Impact of surface laser treatment on the high-frequent cyclic ablation of vermicular graphite cast iron

Abstract

The cylinder head of a high-power diesel engine is often subjected to a harsh cyclic ablative environment. Vermicular graphite cast iron exhibits commendable mechanical properties and high-temperature performance. However, the occurrence of thermal cracking can lead to a deterioration in cyclic ablative resistance. Surface laser treatment can enhance the thermal stability of the material, which exists potential to mitigate such failures. To investigate the impact of surface laser treatment on the high-frequent cyclic ablation of vermicular graphite cast iron, we prepared surface-modified vermicular graphite cast iron by applying varying laser power to its surface. The results indicated that different microstructures were observed on the laser-treated surface of vermicular graphite cast iron. Vermicular cast iron subjected to laser treatment at power levels of 300 W and 500 W demonstrates an increase in hardness, which can be attributed to the formation of fine ledeburite and martensite on its surface. The 500 W treated vermicular graphite cast iron showed the best ablation resistance. The mass and line ablation rates are −0.026 mg/s and −0.12 μm/s, respectively. The damage to the matrix is less significant compared to that of other materials. The reason lies in its small and uniform surface structure, which can mitigate thermal stress damage during the initial stages of ablation and enhance its oxidation resistance. By reducing the thickness of the oxide layer, the thermal conductivity of the surface is improved, resulting in a decrease in surface temperature and an enhancement in the material's resistance to high-frequent cyclic ablation.