PREPARATION OF DISPERSION-STRENGTHENED COPPERS WITH NBC AND TAC BY MECHANICAL ALLOYING

To prepare a dispersion-strengthened copper-based alloy, mechanical alloying was carried out using pure copper, niobium, tantalum and graphite powders. After mechanical alloying for 144.0 ks, a Cu-Nb-C solid solution + NbC mixture powder and a Cu-Ta-C solid solution + Ta + TaC mixture powder were obtained in the Cu-Nb-C and Cu-Ta-C systems, respectively. These powders were heat-treated in an evacuated state at temperatures from 873 to 1323 K. In the Cu-Nb-C and Cu-Ta-C systems, C and Nb or Ta reacted, resulting in precipitation of very fine NbC and TaC particles in copper. The mean particle sizes of the NbC and TaC particles were about 3.0 nm by the heat-treatment at 873 K for 3.6 ks and 15.0-20.0 nm at 1273 K for 3.6 ks. In the Cu-Nb-Ta-C system, a very fine (Nb, Ta)C particle was precipitated. The mean particle sizes of these carbide particles tended to decrease as the heat-treatment temperature was decreased. The hardness of the NbC- and TaC-dispersion-strengthened coppers was high. For example, the room temperature hardnesses (Hv) of Cu-2.5 vol% NbC and Cu-10.0 vol% NbC alloys were 280 and 350, respectively, after mechanical alloying for 72.0 ks followed by the heat-treatment at 873-973 K for 3.6 ks.