Evolution of tribological properties of reactor-grade NiCr-B coating

Abstract

The tribological properties of reactor-grade NiCr-B hardfaced coating were studied at a constant load and sliding velocity. The objective of the present article is to investigate the changes in coefficient of friction that accompanies morphological and phase changes occurring in wear scars. Such changes result from the sliding with a spherical steel ball. The transition from the low to high coefficient of friction at higher sliding distance is attributed to severe cracking as well as fretting wear-induced deformation of surface oxide scales. Increased value of coefficient of friction arises from protracted sliding over longer distances continued to deform and detachment of weakly adhered oxides like Fe₂O₃ and Cr₂O₃. Such scales are tribochemically formed on the wear scars and contribute to alteration in the coefficient of friction. The evolution of oxide phases in wear scars is found to be one of the main mechanisms for dissipation of frictional force.