Improvement of the Corrosion Resistance and Potential for Metal Ion Release of Titanium Alloy Ti-6Al-4V ELI in Hanks Balanced Salt Solution (HBSS) after Thermomechanical

Abstract

Ti-6Al-4V ELI is one of the titanium alloys commonly used as an implant material for its good biocompatibility. However, it has problems related to its corrosion behavior, especially when it is used for a long time. This study aimed to analyze the corrosion behavior of the implant material Ti-6Al-4V ELI in Hanks’ Balanced Salt Solution (HBSS) for a certain period, using the weight loss method in HBSS as the corrosive medium at 37°C. The immersion time was varied from two, four, until six weeks. Before immersion, the sample was thermomechanically treated with a combination of solution heat treatment at a temperature of 950°C and a holding time of 1 hour, water quenching, plastic deformation with deformation variations of 10%, 15%, and 20%, and, finally, aging heat treatment at a temperature of 550°C and holding time for 1.5 hours. The study results show that thermomechanical treatment and increased plastic deformation could reduce the corrosion rate and the metal ions released into the solution. These findings were evidenced by the corrosion rates of the pre-thermomechanical and the thermomechanical Ti-6Al-4V ELI with deformations of 10%, 15%, and 20% at the 6-week immersion of 6.57 x 10-6 mmpy, 4.27 x 10-6 mmpy, 3.89 x 10-6 mmpy, and 2.76 x 10-6 mmpy, respectively, and the metal ions released of 7.3 μg/L, 7 μg/L, 6.3 μg/L, and 6 μg/L, respectively. The corrosion rate of Ti-6Al-4V ELI under thermomechanical treatment, namely 2.76 x 10-6 mmpy, was the lowest compared to other materials in HBSS, while the highest one was that of Ti-6Al-7Nb of 3.05 x10-2 mmpy. In addition, the study results show that Ti-6Al-4V ELI under thermomechanical treatment is the best material compared to others for biomedical applications, based on corrosion resistance and metal ions released into HBSS.

Compressive strength of Ti-6Al-A4 after immersion test with artificial saliva pH 8.0 and dynamic testing

“…The pH variation in the mouth cavity can affect the durability of the metal implants used. Implants can experience corrosion and porosity processes within the human body, resulting from unstable metal changes and increased degradation due to fluctuating ambient temperatures, changes in pH levels, high humidity, stress, and the role of other microorganisms [1,2,3,6 ].…”

“…Dental implants can be affected by saliva pH variations, including infectious diseases, which can lower saliva pH to acid. This can lead to corrosion and porosity in implants due to unstable metals and environmental factors [1,2,3,6]. The necessity for dynamic testing using the ISO 14801 standard puts the idea into practice by simulating the worst-case scenario of implant implantation [10].…”