Evaluation of Fatigue Properties of Bio-Ti-6Al-4V alloys in vitro Environment

摘要

Metallic materials are widely used for orthopedic implants like artificial hip joints that bear high loads throughout its life time. The material is more suitable for its purpose if the metallic material forms hydroxyapatite (HAp) on its surface that enabling living bone bond to the metal. In this study we evaluate fatigue crack propagation properties of bone-induced Ti-6Al-4V alloys in simulated body fluid (SBF). Bone-inducing function was added to Ti-6Al-4V alloys by coating HAp through the alkali-heat treatment. The result of the fatigue test in 37 deg C SBF environment is analyzed in terms of the fatigue crack extension rate (da/dN) vs. stress intensity factor (⊿K) plots. During stable crack propagation regime found in the da/dN-⊿K curve, the crack propagation rates of the HAp coated and alkali-heat treatment Ti-6Al-4V alloys specimens were higher than the same alloy without the coating. The SEM observation of fatigue fracture surface stable crack extension showed the evidence of stress corrosion cracking (SCC) that occurs under SBF environment. This evidence is observed only in the coated and the alkali-heat treatment Ti-6Al-4V alloys.