Effects of metallographic preparation methods on surface quality and electron backscatter diffraction analysis of a dual-phase WMoFeNi multi-principal element alloy

Multi-principal element alloys (MPEAs) are a popular and growing field of alloy study. With a higher number of constituent elements, many of the newly created alloys are compositionally complex in nature, known to contain combinations of relatively soft FCC phases, hard BCC phases, and, in some cases, even harder intermetallic phases. Microstructural study of these new materials is vital to understanding the enhanced properties they may possess, but their complexity can make this study much more challenging than for a typical single-phase alloy. The current study focused on investigating the best way(s) to prepare a complex, multi-phase MPEA for microstructural characterization, specifically with respect to electron backscatter diffraction (EBSD). Combinations of metallographic polishing with silica or alumina, as well as vibratory polishing and broad ion beam polishing, were applied to samples of a WMoFeNi alloy prior to imaging and EBSD analysis. The ability to characterize samples successfully was judged by analysis of band contrast maps and determination of zero-solution percentages at multiple image magnification levels. It was established that sequential alumina vibratory polishing followed by broad ion beam polishing was the best method for comprehensive characterization, based on quantitative analysis of phase identification rates and qualitative analysis of the EBSD maps, as well as congruence between phases with respect to surface topography. Broad ion beam polishing was shown to be an effective ‘surface perfector’, which significantly improves the surface quality of a sample following more conventional metallographic preparation steps (including vibratory polishing) and optimizes it for surface-sensitive characterization techniques such as EBSD.