Cladding Materials Research Articles

Deformation-Induced Martensitic Transformation in Laser Cladded 304 Stainless Steel Coatings.

There are only a few cost-effective solutions for coating applications in combined mechanical loading and corrosive environments. Stainless steel AISI 304 has the potential to fill this niche, showing excellent corrosion resistance while utilizing the deformation-induced phase transformation from γ-austenite to α’-martensite, which results in an increase in strength. However, it is not known whether this can occur in laser cladded material. Therefore, laser cladded AISI 304 coatings in as-cladded condition and after heat treatment at 1100 °C for 60 min were investigated before and after bending deformation, by means of light microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was shown that due to the dendritic microstructure accompanied by an inhomogeneous distribution of the main alloying elements (Cr and Ni), no deformation-induced phase transformation occurred in the as-cladded coating. The applied approach with subsequent solution heat treatment at 1100 °C for 60 min resulted in a homogeneous γ-austenite microstructure, so that a deformation-induced martensitic transformation (DIMT) could occur in the coatings. However, the volume fraction of martensite that had been formed locally at individual shear bands was rather low, which can be possibly attributed to the high Ni content of the feedstock, stabilizing the γ-austenite microstructure. This study shows the possibility of exploiting the DIMT mechanism in heat-treated laser-cladded AISI 304 coatings.

Aluminum hydroxide, bayerite, boehmite, and gibbsite ToF-SIMS spectra in the negative ion mode. I

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed for boehmite (AOH-60) and its potential products of oxidation including pseudo-boehmite (AOH-180), α- and γ-Al2O3, and α- and γ-Al(OH)3. Since boehmite is often incorporated on cladding materials to prevent corrosion, surface analysis techniques are performed to determine the amount of oxidation present. This ToF-SIMS spectral library is of significance because it includes boehmite and its potential oxidation products (i.e., aluminum oxide and hydroxide), which can be used to compare to spectra obtained for real-world samples containing boehmite. Furthermore, ToF-SIMS is often used as a complementary technique to x-ray photoelectron spectroscopy due to its surface sensitivity and ability to compare spectra via a multivariate analysis, therefore establishing that the molecular signatures of boehmite and relevant compounds are essential for peak identification. The SIMS spectra shown are acquired from commercially available powders, which were deposited onto a silicon wafer substrate via liquid slurry drop casting. This library of SIMS mass spectra will serve as a comparison of boehmite [γ-AlO(OH)], pseudo-boehmite [AlOOH⋅nH2O], α- and γ-aluminum oxide [Al2O3], and α- and γ-aluminum hydroxide [Al(OH)3] in the negative ion mode, which compliments those reported in the positive ion mode {Part II [L. Strange et al., Surf. Sci. Spec. 29, 025002 (2022)]}.

Effect of Post-Heat Treatment Temperature on Interfacial Mechanical Properties of Cold-Rolled Ti/Al Clad Material.

Titanium and titanium alloys possess low density, high specific strength, and excellent corrosion resistance, but are expensive and have low formability at room temperature. Therefore, to reduce cost and achieve excellent properties, titanium and titanium alloys are jointed with aluminum and its alloys, which are inexpensive and have low density and excellent room temperature formability. Cladding is a widely used solid-state bonding technique, and the post-heat treatment of titanium/aluminum clad materials is required to improve their interfacial properties, which is important to ensure the reliability of Ti/Al-clad materials. The interfacial properties of Ti/Al-clad materials are significantly affected by changes in the microstructure and mechanical properties after the post-heat treatment. Thus, in this study, the relationship between the microstructure and mechanical properties at the interface of Ti/Al-clad materials was analyzed after the post-heat treatment at several different temperatures. The thick diffusion and intermetallic compound layer was formed with post-heat treatment owing to the active diffusion of Al atoms. As a result, their uniaxial and nanomechanical properties were varied with the interfacial characteristics of the Ti/Al-clad material.

Measurement of hydrogen trapping in cold-work dislocations using synchrotron X-ray diffraction

In water-cooled nuclear power plants containing zirconium alloys as the clad material, embrittlement of the cladding can occur from hydrides produced by the water-zirconium alloy interaction, thus limiting the life of the fuel assembly (Motta et al., 2019). The hydrogen produced at the water-zirconium interface can also be trapped in neutron irradiation-induced microstructural defects, reducing the amount of hydride present at any given time/temperature. Knowledge of the extent of hydrogen trapping by various microstructural features in zirconium and its alloys is therefore key for accurate predictions of hydride-induced embrittlement. A novel method for quantifying both trap capacity and trap binding energy using synchrotron X-ray diffraction is described and demonstrated for a cold-worked, Zircaloy-4 sample in which line dislocations provide an analogue for irradiation-induced dislocation loops as hydrogen trap sites. This study has experimentally determined the following parameters for cold-work dislocations: Thermal stability; Binding energy; Maximum capacity for hydrogen; Number of equivalent hydrogen trap sites. These parameters may be used in modelling hydrogen embrittlement of zirconium alloys, as experimental estimates for their analogue of irradiation-induced dislocation loops. More importantly, this pilot study has successfully demonstrated the methodology and results of a novel technique that may be applied generally to irradiated material to quantify hydrogen trapping at other irradiation-induced microstructural defects.

