Densification behavior of mechanically alloyed W-Cu composite powders by the double rearrangement process

Abstract

Department of Materials Engineering, Hanyang University, Seoul 133-791, Korea(Received January 22, 1998)(Accepted in revised form May 25, 1998)IntroductionTungsten-copper(W-Cu) composites are promising materials for thermal managing applications such asmicroelectronic devices because of the low thermal expansion coefficient of tungsten and the highthermal conductivity of copper (1–3). These materials have been produced by conventional Cu-infiltration sintering or by liquid-phase sintering (4, 5). The full densification of W-Cu composites byliquid-phase sintering is attained mainly by the tungsten particle rearrangement due to the capillaryforce and surface tension of Cu-liquid phase (6, 7) as well as solid-state sintering, because W and Cuhave no solubility under equilibrium condition (8). If the constituent phases are extremely finehomogeneous state, the fully dense parts with the homogeneous microstructure can be attained at thestage of particle rearrangement. To promote homogeneity, much works such as the coreduction methodof the raw oxide powders (9, 10) or mechanical alloying of the element powders (11, 12) have beenstudied. The mechanical alloying method is the attractive one from the engineering viewpoint becausethe nanostructured(NS) materials can be easily synthesized in large quantities. Nevertheless, the studiesof nanostructured W-Cu alloys have been focused only on the formation and the fabrication ofcomposite powders by mechanical alloying (11–13). And there were few researches of liquid-phasesintering behavior of NS W-Cu composite powders compared to nanostructure characteristic study.The authors have recently reported on the characteristics of nanostructured W-Cu alloys producedby mechanical alloying method (14, 15). In this study, the new concept of nanosintering was suggestedto explain the drastic grain growth of mechanically alloyed NS W-Cu powders during the solid-statesintering. The high sinterabilty of these mechanically alloyed NS W-Cu alloys was also obtained byliquid-phase sintering. In this present work, the enhanced sinterabilty of mechanically alloyed NS W-Cucomposite powders with sintering temperature is investigated and evaluated by the combination ofnanosintering and conventional liquid-phase sintering.ExperimentalElemental W (99.9% purity, 4.28mm) and Cu(99.5% purity, 50.42mm) powders were used for rawpowders in this experiment. The mechanical alloying was carried out in an attrition mill using a stainlesssteel vial and balls with a speed of 400 rpm. The powder charge was 20g, with balls to powders weightratio of 60:1. The W-20wt%Cu and W-30wt%Cu composite powders were prepared by milling for 100