning the main deformation mechanisms. Furthermore, the deformation behavior is highly dependent on the crystallographic orientation of the β grains.