Interplay between subsurface defects and contact stress fields in the fretting fatigue response of additively manufactured Ti-6Al-4V

Abstract

Fretting is a wear process induced by small-amplitude oscillatory motion under contact pressure, leading to severe surface damage. When combined with bulk cyclic loading, it results in fretting fatigue, which can drastically reduce the service life of components. This study investigates the fretting fatigue behaviour of additively manufactured (AM) Ti-6Al-4V specimens produced using the laser powder bed fusion (L-PBF) technique. A standard bridge-type fretting fatigue test setup was employed to assess the fatigue performance of thermo-mechanically post-processed AM samples. Special emphasis was placed on understanding the interplay between process-induced subsurface defects and the high local stresses at the contact interface. Detailed microscopy analyses of both fretting scars and fracture surfaces were carried out to characterize damage mechanisms. Finite element models were developed to gain deeper insight into the stress distribution within the contact zone. The results obtained revealed a pronounced reduction in fatigue life for AM specimens, comparable to that observed plain fatigue. Fractographic evidence confirmed the presence of a stick–slip regime, with stick occurring at the centre of the contact and slip at the edges, representing one of the most detrimental fretting conditions. Compared to conventionally manufactured counterparts, the AM samples exhibited lower resistance to fretting fatigue, primarily due to variations in local stress and slip behaviour. Additionally, internal defects introduced during the AM process, such as voids and lack-of-fusion regions, acted as critical crack initiation sites in some of the failed samples, further compromising fatigue performance.