Wear Transition of CrN Coated M50 Steel under High Temperature and Heavy Load

Chi Zhang,Le Gu,Yuze Mao,Guangze Tang

doi:10.3390/coatings7110202

Abstract

The combination of high temperature indentation and wear test provides a useful way to investigate wear of CrN coating and wear transition mechanisms. In this paper, the high temperature hardness of CrN coatings and load bearing capacity, Lb, of CrN coated M50 disks were determined from spherical indentation at temperatures up to 500 °C. Wear tests with different normal loads were carried out at the same temperatures as the indentation tests. The results show that wear mechanism of CrN coating changes with external load, P, and temperature, T. Under a tested condition of P < Lb and T < 315 °C, abrasive is the dominant wear mechanism for CrN coating. Under a tested condition of P < Lb and T ≥ 315 °C, wear of CrN coating transitions into mild oxidation wear due to the lubricating effect of chromium oxide film. Under a tested condition of P > Lb and T < 315 °C, wear of CrN coating was controlled by coating fracture. Under a tested condition of P > Lb and T ≥ 315 °C, wear of CrN coating transitions into the severe wear mode, due to the tensile fracture of oxidation films, thereby leading to adhesion between CrN coating and tribo-counterpart. The presented method can be helpful in predicting permissible load and working temperature in tribological applications of CrN coating.

Highlights

Chromium nitride (CrN) films, with good oxidation, anti-corrosive and anti-adhesive properties [1,2,3,4], are promising candidates for protection in high temperature applications, such as for tools or aerospace rolling bearings
When the tested temperature was below 315 ◦ C, the hardness of 2 μm thick CrN coating was higher than 5 μm thick CrN coating
When the tested temperature was above 400 ◦ C, the 5 μm thick CrN coating had higher values in hardness

Summary

Introduction

Chromium nitride (CrN) films, with good oxidation, anti-corrosive and anti-adhesive properties [1,2,3,4], are promising candidates for protection in high temperature applications, such as for tools or aerospace rolling bearings. The wear of such CrN coating–steel substrate systems at elevated temperatures is still not completely understood [5,6,7,8]. This is because the material removal process for CrN coatings is dependent on operation parameters (load, temperature, etc.). Wear mechanism for CrN coatings may be changed when the external load or working temperature are changed. There is still a lack of information about the wear transition of CrN coatings. The aim of this paper is to evaluate dependency of the wear of CrN coatings on both temperature and external load

Objectives

Methods

Results

Conclusion