Investigation of microstructure properties of niobıum carbide-boron (nbc-b) coated hardox 400 steel by thermoreactive diffusion method and evaluation of wear behaviour by taguchi method

In general, it is known that steel materials are out of use because of mechanical effects and cause high damage in the country’s economy. Because the losses caused by interactions such as both wear and corrosion have caused to damage to the country’s economy, the academic and industry communities have taken action and they have started to search for strong materials in terms of hardness and wear properties. Therefore, diffusion, chemical deposition, and physical deposition coating methods have begun to apply to steel materials frequently used in the industry. In this thesis study, Hardox 400 steel used as substrate material has been coated with solid media Thermoreactive Diffusion (TRD) method using Ferro Niobium and Ferro Boron powders from carbide forming element powders. Coating has been carried out in three different temperatures (950, 1000 and 1050 °C) and three different time intervals (1, 2 and 3 hours). After each parameter of coating process carried out by TRD method, microstructures of specimens have been examined by optical microscope, Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD) and hardness values on the coating surfaces have been measured. The effects of coating parameters on coating thickness and hardness have been analysed. In addition, specimens have been subjected to wear tests to determine the effect of hardness and coating parameters on wear. In the wear tests, the Taguchi test design setup has been benefited. The obtained results have been compared with the Hardox 400 steel used under current conditions. It has been seen from optical microscope and SEM images that Hardox 400 steel surface could be coated with TRD method depending on coating parameters, and coating thickness has increased with increasing coating temperature and time. Minimum coating thickness was formed in samples coated with coating temperature of 950 °C for 1 hour, while maximum coating thickness was formed in samples coated with coating temperature of 1050 °C for 3 hours. EDX analysis have showed that the coating layer is composed of B, C, Fe and Nb elements and XRD analysis also have showed that the phase in the coating vi layer is NbC-B. The NbC-B phase has been determined to be an important factor in increasing the hardness, hence the hardness has increased with the increase of the coating temperature and time. Maximum hardness, 2934.2 HV was measured on the sample coated at 1050 °C for 3 hours. In the adhesive wear experiments, it was observed that the wear volume decreased when the coating temperature increased from 950 °C to 1000 °C and started to increase slightly when it increased from 1000 °C to 1050 °C. A similar situation is also valid for the coating time. The increase of the applied load has increased wear volume. According to the Taguchi method, the wear volume of the sample coated at 1000 °C for 2 hours is minimum and the wear volume of the sample coated at 950 °C for 3 hours is maximum. Minimum and maximum wear volumes are approximately 0.063 mm3 and 0.328 mm3. In general, uncoated Hardox 400 steels have been more worn out compared to coated Hardox 400 steels. The samples coated at 950 °C and 1050 °C for 3 hours has more worn out at application loads of 10 N and 15 N. This is thought to be due to the porous structure under the coating layer causing breakage due to plastic deformation during wear tests.