Surface nanostructure and tribological properties of metallic materials

Abstract

Duirng sliding friction of metals, in the surface layer (≈ 10 μ) of metals subjected to sliding friction, ultra disperse structures are formed, which to a considerable extent determine the tribological properties of the surfaces. The structures can be considered to be nanocrystalline (NC): micro-fragments with large-angle boundaries are 0.05 to 0.2 μm in size.

The objects of this investigation were the nitrogen-containing Fe-Mn-(Cr) alloys (wt.%): Fe-19% Cr-10% Mn-2% Si-0.7% N-0.07% C and Fe-18% Cr-20% Mn-0.8% N-0.08% C. To compare the obtained results, we also made use of the tribological characteristics of different alloys: Fe-10% Mn-0.05% C, Fe-20% Mn-0.05% C, Fe-11% Cr-13% Mn-0.03% C, Fe-40%Mn-0.05% C and Fe-18% Cr-12% Mn-0.5% N-0.07% C, differing in phase composition, structure and the stacking fault energy (SFE). Tribological tests were done at laboratory-scale plants in conditions of sliding friction for the steel-alloy and abrasive-alloy pairs.

The NC HCP ε-alloys and NC nitrogen-containing FCC γ-alloys possess low friction adhesion coefficients K and high resistance of abrasive wear ε. In these alloys, the developed basal or planar slip characterized by a smaller quantity of the slip systems condition a decrease in the resistance of NC fragments as a result of rotation and, thus, the improvement of tribological properties.

Thus, the essential lowering of friction adhesion coefficient K and intensity of adhesion wear Ih, as well as the increase in the abrasive wear ε of NC HCP ε-Fe-Mn alloy and nitrogen-containing NC FCC γ-Fe-Mn-Cr alloys are mainly related to decreasing the quantity of slip systems in nanocrystals of these alloys (n → ≤3). As a result, the dislocations travel to the boundaries of nanocrystals more freely.