Microstructural Evolution and Performance of In-situ Ag-Ni Composite after Solidification under Electromagnetic Stirring and Deformation

The effect of electromagnetic stirring（EMS）on microstructure and performance of Ag-8 mass%Ni composite was investigated under both solidified and deformed conditions.Without EMS,the Ag matrix formed short,thick dendrites in the ingot;whereas with EMS,dendrites were long and slim.Ni phase mainly formed particles or ribbons,distributed along boundaries between dendrite arms.Cold drawing of the solidified Ag-Ni ingots,both with and without EMS,produced high strength in-situ metal-matrix composite（MMC）consisting of Ag matrix reinforced by Ni ribbons.EMS improved the ductility of the composite,consequently enhancing its drawability and strength.EMS also increased the electrical conductivity in both solidified ingots and deformed in-situ composite wires.In both cases,hardness and tensile strength remained high.A model based on a combination of the modified linear rule of mixtures and the Hall-Petch relationship was used to rationalize the tensile strength and hardness with respect to its fabrication parameters and the microstructure of Ag-Ni in-situ composite.

Mechanism of primary Si and Fe-segregation for a hypereutectic 90 wt.%Si-Ti alloy melt in directional solidification via electromagnetism

The electromagnetic directional solidification(DS)phase separation experiments of high silicon 90 wt.%Si–Ti alloy were performed under various pulling-down speeds.The results showed that Si enriched layer,Si+TiSi_(2)-rich layer and Si–Ti–Fe alloy layer appeared successively in axial direction of ingot after electromagnetic DS of 90 wt.%Si–Ti alloy melt at different pulling-down speeds.Separation of primary Si and segregation mechanism of metal impurities(Fe)during the electromagnetic DS process were controlled by pulling-down speed of ingot and electromagnetic stirring.When pulling-down speed was 5μm/s,minimum thickness of the Si enriched layer was 29.4 mm,and the highest content of primary Si in this layer was 92.46 wt.%;meanwhile,the highest removal rate of Fe as metal impurity was 92.90%.The type of inclusions in the Si enriched layer is determined by Fe content of segregated Si enriched layer.When the pulling-down speed was 5μm/s,the inclusions in the Si enriched layer were TiSi_(2).Finally,when the pulling-down speed reached greater than 5μm/s,the inclusions in the Si enriched layer evolved into TiSi_(2)+τ_(5).