PSI - Issue 5

Pavol Hvizdoš et al. / Procedia Structural Integrity 5 (2017) 1385–1392 Pavol Hvizdoš et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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Co

C

Fig. 8 EDX analysis inside wear track of 2.2% C material tested at 200 °C against the steel ball - visible oxidation of the worn surface parts.

At the highest testing temperature (400 °C) the highest values of wear rate were observed (5.10 -7 mm 3 /N.m with steel counterpart and up to 3.10 -6 mm 3 /N.m with WC-Co counterpart). The reference material and material containing 1.8 wt.% C show lower wear rate than the material with the highest carbon content (2.2 wt.%), as in previous cases. Wear damage mechanisms at 400 °C are similar to the other testing temperatures but the worn surfaces are strongly influenced by surface titanium oxidation, similarly as documented by the EDS oxygen maps in Fig. 8. 5. Conclusions Three TiTaCN-Co based materials with different amount of graphite addition were prepared by mechanochemical technique. It was found that the graphite addition prevented the formation of undesirable brittle intermetallic compounds. The consequences can be summarized as follows:  Hardness of the experimental materials slightly decreased with increasing carbon amount.  Fracture toughness dramatically increased with increasing carbon amount.  The dependence between temperature, ball material and friction coefficient is complex. At room temperature the friction coefficient between WC-Co ball and experimental materials decreased with increasing carbon addition. In case of the steel ball it was constant. At higher temperatures these trends were not kept, as the microcracking and oxidation became more prominent damage mechanisms.  Wear rates were low against steel, much higher against WC-Co balls, as can be expected base on the hardness of the counterbodies.  Wear rate significantly increased with increasing temperature.  Wear rate increased with increasing carbon content and hardness of the tribopartners.  Main wear damage mechanism at room temperature was abrasion, accompanied by microcracking at porosity. At 200 °C starting of oxidation of Ti, accompanied by adhesion, was observed. At 400 °C microcracking intensified and loosening and smearing of TiO 2 took place. This lead to higher volume loss and thus to reduced wear resistance.

Acknowledgements

The work was financially supported by the projects APVV-0108-12 (ConCer) and APVV-15-0014 (ProCor).

References

Anstis, G.R., Chantikul, P., Lawn, B.R., Marshall, D.B., 1981. A critical evaluation of indentation techniques for measuring fracture toughness: I, Direct crack measurements. Journal of the American Ceramic Society 64, 533-538. Baláž, P., Choi, W.S., Fabián, M., Godočíková, E., 2006. Mechanochemistry in the preparation of advanced materials. Acta Montanistica Slovaca 11, 122-129. Beyer, M.K., Clausen-Schaumann, H., 2005. Mechanochemistry: the mechanical activation of covalent bonds. Chemical Reviews 05, 2921-2944. Chicardi, E., Córdoba, J.M., Sayagués, M.J., Gotor, F.J., 2012. Absence of the core-rim microstructure in Ti x Ta 1-x C y N 1-y -based cermets developed from a presintered carbonitride master alloy. International Journal of Refractory Metals and Hard Materials 33, 38 – 43. Chicardi, E., Torres, Y., Córdob a, J.M., Hvizdoš, P., Gotor, F.J., 2014a. Effect of tantalum content on the microstructure and mechanical behavior of cermets based on (Ti x Ta 1-x )(C 0.5 N 0.5 ) solid solutions. Material Design 53, 435 – 444.