Investigation and Analysis of Liquid Phase Sintering of Fe—Cu and Fe–Cu–C Compacts

Abstract

Mixtures of Fe–10Cu elemental powders were compacted at pressures between 141 and 680 MPa and sintered at 1140°C for 60 min. It was found that as a result of liquid copper penetration into interparticle boundaries and pores inside Fe grains, the volume of the compacts changed. The extent of volumetric growth after sintering was dependent on the internal porosity of the Fe powder. With a low micropore volume, the effects of compacting pressure variation were insignificant. However, with a large micropore volume, volumetric growth increased with compacting pressure. The addition of 1% graphite to the Fe–10Cu compact reduced volumetric growth at all compacting pressures. Increasing the graphite addition incrementally from 0 to 1% at a constant pressure, 283 MPa, served to reduce progressively the volumetric growth. The effect of graphite is to concentrate the copper at the grain corners by increasing the dihedral angle. Quantitative metallographic analysis showed that the amount of undissolved copper after sintering increased as the graphite addition was increased. Examination of the copper concentration inside the Fe grains provided no evidence that graphite lowers the equilibrium solubility of copper. It is suggested that graphite influences the kinetics of copper dissolution inside iron grains. PM/0346