Metal-ceramic interfaces in internally reduced (Mg,Cu)O

Conventional and high resolution TEM observations of the precipitation scale obtained after internal reduction of (Mg,Cu)O single crystals have revealed special orientation relationships between the metal copper and the ceramic matrix MgO. The intermediate valence state of copper induces a mechanism in two steps for this internal reduction. In the first one, cuprite Cu₂O forms in one of the four orientations (T, TA, D, DA); in the second step, while the reaction front penetrates further into the matrix, cuprite particles are reduced to metallic copper. The orientation of the particles within the matrix can either be maintained or evolved into a twinned orientation.     

Effects of Cu,Bi, and In on microstructure and tensile properties of Sn-Ag-X(Cu,Bi, In) solders

Effects of minor additions of Cu, Bi, and In on microstructure, melting temperature, and tensile properties of Sn-Ag-based lead-free solders were investigated. It was found that the intermetallic compounds (IMCs) Ag₂In and Cu₆Sn₅ are formed in In- and Cu-containing solders, respectively. At low concentration, Bi dissolved in the Sn matrix and tended to precipitate pure Bi particles at the solubility limit of 4 wt pct Bi. The formation of large Ag₃Sn precipitates from the solder matrix was suppressed when alloying bismuth into the Sn-Ag alloy. The Bi addition resulted in a significant linear increase of the ultimate tensile strength (UTS) of solders, which is attributed to a solid-solution hardening mechanism. Solder strengthening due to In and Cu is less pronounced and attributed to a dispersion strengthening mechanism. The additions of Cu, Bi, and In all depressed the melting temperatures of Sn-Ag-based solders; however, In is the most effective one.