Cladding Layer Research Articles

Low-threshold AlGaN-based deep ultraviolet laser enabled by a nanoporous cladding layer.

We demonstrated an AlGaN-based multiple-quantum-well (MQW) deep ultraviolet (DUV) laser at 278 nm using a nanoporous (NP) n-AlGaN as the bottom cladding layer grown on the sapphire substrate. The laser has a very-low-threshold optically pumped power density of 79 kW/cm2 at room temperature and a transverse electric (TE)-polarization-dominant emission. The high optical confinement factor of 9.12% benefiting from the low refractive index of the nanoporous n-AlGaN is the key to enable a low-threshold lasing. The I-V electrical measurement demonstrates that an ohmic contact can be still achieved in the NP n-AlGaN with a larger but acceptable resistance, which indicates it is compatible with electrically driven laser devices. Our work provides insights into the design and fabrication of low-threshold lasers emitting in the DUV regime.

Interactions between silver-palladium alloy and silicon carbide cladding layer in TRISO fuel: An in-depth analysis

High-temperature gas-cooled reactors (HTGRs) have garnered considerable interest due to their superior efficiency and inherent safety. This study systematically investigates the interaction between silver-palladium (Ag-Pd) alloy and silicon carbide (SiC) coating in tri-structural isotropic (TRISO) particles of HTGRs, focusing on the potential release of radioactive Ag-110 m through SiC cladding. Operating temperatures ranging from 800–1100 °C were examined to understand the mechanisms of Ag-Pd migration in SiC. Advanced techniques like transmission electron microscopy (TEM), focused ion beam (FIB) coupled with 3D visualization and scanning precession electron diffraction (SPED) integrated with machine learning were employed to identify two pathways of Pd-assisted Ag migration: (1) (Pd,Ag)2Si and (Pd,Ag)3Si acting as migration channels, and (2) Pd-rich phases increasing SiC disorder, enhancing Ag diffusion. Significantly, a carbon barrier formation above 1000 °C was observed, which inhibits Ag-Pd/SiC interaction. These findings offering new insights for predicting nuclear reactor lifespan and data support to optimize TRISO particles' structural design.

Study on the mechanism and correlation of double-pit pitting in ductile iron IN625 laser cladding layer

With its excellent strength and toughness, ductile iron is widely utilized in marine applications, including ship propellers, rudders, ship cabin pumps, valves, and pipes. Laser cladding is an emerging environmentally-friendly surface-strengthening technology. Numerous corrosion pits on the cladding layer surface accelerate the corrosion failure process. It is of great significance to quantitatively reveal the evolution of microscopic corrosion transients on the cladding layer and to analyze the interaction mechanism between adjacent corrosion pits. In this article, a cladding layer of IN625 was prepared on the surface of QT600 ductile iron. The microscopic morphology and Energy Dispersive Spectroscopy (EDS) were used to observe the cladding layer. The relationship among ion concentration, ion migration, pH, electrode potential and corrosion rate was analyzed by numerical simulation. Electrochemical corrosion experiments were conducted using the CorrTest electrochemical workstation. The results show that the IN625 cladding layer can effectively improve the corrosion resistance of QT600 ductile iron. The polarization curves show that the corrosion current density decreases by two orders of magnitude, and the corrosion rate decreases by 395.5 times after laser cladding. This study can provide new ideas and methods to enhance the service performance enhancement of ductile iron laser cladding layers in marine environments.

Achieving Multiwavelength Optical Amplification Based on Polymer Waveguides Doped with NaYF4:Er3+, Yb3+ Nanoparticles under Commercial and Convenient Led Pumping

AbstractRelying on a reverse energy transfer mechanism between erbium (Er3+) and ytterbium (Yb3+) ions, optical gains at wavelengths of 1550, 980, and 1067 nm are achieved in NaYF4: Er3+, and Yb3+ nanoparticles‐doped polymer waveguides under excitation of low‐power light‐emitting diodes (LEDs) instead of 976 or 1480 nm semiconductor laser as pump sources. The optical gains at 1550, 980, and 1067 nm are demonstrated in five waveguide structures: active‐rectangular, evanescent‐field with and without an aluminium (Al) reflector, and dual‐active hybrid with and without an Al reflector. The maximum relative optical gains of 6.6, 4.0, and 3.8 dBcm−1 are realized at 1550, 1067, and 980 nm, respectively, in a 5 mm long dual‐active hybrid waveguide with cross‐section of 4 × 10 µm, and a ≈100 nm‐thick Al reflector grown under the lower cladding layer under excitation of a 395 nm LED. This work proves the feasibility of using a low‐cost LED to realize multi‐wavelength amplification in a dense wavelength‐division multiplexing system and is thus valuable for the development of complex multi‐functional photonic‐integrated‐module mixed‐band optical communication systems.

