Tribological behavior of Ni-based self-lubricating claddings containing sulfide of nickel, copper, or bismuth at temperatures up to 600 °C.

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. Ni 3 S 2 , CuS, or Bi 2 S 3 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 Bi 2 S 3 -added cladding, due to the prevalent existence of lubricious phases of chromium sulfide (Cr x S y) along with others (NiBi, Bi) and leading to 'self-healing' phenomena. The results are reported in comparison to the unmodified NiCrBSi alloy. • Self-lubricating NiCrBSi alloy containing Ni 3 S 2 , CuS, or Bi 2 S 3 produced by laser cladding. • Bi 2 S 3 addition results in the encapsulation of pure Bi within Cr x S y phase. • Friction reduction by 60 % and 40 % for sulfide claddings at RT and 400 °C. • Tribolayer self-healing was observed for sulfide claddings at RT and 400 °C. • At 600 °C, oxidation (3rd body) causes high friction and wear of sulfide claddings. [ABSTRACT FROM AUTHOR]