article · Materials
This laboratory study evaluated the effect of microstructure and chemical composition on passive layer growth kinetics and corrosion breakdown in three titanium-based alloys: Ti-6Al-4V, Ti-6Al-7Nb, and TC21. Testing took place in a 0.9 percent sodium chloride solution at 37 degrees Celsius, with results benchmarked against ultrapure titanium. Across all examined alloys, the microstructure featured an alpha matrix reinforced by a beta phase. The highest volume fraction of beta phase occurred in the TC21 alloy, whilst the lowest was observed in the Ti-6Al-7Nb alloy. Electrochemical assessments revealed that susceptibility to pitting corrosion increased from Ti-6Al-7Nb to Ti-6Al-4V, and was highest in TC21. Concurrently, Ti-6Al-7Nb demonstrated the lowest pitting corrosion resistance among the alloys, nearing the performance of pure titanium. Microstructural differences and surface chemistry analyses explained the notable variations in corrosion behaviour.
Titanium alloys are widely relied upon for their mechanical strength and resistance to degradation. Understanding how microscopic phase arrangements and passive surface layers influence corrosion in warm saline environments provides critical insight into material durability. This comparative baseline helps researchers and engineers evaluate how alloy composition affects resistance to uniform and localized pitting corrosion.
This work represents early-stage materials characterisation conducted under simulated laboratory conditions. While the abstract does not indicate an explicit application pathway, industry partner, or commercialisation timeline, the comparative electrochemical data could assist metallurgical developers and materials engineers when selecting or optimising titanium formulations for environments exposed to saline solutions at body temperature.
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The effect of microstructure and chemistry on the kinetics of passive layer growth and passivity breakdown of some Ti-based alloys, namely Ti-6Al-4V, Ti-6Al-7Nb and TC21 alloys, was studied. The rate of pitting corrosion was evaluated using cyclic polarization measurements. Chronoamperometry was applied to assess the passive layer growth kinetics and breakdown. Microstructure influence on the uniform corrosion rate of these alloys was also investigated employing dynamic electrochemical impedance spectroscopy (DEIS). Corrosion studies were performed in 0.9% NaCl solution at 37 °C, and the obtained results were compared with ultrapure Ti (99.99%). The different phases of the microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Chemical composition and chemistry of the corroded surfaces were studied using X-ray photoelectron spectroscopy (XPS) analysis. For all studied alloys, the microstructure consisted of α matrix, which was strengthened by β phase. The highest and the lowest values of the β phase's volume fraction were recorded for TC21 and Ti-Al-Nb alloys, respectively. The susceptibility of the investigated alloys toward pitting corrosion was enhanced following the sequence: Ti-6Al-7Nb < Ti-6Al-4V << TC21. Ti-6Al-7Nb alloy recorded the lowest pitting corrosion resistance (<i>R</i><sub>pit</sub>) among studied alloys, approaching that of pure Ti. The obvious changes in the microstructure of these alloys, together with XPS findings, were adopted to interpret the pronounced variation in the corrosion behavior of these materials.
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DOI: 10.3390/ma12081233
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