Microstructural evolution on the sintered properties of W-8 pct Mo-7 pct Ni-3 pct Fe alloy

The microstructure of W-8 pct Mo-7 pct Ni-3 pct Fe alloy has been found to evolve in concomitance with the reprecipitation of tungsten atoms from the matrix phase onto the grains. With increase in isothermal holding time at 1 480 degrees C, the concentration of tungsten in the matrix phase reduces fr om 53.7 wt pct for an isothermal holding time of 5 minutes, and gradually a pproaches an equilibrium value of about 18 wt pct. The continuous solid-liq uid reactions result in gradual penetration of the liquid phase into the bo undaries of the skeletal solid grains. Consequently, contiguity of the tung sten based grains drops sharply during the initial stage of isothermal hold ing, and reaches minimum after an isothermal holding time of 120 minutes. T he contiguity subsequently increases again as the coalescence of grains com mences. Simultaneous diminishing of the concentration of tungsten in the ma trix phase along with decrease in contiguity of the grains result in an opt imal combination of mechanical properties after an isothermal holding time of 120 minutes. Molybdenum has been found to bring about a substantial micr ostructural refinement, whereby a mean grain size of only 22 mu m is attain ed from an isothermal holding time of as long as 240 minutes. (C) 2000 Kluw er Academic Publishers.