DISLOCATION-STRUCTURE AND FATIGUE-CRACK GROWTH IN TITANIUM-ALLOY VT5-1CT AT TEMPERATURES OF 293-11-K

Transmission electron microscopy measurements of dislocation structure adjacent to the fatigue crack tip in a single-phase titanium alloy VT5-1ct are carried out at 293, 93 and 11 K in high vacuum and at 293 K in air. The rate of crack growth is estimated. It is found that adjacent to the crack tip (r congruent-to 0.15 mm) an equiaxial subgrain dislocation structure with a preferred subgrain size of 0.5-2.0 mum is formed, the size being independent of DELTAK, environment and temperature. As the tip-structure separation increases and becomes equal to about 0.5 mm, a typical structure consists of extended subgrains, and then, with a further increase in the separation, one can observe a substructure with a higher dislocation density. The crack growth rate rises for all DELTAK values as the temperature is reduced from 293 to 11 K; the rate increase is not, however, a result of the changes in the substructure.