Toughness and microstructural factors of Ti6Al4V alloy

The instrumented Charpy impact test, the dynamic fracture toughness test and the static fracture toughness test using the DC electrical potential method were carried out on Ti6Al4V alloys. Ti6Al4V alloys with various microstructures were used to investigate the relation between microstructural factors, including fractographic measurements, and various toughness criteria, i.e. Charpy absorbed energies (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 (EPM), by DC electrical potential method or K_Q); static fracture propagation resistance curve (J_R curve); and static tearing modulus T_mat.

The toughness of the Ti6Al4V alloy as evaluated by the Charpy test was different from that given by the dynamic toughness test mainly because the microstructural unit which controlled the fracture was different in the different tests. The toughness evaluated by means of the J_R curve or T_mat does not always coincide with that given by J_Ic (EPM). Therefore it is necessary to use an appropriate toughness criterion that corresponds to the method of design. It was found that the microstructure had a greater influence on T_mat than on J_Ic (EPM). In addition, the relationships between microstructural factors (i.e. the areal fraction of the primary α phase, the mean free path in the primary α, the depth of dimples, the prior β grain size) and the various toughness criteria mentioned above must be clearly defined.