Assessment of the Fatigue Behavior of Ti-6Al-4V ELI Alloy with Surface Treated by Nd:YAG Laser Irradiation

Abstract

The effect of a surface treatment by Nd:YAG laser irradiation on the fatigue behavior of Ti-6Al-4V ELI was studied. Axial fatigue tests were performed to obtain S-N curves in polished and laser treated conditions. Roughness measurements and scanning electron microscopy were used to characterize the features of the modified surface. A reduction in the fatigue strength of around 35% was obtained after the laser treatment of the material surface. Although the surface roughness was in the micrometer scale, a notch effect was suggested to be the reason for the deleterious influence of the laser on the fatigue strength. The reduction in the fatigue strength obligatory demands redesign of implants for laser modified surfaces of Ti-6Al-4V alloy.

A review on the recent advances concerning the fatigue performance of titanium alloys for orthopedic applications

“…Tarr et al [37] reported in the same ASTM publication the fatigue stress value of 550 MPa as a failure criterion for a Ti-6Al-4V alloy to be employed in femoral stems. These values are nearly within the same range pointed out by Potomati et al [34] when Fig. 8 is considered.…”

“…Potomati et al [34] also reported a deleterious effect of a Nd:YAG laser irradiation (power of 22.5 W and intensity of 3.44 × 10 9 W/cm 2 ) in the fatigue behavior of the Ti-6Al-4V ELI alloy. The axial fatigue tests revealed a fatigue strength value of 840 MPa for the untreated material, against 550 MPa of the laser-treated alloy.…”

“…In this paper [34], an interesting analysis was performed when the experimental fatigue limit was confronted with the requirements of real hip stems. A large concern with hip stems was formerly reported by Ploeg et al [32] when the accuracy of fatigue test prediction methods was evaluated through an extensive research on the deformation partitioning method.…”

“…A large concern with hip stems was formerly reported by Ploeg et al [32] when the accuracy of fatigue test prediction methods was evaluated through an extensive research on the deformation partitioning method. In the case of the previous article [34], a simpler but very appropriate assessment drew the attention to the cautions that are necessary when dealing with a surface modification process that aims to increase the roughness for osseointegration improvement. The authors mentioned that principal stresses above 500 MPa were typically reported in the literature at critical points of such hip stems.…”

A review on the recent advances concerning the fatigue performance of titanium alloys for orthopedic applications

“…Therefore, the fatigue decrease was rigorously due to the notch effect. Potomati et al [34] also reported a deleterious effect of a Nd:YAG laser irradiation (power of 22.5 W and intensity of 3.44 × 10 9 W/cm 2 ) in the fatigue behavior of the Ti-6Al-4V ELI alloy. The axial fatigue tests revealed a fatigue strength value of 840 MPa for the untreated material, against 550 MPa of the laser-treated alloy.…”