A study on iron oxides and surface roughness in dry and wet wheel−rail contacts

Results indicate that the surface roughness after testing tends towards a saturation level in dry contacts under the given contact condition. The low adhesion problem is unlikely to occur under dry conditions, while thick oxides on rough surfaces result in extremely high adhesion and wear. Under wet conditions, thin oxides help to protect contacting surfaces, producing negligible wear and a smooth surface. Either increasing surface roughness or having thick oxides increases wear. A rough surface is efficient in removing the thin oxide layer in order to recover adhesion under the wet conditions.