Effects of gas nitriding pressure on the formation of nanocrystalline AlN in plasma nitrided Fe–9Al–28Mn–1.8C alloy

• Published in: Surface & coatings technology 2014-09, Vol.254, p.313-318
• Main Authors: Chang, K.M., Kuo, C.C., Chang, Y.W., Chao, C.G., Liu, T.F.
• Format: Article
• Language: English
• Subjects: Aluminum nitride; Applied sciences; Corrosion; Corrosion environments; Corrosion resistance; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Ferrous alloys; Fe–Al–Mn–C alloy; Formations; Heat treatment; Ion nitriding; Materials science; Metals. Metallurgy; Microhardness; Nanocrystalline AlN; Nanocrystalline γ′-Fe4N; Nanocrystals; Nitriding; Physics; Plasma nitriding; Production techniques; Surface hardness; Surface treatments; Thermochemical treatment and diffusion treatment
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2014.06.042

The effects of gas nitriding pressure on the formation of nanocrystalline nitrided layer and its effect on the performance of the Fe–9Al–28Mn–1.8C alloy (in wt.%) were investigated. Plasma nitriding was conducted at 450°C for 12h under nitriding pressures ranging from 133 to 798Pa. The results evidently demonstrated that, due to the unique as-quenched microstructure of the present alloy, the effect of nitriding and aging could be achieved simultaneously with one-step plasma nitriding scheme. Both the thickness of nitrided layer and the nitrogen concentration at the outmost surface were found to increase with increasing gas nitriding pressure in the range of 133–798Pa. Detailed microstructural analyses indicated that the nitrided layer is composed predominantly of nanocrystalline face-centered-cubic (FCC) B1-AlN and FCC γ′-Fe4N with minor amount of expanded austenite phase, which accounts for the excellent surface microhardness and corrosion resistance in 3.5% NaCl solution. The increase in gas nitriding pressure led to a thicker nitrided layer and smaller AlN particles, which in turn, resulted in higher surface microhardness and better corrosion resistance. •Nitriding and aging effects were obtained simultaneously by one-step plasma nitriding.•Effect of pressure on constituent phases formed in nitrided layer was delineated.•Nanocrystalline AlN and γ′-Fe4N are responsible for high corrosion resistance.•Surface hardness reaching 1710Hv and pitting potential above +1.7V were attained.