Toughness and Microstructural Factor of Ti-6Al-4V Alloy

Abstract

Instrumented Charpy impact test, dynamic fracture toughness test and static fracture toughness test by DC electrical potential method were carried out on Ti-6Al-4V alloys with various microstructures to investigate the effect of microstructural factors including fractographic measurements on various toughness criteria, i.e., Charpy absorbed energy (E_t: total absorbed energy, E_i: apparent crack initiation energy, E_p: apparent crack propagation energy), dynamic fracture toughness ( J_d), static fracture toughness ( J_IC or K_Q), static crack propagation resistance curve ( J_R curve), and static tearing modulus (T_mat).
Evaluated toughness of Ti-6Al-4V alloy appeared different between Charpy test and dynamic toughness test mainly because the microstructural unit which controls the fracture may be different between these tests. Evaluated toughness by J_R curve or T_mat did not necessarily coincide with that by J_IC. Thus, it is necessary to use a proper toughness criterion according to the method of design. It was found that microstructure had a more significant role in influencing the T_mat rather than J_IC. Further, the relationships between microstructural factors, i.e., areal fraction of primary α, mean free path of primary a, depth of dimples, prior β grain size, and block size, and various toughness criteria mentioned above are clearly defined.