Internal fatigue crack initiation in drawn Ti–6Al–4V wires

Abstract

Fatigue cracks in titanium alloys are often found to initiate at faceted alpha grains. In the very high cycle fatigue regime, crack initiation tends to shift from the surface towards the interior of the material, and more initiation facets can be found on the fracture surface. In this study, fatigue tests were performed on drawn and heat-treated Ti-6Al-4V wires. Only a few samples fractured due to interior initiation. The facets at the initiation sites of these samples were not flat, but had markings on the nano-scale, and were highly inclined. A possible explanation for these aspects is the crystallographic texture of the wire, and a reflection is made on the suggested mechanisms of facet formation.

Titanium Alloy Materials with Very High Cycle Fatigue: A Review

“…In 2014, Everaerts et al [ 90 ] used SEM to explore the fatigue fracture mechanism of Ti-6Al-4V under tensile conditions. They discovered that the crack initiation tended to move from the surface toward the interior of the material in the HCF regime.…”

Effect of HIP post-processing at 850 °C/200 MPa in the fatigue behavior of Ti-6Al-4V alloy fabricated by Selective Laser Melting

“…Numerous authors have studied the necessary conditions for the formation of a facet in the α phase of the Ti-6Al-4V alloy, as a consequence of the reduced slip planes and the anisotropy of the hcp lattice [53][54][55][56]. A theory proposed by Bache [57], which is outlined in Fig.…”

“…12.b). The facet formation mechanism proposed by Everaerts [55] also involves a dislocation pile-up origin in the grain (1), but in this case it is caused by the presence of a neighbouring weak grain (2) that induces the facet formation in the grain (1) and then the crack can propagate with a ductile behaviour in the grain (2). This type of mechanism would present inclined facets with respect to the tensile axis, which is observed in the mechanism of the reference material that presents an equiaxial microstructure.…”

Environment effect on internal fatigue crack propagation studied with in-situ X-ray microtomography

“…The majority of high cycle fatigue cracks initiate from the specimen surface. However, for very low stress amplitudes, the probability to observe initiation sites in the interior of the material increases [1,11,9,55]. Such internal fatigue crack initiations could lead to important industrial problems as explained by [28,2,3] but experimental methods to study this type of crack are very limited.…”