Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of AISI 4140 steel. Plasma nitrocarburizing was conducted for 3 h at 570 ℃ in the nitrogen, hydrogen...Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of AISI 4140 steel. Plasma nitrocarburizing was conducted for 3 h at 570 ℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe2-3(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ′-Fe4(N,C) phase. The thickness of the compound layer was about 10 μm and the diffusion layer was about 300 μm in thickness, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at a constant temperature of 500 ℃ for 1 h. The very thin magnetite (Fe3O4) layer 1-2 μm in thickness on top of the compound layer was obtained by plasma post oxidation. It was confirmed that the corrosion characteristics of the nitrocarburized compound layer can be further improved by the application of the superficial magnetite layer.展开更多
Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel.Plasma nitrocarburizing was conducted for 12 h at 540℃in the nitrogen, hydrogen and ...Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel.Plasma nitrocarburizing was conducted for 12 h at 540℃in the nitrogen, hydrogen and methane atmosphere to produce theε-Fe-（2-3）（N,C） phase.The compound layer produced by plasma nitrocarburising was predominantly composed ofε-phase,with a small proportion ofγ′-Fe-4 （N,C） phase. The thickness of the compound layer and the diffusion layer are about 10μm and about 200μm,respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃for 1 h.The very thin magnetite （Fe-3O-4） layer of 1-2μm in thickness on top of the compound layer was obtained.Anodic polarization test revealed that plasma nitrocarburizing process contributed a significant improvement of corrosion resistance of SKD 61 steel.However,the corrosion characteristics of the nitrocarburized compound layer was deteriorated by oxidation treatment.展开更多
The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs...The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.展开更多
文摘Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of AISI 4140 steel. Plasma nitrocarburizing was conducted for 3 h at 570 ℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe2-3(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ′-Fe4(N,C) phase. The thickness of the compound layer was about 10 μm and the diffusion layer was about 300 μm in thickness, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at a constant temperature of 500 ℃ for 1 h. The very thin magnetite (Fe3O4) layer 1-2 μm in thickness on top of the compound layer was obtained by plasma post oxidation. It was confirmed that the corrosion characteristics of the nitrocarburized compound layer can be further improved by the application of the superficial magnetite layer.
文摘Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel.Plasma nitrocarburizing was conducted for 12 h at 540℃in the nitrogen, hydrogen and methane atmosphere to produce theε-Fe-（2-3）（N,C） phase.The compound layer produced by plasma nitrocarburising was predominantly composed ofε-phase,with a small proportion ofγ′-Fe-4 （N,C） phase. The thickness of the compound layer and the diffusion layer are about 10μm and about 200μm,respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃for 1 h.The very thin magnetite （Fe-3O-4） layer of 1-2μm in thickness on top of the compound layer was obtained.Anodic polarization test revealed that plasma nitrocarburizing process contributed a significant improvement of corrosion resistance of SKD 61 steel.However,the corrosion characteristics of the nitrocarburized compound layer was deteriorated by oxidation treatment.
基金supported by the National Basic Research Program of China(No.2009CB623704)the National Natural Science Foundation of China(Nos.51071064 and 51171063)+2 种基金the Nature Science Foundation of Hunan Province(Grant No. 09JJ6002)Instrumental Innovation Foundation of Hunan Province(No.2011TT1003)the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province
文摘The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.
