Abstract
A polycrystalline alpha-beta TiAl6V4 alloy in the annealed condition was used for the three-point bending fatigue test at frequencyf∼100 Hz. The static preloadFstat. = −15 kN and variable dynamic forceFdyn. = −7 kN to −13.5 kN were set as fatigue test loading parameters. The fatigue life S-N curve presented the stress amplitudeσaas a function of a number of cycles to fractureNf. A limiting number of cycles to run out of 2.0 × 107cycles were chosen for the 3-point fatigue tests of rectangular specimens. In addition, the Smith diagram was used to predict the fatigue life. The alpha lamellae width has a significant influence on fatigue life. It is assumed that the increasing width of alpha lamellae decreases fatigue life. A comparison of fatigue results with given alpha lamellae width in our material to the results of other researchers was performed. The SEM fractography was performed with an accent to reveal the initiation sites of crack at low and high load stresses and mechanism of crack propagation for the fatigue part of fracture.
Highlights
Introduction eTiAl6V4 alloy has a relatively high resistance in cyclic loading [1,2,3,4]
The course of fatigue damage, depends on the content of the additive elements, microstructure, surface treatment, and size and type of applied stresses. e fatigue strength value for smooth samples is more than 50% of the tensile strength, but it is largely dependent on surface quality. e greater the roughness of the surface, or the surface saturated with oxygen or nitrogen, the worse the fatigue properties of titanium. e presence of a notch causes a fatigue reduction of 30–35%. e fatigue range for titanium alloys is reached at 106-107 cycles, but it is dependent on the load frequency [5]
Gao et al [6] and Moussaoui et al [7] have performed an intensive study about influence α grain size, degree of age hardening, and oxygen content on fatigue life of TiAl6V4. ey show that the fatigue properties of twophase near − α and α + β alloys are strongly influenced by the morphology and arrangements of the two phases α and β (β grain size, colony size of α and β lamellae, and the width of α lamellae in lamellar microstructures)
Summary
Figure 3: ree-point bending fatigue test: (a) ZWICK/ROELL Amsler 150HFP 5100 resonance pulsator and (b) sample position on pulsator at the three-point bending fatigue test. E grain size and α lamellae length and width were measured by using NIS-elements 4.20 metallography software. E fractography analysis of specimens’ surface after the fatigue test was performed using the TESCAN VEGA LMU II scanning electron microscope with the aim to detect the. Fatigue initiation site, fatigue crack propagation, and static fracture area analysis
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