Comparative Study of Tribological Behavior of Electroless Ni–B, Ni–B–Mo, and Ni–B–W Coatings at Room and High Temperatures

Abstract

Ni–B alloys deposited by the electroless method are considered to be hard variants of the electroless nickel family. Inclusion of Mo or W to form ternary alloys improves the thermal stability of electroless nickel coatings. Therefore, in the present work, Ni–B, Ni–B–Mo, and Ni–B–W coatings are deposited; and their tribological behavior at room and high temperatures are investigated. Electroless Ni–B, Ni–B–Mo, and Ni–B–W coatings are deposited on AISI 1040 steel substrates. The coatings are heat treated to improve their mechanical properties and crystallinity. Tribological behavior of the coatings is determined on a pin-on-disc type tribological test setup using various applied normal loads (10–50 N) and sliding speeds (0.25–0.42 m/s) to measure wear and coefficient of friction at different operating temperatures (25 °C–500 °C). Ni–B–W coatings are observed to have higher wear resistance than Ni–B or Ni–B–Mo coatings throughout the temperature range considered. Although for coefficient of friction, no such trend is observed. The worn surface of the coatings at 500 °C is characterized by lubricious oxide glazes, which lead to enhanced tribological behavior compared with that at 100 °C. A study of the coating characteristics such as composition, phase transformations, surface morphology, and microhardness is also carried out prior to tribological tests.