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

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

Corrosion Fatigue-Cracking Behaviors of Low Alloy Steels in Seawater for Offshore Engineering Structures

“…According to the Eq. [6], the CFCG rate at different frequencies in seawater, can be predicted by the FCG rate at corresponding frequencies in air.…”

“…Therefore, many scholars from various countries have contributed a lot of research and discussion on the influencing factors of CFCG. [6][7][8][9] There is no doubt about the influence of mechanical factors on the CFCG rate. The amplitude of fatigue load, the magnitude of average stress, stress ratio, residual stress, loading frequency, loading waveform and other mechanical factors [10][11][12][13][14] have different effects on it.…”