INFLUENCE OF A LASER TREATMENT ON THE TRI BOLOGICAL PROPERTIES OF DUCTILE CAST-IRON - APPLICATION TO LASER SPOT TREATMENTS

Cast irons are unique tribological materials that can be used in a wid e range of applications, particularly those in which wear resistance i s important. Laser processing permits the improvement of material wear and friction characteristics. The unlubricated wear of ductile cast i ron sliding against an alumina counterbody under mild pin-on-disc test ing conditions was studied. The evolution of the wear coefficient as w ell as metallographic observations revealed an oxidational wear mechan ism, characterized by hematite formation. The estimation of contact te mperatures cannot explain only the formation of this oxide. The wear o f the cast iron is significantly influenced by the variation of operat ional conditions (normal load, sliding velocity and humidity). The stu died cast iron has been treated using a CO2 laser in both continuous a nd pulsed modes). The initial pearlite is transformed to martensite. A nalyses of the laser processed surfaces showed a dramatic increase in microhardness. The same oxidational wear mechanism as in the case of t he non treated material occurs. The wear resistance of the laser treat ed cast irons is significantly enhanced; it has a better resistance to abrasion and plastic deformation due to the fine and homogeneous micr ostructure produced by laser treatment. The wear of the laser treated cast iron is not influenced by the variation of operational conditions (normal load, sliding velocity and humidity). The above tribological study has been applied in an original type of laser spot treatment, wh ose principle is based on the partial treatment of the surface accordi ng to a given pattern. The variation of hard and soft zones could poss ibly lead to topography changes, which can be beneficial for tribologi cal applications. Under the studied conditions, the different patterns of laser spot treatment had no influence in the cast iron wear resist ance. The improvement of the laser-treated areas wear resistance canno t overcome the favourable effect of oxidation on the untreated areas.