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.