The study involved plasma arc transfer welding (PTAW) for preparing coatings of Inconel 625 alloys that contained different amounts of nano-sized hafnium carbide (nano-HfC) particles. The impact of nano-HfC on the microstructure evolution and mechanical properties of PTAWed Inconel 625 were investigated. The research reveals that nano-HfC decomposes during the high-temperature plasma arc process and then react with O element to generate nano-HfO 2 . These HfO 2 can serve as nucleation sites for MC carbides, which restricts the growth of secondary dendrite arms, leading to a more disordered grain growth direction. Simultaneously, the decomposition of HfC can increase the C/Nb ratio of the matrix, effectively suppressing Laves phase formation while encouraging the development of MC carbides. Compared with IN625, the wear rate of composites at room temperature and 600 °C were decreased. Notably, at 600 °C, the wear rate of the coating with 0.5 wt% HfC is the lowest among all the samples, as reflected by a noteworthy reduction in wear rate of 50 %. This is mainly attributed to the refinement of γ matrix, reduction of Laves phase as well as precipitation of the fine-sized MC carbides. This work illustrates that adding nano-HfC is an effective way to improve the wear resistance of the PTAWed Inconel 625.
An innovative and simplified method of electroless pure‑nickel coating was plated on graphene nanoplatelets (GNPs). The nickel-coated graphene nanoplatelets (NiGNPs) were uniformly dispersed in Inconel 625 (IN625) powder with the ratio of 1:9 by ball milling . Then laser cladding was used to fabricate the NiGNPs reinforced IN625 composite coatings . The survivability of NiGNPs, morphology of precipitated phase, microhardness through transverse section and wear resistance at room and elevated temperatures were studied. The results indicated that the NiGNPs were successfully incorporated into IN625 coatings by laser cladding. Part of them were deduced to be damaged or dissolved into molten pool, which benefited the formation of NbC, but most of them could be observed as exposed GNPs and well-distributed welded GNPs. Compared to laser cladded IN625 coating, the composite coating showed higher hardness at bottom region of cladded coating and smaller size of HAZ due to the improvement of thermal conductivity by additional NiGNPs. Furthermore, comparative wear test demonstrated that friction coefficient (COF) and wear rate were decreased at both room and elevated temperatures. Combined with wrinkled, tiled and rolled GNPs observed on the worn surface, it was revealed that the wear properties were efficiently benefited from superior lubrication between interlayers of GNPs.
In this study, homogeneous dispersion of 1 wt% nano-sized Y₂O₃ particles in Inconel 625 powder was achieved via high-energy acoustic resonance mixing. Subsequently, a dense oxide-dispersion-strengthened (ODS) IN625 superalloy with a relative density of 99.86% was fabricated via laser directed energy deposition. Results showed that Y₂O₃ particles reacted with Al in the matrix to form Y-Al-O complex oxides with sizes ranging from 100 to 200 nm. The nano-Y₂O₃ particles exhibited an active flux effect, enlarging the melt pools and reducing the thermal gradient, which promoted coarser primary grains. Concurrently, Y₂O₃ acted as heterogeneous nucleation sites, suppressing epitaxial columnar growth and promoting a more homogeneous grain structure. This grain homogenization enhanced both room temperature and 700 °C elongation. However, strength reduction occurred due to weakened Hall-Petch strengthening from the coarser primary grains and reduced solid solution strengthening from Nb/Mo segregation, which outweighed the limited dispersion strengthening. During cyclic oxidation at 1000 °C, Y-Al-O oxides provided additional nucleation sites for Cr₂O₃, facilitating the early formation of a continuous and dense protective scale. Y segregation at Cr₂O₃ grain boundaries inhibited outward cation diffusion, shifting the oxidation mechanism to inward oxygen diffusion, thereby reducing the oxide scale growth rate and minimizing growth stresses. Compared to Y₂O₃-free IN625, the ODS-IN625 alloy exhibited a 40.9% reduction in mass gain after 100 h of oxidation, with a dense and continuous oxide scale and no significant internal oxidation.
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