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2088 |
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Monday, May 03, 2010, Olivia Room 2:20 PM HVOF 1 |
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HVOF spraying of ultrahigh boron high carbon tool steel coating for wear resistance applications |
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Rajasekaran Balasudaram* / Forchungszentrum Juelich, Germany Georg Mauer / Institute of Energy Research, IEF-1: Materials Synthesis and Processing, Forschungszentrum Jülich , Germany Robert Vaßen/ Institute of Energy Research, IEF-1: Materials Synthesis and Processing, Forschungszentrum Jülich , Germany Arne Röttger/ Faculty of Mechanical Engineering, Institute for Materials, Chair of Materials Technology, Rur University Bochum , Germany Sebastian Weber/ Faculty of Mechanical Engineering, Institute for Materials, Chair of Materials Technology, Rur University Bochum , Germany Werner Theisen/ Faculty of Mechanical Engineering, Institute for Materials, Chair of Materials Technology, Rur University Bochum , Germany |
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In recent years, Fe-based thermally sprayed coatings gained importance for wear and corrosion protection applications. Thus, such Fe-based hard alloys show the potential to replace high cost Ni and Co base alloys. In this context, tool steels are attractive candidates for wear resistance applications as they are characterized by high strength and high hardness due to the presence of large volume fractions of hard phases like carbides, nitrides and borides. The best results in terms of microstructure and mechanical properties have been obtained using powders as starting materials. Therefore, powder metallurgy and rapid solidification are the most suitable methods to produce such tool steels. These production routes ensure the homogeneous distribution of fine hard phases in the microstructure resulting in improved mechanical properties compared to conventional ingot metallurgy. Thermal spray technology can be used to produce rather thick coatings of wear resistant tool steels. Especially high velocity oxy-fuel (HVOF) spraying is able to deposit dense coatings with a low tendency of oxidation of feedstock powders during deposition. Thus, it provides the scope to work on ultrahigh boron containing tool steel coatings. The present study aimed to investigate the feasibility of HVOF spraying of tool steel coatings with high boron and high carbon contents. A full factorial experimental design was established to investigate the influence of process parameters on coating formation. The coatings were investigated by optical and scanning electron microscope, XRD and microhardness measurements. The microstructural studies revealed that the coatings are strongly characterized by high density micro-cracks. From the results of experimental design, spray distance was identified to be the most influencing process parameter on the coating characteristics. Micro-cracks were found to be decreased as the spray distance increases. However, micro-cracks in the coating could not be eliminated completely. Phase analysis showed that the coatings are composed of complex borides which resulted in high hardness values of 980 HV0.05 and show the potential for wear resistance applications. |