A study of densification of 40wt.% Ni-Fe nanopowder prepared by mechanical alloying and sintered by SPS apparatus

Abstract

Mechanical alloying through high energy ball milling was used to produce 40wt.%Ni-Fe alloy powder of average particle sizes 80 µm and 25 µm respectively. High energy planetary ball milling at room temperature was performed for various time durations of 16, 32, 64 and 100 hours. Sintering was carried on (SPS 515S) Spark Plasma Sintering System. Samples were sintered at constant temperature of 950oC and pressure of 30 MPa for all samples. This study exhibits in same alloy, but increases of milling hours, the densification of the sintered samples decreases and also porosity of the sample increases. This may be due to the reasons of increases in the surface area of the milled nanopowder (i.e., reduction of particle size), low green body density of long milling powders by agglomeration of powders and oxidation of powders during a milling process. However, this study revealed that optimum temperature of the spark plasma sintering was depended on particle size and impurities formed while mechanical alloying. Densification of 89% was achieved in 16 hours milled sample.