Comparative Analysis of Fracture Mechanics Parameters for Wrought and SLM-Produced Ti-6Al-7Nb Alloy

Abstract

Featured Application: The featured application of this research lies in enabling engineers to predict service life through crack growth curves derived from Paris’ law parameters. The comparative analysis of ΔKth values and fracture toughness data for two production processes of Ti-6Al-7Nb guides the process selection for load-bearing implants. The quantified crack growth rates allow computational modeling of cycles-to-failure under stresses, critical for fatigue life assessments. The research presented in this paper is based on the need for personalized medical implants, whose serial production is impossible, so the need for production process adjustments is inevitable. Conventional production technologies usually set geometrical limitations and generate a lot of waste material, which leads to great expenses, especially when the material used for production is an expensive Ti alloy. Additive technologies offer the possibility to produce a product almost without waste material and geometrical limitations. Nevertheless, the methods developed for additive production using metal powder are not significantly used in biomedicine because there is insufficient data published regarding the properties of additively produced parts, especially from the fatigue and fracture standpoint. The aim of this research is the experimental determination of fracture mechanics properties of additively produced parts and their comparison with the properties of parts produced by conventional technologies. Drawing is the first production process in the comparison, and the second one is selective laser melting (SLM). The Ti-alloy Ti-6Al-7Nb, used for medical implants, was selected for this research. Experimental testing was performed in order to determine ΔKth fracture mechanics parameters and resistance curves according to ASTM E1820. Test specimen dimensioning and the experiments were carried out according to the respective standards. For the drawn test specimen, the value obtained was ΔKth = 3.84 MPam0.5, and the fracture toughness was Kc = 84 MPam0.5, while for SLM produced test specimens the values were ΔKth = 4.53 MPam0.5, and Kc = 21.9 MPam0.5.