In-Situ SEM Observation on Fracture Behavior of Titanium Alloys with Different Slow-Diffusing β Stabilizing Elements.

The fracture-behaviors of two Ti-Al-Sn-Zr-Mo-Nb-W-Si alloys with different slow-diffusing beta stabilizing elements (Mo, W) were investigated through in-situ tensile testing at 650 degrees C via scanning electron microscopy. These alloys have two phases: the alpha phase with hcp-structure (a = 0.295 nm, c = 0.468 nm) and the beta phase with bcc-structure (a = 0.332 nm). Three-dimensional atom probe (3DAP) results show that Mo and W mainly dissolve in the beta phase, and they tend to cluster near the alpha/beta phase boundary. Adding more slow-diffusing beta stabilizing elements can improve the ultimate tensile strength and elongation of the alloy at 650 degrees C. During tensile deformation at 650 degrees C, microvoids mainly initiate at alpha/beta interfaces. With increases in the contents of Mo and W, the beta phase content increases and the average phase size decreases, which together have excellent accommodative deformation capability and will inhibit the microvoids' nucleation along the interface. In addition, the segregation of Mo and W near the alpha/beta interface can reduce the diffusion coefficient of the interface and inhibit the growth of microvoids along the interface, which are both helpful to improve the ultimate tensile strength and plasticity.