Dislocation structure and fatigue crack growth in titanium alloy VT5-1ct at temperatures of 293-11 K

Abstract Transmission electron microscopy measurements of dislocation structure adjacent to the fatigue crack tip in a singlephase titanium alloy Vt5-1 ct 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 ⋍ 0.15 mm ) an equiaxial subgrain dislocation structure with a preferred subgrain size of 0.5–2.0 μm is formed, the size being independent of ΔK , 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 ΔK 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.