•A novel laser polishing method for Al2O3 ceramics with original high surface roughness is proposed.•Picosecond laser is used to form a remelting layer on the surface to eliminate surface void ...defects.•The remelt layer is then quickly removed using femtosecond laser ablation fracture processing to eliminate the cracks.•Finally, the surface is precision polished using a layer-wise ablation to obtain a submicron smooth surface.
Al2O3 ceramics are widely used in industry due to their excellent mechanical and physical properties. However, microcracks, voids and high surface roughness (Sa) on the surface of Al2O3 ceramic parts produced in conventional industrial or additive manufacturing have been one of the technical bottlenecks limiting their high-performance applications. In this paper, a novel method of ultrafast laser ablation fracture polishing (ULAFP) of Al2O3 ceramic parts is proposed for improving the surface quality and enhancing the mechanical properties of the polished surfaces. The ULAFP method is developed with an ultrafast laser, which can be set up as a picosecond (PS) or a femtosecond (FS) laser. The PS laser is used to form a remelting layer on the surface to eliminate surface void defects. Combining laser ablation and laser thermal stress-induced crack extension effects, the FS laser is used to rapidly remove the remelted layer and obtain a surface free of crack defects and finally implement FS laser layer-wise ablation to achieve smoother surface finish. The FS laser energy density is controlled at a critical state close to the ablation threshold of the material to avoid surface defects. This ULAFP can reduce the surface roughness (Sa5.254 μm) polishing of Al2O3 ceramics to 0.80 μm, while controlling the total ablation depth of the polishing process to below 100 μm maintaining the dimensional accuracy of the part and dramatically improving the mechanical properties of the polished surface. Compared with the original surface, the hardness and elastic modulus of the polished surface improved by 104.6% and 63.9%, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A hypoeutectic, Fe-modified Al–Ce–Ni alloy (Al–6Ce–3Ni-0.7Fe, wt.%) is studied in terms of microstructure, thermal stability, ambient temperature strengthening, and creep resistance. The as-cast ...microstructure consists of primary Al dendrites and interdendritic binary eutectic regions (Al–Al11Ce3 and/or Al–Al9(Fe,Ni)2), with micron/submicron lamellar spacing, depending on the location along the height of the ingot. The cast alloy exhibits excellent coarsening resistance at 400 °C, with mostly unchanged microstructure and microhardness after 6 weeks of aging, indicating good thermal stability of Al11Ce3 and Al9(Fe,Ni)2. Orowan strengthening and load transfer are identified as strengthening mechanisms at ambient and elevated temperature. A high volume fraction of the intermetallic phases (providing load transfer) and relatively coarse eutectic spacing (for modest Orowan strengthening) result in a moderate as-cast microhardness of 566 ± 32 MPa. Creep resistance at 300 and 350 °C is similar to a binary Al-12.5Ce eutectic alloy (with twice the Ce content) because of two countering effects: Al–6Ce–3Ni-0.7Fe shows a higher volume fraction of strengthening intermetallic phases, but it also exhibits a large fraction of primary Al dendrites which weaken the alloy. By contrast, the alloy, when laser-remelted at the surface, has a fully eutectic microstructure without primary aluminum dendrites achieved by high undercooling on solidification, with a refined network of eutectic phases that doubles the microhardness as compared to the cast alloy. Whereas coarsening is faster due to the shorter diffusion distances between the eutectic phases, hardness remains ∼30% higher than the as-cast alloy after ∼6 weeks aging at 400 °C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•An attempt, combined with laser cladding and laser remelting, was used to develop HEA coating.•After laser remelting, the phase composition remains unchanged.•The micro-hardness of as-remelted HEA ...coatings is increased, up to ∼900HV.•The wear resistance of as-remelted HEA coatings is improved.•The results suggest practical applications, like coatings on brake pads for wear protection.