Ultra-Low Power All-Optically Tuned Hybrid Graphene Ultra Silicon-Rich Nitride Ring Resonator-Based Add-Drop Filter for DWDM Systems

This research work conducted a design and simulation of an ultra-low power all-optically tuned nonlinear ring resonator-based add-drop filter. The purpose of this study is to investigate a CMOS-compatible nonlinear material system for an optical filter with temperature resilience, polarization insensitivity, and fast and energy-efficient tunability. The all-optical tunability was achieved using an optical pump that photo-excites the high nonlinear Kerr effect in the device material system. A three-dimensional multiphysics approach was used, combining the electromagnetics and thermo-structural effects in the filter. Hybrid graphene on an ultra-rich silicon nitride ring resonator-based filter enabled the realization of an ultra-high tuning efficiency (0.275 nm/mW for TE mode and 0.253 nm/mW for TM mode) on a range of 1.55 nm and thermal stability of 0.11 pm/K. This work contributed to the existing literature by proposing (1) the integration of a high Kerr effect layer on a low loss, high index contrast, and two-photon absorption-free core material with an athermal cladding material system and (2) the use of a cross-section shape insensitive to polarization. Moreover, the tuning mechanism contributed to the realization of an all-optical on-chip integrable filter for Dense Wavelength Division Multiplexing systems in the less occupied L band.

Cladding‐Free Antiresonance in Tubular Structures

Antiresonance reflection (ARR) effectively turns tubular structures into functional devices ranging from waveguides to spectrometers and sensors, thus attracting a growing number of interests in recent years. Yet, ARRs are generally enabled inside the designed tube cladding with certain structural properties, which essentially acts as a quasi‐Fabry–Pérot (F–P) cavity. This limits the application of the ARR effect on popular tubular entities in non‐F–P cladding morphology, such as the chiral helical material or the self‐rolled‐up ultrathin/meshy membrane. Here, the scheme of core‐antiresonant reflection (core‐ARR or CARR) based on the leaky F–P effect is proposed, which validates ARRs inside the central core rather than the cladding of hollow tubes, hence expanding the optional scope of materials and constructions for tubular substances. Briefly, the CARR behavior is demonstrated in cylindrical, polyhedral, spiral, meshy, and notched hollow tubes with either transparent or opaque cladding materials. More importantly, tubular structures with CARR modes can be flexibly tuned in terms of the resonant frequency, which is used herein for sensitive detection of the environmental pressure, humidity, and thermal influence. As the CARR effect promotes interactions between light and various tubular structures, it holds promise for future opportunities in fields of physics, biophotonics, and material science.

Experimental investigation of CMT discontinuous wire arc additive manufacturing of Inconel 625

Additive manufacturing (AM) is a progressive technology which holds promise for manufacturing of heat resistant super alloys. One of the most productive methods is wire arc additive manufacturing (WAAM). In this article, an alternative WAAM strategy is investigated. Experimental clads and material tests were performed to evaluate the material properties obtained through a cold metal transfer (CMT) discontinuous WAAM of Inconel 625 alloy. Using the modern terminology of Fronius Gmbh this method is called CMT cycle step. The difference is that it is automatically controlled by the welding source. CMT discontinuous WAAM has lower productivity and a higher consumption of shielding gas. However, it excels in low heat input and precise material cladding in comparison with a standard CMT continuous WAAM. It enables fabrication of finer details even on thin-walled components or in sections with problematic heat dissipation. Samples manufactured using this strategy were also compared with samples manufactured through a standard CMT continuous WAAM. Two sets of manufactured samples were thus tested. The following material tests were performed: (i) metallographic analysis, (ii) x-ray tomography, (iii) SEM analysis, (iv) hardness, (v) tensile strength (20 °C, 650 °C) and (vi) pin-on-disc (20 °C, 650 °C). The results show that the CMT discontinuous WAAM led to improved material properties in the Inconel 625 samples. Ultimate tensile strength improved by 15% at 20 °C and by 4% at 650 °C. Wear resistance at 650 °C was about two times higher. This paper concludes that the CMT discontinuous WAAM for Inconel 625 is definitely suitable for manufacturing of complex shapes, fine details and thin-walled components.

