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

Abstract

The fracture-behaviors of two Ti-Al-Sn-Zr-Mo-Nb-W-Si alloys with different slow-diffusing β stabilizing elements (Mo, W) were investigated through in-situ tensile testing at 650 • C via scanning electron microscopy. These alloys have two phases: the α phase with hcp-structure (a = 0.295 nm, c = 0.468 nm) and the β phase with bcc-structure (a = 0.332 nm). Three-dimensional atom probe (3DAP) results show that Mo and W mainly dissolve in the β phase, and they tend to cluster near the α/β phase boundary. Adding more slow-diffusing β stabilizing elements can improve the ultimate tensile strength and elongation of the alloy at 650 • C. During tensile deformation at 650 • C, microvoids mainly initiate at α/β interfaces. With increases in the contents of Mo and W, the β 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 α/β 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.

Effect of Molybdenum Content on Microstructure and Mechanical Properties of Ti-Mo-Fe Alloys by Powder Metallurgy

“…Thus, the pore fraction rate of the TMF 54P/M alloy was measured to be 1.4% higher because the Mo content of TMF 54P/M was increased more than that of TMF 34P/M. In addition, it is known that the low diffusivity of Mo interferes with the movement of the particle boundary and affects grain refinement [33]. Figure 5 shows the pore analysis table observed in the P/M alloys.…”

“…Thus, the pore fraction rate of the TMF 54P/M alloy was measured to be 1.4% higher because the Mo content of TMF 54P/M was increased more than that of TMF 34P/M. In addition, it is known that the low diffusivity of Mo interferes with the movement of the particle boundary and affects grain refinement [33]. According to the IPF map in Figure 6, schematized by measuring the misorientation of the TMF design alloy, the size of the prior β grain decreased from 226.55 μm to 211.99 μm when the Mo content increased from the actual TMF 34 P/M to TMF 54 P/M.…”

Effects of W Addition on Microstructure and 650 °C Mechanical Properties of Ti-Al-Sn-Zr-Mo-Nb-W-Si Alloy

“…The service temperature of the existing common high-temperature titanium alloy is only 600 ℃. In order to ensure the high-temperature performance, the aluminum equivalent ([Al]eq) of the common high-temperature titanium alloy design has reached the limit [5], such as IMI834 [6], Ti-1100 [7], Ti60 [8], Ti600 [9]. Therefore, it is meaningless to continue increasing the content of α stabilizing element and the neutral element in the design of titanium alloy used at higher temperature, and the content of β stabilizing element should be adjusted.…”