Adaptability of WC/Tool Steel Coatings Controlled by Tribosynthesis of FeWO₄

The aim of the work is to study the effect of sliding velocity on the evolution of the subsurface structure and tribooxidation in a high-speed steel coating reinforced with WC after friction on a steel counterbody without a lubricant.

In this work, we studied the tribological behavior of electron-beam composite coatings obtained from a mixture of R6M5 powder steel and WC in contact with a counterbody made of SHH15 steel. It was found that the structure of the coatings is a matrix based on γ+α' iron, reinforced with skeletal structures of eutectic carbides. A simultaneous decrease in the friction coefficient and wear rate of the coatings with an increase in the sliding velocity from 0.8 m/s to 3.6 m/s was obtained. This is due to the tribochemical formation of iron tungstates FeWO₄ and Fe₂WO₆ at sliding speeds of 2.4 m/s and 3.6 m/s, which then allows the formation of a surface mechanically mixed layer, which, in addition to the said iron tungstates, includes fragments of carbides and metal particles of the coating matrix. Such a friction surface structure provides a solid lubrication effect and protects the underlying coating structures from destruction. The specificity of such an adaptation mechanism is that it is realized at relatively low sliding speeds, which corresponds to the maximum calculated flash temperature of about 290 °C. The discovered tribological adaptation mechanism should contribute to the successful use of electron-beam composite coatings WC/tool steel in various industries.

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