Significance Statement
Plasma Nitriding is a conventional industrial thermochemical process used for improving the surface mechanical and tribological properties of different alloys including steels. Cathodic cage plasma nitriding (CCPN) is a relatively recent alteration of the conventional plasma nitriding (CPN) design, which eliminates several shortcomings of CPN. In a short duration environment-friendly CCPN process, the surface hardness can be enhanced several times. Therefore, with just a 10 % increase in the cost of the samples, their lifetime can be increased several times. Plain carbon steel is much cheaper than the alloy steel, but generally, it has limited use in several industrial applications due to its unsuitability for plasma nitriding. The work shows the first industrially compatible process to nitride the plain carbon steel.
In CCPN process, a perforated cylinder (or cathodic cage) surrounds the specimens to be nitrided. The discharge is established between the grounded vacuum vessel (anode) and the perforated cylinder (cathode). A pulsed dc power supply is used to avoid switching of the discharge from abnormal glow to the arc mode. The cathode cage material sputtered by the accelerated nitrogen ions is eventually deposited on the specimens. The work showed that the effectiveness of the nitriding performance is linked to the peak discharge current density (current/cathode cage area). The peak discharge current density is increased independent of plasma power, by decreasing the duty cycle to 15 % and reducing the cathodic cage diameter. When an AISI-304 (containing 18.8% Chromium(Cr)) cathodic cage is used for the nitriding of plain carbon steel at high current density, some Cr is deposited on the sample surface which helps to trap nitrogen. This deposition of nitrogen-trapping chromium from the AISI-304 cathodic cage enabled successful nitriding of plain carbon steel, which is generally considered inappropriate for plasma nitriding.
The concept is extended by using two steps of nitriding using aluminum and AISI -304 cathodic cages in alternate order, for the nitriding of alloy steel. The double step process developed a duplex coating in a single CCPN setup, with much better properties than the single step. Besides surface hardness up to seven times, corrosion and wear rates are significantly reduced. The results are verified by the XRD and the surface and cross-sectional SEM images. The use of higher current densities and various cage materials in CCPN system can be used to develop multi-layer coatings using a single industrially scalable setup.
References
- Naeem, M. Shafiq, M. Zaka-ul-Islam, A. Ashiq, J. C. Díaz-Guillén, M. Shahzad, M. Zakaullah, Enhanced surface properties of plain carbon steel using plasma nitriding with austenitic steel cathodic cage, Mater. Des. 108 (2016) 745–753.
- Naeem, M. Waqas, I. Jan, M. Zaka-ul-Islam, J. C. Díaz-Guillén, N. U. Rehman, M. Shafiq, M. Zakaullah, Influence of pulsed power supply parameters on active screen plasma nitriding, Surf. Coat. Technol. 300 (2016) 67–77.
- Naeem, M. Shafiq, M. Zaka-ul-Islam, N. Nawaz, J. C. Díaz-Guillén, M. Zakaullah, Effect of cathodic cage size on plasma nitriding of AISI 304 steel, Mater. Lett. 181 (2016) 78–81.
- Naeem, M. Zaka-ul-Islam, M. Shafiq, M.I. Bashir, J.C. Díaz-Guillén, M. Zakaullah, Influence of cathodic cage diameter on mechanical properties of plasma nitrided AISI 304 steel, Surf. Coat. Technol. 309 (2017) 738-748.
- Naeem, M. Shafiq, M. Zaka-ul-Islam, J. C. Díaz-Guillén, C. M. Lopez-Badillo, N. Ullah, M. Zakaullah, Improved surface properties of AISI-304 by novel duplex cathodic cage plasma nitriding, Mater. Lett. 189 (2017) 213–216.
Citation:
M. Naeem1, M. Zaka-ul-Islam2, J.C. Díaz-Guillén3, M. Shafiq1, M. Zakaullah1*. The use of cathodic cage material and plasma current density for the enhancement of the surface properties of plasma nitrided steel. Advances in Engineering feature, 5th April 2017.
[expand title=”Show Affiliations”]- Department of Physics, Quaid-i-Azam University, 45320 Islamabad, Pakistan.
- Department of Physics, Faculty of Science, Jazan University, P.O. Box 114, Jazan, Saudi Arabia.
- Department of Physics, Faculty of Science, Jazan University, P.O. Box 114, Jazan, Saudi Arabia.
* Corresponding author: [email protected] (M. Zakaullah).