en گروه سطح پوشش و خوردگی Surface Coatings and Corrosion Research Paper Research Paper <p><strong>- </strong>The mechanism of diffusion layer growth in plasma nitrided coatings applied on a St52 steel using an active screen is investigated. The nitriding was performed at 450,500 and 550 ◦C temperature nitriding times of 5, 10 and 15 h, in a gas mixture containing 20 vol. % H2: 80 vol. % N2 and DC-pulsed plasma nitriding unit.</p> <p>The surface, cross section and the thickness of diffusion of specimens was studied in terms of optical and scanning electron microscopy. According to the measurements of diffusion layer thickness, values of Q and D₀ for nitrogen diffusion in substrate were calculated as 50585 (j/mol) and 4.11&times;10^-10 (m²/s)respectively. The variations of depth of hardness during nitriding period was determined</p> plasma nitriding, A St52 steel,Diffusion zone, Growth mechanism 24 31 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-78-16&slc_lang=en&sid=1 M. Soltanieh mansour_soltanieh@iust.ac.ir 180031947532846005643 180031947532846005643 Yes Iran University of science and Technology Department of Materials and Metallurgical Engineering Iran University of Science and Technology, M. Kiani Mohammad_kiani@metaleng.iust.ac.ir 180031947532846005644 180031947532846005644 No Department of Materials and Metallurgical Engineering Iran University of Science and Technology, M. Hasheminiasari mhashemi@iust.ac.ir 180031947532846005645 180031947532846005645 No Department of Materials and Metallurgical Engineering Iran University of Science and Technology,