Influence of Temperature on Microstructure and Mechanical Properties of Ni-40Fe-10Co Alloy Consolidated by Spark Plasma Sintering

摘要

The unique features of the Spark Plasma Sintering (SPS) technique were used to investigate the effect of sintering temperature on mechanically milled nickel and iron respectively, with Co additions (Ni40Fe10Co), on the densification and microstructural evolutions. Admixed powders were sintered at various temperatures ranging between 900 and 1100 °C. Material characterizations of powders and sintered compacts was done using scanning electron microscopy (SEM), Optical microscopy and X-ray diffraction (XRD). Milling of Ni for 20 hrs was found to be producing larger cold welded clusters, while Fe milling resulted in finer rod-shaped particles. The observed behaviour of Ni during milling was due to its ductility; of which further milling might probably start disintegrating the agglomerates. With an increase in sintering temperature, no substantial detectable new phases were observed. Furthermore, optical images of polished surfaces revealed that with an increasing sintering temperature, the pores coalesce, becomes spherical and thereafter grows. This is attributed to the interdiffusion/phase transformations between the ternary particles upon heating and cooling cycle during sintering. This phenomenon was suspected to be the cause of density and microhardness drop with temperature increase.