Surface fatigue of molybdenum and Al-bronze coatings in unlubricated rolling/sliding contact

Surface fatigue phenomenon of Mo and Al-bronze coatings was investigated by using two-disc machine under various loadings. Life to flaking and life to complete surface failure of two different types of coatings on low carbon steel substrates were determined in rolling line contact with hardened steel disc as the counter surface. The experimental findings revealed that Mo coatings had superior life to surface failure when compared to Al-bronze coatings under pure rolling and rolling/sliding contacts. The life to flaking decreased for Al-bronze particularly with an increase in the load. An increase in the slip ratio had a negative effect on the Al-bronze coatings giving rise to a very severe wear and sudden surface failures. Optical microscopy and scanning electron microscopy studies also indicated that Mo coatings were subjected to relatively mild wear as compared to those of Al-bronze coatings.