The effect of surface nanocrystallization on plasma nitriding behaviour of AISI 4140 steel |
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Authors: | Yang Li Dandan Zhang Lie Shen |
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Institution: | Department of Materials Science & Engineering, Dalian Maritime University, Institute of Metals and Technology, 1# Linghai Street, Dalian 116026, PR China |
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Abstract: | A plastic deformation surface layer with nanocrystalline grains was produced on AISI 4140 steel by means of surface mechanical attrition treatment (SMAT). Plasma nitriding of SMAT and un-SMAT AISI 4140 steel was carried out by a low-frequency pulse excited plasma unit. A series of nitriding experiments has been conducted at temperatures ranging from 380 to 500 °C for 8 h in an NH3 gas. The samples were characterized using X-ray diffraction, scanning electron microscopy, optical microscopy and Vickers microhardness tester. The results showed that a much thicker compound layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples after nitriding at the low temperature. In particular, plasma nitriding SMAT AISI 4140 steel at 380 °C for 8 h can produced a compound layer of 2.5 μm thickness with very high hardness on the surface, which is similar to un-SMAT samples were plasma nitrided at approximately 430 °C within the same time. |
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Keywords: | Plasma nitriding AISI 4140 steel Nanocrystalline materials |
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