Applying of Electron Backscatter Diffraction ( EBSD ) for Studying Structural and Phase Composition of Multilayer CrN/MoN Coatings Fabricated by Arc‐PVD

Abstract

Main proposes of produced CrN/MoN coatings in this research are protection of various tools, machines and materials. For this aim they need to have predicted properties and characteristics in hardness, elasticity and plasticity. Structural and phase composition of films play an important role in this case. Electron Backscatter Diffraction (EBSD) is a powerful quantitative technique which has been significantly developed and spread over the last few decades. Nowadays it's used both in R&D sector and industry. Usually in labs EBSD occurs as an additional option of scanning electron microscope (SEM): another detector embedded into the same chamber, as it is probably more common for energy‐dispersive X‐ray spectroscopy (EDS) devices. Also it is clear that limits of maximum potential for this technique haven't been achieved yet. The present paper is dedicated to investigation of structural and phase composition of multilayer metal nitride coatings by EBSD. Studied coatings are multilayer films based on nitrides of Cr and Mo metals. CrN/MoN coatings were deposited on steel substrate using Arc‐PVD deposition. Total thickness of films is in range 8‐13 µm. Samples have various numbers of layers in coatings: 11÷354, and, hence, they have different bilayers thickness from 100 nm up to 2 µm. Coatings were studied by observing polished cross‐sections of samples as well as side of top surface. The films thickness and bilayer thickness were measured using scanning electron microscope JEOL JSM‐7001F and FEI Quanta 400FEG with EDAX EBSD Forward Scatter Detector System and high resolution DigiView III camera. This unit also was used for main part of reported research – EBSD studying of structure and phase composition. Crosschecking analysis of coatings structure was performed by X‐ray Diffraction (XRD) using Panalytical X'Pert diffractometer. Figure 1 shows the sample of CrN/MoN cross‐section coating with layer thickness 300nm and 22 bilayers in total. Good interfaces and contrast between layers are present in films. Using EBSD and corresponding software Uniqe Grain Color Maps for samples were designed. Columnar structure and grains growth was observed (see Figure 2). It is should be noted that only CrN layers gave a good diffraction pattern, which probably corresponds to soft material of MoN layers, surface deformation or present of noncrystalline compounds. Crystals orientation in films was studied and visualized by pole figures (Figure 3). Results of phase and orientation analysis were confirmed by cross‐checking XRD measurements. The relation between bilayer thickness and grain size of films was found. Figure 4 demonstrates grainsize distribution in films with different bilayer thickness. As thinner layers in coating as smaller grain size in proposed samples serial. Decreasing of grain size in films may cause different mechanical properties due to higher amount of interfaces. It is an important characteristic for hardness, elasticity of material and in its turn wear resistance and other protective features. Analysis of mechanical properties of considered coatings is a next step in subsequent research.