POWDER METALLURGICAL MANUFACTURE OF ELECTRIC CONTACT PIECE OF COPPER CHROMIUM SOLID SOLUTION FOR VACUUM ENCLOSED SWITCH

The process is characterised by the sequence of the following process steps: a) preparing a mixture of from 20 to 70% by weight of copper powder and from 80 to 30% by weight of chromium powder, the chromium powder having powder particle sizes between 0 and at most 210 mu m and a powder particle size distribution which is characterised by approximately equal proportions, normalised to the width of the respective fraction, in the particle size fractions from 0 to 30 mu m, from 30 to 60 mu m, from 60 to 90 mu m, from 90 to 120 mu m, from 120 to 150 mu m, from 150 to 180 mu m and from 180 to 210 mu m, as well as by a mean powder particle size between 100 mu m and 120 mu m; b) compacting contact piece preforms from the powder mixture; c) sintering the preforms in the solid phase, i.e. at a temperature below the melting point of copper until a relative density between 93% and 97%, based on the theoretically achievable maximum density, has been reached; d) thermal secondary treatment of the contact pieces in such a way that the chromium particles segregating in the copper remain smaller than 1 mu m (diameter). c