Metal matrix composite (MMC) has attracted extensive investigation in material science and engineering due to its excellent properties such as good wear resistance, corrosion resistance and high temperature properties. Recent literatures show increased interests in laser cladded MMC coatings containing various volume fractions of ceramic particles. Our previous research approves that laser melting high-carbon-equivalent powders containing strong-carbide-formation elements (SCFEs) such as Ti, Zr, Nb and V, is favorable for the formation of dispersed, homogeneous and in situ synthesized carbide particles in melt. The particles reinforcement MMC coating displays excellent wearability and good combination of strength and toughness, which has been successfully applied in industrial applications. It is revealed that two or more SCFEs have significant effects on the in situ precipitation of multiple carbide particles and distribution. However, the formation mechanism of the in situ multiple carbide particles was not clearly up to date. This paper focuses on the morphology characteristics and precipitating behavior of the multiple carbides.

The results show that the microstructure of the coatings is typical metastable hypo-eutectic, consisting of twin martensite (M), cementite (Fe3C), residual austenite (γ’) and dispersed in situ synthesized carbide particles. EDS and TEM analyses indicate that the particles are multiple carbides with peritectic structures, indicating their nucleation and growth process. During the in situ precipitation of the multiple carbides, zirconium and titanium play a key role in promoting the nucleation of the particles. ZrC precipitates before TiC, while TiC before WC. The study also shows that Ti is the strongest carbide-formation element.

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