Survey of the Compound and Diffusion Layer Growth in the Process of Plasma Nitriding on Cold Work Tool Steel AISI D2

Plasma nitriding is an advanced surface modification technology that has experienced industrial components to improve their surface properties. The mechanism of white layer growth in plasma nitrided coatings applied on a typical D2 cold work tool steel is investigated. For nitriding, specimens were plasma nitrided at 450, 500 and 550 ◦C temperatures for 2.5, 5, 7.5 and 10 hours in an atmosphere of 25 % H2 - 75 % N2. The coating assemblies have been compared in terms of white layer thickness and surface morphology and roughness. The compositions of the coatings have been studied by X-ray diffraction analysis. The surface morphology was examined by using optical metallography and scanning electron microscopy. Surface roughness of plasma nitrided specimens and height of the surface nitrides was measured by atomic force microscopy. Diameter of the surface nitrides was measured by the use of image analyzer software. It was shown that in the surface of all specimens, two common nitride phases have formed that are ε (Fe2-3N) and γ' (Fe4N). By increasing the time of the process, ε will disappear slowly and γ' become the most common phase and by increasing the temperature, ε will have stronger peaks due to more formation of it in the higher temperatures.

Keywords:

AISI D2 cold work tool steel , plasma nitriding , surface morphology , surface nitrides