Investigations On Dynamic Fracture Properties Of A New Type Zirconium-Titanium Alloy

The dynamic fracture properties of a new type Zirconium-Titanium alloy were studies by the SHTB dynamic tensile experiment and the dynamic fracture toughness experiment.Dynamic tension tests are conducted by SHTB technique to study the tensile fracture behavior of Zirconium-Titanium alloy. The dynamic mechanical properties of Zirconium-Titanium alloy at room temperature are investigated under high strain rates ranging from1000to4150s-1in this study. The results show that the dynamic yield, tensile strength and fracture elongation of this alloy is570MPa,754MPa, and10.3%, respectively. Its average dynamic destruction energy density is56.3J/mm3in terms of the energy analysis. The mechanical behavior of Zirconium-Titanium alloy shows dependence on strain rate, the strengths (including σ0.2and σb), unstable strains, elongation and strain energy density increased with strain rates increasing. SEM fractographic observations shows that there exists strain rate dependence of fracture mode for Zirconium-Titanium alloy. The fracture modes change from quasi-cleavage fracture to ductile fracture with increasing strain rates. The fracture mechanism of Zirconium-Titanium alloy is controled by voids coalesce fracture. SEM observations show that a lamellae grain size decreases with increasing strain rates during the dynamic tensile process, which plays the most important role for improving the mechanical properties. SEM observations show that a grain gradually orientates along the parallel to the tensile direction with increasing strain rates. TEM analysis are performed to investigate the deformation mechanism of Zirconium-Titanium alloy under room temperature and different strain rates. The results show that dislocation density and dislocation slip increase with increasing strain rates, the ability of form the subgrain can be enhanced. However, mechanical twins decrease with increasing strain rates. In the lower strain rate range, the entire deformation process is dominated by dislocation motion mechanism and mechanical twinning. In the higher strain rate range, the entire deformation process is dominated by dislocation motion mechanism.With a notched semicircular bend (SCB) specimen dynamically loaded by a modified split Hopkinson pressure bar (SHPB) apparatus, mode-I dynamic fracture parameters of the Zirconium-Titanium alloy were measured, including the fracture initiation toughness, fracture energy, and fracture propagation toughness. The dynamic fracture behavior and its loading rate effects of the alloy under high-speed impact are investigated. The results show that its the dynamic fracture initiation toughness, fracture propagation toughness and fracture energy were89.1MPa·m1/2,86.3MPa·m1/2, and6.54x104MPa-m, respectively. Both the initiation and propagation toughness of alloy decrease with increasing loading rates. The initiation toughness is larger than the propagation toughness. Within the loading rate range, Zirconium-Titanium alloy is ductile fracture, and there are a lot of dimples in the fracture surface, the fracture mechanism of Zirconium-Titanium alloy is controled by voids coalesce fracture. During the crack propagation, there exists two propagation ways:internal necking and shear expansion. Compared with the latter, the former enlarged the crack propagation path, the fracture process consumes more energy, the fracture toughness is higher than the latter.The comparison of the energy rate shows that the dynamic fracture performance of Zirconium-Titanium alloy in the dynamic tensile failure and the dynamic fracture toughness are equivalent in our experiments.