Method for producing a contact material for contact pieces for vacuum switch devices, and a contact material and contact pieces therefor

A method for producing a contact material made of copper and chromium in a proportion of 40 to 75 wt.-% copper and 25 to 60 wt.-% of chromium in a form of a semi-finished product, from which individual contact pieces are produced for use in vacuum switch devices, the method comprising the steps of:

• pressing one of a chromium powder in an amount corresponding to a chromium content of the contact material to be produced and a mixture of the chromium powder in an amount corresponding to the chromium content of the contact material to be produced and of a copper powder in an amount which is less by 5 to 15 wt.-% with respect to a copper content of the contact material to be produced, using pressures between 200 and 1000 MPa, into a porous compact having a density corresponding to 75 to 90% of a theoretical density;
• covering the porous compact with an amount of the copper which at least corresponds to a copper amount missing from the contact material to be produced;
• thereafter, heating the compact covered with copper in a high vacuum to a temperature up to or above a melting point of the copper, wherein the compact is sintered, forming one of a chromium matrix sinter body and a copper-chromium matrix sinter body, and one of chromium matrix sinter bodies and copper-chromium matrix sinter bodies being created are simultaneously infiltrated by a liquefied copper covering the compact;
• obtaining one of a copper-infiltrated chromium sinter body and a copper-infiltrated copper-chromium sinter body which has a copper content increased in comparison with the compact and has a density corresponding to 96 to 98% of the theoretical density;
• subsequently forming the one of the obtained copper-infiltrated chromium sinter body and the copper-infiltrated copper-chromium sinter body into a semi-finished product constituting the contact material by extrusion in a stretching direction, wherein chromium grains in the sinter bodies are pulled out in the stretching direction to form chromium columns and an elongated straightened structure, and wherein a shaping degree of the sinter bodies is at least 30%;
• and
• obtaining a semi-finished contact material product which has a straightened structure and a density which corresponds to at least 99%, in particular 99.5 to 99.9% of the theoretical density.