| In order to obtain uniformly distributed tungsten-copper powder, the submicron tungsten powder was coated with copper by a newly developed process : fluidized bed reduction. Tungsten powder was initially coated with copper dichlorides and then reduced in fluidized beds by hydrogen gas flow. By the same method, cobalt was added to this binary alloy for the purpose of altering the chemical relations between tungsten and copper. In case of 75W-25Cu, full densification could not be attained even after the prolonged sintering of 4 hours at 1200 C because of a large wetting angle of copper on tungsten. The addition of cobalt of 0.5 weight percent, however, considerably enhanced the densification of 75W-24. 5Cu-0.5Co and high density above 95% was attainable within ramping-up to 1200℃. The enhancement of sintering by cobalt addition was revealed to result from the decrease of the wetting angle of liquid copper, which was due to the formation of an intermetallic compound between tungsten and cobalt dissolved in liquid copper. |
|
