Improvement of the fretting fatigue and fretting wear of Ti6Al4V by duplex surface modification

Ion-beam-enhanced deposition (IBED) was investigated as a way to increase the fretting fatigue resistance of Ti6Al4V. Both hard CrN coatings with good toughness and soft CuNiIn coatings of low friction have been applied on the base material, and shot peening combined with coatings has also been studied in order to improve the fretting fatigue (FF) resistance. Since these IBED coatings exhibit a good bonding strength even after shot peening, they do not spall off during fretting fatigue and fretting wear tests. When the contact stress is not severe and gross slip contact conditions are operative, both CrN and CuNiIn show a better fretting fatigue resistance than that of shot-peened Ti6Al4V. As the contact stress concentration of fretting fatigue is high coatings combined with shot peening achieved high levels. The fretting fatigue lifetime is largely dependent on the sliding contact conditions such as contact geometry, sliding distance and contacting materials. Under partial slip, cracks initiate at an early stage limiting the fretting fatigue lifetime, while under gross slip, a much higher fretting fatigue limit is achieved. Compressive residual stresses are particularly important to improve the fretting fatigue lifetime, when crack propagation is predominant during the failure progress.