Multiaxial Fatigue Behavior of Near Alpha Titanium Alloy for Aeroengine Applications

Abstract

Titanium alloys are considered as an attractive material for aerospace applications owing to their unique characteristics such as high specific strength, good ductility, and better corrosion resistance. IMI 834 alloy is a near α Ti alloy that is used in the compressor discs and blades of turbine engines. These components rotate at very high rotational speed and often experience the combined effect of axial and centrifugal stress. It has been noticed that the failure of these components occurs due to the cyclic load during its normal operation. Hence, the aim of the present study is to evaluate the tensile and multiaxial fatigue behavior of IMI 834 alloy at room temperature. Tensile tests are performed at a strain rate of 6.67 × 10^–4 s⁻¹. Fully reversed pure axial, pure torsion, and combined axial-torsion fatigue experiments are conducted on the tubular specimen in in-phase load conditions at a frequency of 0.3 Hz. Hysteresis loops are determined for all the fatigue tests at half of the fatigue life. Cyclic stress response curves are generated and noted that the alloy tends to show neither cyclic hardening nor cyclic softening during the pure axial fatigue. On the other hand, it shows cyclic softening for the case of pure torsion and combined axial-torsion fatigue. Subsequently, the fatigue life is correlated to Von-Mises equivalent stress and strain under various load combinations. The alloy exhibits the lowest fatigue life under combined axial-torsion load and the highest life under pure torsion fatigue. It is noteworthy to observe that the effect of axial fatigue is more dominant under the combined axial-torsion fatigue. Pure torsion fatigue specimens are noted to fracture at 45° whereas pure axial fatigue specimens fracture at 90° to the specimen axis.