Understanding the High-Temperature Fatigue Crack Growth from Exceptional Nano-α Phases and {10$$ \bar{1} $$2} Deformation Twins in Hot Deformed Titanium Alloy

Abstract

Abstract In this study, the fatigue crack growth rate (FCGR) of Ti-6Al-4V alloy at 723 K was measured by direct current potential drop (DCPD) method, and exceptional nano-α phases and {10$$ \bar{1} $$ 1 ¯ 2} deformation twins were newly found at the crack tip in Ti-6Al-4V alloy. The results showed that nano-α phases have Burgers orientation relationships (OR) (0001)α//(110)β, [$$ \bar{2} $$ 2 ¯ 110]α//[$$ \bar{1} $$ 1 ¯ 11]β with β phases. The terraced-structure interface consisted of (0$$ \bar{1} $$ 1 ¯ 10)α//(1$$ \bar{1} $$ 1 ¯ 2)β and (10$$ \bar{1} $$ 1 ¯ 0)α//(1$$ \bar{1} $$ 1 ¯ 0)β. Numerous dislocations accumulated in the β phase and became the diffused channels of O and V atoms. The α stabilizers (O element) diffused into the crystal lattice and β stabilizers (V element) spread out of the crystal lattice which accelerated the nano-α phases nucleation. <a> and <c + a> dislocations piled up at the primary α grain, interface and low angle grain boundaries (LAGBs), and dissociated into twinning dislocations to promote the twin nucleation. Dislocation transformation enabled nano-twins to grow through the primary α/β interface and strain transfer led that deformation twins nucleated in the adjacent primary α grains. With the effects of nano-α phases, LAGBs and twins, the resistance of crack propagation increased and the driving force decreased, and resulted in the low FCGR. Graphic Abstract