An anisotropic mesoscale model of fatigue failure in a titanium alloy containing duplex microstructure and hard α inclusions

In this paper the effect of isothermal forging process parameters on the microstructure and the mechanical properties of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy was researched. The results of the tests indicate that, in the temperature range of 755~905 °C and the deformation degree range of 20~60 %, with the increase of deforming temperature, the volume of primary α-phases decrease, but the globularization extent of the α-phases increases and partial secondary α-phases transform into equiaxed shape. At the temperature of 860 °C, the alloy exhibits excellent strength and plasticity, as the uniform and fine duplex microstructure formed after isothermal forging. When the deformation degree increased from 20% to 60%, primary and secondary α-phases were gradually broken and the recrystallization energy was continually accumulated, which ceaselessly strengthened the properties of the alloy. With the increase of forging times, the globularization extent of decreases, leaving the chain of α-phases, which damages the strength and plasticity of the alloy.

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Influence of Welded Pores on Very Long-Life Fatigue Failure of the Electron Beam Welding Joint of TC17 Titanium Alloy

Materials ◽

10.3390/ma12111825 ◽

2019 ◽

Vol 12 (11) ◽

pp. 1825 ◽

Cited By ~ 4

Author(s):

Fulin Liu ◽

Hong Zhang ◽

Hanqing Liu ◽

Yao Chen ◽

Khan Muhammad Kashif ◽

...

Keyword(s):

Titanium Alloy ◽

Electron Beam ◽

Fatigue Life ◽

Base Metal ◽

Fatigue Failure ◽

Electron Beam Welding ◽

Welded Joint ◽

Fatigue Cracks ◽

Failure Behavior ◽

Long Life

The electron beam welding process is widely used in the connection among titanium alloy material parts of aero-engines. Its mechanical properties need to meet the requirements of long life and high reliability. In this paper, the static strength and the fatigue failure behavior of the electron beam weldments of TC17 titanium alloy were investigated experimentally under low amplitude high frequency (20 kHz), and the mechanical response and failure mechanism under different external loading conditions were analyzed. In summary, the samples were found to have anisotropic microstructure. The tensile strength of the PWHT of TC17 EBW joint was ~4.5% lower than that of the base metal. Meanwhile, compared with the base metal, the fatigue strength was reduced by 45.5% at 109 cycles of fatigue life. The fracture analysis showed that the fatigue failure of the welded joint of TC17 alloy was caused by the welded pores and the fatigue cracks initiated from the welded pores. A fine granular area (FGA) was observed around the crack initiation region. The existence of pores caused the stress intensity factor of the fine granular area (KFGA) to be inversely proportional to the fatigue life. The KFGA calculation formula was modified and the fatigue crack propagation threshold of the welded joint of TC17 alloy was calculated (3.62 MPa·m1/2). Moreover, the influences of the effective size and the relative depth of the pores on the very long fatigue life of the electron beam welded joint of TC17 titanium alloy were discussed.

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