Ti-6Al-4V合金の疲労き裂発生機構の解明

抄録

The influence of microstructure on crack initiation behavior of Ti - 6Al - 4V was investigated with atomic force microscope (AFM) and electron backscattered diffraction (EBSD). Also, fatigue crack initiation point was identified by the replica method. Experimental results showed that the fatigue crack was generated by the basal plane activity of the hcp crystal structure. In addition, the fatigue crack occurred in α phase with high values of both the Schmid factor (SF) and the slip angle γ on the basal plane, because of the higher force perpendicular to the plane of the resolved shear stress, intrusion and extrusion grown earlier than other grains. With the increase of the number of cycle of fatigue test, fatigue crack occurred in the α phase of grains with very high basal SF and orientation change. Even in α phase with low force perpendicular to the plane of the resolved shear stress, with the increase of the number of cycle of fatigue test, intrusion and extrusion grew gradually in α phase of grains with very high basal SF and orientation change, which may lead to fatigue crack initiation. Therefore, when considering the crack initiation site, SF×sin γ was appropriate in low cycles and SF and GROD was appropriate in high cycles.