Surface characterization of multiple coated H11 hot work tool steel by plasma nitriding and hard chromium electroplating processes

Abstract: Formation of multi-layer coating by plasma nitriding and hard chromium electroplating on the surface of H11 hot work tool steel was investigated. Specimens were coated via a triple process containing plasma nitriding, hard chromium electroplating and plasma nitriding. Surface composition has been studied by X-ray diffraction analysis. The surface morphology and elemental analysis was examined by using scanning electron microscopy. Wear tests were conducted by the use of pin-on-disk method, a cemented tungsten carbide pin and 1000 gF load. Polarization corrosion tests were carried out in distilled water solution containing 3% NaCl. The improvement in hardness distribution after third step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the formed phases in the hybrid coating were determined to be CrN + Cr2N + Cr + Fe2–3N + Fe4N. Wear results showed that although the multi-layer coated specimens have higher wear resistance in comparison with the reference specimen, their wear resistance is less than that of two and one layer coated specimens due to micro-ploughing and removal of hard surface nitrides from the surface. By increasing the third step time and temperature, the wear resistance of specimens increases due to higher diffusion of nitrogen in the chromium layer. But polarization results showed that triple coated specimens have the lowest corrosion rate. [Copyright &y& Elsevier]