Non-acid, alcohol-based electropolishing enables high-quality electron backscatter diffraction characterization of titanium and its alloys: Application to pure Ti and Ti-6Al-4V

Abstract

This paper conceives an electropolishing sample preparation procedure aimed at characterization of titanium (Ti) and its alloys using electron backscatter diffraction (EBSD). Specifically, it is shown that a single non-acid, ethanol-ethylene glycol-NaCl electrolyte solution can be used to electropolish Ti and its alloys for obtaining high-quality EBSD datasets. As a result, the use of hazardous acids common in standard Ti metallographic preparation procedures, such as hydrofluoric, perchloric, and sulfuric acid, can be circumvented. Moreover, electropolishing Ti with an ethanol-ethylene glycol-NaCl electrolyte is performed at room temperature with low voltage, as opposed to the low temperatures and/or high voltages used when electropolishing Ti in traditional solutions. The utility of the novel procedure is demonstrated on samples of pure α-Ti before and after plastic deformation and on samples of alloy Ti-6Al-4V created by additive manufacturing (AM) in stress-relived and heat-treated conditions. EBSD scans performed on undeformed pure α-Ti had high-quality diffraction patterns, which allowed for large areas to be scanned at fast speeds without sacrificing indexing accuracy. The electropolishing created excellent surfaces on the deformed pure α-Ti sample despite elevated lattice strains and numerous deformation twins in its microstructure. It also allowed for detailed EBSD mapping of fine sub-grain features in AM Ti-6Al-4V despite the alloying additions of aluminum and vanadium, the inhomogeneous AM microstructure, and the different processing conditions. It is anticipated that the major breakthrough achieved in this work will streamline and make safer future metallographic studies of Ti and its alloys.