Study on numerical calculation method of corrosion mechanism for Co-12 laser cladding layer

Purpose The restoration and strengthening of QT600 is an industry bottleneck challenge. The Co-12 cladding layer has great wear and corrosion resistance. The purpose of this paper is to quantitatively reveal the transient evolution law of the corrosion process of Co-12 cladding layer on QT600 surface. Design/methodology/approach In this paper, a three-dimensional numerical model of the corrosion process of Co-12 cladding layer by QT600 laser cladding is established. The interaction between pitting pits and corrosion medium is considered to reveal the transient evolution of ion concentration, electrode potential, pH and corrosion rate at different locations. Findings The calculation shows that the ion concentration in pitting pit changes Cl−>Co2+>Na+, pH value decreases from top to bottom and corrosion rate at bottom is greater than that at top. The electrochemical corrosion test of Co-12 cladding layer was carried out. It is shown that the current density of QT600 increases by an order of magnitude compared to the Co-12 cladding layer, and the corrosion rate is 4.862 times higher than that of the cladding layer. Originality/value The results show that Co-12 cladding layer has great corrosion resistance, which provides an effective way for QT600 protection.

Lasing Threshold Reduction of AlGaN‐Based Ultraviolet‐C Laser Diodes Using Strain Relaxed Lower Cladding Layer

The dependence of the performance of ultraviolet‐C (UV‐C) laser diodes on the strain relaxation of lower cladding layer (LCL) is numerically investigated. As the strain relaxation increases from 0% to 100%, the threshold current density decreases from 25 to 12.7 kA cm−2, and the slope efficiency increases from 0.039 to 0.087 W A−1, thanks to an increase in internal quantum efficiency (IQE). The improvement of IQE is mainly due to the enhanced hole injection resulting from the increased hole concentration in the distributed polarization doping layers and the reduced hole blocking barrier height of the upper waveguide layer with increasing the strain relaxation. Additionally, the effective screening of the polarization field within the quantum well ameliorates the quantum‐confined Stark effect, further improving the IQE. Our study reveals that strain relaxed LCL is imperative to achieve low‐threshold UV‐C laser diodes.

Effect of Mo on wear resistance of Stellite31 cladding layer

Stellite alloys are a kind of cobalt-based alloys, which have excellent properties and are widely used in numerous areas. However, the wear resistance of Stellite alloys is poor at room temperature. In this study, Stellite31 cladding layers added with 0%, 1%, 2% and 3% of Mo(wt-%) were prepared by laser cladding. The grain sizes were measured by scanning electron microscope images, the distributions of Mo were analysed by energy dispersive X-ray spectrometry, the physical phase compositions were analysed by X-ray diffractometer, and the wear resistance was evaluated by reciprocating friction wear tester and wet sand wear testing machine. The results showed that the grain sizes of the cladding layers decreased with the increase of Mo content, the wear loss of the cladding layers became lower and the friction coefficient decreased under the same test conditions. It was concluded that increasing the Mo content could improve the wear resistance of the Stellite31 cladding layer at room temperature.

Denoising of laser cladding crack acoustic emission signals based on wavelet thresholding method.

Due to the influence of thermal stress and other factors during laser cladding, cracks will appear in the cladding layer. To reduce cladding loss, an effective method is to detect cracks early and adjust fusion parameters promptly. The paper utilized acoustic signal detection technology to collect crack defect signals during the laser cladding process. Subsequently, the collected acoustic signals were subjected to time-frequency analysis and wavelet thresholding denoising. Then by applying a custom thresholding approach for each level of wavelet coefficients, the crack signals were denoised. The results showed that this method achieved better denoising effects compared to other signal denoising methods and preserved the crack information to a greater extent, confirming the feasibility of the custom thresholding denoising approach. It helps to achieve online detection and acoustic signal analysis of cracks during the cladding process.

