Key Engineering Materials Vol. 674

Abstract: In this study, the tribological characteristics of plasma thermal spray coatings are studied with particular interest on formation and performance of Cr, Ti and Zr oxides under dry sliding at 500 °С with Pin-On-Disc configuration against NiAl. Plain Cr₂O₃, TiO₂ and ZrO₂ coatings were tested to trace the difference between performance of original and in-situ formed oxides. Friction surfaces were examined using SEM and X-ray spectral analyses. The highest wear resistance of NiAl-CrB₂ composite coatings can be related to the formation of Cr₂O₃ during the tribosynthesis process.

Abstract: Steel and cement industries frequently experience from the failure of its core components due to high temperature (HT) operation at heavy loads causing high stress abrasive wear. In this work the effect of load and temperature on the abrasive wear behaviour is investigated for two Fe-based materials (a ferritic cast iron with Cr-carbide network and a carbide-rich complex alloyed hardfacing) in order to select materials for plant specific demands. Thereby the role of the carbide content and its distribution is of interest. A modified ASTM G65 setup was used for HT abrasive wear testing. The applied loads were 10, 45 and 80 N, and temperatures were room temperature (RT), 500 and 700°C. During testing coefficient of friction was measured and abrasive was collect­ed to characterise the wear behaviour (low stress/high stress condition).High stress abrasion was found to be the dominant mechanism at higher loads for all temperatures. A nearly linear increase of wear rate with raising normal loads was found for both the materials. Wear rates at RT were found to be similar for the two alloys, however the complex alloy showed increased wear at HT. The cast steel formed protective mechanically mixed layers (MML) by abra­sive embedding at HT. The hardfacing on the other hand showed brittle behaviour, which worsened with temperature. Based on these results it was concluded that very hard carbide-rich hardfacings performed unbeneficial at high stress conditions and MML-forming materials should be preferred for HT operation under these conditions.

Abstract: In different fields of high abrasive processes, e.g. in agriculture and mining industry, components made of tempering steel are additionally protected with a wear resistant alloy on high loaded sections. An industrial standard process flow includes heat treatment of components after hardfacing process. However, the exact effect of heat treatment procedure on wear performance of hardfacings is still mostly unknown.The main aim of this study was to determine the influence of substrate heat treatment on iron and nickel based hardfacings under two and three-body conditions. Commonly used wear resistant tempered steel was used as substrate material. Heat treatment investigations were performed on two Fe-based tool steel alloys (M2 and FeVCrC) and a Ni-based alloy reinforced with WC/W₂C (Ni-FTC) deposited by plasma transferred arc technology (PTA), respectively. After hardfacing a heat treatment optimized for tempered steel substrate was performed on hardfaced samples.Microstructure investigations were done by optical microscopy, scanning electron microscopy and hardness measurements. Additionally wear behavior was estimated by dry-sand rubber-wheel test (three-body abrasion) and continuous impact abrasion test (two-body abrasion).Results showed significant influence of heat treatment, due to microstructural changes, on wear performance under 3-body conditions of Fe-based tool steels. This effect was not as pronounced in Ni-based alloy than in types of tool steel. Interestingly, in both M2 tool steel and Ni-based systems heat treatment led to decrease 2-body wear resistance. However, heat treated V-rich tool steel type showed good wear performance in continuous impact abrasion test. Composed wear map, based on this study, shows critical changes in general wear performance for investigated hardfacings.

Abstract: Nitriding of tools and engineering components is a well-established surface modification procedure in many industries to ensure operational efficiency. The focus of this work is laid on understanding the influence of nitriding processing technology on the resulting surface properties which strongly dominate its tribological performance. Therefore, nitriding layers based on salt bath and plasma procedure were realised using 31CrMoV9 substrate. The surface roughness before nitriding was set to a R_a value of ~0.16 μm which corresponds to at technically fine grinded surface. 3D measurements as well as SEM micrographs of the nitrided surfaces were compared to the original surface prior to the nitriding procedure. Additionally, cross-section microscopy and hardness depth profiles were done to describe nitriding layer structure and nitriding hardness depth (NHD). Results show a correlation of nitriding processing parameters with the resulting compound layer formation and nitriding hardening depth (NHD). An increase of surface roughness during nitriding can be correlated with the growth of ɛ-nitrides on top of the surface.

Abstract: Two types of press hardening experiments were carried out to investigate the behavior of ZnFe coated 22MnB5 steel in direct press hardening process. The coating properties were studied using variable process temperatures and times with a flat-die and a forming tool. Coatings were analyzed with optical and scanning electron microscopes. The results indicated that steels that have low coating weights may be processed successfully with short dwell times. For high coating weights a significantly longer dwell time is needed. The behavior of ZnFe coating in hot press forming experiments was in line with literature and the findings of the flat-die experiments. Thus, the feasibility of the experimental press hardening equipment was confirmed.