The rheological and sintering behavior of W–Ni–Fe nano-structured crystalline powder

Nano-crystalline powder of W–Ni–Fe alloy used for metal injection molding (MIM) was studied. This nano-powder, prepared by mechanical alloying (MA), was mixed with a wax-based binder to form a feedstock. The effects of MA milling time, nano-powder volume fraction and temperature on the rheological behavior of the feedstock are discussed. With increase of the milling time, the viscosity of the feedstock and the sensitivity of viscosity to shear strain rate decrease. Therefore the fluidity and formalization of this powder feedstock under conditions of longer time milling become better. With increase of the powder volume fraction, the viscosity of the feedstock has a non-linear increase which follows the equation η=η0A[1−(Φ/Φm)]−n. Here n is equal to 0.68. The change of viscosity with temperature and shear strain rate is small for the MA powder, so the quality of these MIM products is not affected strongly by the changes of temperature and injection speed. The experiments show that the milling of W–Ni–Fe powder leads to high density below the liquid sintering temperature. The sintering characteristics of this nano-powder by MA are also discussed. Because the lattice distortion, grain refining and supersaturated solid solution of MA powder promote the consolidation process, higher density and strength of W–Ni–Fe nano-powder products can be obtained.