Abstract
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.
Highlights
Titanium alloys are widely used in engineering application where high strength, good fracture toughness, and resistance against fatigue fracture at ambient and elevated temperature are required to meet the safe life and damage tolerance design requirements for high-reliability conditions [1,2].The α-β phase titanium alloy TC17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) with the β-phase stable element is mainly used in the aero-engine, compressor blade discs, and large-section forgings to save the weight and increase thrust-to-weight ratio [3,4,5].The aerospace components are required to join frequently to meet the aerodynamic requirements
The use of laser beam, linear friction, friction stir, and electron beam welding is continuously increasing in the aerospace components [6,7,8,9,10,11]
The material was processed into test plates with a size of 200 mm × 40 mm × 14 mm by means of machining, and the welding process was performed by vacuum electron beam welding
Summary
The aerospace components are required to join frequently to meet the aerodynamic requirements. The welding process realizes the requirements for integration and weight reduction of metal components. The use of laser beam, linear friction, friction stir, and electron beam welding is continuously increasing in the aerospace components [6,7,8,9,10,11]. The electron beam welding is carried out in a vacuum, which completely avoids the oxidation problem of titanium alloy in the atmosphere and ensures the purity of the welding seam. The EBW offers accurate control of process parameters which ensure the welding stability and the high welding quality preferred in aerospace components
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