Copper based composites using liquid phase processing techniques and Ni coated graphite particles

摘要

The metallurgical interactions taking place between Cu powder and a Ni-coating on graphite powder during processing have been investigated using DSC. Quantitative enthalpy measurements on pressed powder compacts indicate that interdiffusion in the solid-state between the Cu powder and Ni coating occurs during heating. This reduces the amount of liquid forming in the compact and has a negative impact on densification. DSC measurements during cooling from the sintering temperature and reheating past the previous peak temperature indicates that interdiffusion between the Cu and Ni continues in the liquid state. This results in a further reduction in the liquid fraction due to isothermal solidification, a shift in the liquid composition to a more Ni rich value and an increased melting point. These processes occur rapidly when the liquid is first formed and likely contributes to the poor densification behavior of the powder compact. Separation of the Cu and Ni/graphite powders into a layered structure decreases solid-state interdiffusion and consequently increases liquid fraction and densification. Processed densities in excess of 95% for Ni coated graphite contents up to 25 wt% (or 30 vol% graphite) can be achieved using this layered technique.