Process-property correlations for spherical composite Al·Ti powders prepared by emulsion-assisted milling

Spherical composite powders desired in many applications can be produced using emulsion-assisted milling. This study is focused on finding correlations between the milling process parameters and characteristics of the produced spherical powders. A composite Al·Ti powder served as the test material system. Spherical powders were prepared using a planetary mill and using an emulsion formed by hexane and acetonitrile as continuous and droplet phases, respectively. Milling conditions including the ratio of immiscible liquids (LR), ball to powder mass ratio (BPR), rotation rate (RPM) and milling time were varied. Optical microscopy images of the powders produced served to recover descriptors of the product particle shapes and sizes. Analysis of the generated image-based data enabled classification of the produced powders, separating spherical and nonspherical particles. This made it possible to recover characteristics of spherical particles, which were correlated with the milling conditions. The quality of the produced spherical powders was assessed using a parameter, Q, maximized when a large fraction of spherical particles with the narrowest size distribution was produced. A correlation was found between Q and a compounded milling process parameter taken as product of grouped parameters: X=BPR∙RPM∙time, Y=BPR∙RPM∙LR, and Z=RPM/BPR, each raised in a separate power, x, y, and z, respectively. The correlation formed a maximum around the conditions leading to formation of the spherical powders with the best quality (highest Q). For the same milling conditions, for which the highest quality spheres were formed, the refinement of the material was maximized, based on the smallest crystallite sizes for both Al and Ti.