Effect of cobalt addition on the liquid-phase sintering of W-Cu prepared by the fluidized bed reduction method
- PDF / 800,546 Bytes
- 4 Pages / 598 x 778 pts Page_size
- 53 Downloads / 208 Views
I.
INTRODUCTION
F O R many years, W-Cu composite has received great attention because of its practical importances such as high melting temperature, high electrical conductivity, and high mechanical strength. Im,3J Since these two elements, however, show extremely small solubility, only the infiltration process has been known to be successful commercially, t4,51 where the liquid copper is supposed to fill up the voids of cold-pressed tungsten powder by the liquid-phase sintering. A new process to produce a low-copper content W-Cu composite and to fabricate complicatedly shaped parts has been introduced earlier, where uniform mixing of tungsten and copper can be accomplished by coating the tungsten powder with copper by the fluidized bed reduction (FBR) method prior to the liquid-phase sintering. It is well known that there are three stages in the liquid-phase sintering, namely, rearrangement, solutionreprecipitation, and solid-state reaction, t6-~~ Small wetting angle of the liquid phase, tJ~l high solubility of the solid with respect to the liquid phase, and low solubility of the liquid phase to the solid t12A31are important factors in obtaining the high density after the liquid-phase sintering. In the W-Cu system, not only is the wetting angle of the copper large 1~41but also tungsten does not show any solubility in the liquid copper, t~Sl Hence, it is very difficult to get the high-density composite with this system. It has been reported that the sintering temperature can be reduced considerably by the addition of nickel to tungsten. 1~6,~7]Some transition metals such as cobalt and nickel have been known to improve the electrical contact properties of the W-Cu system when they have been added to copper, ~8,~9] but few have been reported on the effect of these additives on the liquid-phase sintering process yet. In this work, submicron tungsten powder has been coated with copper by the fluidized bed reduction process, and then the effect of the cobalt addition was carefully investigated. Effects of tungsten powder size, and SEUNG-KI JOO, Professor, SEOK-WOON LEE, Graduate Student, and TAI-HYOUNG IHN, Graduate Student, are with the Department of Metallurgy, Seoul National University, Seoul 151-742, Korea. Manuscript submitted November 4, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
the amount of cobalt as well as sintering temperature are discussed. II.
EXPERIMENTS
Hydrogen-reduced tungsten powder obtained from Korea Tungsten and Mining Company was dipped into the copper dichloride solution and then dried. The dried cake was crushed into powder where hydrogen gas was used to float the crushed powder in a vertical tube furnace and then reduced to get the copper-coated tungsten powder by the FBR method. Concentration of copper was determined prior to the reduction process and fixed to 25 wt pct in the present work. Cobalt was added as a cobalt dichloride (COC12 6H20) in the copper dichloride, and the amount was varied from 0 to 5 wt pct. Copper-coated tungsten powder was cold pressed at 200 MPa, and the dis
Data Loading...
