Microstructural and surface characterization of Ti-6Al-4V alloys after fretting fatigue

Ti-6Al-4V alloy specimens were tested under conditions of fretting fatigue, with the contact geometry, the normal stress, as well as the cyclic stress selected such that the mixed, slip-stick regime prevails during the experi ments. Following testing, the specimens were characterized using white ligh t interference profilometry, scanning electron microscopy, microhardness, a nd electron dispersive spectroscopy (EDS). The results revealed that the su rface roughness of the dip region increases compared to the roughness of th e stick, and non-contact ones. In addition, at the higher spatial frequenci es, the power spectral density (PSD) of the slip region increases compared to the PSD of the stick and non-contact regions, thus revealing that an inc rease of the population of the smaller size asperities occurs. The microstr ucture of the material below the slip zone was found to be transformed to a finer one; and the percentage of the transformed beta phase has been decre ased substantially. This area of the transformed microstructure, has also a higher hardness compared to the hardness of the bulk structure. EDS analys is revealed a high concentration of oxygen on the specimen's surface at the slip region of the two contacting bodies. This finding indicates that elev ated temperatures are developed during fretting fatigue and enable the diff usion of oxygen from the atmosphere to the alloy. (C) 1999 Elsevier Science S.A. All rights reserved.