Abstract
Self-lubricating coatings extend the efficient dry-operational life of cutting and forming tools. In the current work, millimeter-thick NiCrBSi coatings with 10 wt% metal sulfide i.e. Ni3S2, CuS, or Bi2S3 were fabricated on a stainless steel substrate by laser cladding (in-situ alloying). Thermodynamic modelling utilizing the calculation of phase diagrams method (CALPHAD) was performed to predict the phase evolution during laser melting. Electron microscopy methods combined with X-ray diffraction and Raman spectroscopy were used to elucidate the developed microstructure. The coatings were further subjected to reciprocating dry sliding wear against a martensitic steel ball counterbody using a ball-on-plate configuration at 0.1 m/s and 50 N (Hertz contact pressure 1.7 GPa). The tests were conducted at room temperature (20), 400, and 600 °C. The results demonstrate a self-lubricating behavior of the sulfide coatings resulting in friction reduction by ⁓60 % at room temperature and ⁓40 % at 400 °C sliding, particularly for Bi2S3-added cladding, due to the prevalent existence of lubricious phases of chromium sulfide (CrxSy) along with others (NiBi, Bi) and leading to ‘self-healing’ phenomena. The results are reported in comparison to the unmodified NiCrBSi alloy.
Published Version
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