Microstructure and mechanical properties of copper–titanium–nitrogen multiphase layers produced by a duplex treatment on C17200 copper–beryllium alloy

• The duplex treatment of plasma nitriding of Ti deposited Cu alloy is investigated.
• A gradient thermal diffusion surface layer is produced by the duplex treatment.
• The surface hardness of the duplex treated layer is comparable to nitrided steels.
• The tribological property of the duplex treated layer is significantly improved.

In this study, a copper–titanium–nitrogen multiphase coating was fabricated on the surface of C17200 copper–beryllium alloy by deposition and plasma nitriding in order to improve the surface mechanical properties. The phase composition, microstructure and microhardness profiles of the as-obtained multiphase coating were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and Vickers microhardness measurements, respectively. Pin-on-disk tribometer and SEM equipped with energy dispersive spectrometer (EDS) were applied to measure tribological properties and analyze wear mechanisms involved. The XRD results show that the phase composition changes with nitriding temperature. The Ti2N layer is replaced by a Cu–Ti intermetallic layer when the nitriding temperature is higher than 700 °C. The Cu/Ti ratio in the multiphase coatings remains at a constant value of 2:1 due to the incorporation of nitrogen atoms. The surface hardness achieves a maximum value of 983 HV at 650 °C, and decreases as the nitriding temperature increases. The increased hardness corresponds to the improved wear resistance and decreased frictional coefficient and the surface hardness is proportional to the wear rates. The wear mechanism depends on the phase composition of the multiphase coatings. With the nitriding temperature increasing, the oxidative wear mechanism changes to adhesive and abrasive mode.

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