As Coated Compounding of Intermetallics From Composite Powders of High and Low Melting Points by Cold Spraying

It has been well known that inlet temperature of spraying gas affects on the impact velocity of particles, in turn, on the mechanical and chemical properties of final coating. From cold spray of high-and-low melting point composite powders such as Cu-Sn, it was found that those effects can vary along with processing parameters (particle size, shape, inlet temperature and pressure). The powders with different shapes such as spherical (under 10 um) and dendritic (under 25 um) Cu powders were selected as feedstock. The Cu₆Sn₅, intermetallic compound (IMC) of Cu-Sn was formed in as-coated state at and above gas in-let temperature of 200 ºC in case of spherical Cu powders, while at least 300 ºC or higher was needed for the dendritic Cu powders. As temperature increase, another IMC, Cu₃Sn, was also formed. On-set temperature of this additional IMC was 450 ºC for both shape. Below 300 ºC, both Cu and Sn were in solid state and thermodynamic driving forces were drawn from impact energy. Therefore, the spherical but small size particles were accelerated more than large dendritic shape to yield larger stored energy to initiate IMC formation. On the contrary, above 450 ºC at which Sn powders probably were in partial or whole melt states, the particle shape and size did not produce much differences on the IMC formations.