Three-dimensional particle size, shape, and internal porosity characterization: Application to five similar titanium alloy (Ti–6Al–4V) powders and comparison to two-dimensional measurements

Abstract

Two-dimensional (2D) dynamic image analysis (DIA) is often used to measure particle size and shape distributions of metal powders in terms of various size and shape parameters. In this present work, five titanium alloy (Ti–6Al–4V or Ti64) powders that were previously characterized with DIA are now characterized in three dimensions (3D) using a combination of X-ray computed tomography (XCT) and mathematical analysis, with various size and shape parameters, including porosity, measured and calculated for each particle. Measured 3D XCT-measured parameters are compared to 2D DIA-measured parameters. The 3D characterization was also used to mathematically generate 2D projection data, with particle orientation averaged over many directions, so that comparisons could be directly made to the previous DIA measurements. The 3D characterization is used to clearly see differences between the powders, including internal porosity and the percentage of single near-spherical particles (SnS) and non-spherical (NS) particles (mostly multi-particles) in each powder. In addition, the 3D data was used to generate 2D projections that were oriented along different directions, which was employed to show that the DIA instrument generated particle projections that were partially oriented along different dimensions of the particles. This partial orientation was apparent in the 2D particle shape data, not the particle size data. All these results show that current powder standards, which all five powders met, are inadequate to completely characterize powder size and shape parameters that could be important in a metal additive manufacturing process.