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Hastelloy C276-NbC Composite Coatings: Outlining Their Features from a Macro- to Microscale
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DOI：10.1007/s11666-026-02295-2.png)
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Abstract
En 中文
The synthesis of composite coatings by laser cladding has been extensively researched, although it still has some inherent challenges, such as the non-uniform distribution of reinforcement particles and microstructure predictability. This work focused on a macro- and microscale evaluation of Hastelloy C276TM reinforced with 10, 30, and 50% NbC. The characterization involved scanning electron microscopy, Vickers hardness, and wear performance from localized scratching and ball-on-flat reciprocating wear tests. Results showed that the addition of 10% NbC leads to an increase in interdendritic networking carbides. From 30% reinforcement onward, the metal matrix is reinforced with unmelted NbC particles, primarily solidified petaloid-like NbC and an interdendritic carbide network. Being NbC petals the first constituent to solidify, the higher their fraction, the lower the interdendritic network formed. Besides, the distribution of unmelted particles is visibly heterogeneous, showing accumulation close to the weld interface between beads due to the Marangoni and buoyancy effects. Beyond that, pores are concentrated, but not limited, to the weld interface, showing the harmful effect of niobium-iron oxides as contaminants from the NbC powder feeding. Otherwise, the most promising and wear-resistant microstructural region was that containing large contact patches of unmelted NbC particles, in turn, confirmed by the scratch testing. Nevertheless, given the brittle nature of the reinforcement and the low hardness of the nickel matrix, NbC cracking was observed under contact loading. Therefore, the distribution of unmelted particles and the hardness of the metal matrix remain optimization topics to be further addressed in depth. Metal-matrix composites (MMCs) are currently a topic of study in laser processing due to their strong potential for achieving desirable mechanical properties in the cladding layer. However, their synthesis has some inherent challenges, such as the non-uniform distribution of reinforcement particles and microstructure predictability. The main contribution of this study lies in critically discussing the microstructure of multi-bead coatings, contributing to their predictability and also pointing out potential improvements, providing experimental evidence and groundwork for future research, beyond the valuable insights that can shed light on the development of laser composite coatings.
Keywords:
hardness
hastelloy C276TM alloy
laser cladding
microstructure
multi-beads
NbC
niobium carbide
scratch and wear resistance
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