Solid or liquid phase sintering of nanocrystalline WC/Co hardmetals

Nanocrystalline WC/Co hardmetal powder has been sintered at various temperatures in vacuum and HIP sintered under different pressures. In addition, hot stage optical microscopy (HSM) and differential thermal analysis (DTA) was performed on a similar powder All the results indicate that the matrix of the nanopowder starts to melt at about 1150 degrees C; however, the melting is confined to locations that are still nanocrystalline. With increasing temperature, more material melts and at about 1330 degrees C the melting of the matrix is complete. High density can be achieved below this temperature, but not below 1200 degrees C. Compared with previous sintering results on micron sized powder, the conclusion is that the nanopowder densifies mostly in the solid state, while the latter mostly in the liquid state. (C) 1998 Acta Metallurgica Inc.