| Popis: |
Pin-on-disc wear and friction of hypereutectic ductile iron, the type employed for automotive components, was investigated at sliding speeds of 5 and 7.5 m $s^{-1}$, before and after laser surface treatment by $CO_2$ continuous- wave and Nd-YAG pulsed lasers. A significant increase in transition load and wear resistance upon laser treatment has been attributed to the ultrafine microstructure and high hardness; laser-melted ledeburite was superior to martensite by transformation hardening. Wear rate at a specific contact pressure and sliding speed bears a log-linear relationship with the harmonic mean of tensile and fatigue stress of ductile irons. The role of lubrication by graphite during mild wear and plastic deformation in severe wear of pearlitic ductile iron, and its enhanced resistance to plastic flow on laser melting, have been confirmed. The coefficient of friction of a ductile iron pin sliding on a steel disc before and after laser melting has been determined and compared with that of white iron of identical composition and structure obtained by conventional chilling. |
