In this work, Fe-based coatings were prepared by laser cladding and the effects of multi-step laser remelting (MLR) on phase components, microstructure evolution, hardness and wear behavior were ...investigated. The as-cladded coating exhibits a complex phase structure and no obvious variation is observed when remelted for 1–3 times. The as-cladded coating comprises three structures including Mo-rich dendrites, γ-(Fe, Cr) matrix and several kinds of intermetallic compounds. The Mo-rich dendrites were gradually refined to nanoscale size grains with the increase of remelting times. The Vickers hardness and wear resistance of the Fe-based coatings improves firstly and then aggravates with the MLR process. The highest hardness of 1487.4 HV0.1 and the smallest wear rate of (0.21 ± 0.01) × 10−6 mm3/(N·m) is obtained when the coating is remelted twice. The improved wear performance mainly comes from the existence of hard intermetallic compounds and the refinement of Mo-rich dendrites. Despite a slight compensation of hardness and wear resistance, the coating remelted for three times also exhibits an excellent wear performance due to the microstructure homogenization and the absence of fatigue damage. This work broadens the opportunities to the microstructure modification and property optimization for laser-cladded coatings and presents further understanding on laser manufacturing technology.
•Multiphase Fe-based coatings with super-high Vickers hardness and excellent wear resistance were prepared by laser cladding.•Multi-step laser remelting process can refine Mo-rich dendrites to nanoscale size, thereby promoting microstructure homogeneity and release lattice stress.•The coating remelted twice has the highest hardness of 1487.4 HV0.1 and the lowest wear rate of (0.21 ± 0.01) × 10−6 mm3/(N·m).•Remelting for three times can prevent the coating from fatigue wear damage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Selective laser melting (SLM) was employed to fabricate an AlSi10Mg matrix composite reinforced by in-situ Al2O3 particles in this study. Immediate laser remelting was then employed to remelt the ...already solidified layer during SLM. The results show that the laser remelting reduces the large irregular pores and enhances the relative density. However, the laser remelting increases the number density of gas pores and results in a high porosity level. The laser remelting also has a significant effect on the microstructure by generating the small melt pools with a homogeneous morphology and refining the cell-like microstructure. Besides, the laser remelting promotes the epitaxial growth of the grains with a preferred orientation and the in-situ formation of Al2O3 particles. Although the promoted formation of Al2O3 particles and fine cell-like microstructure can provide the remarkable hardening effect, the laser remelting can not improve the microhardness due to the porosity-induced softening behavior.
•The in-situ Al2O3 particles reinforced AlSi10Mg matrix composite was fabricated by selective laser remelting.•The in-situ formation of Al2O3 particles was promoted by selective laser remelting.•The reaction between Al and ZnO was activated under the high energy density of laser beam.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In-situ multicomponent alloying in additive layer manufacturing shows inhomogeneous elemental distribution. This study aimed to minimize this inhomogeneity in equiatomic CoCrFeMnNi high entropy alloy ...(HEA) produced by selective laser melting (SLM) from a mixture of elemental powder. A detailed study was undertaken regarding the effects of remelting scan strategy on microstructural and mechanical properties, melt pool geometry, and elemental distribution of CoCrFeMnNi HEA manufactured using the SLM process. The SLM sample with remelting scan strategy showed a homogeneous elemental distribution. The remelted SLM sample showed a homogeneous hardness distribution. The X-ray diffraction of the as-built and remelted SLM showed a single-phase FCC structure, typical for a HEA. Prediction and observation of melt pool depth exhibited a lower depth in the remelted SLM samples. The microstructure of the melt pools of both as-built and remelted SLM showed a fine grain morphology, typical of rapid solidification. The boundary of melt pools in the as-built SLM and the inter-space of melt pools in the remelted SLM consisted of both coarse and equiaxed/columnar dendritic grains. The present results confirmed the possibility of fabricating a homogenized CoCrFeMnNi HEA from mixed elemental powders using SLM with remelting scan strategy.
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•In-situ alloying of equiatomic CoCrFeMnNi HEA using SLM process was investigated.•Laser remelting effect on elemental distribution and grain morphology was examined.•Melt pool size of SLM samples was estimated and compared with experimental value.•Laser re-melting – microstructure – mechanical property relationships were studied.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The forming quality of thermally sprayed coatings is often severely impacted by inherent defects, including porosity, microcracks, and mechanical bonding. The poor adhesive strength hinders the ...utilization of thermal spray technology when fabricating ceramic-reinforced metal matrix composite coatings (MMCCs). Thus, in this study, a negative defocus laser remelting and injection method (LRI) is introduced to modify a thermally sprayed coating with WC ceramics. The microstructure and mechanical property (microhardness, elastic modulus, and wear resistance) evolution of a LRI-modified WC reinforced composite coating is systematically characterized and compared with that for an as-sprayed coating. The LRI method is proven to improve the inherent defects of the initial coating and avoid severe reactions and dissolution of reinforced particles at high temperatures, and can be used to form a high-quality composite coating with a maximum strengthening effect of the ceramic particles. Compared with the initial coating, the elastic modulus and microhardness of the LRI coating are increased by 57.22% and 111.06%, respectively, whereas the abrasion rate is decreased by 54.33%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A new FEM model for laser remelting and surface structure formation was introduced.•Surface structure formation results from deformation of the melt pool ...surface.•Marangoni-convection has virtually no effect on surface structure formation.•Density discontinuity, thermal expansion, and melt pool dynamics are key factors.•Structure height scales linearly for continuous and discontinuous remelting process.
