THE POSSIBILITIES OF STRENGTHENING OF THE SURFACE LAYER OF NODULAR IRON BY LASER ALLOYING WITH SILICON NITRIDE ON THE EXAMPLE OF A ROCKER ARM

Abstract

In the order to increase the resistance to the friction wear of machine parts appropriate surface treatment application is needed. The aim of presented research was to evaluate the laser alloying with silicon nitride effects obtained in the surface layer of nodular iron and to select the laser treatment parameters that should be appropriate for the treatment of the one of the engine parts, which is a rocker arm. After implementation of silicon nitride into the nodular iron surface layer using laser heating, a uniform, fine, dendritic microstructure similar to the hardened white cast of the allayed zone was created in all performed variants. This microstructure resulted in at least 4-times higher hardness in comparison to the core material. The hardness and the alloyed zone dimensions were dependent on the laser heat treatment variant. The laser beam power density of 41 W/mm2 and its velocity of 2.8 mm/s were selected for the treatment of the rocker arm. It was caused by the effects obtained in the surface layer. With these parameters, it was possible to achieve the hardness of 1300 HV0.1 and the width of the alloying zone of over 4 mm, which is enough to strengthen the surface area of the rocker arm most exposed to the tribological wear.