Introduction
In most cases, the failures of engineering materials initiate from the surface, and are very sensitive to the structure and properties of the surface. Optimization of the surface structure and properties may effectively enhance the overall performance of the materials. With increasing evidence of unique properties for nanocrystalline materials, surface self-nanocrystallization [1] is expected to be a new approach to improve the fatigue resistance of conventional materials. Literatures indicate that nanostructured surface layer can lead to a significant enhancement of the failure resistance. For instance, the friction coefficients decreases and wear resistance is enhanced for a surface nanocrystallized low carbon steel [2], the 304 stainless steel with nanocrystalline surface treated by a sandblasting and annealing exhibits considerably high resistance to the corrosion, wear and the corrosive wear compared with those of regularly grained 304SS specimens [3].
So far, most investigations on surface nanocrystallization of metals have focused on annealed materials and low hardness materials, such as pure metals (Fe, Al, Ti) and stainless steel [4], [5], [6] and [7]. However the detailed reports concerning surface nanocrystallization of heat-treated alloy steel and the corresponding friction and wear properties are rare.
The objective of this work is to evaluate the beneficial effects on wear resistance of a nanocrystalline surface layer on quenched and tempered chrome–silicon alloy steel. A nanostructured surface layer was fabricated by supersonic fine particles bombardment (SFPB). The microstructure of the nanocrystalline layer was characterized by different techniques and its friction and wear properties were studied in comparison with the untreated sample. The reasons responsible for the improvement in the tribological properties of surface treated samples were discussed.