Conventional surface structuring processes often share two crucial disadvantages. Firstly, an additional surface finishing is usually required. Secondly, excess material is wasted. In contrast, during laser remelting, a redistribution of material can be achieved that results in a structured surface with a low micro-roughness. Therefore, this investigation focuses on the mechanism of surface structure formation during laser remelting on the hot work steel H11. A newly developed FEM-model is introduced and surface structure formation is investigated specifically for a sinusoidal modulation of laser power. A fiber coupled Nd:YAG laser was used to emit laser radiation with a focal beam diameter of 250 µm and laser power between 15 W and 215 W. At a scanning speed of 50 mm/s, the structuring of wavelengths from 0.25 mm to 4 mm was investigated. After one process step, structure heights of up to 12 µm were achieved for single tracks. In addition, the theoretical model revealed that melt pool changes lead to a deformation of the melt pool surface, which results in the formation of surface structures. Furthermore, the agreement between simulations and experiments indicates that the Marangoni-convection has only a minor impact on surface structure formation during laser remelting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Surface polishing by laser remelting (SP-LRM) is a novel, versatile, high-speed, and low-cost advanced manufacturing technology for producing high-quality surface finishes. The process utilizes a ...high-power laser that delivers a large amount of instantaneous energy melting a superficial thin layer of material to a molten state. This allows the melt pool to flow driven by thermocapillary and surface tension forces. The target of the process is to melt, reallocate, and resolidify surface peaks into valleys in order to yield a low surface roughness (Sa). SP-LRM, complexity arises from instabilities occurring during laser-material interactions, resulting from non-linear thermodynamics, initial surface topography, overheating, abrupt changes in laser path trajectories involving acceleration and deceleration, and various other factors. These process instabilities significantly affect the attainment of a desired smooth final surface. Presently, the identification of anomalies resulting from a specific set of laser parameters in laser remelting (LRM) is performed offline by assessing the surface topography of LRM using optical profilometer and correlating it with surface non-uniformities that are indicative of process instabilities. This study streamlines the anomaly detection process and identifies the presence of irregularities using an unsupervised clustering machine learning (ML) technique, specifically K-means clustering. During the laser remelting (LRM) process, a high-speed near-infrared (NIR) camera captures relative thermal emission images, which are then classified into a minimum of three clusters using the K-means algorithm. These clusters correspond to positive and negative axial laser beam positions, indicating shifts in the laser spot on the image, and the stability states of laser-material interactions. Preliminary findings show promising results in the employment of artificial intelligence (AI) to enhance LRM as a conventional industrial technology for polishing and structuring tooling surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study explores the impact of micron-Ti microalloying and laser remelting on the microstructure and mechanical properties of laser powder bed fusion (LPBF) Al–12Si alloy, analyzing the underlying ...reasons. The findings show that the tensile strength and elongation at 300 °C (184 ± 13 MPa and 7.4 ± 1.4 %) are on par with other LPBF heat-resistant Al alloys, such as near-eutectic Al–Ce and Al–Ni. Introducing micron Ti (1 wt%) to AlSi12 effectively eliminates the α-Al texture and refines the grain structure, thanks to the strong nucleation effect from the formed D022-(Al, Si)3Ti, leading to enhanced tensile strength in both as-built and heat-treated (300 °C for 2 h) samples, while maintaining ductility within the typical range for LPBF near-eutectic Al–Si alloys. Laser remelting further decreases the presence of unmelted Ti powder in AlSi12Ti and encourages the formation of D022-(Al, Si)3Ti, offering insights into LPBF Al alloy composition design through promoting the melt of the modified powder and improving material homogeneity, especially for incorporating micron powders with high melting points. Additionally, the superior mid-high temperature properties (300 °C) of AlSi12+1 wt% micron-Ti contribute to expanding the database of LPBF Al alloys.
•AlSi12 and AlSi12 + 1 wt% micron-Ti alloys were prepared by LPBF.•Ti microalloying refines the grain size and eliminates α-Al texture of AlSi12.•The laser remelting strategy facilitates the dissolution of unmelted Ti powder.•The tensile strength at 300 °C of AlSi12 was improved through 1 wt% Ti microalloying.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present study assessed the resistance against MD corrosion in a single-layer, oxide-forming NiCrAlSiTaY coating, and a double-layer NiCrAlSiTaY/laser-remelted (LRed) Al2O3 coating on an Inconel ...625 (IN625) alloy. The NiCrAlSiTaY and Al2O3 coatings were applied onto the IN625 substrate using high velocity oxy-fuel spraying (HVOF) and air plasma spraying (APS) techniques, respectively. Coated and non-coated coupons were exposed, for 70 cycles, to a strong carburizing atmosphere of CO-50 % H2 in the temperature range of 550–750 °C to evaluate MD behavior. The results showed that the non-coated IN625 alloy contained a carbide free zone (CFZ), and secondary carbide precipitations of M23C6 and M6C and their subsequent in-situ oxidation were observed in the sub-surface layer. Such a development was indicative of the type III MD characteristic. The results also showed that the single-layer coating successfully protected the alloy, and only a part of the substrate underwent local oxidation. In addition, performing laser remelting (LR) on the Al2O3 coating significantly increased the resistance against the MD of the alloy through the removal of defects such as interconnected porosities, and via alumina phase transformation (γ → α). The lowest weight gain after 70 cycles of MD test was recorded for the double-layer coating coupons.
•Type III metal dusting mechanism was identified in IN625 alloy after 70 cycles of MD test.•Single-layer coating improved resistance against the MD corrosion of the IN625 alloy.•Post laser remelting of double-layer NiCrAlSiTaY/Al2O3 coating improved MD resistance.•The lowest weight gain occurred in the double-layer LRed coating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
