Two‐Step Nitriding Behavior of Pure Iron with Nanostructured Surface Layer
ADVANCED ENGINEERING MATERIALS(2019)
摘要
A two-step gas nitriding treatment (280 degrees C for 2 h plus 550 degrees C for 6 h) is designed for pure iron with a nanostructured surface layer induced by surface mechanical attrition treatment (SMAT). The microstructure and surface properties of the SMAT sample after two-step nitriding treatment are investigated in comparison with those of the SMAT sample after single-step nitriding treatment (550 degrees C for 6 h). Experimental results show that a much thicker compound layer (up to 25 mu m in thickness) is generated on the surface of the SMAT sample after two-step nitriding treatment, in which the mean grain size of the Fe2-3N phase is below 25 nm. The enhanced nitriding kinetic may be attributed to the formation of a large number of Fe(N) solid solutions and a small amount of dispersed Fe2-3N particles on the SMAT sample after first low-temperature nitriding, which enhances the thermal stability of nanostructured iron grains. Due to the enhanced nitriding kinetic and refined nitride structure, the SMAT sample after two-step nitriding treatment displays higher surface hardness and improved wear resistance relative to its single-step nitrided counterpart.
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关键词
diffusion,nanostructured,surface mechanical attrition treatments,surface properties,thermal stability,two-step nitriding
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