A Feasibility Study on the Surface Hardening of Sintered Iron Nanopowder by Plasma Ion Nitriding

This study has been performed on the full density sintering of Fe nanopowder and the surface hardening by plasma ion nitriding. The Fe sintered part was fabricated by pressureless sintering of the Fe nanopowder at 700oC in which the nanopowder agglomerates were controlled to have 0.5-5 ��m sized agglomerates with 150 nm Fe nanopowders. The green compact with 46% theoretical density(T.D.) showed a homogeneous microstructure with fine pores below 1 ��m. After sintering, the powder compact underwent full densification process with above 98%T.D. and uniform nanoscale microstructure. This enhanced sintering is thought to be basically due to the homogeneous microstructure in the green compact in which the large pores are removed by wet-milling. Plasma ion nitriding of the sintered part resulted in the formation of ��'-Fe4N equilibrium phase with about 12 ��m thickness, leading to the surface hardening of the sintered Fe part. The surface hardness was remarkably increased from 176 Hv for the matrix to 365 Hv