Ultra-fine bimodal (α + β) microstructure induced mechanical strength and corrosion resistance of Ti-6Al-4V alloy produced via laser powder bed fusion process

Abstract

The Ti-6Al-4V samples have been fabricated by the laser powder bed fusion (LPBF) process, in which the special emphasis is given on the optimization of laser power and scan speed to attain better mechanical strength and corrosion resistance. In the present study, the percentage elongation was recorded using extensometer and the sample recorded with higher elongation and tensile strength are subjected to corrosion resistance studies and the results are correlated with the microstructural features. The grain refinement occurs during the heat treatment process, the fine grain distribution less than 10 µm results in improved tensile strength and reasonable value of percentage elongation as per the Hall – Petch effect. The finer grain has resulted in improved corrosion resistance and tensile strength which is scarcely reported. The results reveal that as printed Ti-6Al-4V samples contain both the α and β phases in more or less equal percentages. The grain sizes of both α and β phases appear larger in as printed samples, whereas ultra-fine for heat-treated Ti-6Al-4V samples. The formation of ultra-fine grains is due to the dissolution and recrystallization of α and β phases. The corrosion studies in both NaCl and phosphate buffer electrolytes reveal that non-heat treated Ti-6Al-4V samples undergo high corrosion rates, while the heat-treated Ti-6Al-4V samples demonstrate lower corrosion rates. The electrochemical impedance results also reflect a similar trend, where the low corrosion rates were attained due to the formation and buffer layer effect induced by ultra-fine grain structures of β colonies. To highlight, this work paves a new pathway for producing the Ti-6Al-4V alloy samples with high ductility and corrosion resistance through the variations in process parameters and heat treatment conditions.