Microstructure and Mechanical Properties of Cermet Composite Coating on TC4 Surface

In order to improve the surface quality and performance of TC4, the TC4-HfC-TaC metal-ceramic composite cladding coating was prepared on the surface of TC4 by using different process parameters by laser cladding technology. Through digital testing equipment, the macro morphology, molten pool size, dilution rate, Rockwell hardness (HRC), geometry, microstructure and other comprehensive properties of the coating are studied and analyzed. The results show that the performance characterization of TC4-HfC-TaC cladding layer is closely related to the melting state of refractory carbide ceramic phase HfC and TaC powder, when the laser beam energy density is not enough to completely melt the ceramic phase powder, with the increase of energy density, the coating surface tends to be flat, the molten pool size and dilution rate increase, the hardness gradually increases, the metallographic structure is refined uniformly, and the surface quality is improved. Excessive energy density of the laser beam can easily lead to excessive dilution rate of the cladding layer, reduced coating hardness, coarse metallographic structure, and reduced surface quality. Finally, the best combination of process parameters was screened out: laser power 3000 W, scanning speed 300 mm/min, spot size 2.5 × 11.5 mm, rectangular spot lap rate 40%, preset powder thickness 1.5 mm, at which time the coating hardness increased to 63.22 HRC. It is about 2.1 times the hardness of TC4 substrate, with the best performance, and the metallographic structure is densely arranged fine cell-like crystals, with outstanding microscopic characteristics, which realizes the purpose of preparing high-quality TC4-HfC-TaC cermet composite cladding coating on the surface of TC4 titanium alloy.

Microstructural Analysis of Grain Morphology and Precipitations on Molybdenum Cladding Layers Fabricated by the Direct Energy Deposition Process

Microstructural Analysis of Grain Morphology and Precipitations on Molybdenum Cladding Layers Fabricated by the Direct Energy Deposition Process

Slippery Core‐Sheath Hydrogel Optical Fiber Built by Catalytically Triggered Interface Radical Polymerization

AbstractHydrogel‐based optical waveguides have attracted extensive attention in optogenetics, implantable photomedicine, and biosensors due to their excellent biocompatibility and tissue‐like modulus in compared with traditional SiO2‐based rigid optical fibers. However, the existing ion‐induced supramolecular assembly of alginate‐based hydrogel optical fibers commonly lack of long‐term stability due to poor mechanical property accompanied with swollen. In this paper, a novel catalytic surface polymerization method is developed based on a redox reaction mechanism to in situ grow robust and slippery cladding layer on a core poly(ethylene glycol) dimethacrylate (PEGDA) hydrogel fiber by using the alternative H‐bonding poly(N ‐acryloyl glycinamide) (PNAGA) hydrogels. The resultant hydrogel optical fiber with core‐cladding heterogeneous structure can achieve the desirable total reflection condition, leading to good light transmission and low light loss. The PNAGA cladding with robust H‐bonding network endows the hydrogel optical fiber with high stability and outstanding lubrication in humid environment. More importantly, the hydrogel optical fiber possesses good tissue‐like mechanical performance together with excellent biocompatibility, which shows the great advantages for biomedical applications in compared with traditional glass optical fibers. This work will broaden implantable hydrogel optical fibers in material design and structure processibility, promoting the use of hydrogel‐based optical fibers in various applications.

Room‐Temperature Continuous Wave Lasing of Circular Defect in 2D Photonic Crystal (CirD) Laser with AlOx Cladding Layers Fabricated by One‐Step Dry Etching

The use of photonic crystal (PhC) to form photonic bandgaps is expected to be applied to optical communications, and various studies have been conducted on this technology. In a previous study, the current‐injected Circular Defect (CirD) in 2D PhC laser is proposed. At that time, the dry‐etching process involves three steps. However, three‐step dry etching cannot be used to simultaneously form drainage trench and PhC air holes. In this study, a one‐step dry‐etching process for CirD lasers is conducted. Optical measurements are performed on the successfully fabricated samples. As a result, the first lasing of a CirD laser with a contact layer and an upper cladding layer fabricated with a one‐step dry etching is confirmed.

