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 (Et: total absorbed energy, Ei: apparent crack initiation energy, Ep: apparent crack propagation energy), dynamic fracture toughness ( Jd), static fracture toughness ( JIC or KQ), static crack propagation resistance curve ( JR curve), and static tearing modulus (Tmat).
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 JR curve or Tmat did not necessarily coincide with that by JIC. 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 Tmat rather than JIC. 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.