Microstructural characterization of additively manufactured Ti-6Al-4V with the addition of β-stabilizer, niobium

Abstract

This study investigated the influence of beta stabilizer niobium on the microstructure and hardness of Ti-6Al-4V. The relationship between increased the concentration of alloying elements into Ti-6Al-4V is generally associated with an increase in hardness due to solid solution strengthening. The research involved the fabrication of a series of laser engineering net shaping (LENS™) Ti-6Al-4V alloys with varying concentrations of niobium (13%, 20%, and 28%) to determine whether increasing the Nb content has an influence on the concentration of Nb dissolved into Ti-6Al-4V. The microstructures of these alloys were analysed the hardness examined. the results revealed that the solid solution strengthening did not lead to a proportional increase in hardness as expected. Further microstructural examination showed that the alloy with 13% Nb exhibited a distinct microstructure with a higher concentration of un-melted Nb particles, whereas the alloy with 28% Nb had a higher dissolution of Nb into the Ti-6Al-4V. The least percentage of Nb dissolved into the Ti-6Al-4V compared to the addition of 28% Nb. Increased Nb content resulted in a higher percentage of Nb dissolved in Ti-6Al-4V but the lower hardness value. The undissolved Nb did not contribute solid solution strengthening but rather the presence of defects, and features of microstructure are responsible for hindering the ease of plastic deformation.