Abstract
Features of the microstructure formation of Cr-Cu composites under impregnation followed by liquid phase sintering of reduced and electrolytic chromium powders at 1200?C in a vacuum of (2-4)?10-3Pa have been studied. The refractory component particle size distribution in the microstructure of samples with reduced chromium sintered for 60 min is shown to obey a normal logarithmic law; with distribution parameters being sensitive to the volume fraction of the refractory particles. The calculated values of the dihedral angle are close to the value of one of the modes in the experimental dihedral angle distribution for the microstructure of electrolytic chromium based samples (115?). The interfacial and interparticle surface energies ratio ?sl/?ss>0.5 is shown to correspond to theory for the Crs-Cul system in equilibrium, which indicates the presence of skeleton structure elements in the course of composition formation under liquid phase sintering (including the case of excess liquid phase). Experimentally determined interparticle and interfacial surface areas, solid particle contiguity and continuity are discussed in terms of concurrent diffusion-controlled particle coarsening (in Lifshitz, Slyozov and Wagner theory) and particle coalescence (in German?s model). The kinetics of shrinkage for the composites with 50...55 % solid-phase volume-fractions at heating and isothermal sintering in a vacuum at a temperature of 1200?C in terms of linearly viscous rheological theory are discussed.
Highlights
Cr-Cu composites are widely used as contact materials for medium-voltage and highcurrent interrupters
Liquid-phase sintered microstructures are characterized in terms of the solid phase volume fraction, Vp, scale, R, the surface-to-volume ratio, Sv
The specimens were produced by impregnation of freely poured chromium with copper at 1200oC in a vacuum of (2-4)⋅10-3Pa and subsequent isothermal liquid sintering for 3-90 min
Summary
Cr-Cu composites are widely used as contact materials for medium-voltage and highcurrent interrupters. A variety of their properties (abrasive, erosion-resistant, specific resistant and others) are produced by тхе liquid phase sintering process. The properties of these depend largely on the microstructure developed during sintering. Liquid-phase sintered microstructures are characterized in terms of the solid phase volume fraction, Vp, scale (average solid particles radius), R , the surface-to-volume ratio, Sv. Solid phase morphology is conditioned on interfacial and interparticle surface energies ratio σsl/σss and can be quantified by тхе dihedral angle ψ, (between two particles on the boundare with liquid phase), contiguity, Cc (interparticle surface area as a fraction of the total surface area), and continuity, Cp (the number of solid-solid particle contacts per particle).
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