Solidification microstructure of in-situ laser-synthesized Fe-TiC hard coating

- Fe-TiC composite coating is synthesized by In-situ reduction of ilmenite with graphite.
- Planar, cellular, dendritic and eutectic solidifications were occurred toward surface.
- The spontaneous progress of size and morphology of TiC particles was studied.
- Gradual change of coating microstructure resulted in appropriate hardness increment.

Synthesis of Fe-TiC hard coatings on carbon steel substrates was the subject of several researches in previous decades. Various microstructural aspects were mentioned about the matrix and hard particles, therefore a more comprehensive perspective is required for investigation of the microstructures. In this study, a new method was applied for in-situ synthesis of Fe-TiC composite coating. The TiC particles were produced by laser surface treatment of a precursor of ilmenite and graphite powders. By progress of solidification front from substrate to surface, different microstructures were developed in the matrix, including planar growth, cellular and dendritic regions and lamellar eutectic. Some new structural aspects were also detected regarding development of cementite plates through the thickness of coating. Moreover, by variations of solidification conditions gradients of size, morphology and distribution of particles were observed. Microhardness measurements verified that formation of a graded microstructure resulted in appropriate properties.

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