COMPARISON BETWEEN NANOPHASE FORMATION DURING FRICTION INDUCED SURFACE WEAR AND MECHANICAL ATTRITION OF A PEARLITIC STEEL

The surfaces of steel railroad tracks experience wear-induced hardenin g within a surface layer more than 100 mu m in thickness. The grain si ze is reduced to 15 - 20 nm, resulting in an increase of Vickers hardn ess by a factor of four, as determined by nanoindentation measurements . For comparison, the microstructure of mechanically alloyed powder sa mples is found to be similar to those of the wear-induced surface laye r. As such, the ball Milled powder samples can be used as a model syst em for characterizing the chemical, mechanical (hardness, Young's modu lus, coefficient of friction) and thermal properties of the wear induc ed nanophase surfaces.