Evolution behavior of ex-situ NbC and properties of Fe-based laser clad coating

Abstract

The NbC-reinforced Fe-based laser clad coatings were obtained by ex-situ processing. The evolution behavior of ex-situ NbC was quantitatively researched and the microhardness and wear resistance of laser clad coatings were also investigated. The results show that the ex-situ NbC added in clad powder can decompose and re-precipitate during the laser clad process, which affects significantly the content and morphology of NbC. After the added NbC particles decompose during the heating process of laser beam, Nb and C atoms are released into the molten pool. However, a part of Nb atoms cannot react with C to form NbC, but dissolve into the coating matrix or form Fe2Nb with Fe atoms, which decreases the content in NbC in clad coating. Moreover, Most of re-precipitated NbC phases belong to eutectic microstructure and exist in coatingin the form of network or featherlike structure instead of theoriginal particle shape. As heterogeneous nucleation core, the undecomposed NbC can promote the re-precipitation of new NbC phases. These new NbC can precipitate on the surface of undecomposed NbC particle, and then form the larger block and petaloid NbC phase with core. Both dissolved Nb atom and NbC precipitate can enhancethe microhardness and wear resistance of coating, but the promotion role on the wear resistance is more obvious.