Nanostructured(ns)materials,i.e.,polycrystalline materials with grain sizes in the nanometer regime(typ- ically below 100 nm),have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness.Wear resistance of ns materials,one of the most important properties for engineering materials,has been extensively investigated in the past decades.Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained(cg) counterparts,consistently correlating with their unique structure characteristics and mechanical properties. On the other hand,the superior tribological properties of ns materials illustrate their potential applications under contact loads.The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials,including ultrafine-grained(ufg)materials in recent years.Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear con- ditions including abrasive wear,sliding wear,and fretting wear.Their correlations with mechanical properties will be analyzed.Perspectives on development of this field will be highlighted as well.