Simulation and analysis of supercontinuum generation in the waveband up to 25 µm.

The ultra-wideband supercontinuum generation (SCG) in a Te-based chalcogenide (ChG) photonic crystal fiber (PCF) is simulated in the mid-infrared (MIR) waveband. The PCF core and cladding materials are Ge20As20Se15Te45 and Ge20As20Se17Te43, respectively. The supercontinuum (SC) broadening affected by the core diameter and fiber absorption is considered. The selected PCFs at different pumping wavelengths can demonstrate the generation of ultra-wideband MIR supercontinuum according to the simulated results. We consider SC broadening with and without fiber absorption. A SC range from 3 to 25 µm is demonstrated by simulation in a PCF with a core diameter of 8 µm and a pump wavelength of 6 µm considering the fiber absorption. With the increase of the peak power and the pulse width and the decrease of the core diameter, the degree of coherence gradually degraded. To the best of our knowledge, this is the first demonstration of the possibility of SCG up to the waveband of 25 µm in fiber. Our results highlight the potential of a novel Te-based chalcogenide multi-material PCF for SCG. We also provide a way to generate the SCs to longer wavebands than 20 µm in fiber, especially up to the far-infrared waveband.

The influence of surface on direction of diffusion in Al-Fe clad material

Aluminium-steel clad composite was manufactured by twin-roll casting. An intermetallic layer of Al 5 Fe 2 and Al 13 Fe 4 formed at the interface upon annealing above 500 °C. During in-situ annealing in transmission electron microscope, the layer grew towards the steel side of the interface in tongue-like protrusions. A study of furnace-annealed samples revealed, that the bulk growth of the interface phase proceeds towards the aluminium side. The growth towards steel is a surface effect that takes place simultaneously with the bulk growth towards aluminium. At the beginning of the intermetallic layer formation diffusion of Fe into aluminium prevails, afterwards Al atoms diffuse throught the newly formed intermetallic layer towards steel and the whole interface shifts towards aluminium. The kinetics of growth of the intermetallic layer follows parabolic law in both cases, indicating that the growth is governed by diffusion. • In Al-steel clad material intermetallic layer grows towards Al in bulk material. • During in-situ heating in TEM layer grows towards steel. • Steel-facing layer is a surface phenomenon. • Growth of the intermetallic layer follows parabolic law.

Enhanced corrosion resistance in accident-tolerant FeCrAl alloy by water-assisted laser surface modification

FeCrAl alloys have been widely developed as an alternative accident-tolerant cladding material in light water reactors since the Fukushima nuclear accident in 2011. A large thermal neutron cross-section is the most severe challenge for FeCrAl alloys in the final commercial use, and a thinner cladding was necessary to overcome this, which led to higher corrosion resistance requirements. To address this issue, a surface treatment process is described here to enhance the corrosion resistance of the FeCrAl alloy via a water-assisted laser modification. By varying the laser power and laser scanning speed, the relationship between corrosion and processing parameters was investigated to better understand the mechanism with various characterizations. A heat-transfer model with boiling heat transfer boundary conditions was built and simulated using a finite element method to reveal the change in temperature field during processing. A corrosion test was performed with a simulated light water reactor (LWR) hydro-thermal environment for 120 h. The corrosion rate and oxide film thickness of the water-assisted laser modified FeCrAl alloy sample decreased by 83 % and 50 %, respectively, compared to the as-received one, and this was ascribed to the formation of protective oxide film during laser processing, along with grain refinement and elimination of holes and scratches.

Evaluation of Microstructural Evolution in Isothermally Aged Ferritic Candidate Cladding Materials for Sodium-cooled Fast Reactor Applications

Evaluation of Microstructural Evolution in Isothermally Aged Ferritic Candidate Cladding Materials for Sodium-cooled Fast Reactor Applications

Effect of PVD-coated chromium on the subcooled flow boiling performance of nuclear reactor cladding materials

