Laser induced microstructural modification of ductile iron has been studied as a function of processing parameters such as power density and beam-substrate interaction time. The high energy density CO2 laser source changes and refines the microstructure of the near surface layer, leading to enhanced hardness and wear resistance. Two basic types of microstructure are produced by laser processing, depending on the solidification/cooling rate of the melted zone. High solidification/cooling rates produce a mechanically metastable austenitic matrix, and a dendritic microstructure with interdendritic cementite films. Low solidification/cooling rates produce a very hard, lamellar ferrite+cementite microstructure. A mixed microstructure of intermediate hardness is produced at intermediate cooling rates. Detailed optical and electron microscopy studies of these microstructures as a function of laser processing parameters are reported.
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