Tailoring corrosion resistance of laser powder bed fusion produced Ti-6Al-4V via heat treatment at 700 °C in potential biomedical applications: Microstructural evolution and electrochemical behavior

Abstract

Ti-6Al-4V alloys fabricated by laser powder bed fusion (LPBF) have emerged as promising candidates for orthopedic implants due to their high specific strength and complex geometry capability. However, the influence of post-fabrication heat treatment on their corrosion resistance remains controversial, particularly regarding the effect of cooling rates on microstructure-electrochemical property relationships. This work systematically investigated the microstructural evolution and corrosion behavior of LPBF-produced Ti-6Al-4V after heat treatment at 700 °C for 2 h followed by furnace cooling (FC700) or air cooling (AC700). Electrochemical tests in Hank’s solution at 37 °C revealed that air cooling significantly enhanced corrosion resistance: AC700 exhibited a 12.5% lower corrosion current density (0.112 μA cm −2 vs. 0.128 μA cm −2 for as-built LPBF), a 12.3% higher passive film impedance (0.91 MΩ cm 2 vs. 0.81 MΩ cm 2 ), and improved energy absorption capacity compared to the as-fabricated alloy. In contrast, furnace cooling (FC700) deteriorated corrosion performance with a 65.6% increase in corrosion rate. Electron backscatter diffraction (EBSD) analysis demonstrated that air cooling promoted the decomposition of metastable α' martensite into finer α+β lamellar structures with higher low-angle grain boundary fractions (32.1%) and substructure content, enhancing micro-galvanic effects at phase boundaries. This facilitated the formation of a thicker, defect-reduced passive film with lower donor density (1.28×10 20 cm −3 ) and higher oxygen vacancy diffusion coefficient. These findings provide critical insights into tailoring corrosion resistance through controlled cooling rates, offering a straightforward strategy for optimizing biomedical Ti-6Al-4V implants.

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