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• Pores- and cracks-free TiC/IN625 coatings over AISI 1045 steel were firstly prepared by EHLA. • EHLA TiC/IN625 coatings possessed much more uniform and finer microstructure. • High resistance is attributed to lower surface roughness, smaller dendrite size, smaller grain size, and higher amount of LAGBs. The multi-layer TiC/IN625 coatings were deposited on AISI 1045 steel substrate by conventional laser cladding (CLA) and extreme high-speed laser cladding (EHLA). The surface morphology, microstructure and high-temperature oxidation resistance of the TiC/IN625 coatings were characterized and compared. The results showed that the cladding speed has a significant effect on surface quality. Within the range of the set parameters, the best surface quality is obtained when the cladding speed is 49.8 m/min, where Ra is 11.75 μm and Sa is 13.17 μm. The microstructure of the TiC/IN625 coatings is dominated by dendrites. Smaller dendrites arm spacing and no apparent transition layer are found at the layer-to-layer interface in the EHLA sample. A two-layered oxide structure is formed in the cross-section of all samples. The EHLA sample exhibits a lower mass loss compared to the CLA sample, indicating that EHLA sample can withstand high-temperature oxidation. The improvement of high-temperature oxidation resistance is mainly attributed to the lower surface roughness, smaller dendrite size, smaller grain size, and higher amount of LAGBs. [ABSTRACT FROM AUTHOR]

Extreme high-speed laser cladding (EHLA) was used to develop a pore- and crack-free TiC/IN625 coating. The surface roughness of EHLA could be as low as 6.004 µm. A more uniform dendrite size and composition distribution was obtained by EHLA. The mass gain of EHLA was 57.5% lower than that of the conventional laser cladding sample after hot corrosion in a mixed salt of 75%Na 2 SO 4 + 25% NaCl at 900 ℃ for 60 h. High hot corrosion resistance of EHLA was mainly attributed to the lower surface roughness, smaller dendrite size, smaller grain size, and higher amount of low-angle grain boundaries. • Pores- and cracks-free TiC/IN625 coatings over AISI 1045 steel were firstly prepared by EHLA. • EHLA TiC/IN625 coatings possessed much more uniform and finer microstructure. • The uniformly distributed dendrite sizes and compositions contributed to the formation of a dense oxide film. • Superior hot corrosion behavior of EHLA TiC/IN625 coatings was mainly attributed to the lower surface roughness, smaller dendrite size, smaller grain size, and more low-angle grain boundaries. [ABSTRACT FROM AUTHOR]

Extreme-high-speed laser cladding (EHLA), as a novel surface treatment technique, has attracted great attention because of its high cladding rate and good performance of cladding coatings. However, when depositing coatings with high cracking susceptibility, such as Ni60 coatings, cracks are difficult to avoid. Therefore, an extreme-high-speed laser-induction hybrid cladding technology (EH-LIHC) was innovatively proposed in this study. The effects of different preheating temperatures on the surface morphology, internal defects, microstructure, and mechanical properties of Ni60 coatings that were deposited by EHLA and EH-LIHC were analyzed. The results show that the roughness of the coating deposited by EHLA is 26.228 μm. However, the surface roughness of the coating deposited by EH-LIHC at 400 ℃ decreases to 14.316 μm. Simultaneously, the pores- and cracks-free Ni60 coating was deposited at 400 ℃. The coating dilution rate obviously increases as the preheating temperature rises. When the preheating temperature rises, the size of the grains and precipitates also increases. However, although Fe elemental diffusion is increased, there is no significant effect on the properties of the coating. The hardness of the coating fluctuates between 700 and 900 HV, nearly three times that of the substrate. As the preheating temperature rises, the coating's wear mechanism shifts from abrasive to abrasive and adhesive wear, and eventually back to abrasive wear. The improvement of wear resistance of the Ni60 coating deposited at 400 ℃ was mainly attributed to its high hardness and uniform and dense microstructure. The proposed EH-LIHC technique provides a promising method for the efficient deposit of crack-free coatings with good properties. [ABSTRACT FROM AUTHOR]

While metal additive manufacturing has seen significant growth in recent years, the surfaces produced often need post-processing to improve surface finish, mitigate residual stresses, and remove surface-connected porosity. Laser polishing, by means of remelting a thin layer of the surface, is one post-processing method being investigated for surface finish improvements and other surface enhancements. In this work, the surface morphology and microstructure of laser powder bed fused (L-PBF) stainless-steel 316 L (316 L) before and after laser polishing are characterized by optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscopy (TEM). In addition, the cross-sectional microhardness of the samples is measured and reported. Additionally, the as-built and laser-polished sample's tensile properties are characterized using uniaxial tension tests. The results indicate that the surface roughness of as-built 316 L (Sa = 4.84 μm) can be substantially reduced through laser polishing (Sa = 0.65 μm). After laser polishing, the average grain diameter is reduced and the proportion of low angle grain boundaries (2°~5°) is increased in the L-PBF 316 L. The maximum sub-surface hardness reaches 262 HV, and both the tensile strength and ductility of 316 L are increased after laser polishing. This enhancement is attributed to thermal cycling stresses, grain refinement, the elimination of surface defects, and dislocation strengthening after laser polishing. [ABSTRACT FROM AUTHOR]