INFLUENCE OF HETEROGENEOUS DEFORMATION ON MICROSTRUCTURAL CRACKING IN ALPHA-TITANIUM ALLOYS

Subsurface crack initiation in high-cycle fatigue has been detected as a transgranular cracking in alpha-titanium alloys at and below room temperature. Strain incompatibility due to heterogeneous deformation may cause the cracking and form a crystallographic facet. In the present study, both neutron diffraction and Taylor analyses under tension mode were adopted to discuss the influence of heterogeneous deformation on the cracking. The residual stress distribution was caused clearly detected and was divided into soft and hard grains. The largest residual stress exists normal to (0001). The result agrees with transgranular cracking on (0001). The lower external plastic work rate appeared at the tensile axis tilted 75 to 90 degrees from the c-axis. The {01 (1) over bar0}<11<(2)over bar>0> operation was active, while (0001)<11<(2)over bar>0> was suppressed. The grain in which the highest rate of plastic work was around tensile stress axis of <0001> was hardly relaxed, since the slip systems of {01 (1) over bar1}<11<(2)over bar>3> were in active at all. Thus the tensile stress was accumulated normal to (0001) plane, and may assist to the microstructural cracking.