Effects of Rare Earths on Microstructure and Wear Resistance in Metal Additive Manufacturing: A Review

Rare earth elements (REEs) doping technology can effectively control the microstructure and improve the quality and performance of materials. This paper summarizes the research progress of REEs in metal additive manufacturing (MAM) in recent years and briefly introduces the effects of REEs on the molten pool fluidity, purified structure, and interfacial bonding between the molten cladding layer and substrate. It focuses on the mechanism of the role of REEs in the refinement and homogenization of microstructures, including grain growth, columnar to equiaxed transition (CET), and elemental segregation. The reasons for the influence of REEs on the homogenization of the structure and elemental segregation are analyzed. The effects of REE type, content, and dimension on hardness and wear resistance are investigated. Finally, tribological applications of REEs in biological and high-temperature environments are summarized, and the impact of REEs-modified alloys is summarized and prospected.

Enhanced mechanical properties of Fe-based hardfacing alloy with Al additions fabricated by laser cladding

Laser cladding was used to prepare an Al-containing Fe-Cr-C hardfacing alloy layer on a 316 L stainless steel substrate. The effects of Al addition on the elemental distribution, physical phase composition, and properties of the cladding layers were systematically investigated using experimental observations, finite-element simulation, and performance tests. Aluminum promoted the flow and elemental homogenization of the molten pool, leading to a more dispersed carbide distribution. Aluminum increased the thermal conductivity of the material and accelerated the cooling rate of the melt pool, which suppressed the eutectic reaction L → γ + (Fe,Cr)7C3 and promoted the peritectic reaction L + (Fe,Cr)7C3 → γ + (Fe,Cr)3C. Consequently, the (Fe,Cr)7C3 content decreased, whereas that of (Fe,Cr)3C increased. Aluminum improved the stability of ferrite and promoted its formation. The Al addition resulted in fine-grain, load-transfer, dislocation, and Orowan strengthening, thereby improving the hardness and wear resistance of the Fe-Cr-C hardfacing alloys. Dislocation and Orowan strengthening were the largest contributors, followed by fine-grain and load transfer strengthening.

Study on Microstructure and High Temperature Stability of WTaVTiZrx Refractory High Entropy Alloy Prepared by Laser Cladding.

The extremely harsh environment of the high temperature plasma imposes strict requirements on the construction materials of the first wall in a fusion reactor. In this work, a refractory alloy system, WTaVTiZrx, with low activation and high entropy, was theoretically designed based on semi-empirical formula and produced using a laser cladding method. The effects of Zr proportions on the metallographic microstructure, phase composition, and alloy chemistry of a high-entropy alloy cladding layer were investigated using a metallographic microscope, XRD (X-ray diffraction), SEM (scanning electron microscope), and EDS (energy dispersive spectrometer), respectively. The high-entropy alloys have a single-phase BCC structure, and the cladding layers exhibit a typical dendritic microstructure feature. The evolution of microstructure and mechanical properties of the high-entropy alloys, with respect to annealing temperature, was studied to reveal the performance stability of the alloy at a high temperature. The microstructure of the annealed samples at 900 °C for 5-10 h did not show significant changes compared to the as-cast samples, and the microhardness increased to 988.52 HV, which was higher than that of the as-cast samples (725.08 HV). When annealed at 1100 °C for 5 h, the microstructure remained unchanged, and the microhardness increased. However, after annealing for 10 h, black substances appeared in the microstructure, and the microhardness decreased, but it was still higher than the matrix. When annealed at 1200 °C for 5-10 h, the microhardness did not increase significantly compared to the as-cast samples, and after annealing for 10 h, the microhardness was even lower than that of the as-cast samples. The phase of the high entropy alloy did not change significantly after high-temperature annealing, indicating good phase stability at high temperatures. After annealing for 10 h, the microhardness was lower than that of the as-cast samples. The phase of the high entropy alloy remained unchanged after high-temperature annealing, demonstrating good phase stability at high temperatures.

Suppression of cutting vibration in side milling of laser cladded layer on thin-walled parts with interfacial structures

Laser cladding is being employed for repairing high-end components including thin-walled parts. The heterogeneous interface between cladding layer and substrate can exacerbate cutting vibration during subsequent machining, becoming a bottleneck in remanufacturing thin-walled parts. This paper focuses on exploring the effect of interfacial structures on cutting vibration suppression in side milling of laser cladded layer on thin-walled parts. First, the interfacial structure was proven to be effective for suppressing cutting vibration by increasing modal damping, although the stiffness shows a decreasing trend. Among different interfacial structures, triangular structure showed the best role in cutting vibration suppression, followed by rectangular, semi-circular, and trapezoid. Then, the effects of different structural parameters on cutting vibration suppression were further analyzed based on a Taguchi design. The results showed that the cutting vibration decreases with the smaller interfacial shape factor, larger depth and smaller spacing of interfacial structures. The interfacial structure would be optimal when the interfacial shape factor is 0.06, the interfacial depth is 3.0 mm, and the spacing is 0 mm. As a result, the cutting vibration during milling was reduced by 55.28 %. These findings provide a theoretical basis for high-quality remanufacturing of the thin-walled parts.

