Tribologically modified surface layer results from the energy dissipated in the frictional
contact area. This layer usually has a different elastic modulus and hardness from the
substrate, and its structure corresponds to the intermediate stage between a material of the
first-body and debris of the third-body. Even though, the existence of the tribologically
transformed structure in the fretting contact has been well proven, the formation and
mechanical transformation mechanisms are still not clear. Hence, in this paper, evolution of …

Highlights• Nano-indentation mapping is a powerful technique for probing worn surfaces• In-
situ local friction-induced surface modification process quantified• Tribologically
Transformed Structure forms within the initial fretting cycles• Distinctive structural changes
within the worn layers observed by modified XRD method• The approach can be used to
improve reliability of predictive wear models