Alternative Reagent for Revealing the Entire Microstructure of Additive Manufactured Ti–6Al–4V Alloy

Abstract

The conventional Kroll and Keller’s reagents do not reveal uniformly additive manufactured Ti–6Al–4V microstructures, as etching is not uniform over the surface and only detailed electron back scattering diffraction analyses can reveal the details in the microstructures. In this research, an alternative etching solution has been proposed to reveal the microstructures of additive manufactured Ti–6Al–4V. The alternative reagent, never reported for titanium alloys, is known to be efficient for steel microstructures. It is a basic water-based solution containing NaOH and NaNO3 operational at 90 °C for a holding time of up to 30 s. Similar regions of martensitic microstructures generated in 3D-printed parts using laser powder bed fusion were etched by various reagents and compared. The alternative reagent provides optical image resolution at least one order of magnitude superior to the ones obtained with the conventional reagents. It is particularly efficient at revealing as-built martensitic microstructures and can reveal very fine features down to 0.70 µm. Such precise observation provides valuable information on microstructure evolution after heat treatments or hot isostatic pressing.