An attempt, combined with the technologies of laser cladding and laser remelting, has been made to develop a Ni-Cr-Co-Ti-V high entropy alloy coating. The phase composition, microstructure, micro-hardness and wear resistance (rolling friction) were studied in detail. The results show that after laser remelting, the phase composition remains unchanged, that is, as-cladded coating and as-remelted coatings are all composed of (Ni, Co)Ti2 intermetallic compound, Ti-rich phase and BCC solid solution phase. However, after laser remelting, the volume fraction of Ti-rich phase increases significantly. Moreover, the micro-hardness is increased, up to ∼900HV at the laser remelting parameters: laser power of 1kW, laser spot diameter of 3mm, and laser speed of 10mm/s. Compared to the as-cladded high-entropy alloy coating, the as-remelted high-entropy alloy coatings have high friction coefficient and low wear mass loss, indicating that the wear resistance of as-remelted coatings is improved and suggesting practical applications, like coatings on brake pads for wear protection. The worn surface morphologies show that the worn mechanism of as-cladded and as-remelted high-entropy alloy coatings are adhesive wear.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
WC/Ni-based composite coatings have received much attention in recent years. However, the application of laser cladded WC/Ni-based coatings encounters many issues, such as WC particle distribution ...inhomogeneity and coating cracking. In this study, the integrated method of in-situ temperature field assistance and post-laser remelting (ITFA+PLR) is proposed for NiCrSiBC-WC coating preparation and compared with mere ITFA and PLR. The results show that the three methods eliminate cracks and enhance overall mechanical qualities, outcompeting the single laser cladding process even with higher WC concentration. ITFA helps the interfacial reaction of the WC particles, while PLR distributes large-sized WC particles and produces and disperses refined carbides. With this, ITFA+PLR combines their benefits and achieves a uniform distribution of fine carbides and original WC. When the phases are analyzed, the relationship between microstructure (i.e., large-sized WC and fine carbides) and coating hardness is quantified and established, yielding a generalized microhardness index. With this unitless microhardness index, it is discovered that the increased density of fine carbides dominates the hardness increase. In summary, ITFA+PLR promotes fine carbide formation, improves its distribution, and obtains the highest hardness for NiCrSiBC-WC coating. With the generalized carbide phase-determined microhardness index, this paper guides the design of crack-free WC/Ni-based coatings and enlightens the improvement of NiCrSiBC-WC coating's mechanical properties.
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•Novel ITFA+PLR method is developed for crack-free NiCrSiBC-WC coating.•Large-sized WC and fine carbide evolution in ITFA, PLR, and ITFA+PLR are studied.•Fine carbides are governed by the processing temperature, influencing properties.•Quantitative relationship between hardness and fine carbides is clarified.•A novel unitless microhardness index is proposed for hardness-carbide relationship.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cavitation erosion resistance of 8wt.% yttria stabilized zirconia has been investigated in specimens prepared by atmospheric plasma spraying and laser remelting post treatment. The results indicate ...that as-sprayed coatings involve defects such as primary cavities and initial micro cracks inside a particle and among the interfaces of particles. When the specimens are subjected to cavitation erosion, the micro cracks initiate and coalesce along with chip removals. Laser remelting produces a dense glazed layer with some cracks though the coatings. With the increasing of erosion time, large pieces are delaminated from coating-substrate interface leading to a significant mass loss. However, the resistance of laser remelted coatings to cavitation erosion is significantly improved when they are impregnated with epoxy by vacuum castable mounting. The relationship between cracks formed inside the laser remelted YSZ coatings and their damage mechanism under cavitation is discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The presented article describes the influence of the laser remelting process on microstructural changes, heat-affected zone size, dilution effect and hardness level of hard-facing Ni-based coatings ...based on NiCrBSi system with the addition of W2C\WC carbide in the context of thermal diffusivity and specific heat value. This relationship is practically not described in the literature. Three commercial systems, Metco 15E, Metco 36C and customized Metco 15E + DURMAT® FTC, were deposited by flame-spraying on carbon steel with the following laser remelting treatment with different energetical variants. The total deposited in coatings energy value was used as a comparison criterion. The reflectance effect was also considered as a factor influencing the total energy transferred to the coatings. The dilution effect, heat-affected zone size, and hardness level in the context of microstructural changes caused by the laser remelting process in the context of thermal diffusivity were analyzed. It was revealed that the reflectance factor can be omitted as a negligible form point of view of total deposited energy in the coating. The thermal diffusivity of coating materials is similar, but the difference in HAZ and dilution effect is very significant. It can suggest that the thermal diffusivity is an important factor affecting microstructural changing in laser remelting process of flame sprayed NiCrBSi systems, especially when is considered together with specific heat related to presences of different fraction of tungsten carbide.
•Reflectance value of NiCrBSiC coatings nit affecting on total deposited energy.•Thermal diffusivity is a factor strongly affecting the HAZ size and dilution effect.•The W2C/WC dissolution caused the decreasing of thermal diffusivity value.•The W carbide stabilizing the Cr carbides and borides when dissolve in the matrix.•The relationship between the HAZ, dilution and hardness are complex and multilevel.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
NiCrAlY coatings are widely applied bond coatings in thermal barrier coating systems to prevent high-temperature oxidation of turbine blades. However, the uncontrollable microstructure design and ...high surface roughness seriously affect the oxidation resistance. Herein, NiCrAlY coatings fabricated through arc ion plating were subjected to high-repetition-rate femtosecond laser remelting (HRR-FLR) treatment. This study assessed the surface rumpling behavior, residual stress evolution, and thermally grown oxide (TGO) layer growth under thermal cyclic oxidation at 1100 °C to determine their impact on coating lifetime. The results indicated that the HRR-FLR treatment was effective in reducing surface roughness, restructuring microstructures, and redistributing reactive elements. These improvements facilitated the formation of a flat, continuous, and dense alumina layer, enhancing the spallation and rumpling resistance of TGO. Consequently, the efficiency of HRR-FLR technique was proven in significantly improving the lifetime of NiCrAlY coatings, which provides a new application prospect of femtosecond lasers in remelting and polishing of metallic surfaces.
