The role of microstructure and stress state in dynamic mechanical behavior of Ti-5Al-5V-5Mo-3Cr alloy

By using split Hopkinson bar, scanning electron microscopy and transmission electron microscopy, we studied the mechanical performance, the damage behavior and the fracture mechanism of equiaxial, lamellar and bimodal Ti-5Al-5V-5Mo-3Cr (Ti-5553) titanium alloy during dynamic tension and dynamic compression. Dynamic flow of Ti-5553 alloy is directly related to nano-scale Alpha plates. The dynamic yielding strength of equiaxial alloy is the lowest, and kinking and stress induced martensite (SIM) inside are the main deformation mechanisms. Lamellar Ti-5553 alloy and bimodal Ti-5553 alloy could be strengthened by Alpha precipitations under impact load. Dynamic plasticity of Ti-5553 alloy is strongly influenced by its damage behaviors. Dynamic compressive damage of Ti-5553 alloy is dominated by adiabatic shearing band (ASB), while dynamic tensile damage of Ti-5553 alloy correlates with the formation of interfacial micro-voids. Owning to the strain localization of lamellar units, lamellar Ti-5553 alloy exhibits an obvious embrittlement in dynamic compression and dynamic tension. Comparing with the dynamic mechanical property of equiaxial alloy and lamellar alloy, we found that bimodal alloy processes an outstanding combination of yielding strength (σ_0.2 = 1700 MPa) and plasticity (δ = 21%) at the strain rate of 2000/s, exhibiting wide application prospects in impact-resistance structures.