This study aimed to address the limitations of traditional plasma nitriding methods by implementing a short-term plasma oxy-nitriding treatment on the surface of AISI 420 martensitic stainless steel. This treatment involved the sequential formation of nitride and oxide layers, to enhance surface hardness and corrosion resistance, respectively. The process resulted in the formation of a 20 μm-thick nitride layer and a 3 μm-thick oxide layer on the steel surface. Initially, the hardness increased by 2.2 times after nitriding, followed by a subsequent decrease of approximately 31 % after oxidation. While the nitriding process reduced corrosion resistance, the subsequent oxidation process led to the formation of a passive oxide film, effectively resolving this issue. The pitting corrosion of the oxide passive film started at 82.6 mVssc, providing better corrosion resistance characteristics than the nitride layer. Consequently, the trade-off between surface hardness and corrosion resistance in plasma oxy-nitrided AISI 420 martensitic stainless steel is anticipated to be recognized as an innovative and comprehensive surface treatment process for biomedical components.

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 in which the nanopowder agglomerates were controlled to have 0.5-5 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 . 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 '- equilibrium phase with about 12 thickness, leading to the surface hardening of the sintered Fe part. The surface hardness was remarkably increased from 176 for the matrix to 365 .

This study was to analyse the relationship between process parameters of the sintered composite and plasma nitriding properties with pulsed DC plasma. Fe-40at% composites of full density were fabricated by hot pressing at 1100~. Sintered Fe-40at%Al and Fe-40at% alloys were nitrided under pulsed DC plasma. Excellent surface hardness in the FeAl alloys could be obtained by plasma nitriding. ( :100gf, diffusion layer : 1100~, matrix : 330~) The wear resistance of composites were improved about by 4~6times than FeAl and nitrided were improved about 2 times than matrix.

FeAl 기지 복합재료는 hot-pressing에 의해서 성공적으로 제조할 수 있다. 이러한 FeAl 합금의 기계적 특성에 대한 연구는 많이 진행되었으나 플라즈마 질화에 의한 표면 경화특성에 관한 연구는 아직 미흡한 실정이다. 본 연구에서는 hot-pressing으로 제조된 소결 복합재료의 미세구조와 플라즈마 질화처리시 표면경화의 관계를 분석하였다. FeAl을 기지로 하는 합금은 플라즈마 질화처리에 의해서 표면경도가 상승하는 경향을 보였고, 이러한 경향은 질화처리 시간이 증가할수록 더욱 뚜렷하였다(hv 100gf, 확산층 : 1100~1450kg/mm2, matrix : 330~360kg/mm2). FeAl 합금으로 플라즈마 질화처리에 의해서 매우 우수한 표면경화특성을 얻을 수 있었다. 확산층은 플라즈마 질화처리시간이 증가할수록 두꺼워졌으며, SiC(sub)p의 함유량이 증가함에 따라 확산층은 감소하였다.

Characteristics of plasma nitriding and nitrocarburizing for steam treated sintered steels were studied. Fe-0.8%C powder containing Ni, Cu were sintered at 112 and steamed at 52. Temperature of plasma nitriding and nitrocarburizing was varied from 50 to . Gas mixture of nitriding was set at : =80:20 (vol.%), but was added 1~2 vol.% for nitrocarburizing. Steam treatment for sintered steels brought not only the formation of oxide layer but also decarburizing near the surface. Decrease in hardness near the surface resulted from the formation of ferrite due to decarburizing. Thus, the low hardness was recovered not with plasma nitriding but with plasma nitrocarburixing. Wear resistance properties of steamed specimens and ni-trocarburized specimens were better than those of nitrided specimens according to the pin-on-disk wear test. On the other hand, the fatigue life of steamed specimen was shorter than that of nitrocaiburized specimen.