•NiCrAlY coatings prepared via AIP method were treated via HRR-FLR technique.•Microstructural modification and reactive elemental redistribution were obtained.•The surface rumpling behavior and residual stress evolution of TGO was analyzed.•The dense remelted layer facilitated the resistance of TGO to spallation and rumpling.•HRR-FLR technique is an effective method to improve the service life of NiCrAlY coatings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Laser additive manufacturing is an ideal choice to fabricate metal parts with complicated geometric shapes. In this research, (Fe60Co35Ni5)73.5Si13.5B9CuMo3 magnetic alloys with good saturation ...magnetization and mechanical properties were prepared by laser additive manufacturing and laser remelting. The influence of laser remelting on the hysteresis loop, microhardness, microstructure, and wear resistance of a single layer was investigated. It is found that laser remelting has a beneficial effect on the magnetic and mechanical properties. The microstructure of the remelted alloys is mainly composed of dense and homogeneous dendrites. The alloys are dominated by body-centered cubic microstructures. After laser remelting, the alloys exhibit higher saturation magnetization (165.5 emu/g) and lower coercivity (12 Oe). In addition, with the reduction of grain size, the wear resistance and microhardness of the alloys increase significantly.
•A soft magnetic alloy is optimized by laser additive manufacturing.•Laser remelting has a beneficial effect on the magnetic and mechanical properties.•After laser remelting, the alloys exhibit higher saturation magnetization and lower coercivity.•Composition-microstructure-magnetic property relationships are provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Extremely high-speed-rate laser directed energy deposition has attracted considerable attention for large-scale industrial component manufacturing owing to its outstanding fabrication efficiency. ...However, interlayer metallurgical defects and thickness fluctuation stacking caused by the previous non-uniform rough surface layer hinder the preparation of customized thicknesses of large-scale components with high performance. Herein, an integrated extremely high-speed-rate additive manufacturing technology, that is, extremely high-speed-rate laser-directed energy deposition accompanied by extremely high-speed-rate laser remelting, is proposed to eliminate porosity and reconstruct the microstructure of multilayer parts. The remelted specimens exhibited uniform roughness and ultrafine grains when defocusing amount was less than zero. The relatively lower temperature gradient G and morphology factor G/R in the remelting process led to more favorable subcooling, which further promoted more nucleation sites and contributed to grain refinement and columnar-to-equiaxed transition. A multilayer 316 L stainless steel material with an interlayer remelting treatment was further prepared, and a typical heterogeneous structure dominated by ultrafine equiaxed grains was obtained. The multilayer specimen characterized by such a special structure exhibited a higher yield strength of 546 MPa, along with a ductility of 49.1 %. This novel integrated manufacturing technology highlights a new strategy that can expand the extremely high-speed-rate additive manufacturing window and achieve simultaneous improvements in the manufacturing efficiency and performance of large-scale components.
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•A new method of extremely high-deposition-rate laser-directed energy deposition with interlayer remelting was proposed.•Defocusing amount during laser remelting significantly affected microstructural features.•Heterogeneous dendrite growth was implemented via cellular automata approach.•The formation of interlayer refined equiaxed dendrites was explained.
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Various laser scanning strategies of multitrack products, consisting of a default Raster pattern (R1), a Raster pattern with a changed line order (R2), and a default Zigzag pattern (Z1), with ...different overlap rates ranged from 0.7 to 0.5, have been conducted to investigate microstructure evolution for Mg–3Al–1Zn alloy. As the overlap rate changes from 0.7 to 0.5, the average grain size decreases and the texture is slightly concentrated, except for R2 pattern. For effect of different scanning pattern, a relatively small average grain size can be obtained using the R1, R2 patterns compared to using the Z1 pattern; a relatively weak texture can be obtained using the R1, Z1 patterns compared to using the R2 pattern. The utilization of Z1 pattern results in a further texture weakening compared to that of the R1 pattern. Microstructure evolution of scanning strategy is mainly determined by low-undercooling-required epitaxial growth along temperature gradient directions at the solid/liquid interface. Combined with computational thermal-fluid dynamics simulation, a strong fluid flow within the molten pool promotes side expansion of the molten pool, resulting in the larger overlap area, the corresponding three-times remelting domain and continuous deflections of grain major axes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
