Microstructural evolution during reactive spray forming of dispersion strengthened Cu alloy

Dispersion strengthened Cu alloy was fabricated by injecting Cu-B alloy powders into the spray of Cu-Ti droplets. The microstructures of over-sprayed powders and spray deposited billet were observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The over-sprayed powders were composed of not only Cu-B and Cu-Ti alloy powders but also small amounts of Cu-B alloy powders surrounded by Cu-Ti droplets. Fine dispersoids of TiB were observed in the Cu-B powders surrounded by Cu-Ti, indicating that very rapid reaction of Ti and B had occurred during the flight of the droplets. TiB dispersoids of ∼10 nm having an orientational relationship with the Cu matrix were distributed in the Cu-B alloy powder region and coarser TiB dispersoids of ∼50 nm were observed in the circumferencial Cu-Ti region. The spray deposited billet consisted of the regions showing a fine microstructure of round shape, presumably originating from the injected Cu-B alloy powders, and a relatively coarse cellular microstructure. TiB2 and TiB of ∼200 nm were observed along the grain and cell boundaries. Fine TiB dispersoids of ∼10 nm having an orientational relationship with the Cu matrix were observed in both regions. The solidification behavior, with special interest in (he formation of dispersoids, was examined based on this observation.