Effect of total heat input on coaxiality of rotor shaft in laser cladding

Abstract The total heat input by the laser directly affects the temperature distribution of the rotor shaft during the cladding process, and then affects its coaxiality. This article uses ANSYS for numerical simulation to study the effect of laser heat input on the deformation of the rotor shaft during laser cladding process. Simulate and analyze the temperature and stress fields inside the rotor shaft using thermal coupling. The results show that by changing the pitch, axial cladding width and laser irradiation duration to change the laser induced total heat input, a more uniform temperature distribution can be generated in the rotor shaft. The increase of temperature distribution uniformity can reduce the deformation of rotor shaft during cladding. Using a cladding equipment, iron based customized alloy powder was coated on the 45 steel rotor shaft for cladding experiments. And the mechanical properties and coaxiality of the rotor shaft after cladding were measured. The results showed that the hardness and wear resistance of the cladding layer were significantly improved compared to the substrate, and the changes in coaxiality of the rotor shaft were consistent with the simulation results, with relatively small errors. It is of great significance for repairing damaged rotor shafts.

Effects of welding parameters on Inconel 625 coating synthesised by tungsten inert gas cladding

Inconel 625 coatings were synthesised on AISI 4130 steel substrates by tungsten inert gas welding. Optimisation of process parameters was conducted through a combination of numerical simulations and technological experiments. The welding speed has a significant effect on the width and height of the cladding layer and the welding current mainly affected the penetration. A proper decrease of welding speed with raising heat input was conductive to the decrease of coating residual stress levels and dilution rates, which promoted the solid solution of corrosion resistant elements (Mo and Nb) and favoured the improvement of coating corrosion resistance. The cladding quality and efficiency could be improved by parameter optimisations through the combination of numerical and technological methods.

Impact of CeO2 modification on the quality and wear performance of Al2O3/SiC reinforced metal-based coatings

In the pursuit of enhancing the quality and performance of metal-based composite coatings, we utilized Al2O3 and SiC as reinforcement particles to create Ni62 composite coatings on 65Mn surfaces through laser cladding. This study systematically delves into the influence of various mass fractions of CeO2 on the coating's forming quality and wear resistance. An in-depth analysis of the friction and wear mechanisms of these composite coatings is presented, with particular emphasis on CeO2's inhibitory effect on coating cracks. Our research findings reveal that the addition of an appropriate quantity of CeO2 can notably enhance the surface quality of the coating. However, an excessive amount of CeO2 can introduce defects on the coating surface. Within the central part of the cladding layer, longitudinal cracks propagate horizontally, forming what we term “r-type” cracks. Simultaneously, cracks extend both horizontally and vertically at the bonding interface, creating “T-type” cracks. CeO2 enhances the melt pool's fluidity, reducing the occurrence of pores and inclusions within the cladding layer. It also improves the dispersion of hard ceramic particles within the cladding layer, leading to a more uniform distribution of Cr and Ni elements within the coating. This refinement of grain structure in the coating reduces stress concentration and sensitivity to crack formation. Furthermore, the addition of CeO2 results in the accumulation of Ce elements on the coating surface. This accumulation promotes the movement of ceramic particles within the cladding layer towards the coating surface, ultimately forming a dense protective film on the surface. This protective film includes a new phase known as AlNi3. The primary wear mode observed in the composite coating is abrasive wear, with a minor presence of adhesive wear. Importantly, the incorporation of CeO2 significantly enhances the wear resistance of the composite coating.

Effect of CeO2 on the Microstructure and Properties of In Situ Nano-VC Reinforced Sub-micron Fe-Based Laser Cladding Layers

Effect of CeO2 on the Microstructure and Properties of In Situ Nano-VC Reinforced Sub-micron Fe-Based Laser Cladding Layers