Effects of Laser Marking on Fatigue Strength of Titanium Alloys

Abstract

Abstract Laser marking is a requirement for all medical implants in the biomedical industry. The purpose is to provide permanent identification of the details of an implant, such as the part number, size, lot number, etc., in the form of laser engraving. The intent of this practice is mainly to provide the information needed to correctly identify an implant when removed from its package and before its use and, secondly, to provide the necessary information when an implant is surgically removed from a patient’s body to analyze the cause of removal. However, laser marking can affect the fatigue performance of an implant and create a heat-affected zone, though other factors, such as the positioning of the marking along with the laser marking parameters, can also play a significant role. The improper choice of laser marking parameters can induce high residual stresses on the implant. High tensile residual stresses can result in fracture at the marking region, and hence, compressive or low tensile residual stresses are desired. Therefore, the objective of this study was to evaluate the effect of various laser marking parameters on the residual stresses and fatigue strength of titanium alloy. Laser marking parameters, such as power and pulse speed, were varied and residual stresses were calculated using the X-ray diffraction technique. Heat-affected zones were imaged using a digital microscope. Finally, four-point bend tests were conducted to evaluate the fatigue strength for samples with different laser parameters. The results from the testing demonstrated that laser parameters can have a significant impact on the tensile or compressive residual stresses. Laser-marked samples also showed a reduction in fatigue strength as compared to non–laser-marked samples.