RESPONSE OF OPEN/CLOSED POROSITY TO DENSITY VARIATIONS IN PRE-ALLOYED AND ADMIXED FE-NI-MO P/M ALLOYS

摘要

The evolution of open/closed porosity as a function of density for Fe-Ni-Mo P/M alloys was investigated. Two alloy systems were selected for this study: a pre-alloyed Fe-Ni-Mo, and an admixed system - a pre-alloyed Fe-Mo powder + elemental Ni. The graphite level in both cases was adjusted to produce a common sintered carbon content of 0.6%. Several density levels in the range ～6.6-7.3 g/cm~3 were investigated. In addition, pure Fe was studied at densities up to ～ 7.5 g/cm~3. The open/closed porosity was measured at three manufacturing stages: as-compacted, sintered, and quenched and tempered. The sintered and quenched and tempered data are the most relevant for practical purposes and therefore, these conditions are discussed. The amounts of open/closed porosity after two different sintering procedures were also compared for the pre-alloyed material. An original porosity measurement methodology (gas-impregnation or pycnometric method) involving comparisons of the bulk, pycnometric, and pore-free densities of the specimens was designed and used in this study. Comparisons between the amount of open/closed porosity measured via pycnometric and standard oil-impregnation techniques were made.