MECHANICAL PROPERTIES AND CORROSION RESITANCE OF MECHANICALLY ALLOYED FEBASED NANOSTRUCTURES CONSOLIDATED BY SPARK PLASMA SINTERING

Abstract

In the present work, iron, nickel and nano sized (20-30 nm) powders with compositions 42wt.%Ni, Fe-42wt.%Ni-2wt.%Y2O3 and Fe-2wt.%Y2O3 were prepared by high energy ball milling. The miilled samples were sintered by spark plasma sintering (SPS) at 800, 900 and 1000°C in argon atmosphere with a holding period of 5 min at a pressure of 60 MPa. The density of the sintered alloys increased from 78% at 800oC to 98% at 1000oC. XRD analysis indicates the presence of Fe-Ni phase in sintered the Fe-Ni alloy, while additional presence of intermetallic phases (Ni5Y, Fe17Y2) and oxides (NiO, Fe3O4) observed in the sintered Fe-Y2O3 and Fe-Ni-Y2O3 alloys. The microstructures of the alloys sintered at 1000oC revealed decrease in average grain size from ~10 μm for Fe-Ni to ~1 μm for Fe-Y2O3 and ~500 nm for Fe-Ni-Y2O3. The nanoindentation hardness of the sintered alloys varied from 5.8 GPa for Fe-Ni to 7.2 GPa for Fe-Y2O3 and 7.9 GPa Fe-Ni-Y2O3. Sliding wear tests in dry conditions against alumina ball indicate that average coefficient of friction varied from 0.5 (Fe-Ni-Y2O3) to 1.7 (Fe-Ni) and depth of wear track varied from 5 μm to 20 μm with change in composition of the alloy and sliding load (from 5 to 20 N). The presence of oxide rich layer at the contact surface is found responsible for less coefficient of friction and depth of wear track for the Fe-Ni-Y2O3 alloy. Corrosion tests in 3%NaCl indicate decreased corrosion density (Icorr) from 1.34 μA/cm2 for Fe-Ni and 0.78 μA/cm2 Fe-Ni-Y2O3. The present research work essentially indicates a significant grain refinement with subsequent improvement of mechanical, wear and corrosion properties due to the addition of nano sized ytrria in iron-nickel alloy.