Effect of electrolyte concentration on the surface characteristics of anodized and hydrothermally-treated TI-6Al-7Nb alloy

Jang, Tae Yeob; Song, Kwang Yeob; Bae, Tae Sung

Abstract

STATEMENT OF PROBLEM: Ti-6Al-7Nb alloy is used instead of Ti-6Al-4V alloy that was known to have toxicity. PURPOSE: This study was performed to investigate the effect of electrolyte concentration on the surface characteristics of anodized and hydrothermally-treated Ti-6Al-7Nb alloy. MATERIALS AND METHODS: Discs of Ti-6Al-7Nb alloy of 20 mm in diameter and 2 mm in thickness were polished sequentially from 300 to 1,000 SiC paper, ultrasonically washed with acetone and distilled water for 5 min, and dried in an oven at 50 degrees C for 24 hours. Anodizing was performed at current density 30 mA/cm2 up to 300 V in electrolyte solutions containing beta-glycerophosphate disodium salt hydrate (beta-GP) and calcium acetate (CA). Hydrothermal treatment was conducted by high pressure steam at 300 degrees C for 2 hours using a autoclave. All samples were soaked in the Hanks' solution with pH 7.4 at 36.5 degrees C for 30 days. RESULTS AND CONCLUSION: The results obtained were summarized as follows; 1. After hydrothermal treatment, the precipitated HA crystals showed the dense fine needle shape. However, with increasing the concentration of electrolyte they showed the shape of thick and short rod. 2. When the dense fine needle shape crystals was appeared after hydrothermal treatment, the precipitation of HA crystals in Hanks' solution was highly accelerated. 3. The crystal structures of TiO2 in anodic oxide film were composed of strong anatase peak and weak rutile peak as analyzed with thin-film X-ray diffractometery. 4. The Ca/P ratio of the precipitated HA layer was equivalent to that of HA crystal in Hanks' solution.