We elucidate the separate effect of a thin Cr coating deposited by physical vapor deposition (PVD) on the subcooled flow boiling performance of zircaloy-4. First, we run flow boiling experiments on prototypical zircaloy-4 surfaces mimicking the scratch pattern and surface roughness of nuclear reactor claddings. Then, we PVD-coat a 0.3 µm thick chromium layer on the same exact surface and repeat the same flow boiling investigations. All experiments are run using deionized water at atmospheric pressure, flowing on a 1 × 3 cm2 rectangular cross section channel at a rate of 1000 kg/m2/s and a subcooling of 10 K. We measure the average temperature of the boiling surface at increasing surface heat fluxes, covering a wide range of heat transfer regimes, from single-phase forced convection to the boiling crisis. We also record high-speed videos of the boiling process, which we postprocess to measure bubble nucleation site density, growth time, departure diameter and frequency. The surface analysis reveals that, while the chromium coating does not seem change the surface roughness and morphology, it improves surface wettability. However, it decreases the critical heat flux. The chromium coating causes an increase of nucleation temperature, bubble departure diameter and growth time, and a reduction of the nucleation site density. The concurrence of these observations indicates that a size reduction of the nucleation sites, conformally covered by the chromium coating, may be the cause of the boiling performance deterioration. We confirm this hypothesis repeating the same analysis on a FeCrAl sample prepared and tested using the same protocol as the zircaloy-4 sample, but with a different initial surface texture.

Critical heat flux on zircaloy and accident tolerant fuel cladding under prototypical conditions of pressurized and boiling water reactors

First of a kind high spatial and temporal resolution temperature measurements of Pressurized Water Reactor and Boiling Water Reactor simulated fuel pins (high heat flux cosine profile heaters) in annular rod type geometry during nucleate boiling, departure from nucleate boiling and re-wetting has been performed. Distributed fiber optic measurements of the cladding axial temperature with spatial resolutions down to 2.5 mm axially at up to three equally spaced azimuthal locations per rod have demonstrated the similarities and differences of the different accident tolerant fuel cladding materials. These experiments show the performance of accident tolerant cladding with a precise measurement of the location and evolution of dryout followed by the re-wetting phenomena (see supplementary time history of a critical heat flux event). Experimental parameters varied coolant mass fluxes from 1695 to 2712 kg/m2s, pressures from 10 to 20 MPa, and inlet subcooling from 10 to 55 °C. It was found that the coatings and different material have little effect on the value of the critical heat flux. Any discrepancies between the local critical heat flux verified among the cladding material are attributed to different departure from nucleate boiling phenomena captured during the experiment with the high-resolution optical fiber temperature data. Substantial differences in the performance of the different cladding material to survive a critical heat flux event were however observed by post-test X-ray and optical inspection. External evident damage and internal cracks to the simulated fuel pin having the bare zircaloy cladding were observed in regions associated with the occurrence of the critical heat flux for longer periods. Such damages were associated with zirconium oxidation, and not noticed on the Cr coated zircaloy or FeCrAl claddings. These results indicate that the use of FeCrAl or a Cr coated zircaloy as cladding in Pressurized Water Reactor and Boiling Water Reactor may increase the survivability of the cladding material for short transients.

Multi-scale investigation on local strain and damage evolution of Al1050/steel/Al1050 clad sheet

Macroscopic and microscopic mechanical properties, and damage behaviors of materials should be evaluated through multi-scale investigations to allow for practical industrial applications and promote user safety. Clad metal, a type of heterostructured material, is one of the most promising advanced materials for commercialization. However, heterostructured materials (e.g., clad metals, multi-phase metals, and composite metals) are limited by the possible deterioration of their mechanical properties caused by the strain partitioning at the interface of dissimilar phases when heavily deformed. Therefore, quantitative analysis of multi-scale damage development is necessary for the beneficial future utilization of clad metals as well as structural materials that are currently used in the industry. In this study, the mechanical properties and damage behaviors of Al1050/low-carbon steel/Al1050 clad sheet at multiple scales were quantitatively analyzed using macro-scale digital image correlation (DIC) and micro-scale DIC techniques. The multi-scale investigation results will contribute to the improvement of the reliability of clad materials by quantitatively identifying their mechanical properties and damage behaviors on various scales, which will be beneficial for industrial applications.

Fabrication, Microstructure and Adhesion Properties of BCuP-5 Filler Metal/Ag Plate Clad Material by Using High Velocity Oxygen Fuel Thermal Spray Process

Fabrication, Microstructure and Adhesion Properties of BCuP-5 Filler Metal/Ag Plate Clad Material by Using High Velocity Oxygen Fuel Thermal Spray Process

High-performance silicon TE-pass polarizer assisted by anisotropic metamaterials.

The polarizer is a key component for integrated photonics to deal with the strong waveguide birefringence, especially for silicon photonics. A high-performance silicon TE-pass polarizer covering all optical communication bands with low insertion loss (IL) and high polarization extinction ratio (PER) is proposed here. This polarizer is based on anisotropic subwavelength grating (SWG) metamaterials, which maintain the fundamental TE mode as a guided mode but make the fundamental TM mode leaky. Furthermore, based on this working mechanism, the proposed polarizer can work well for any upper cladding material, including air and silicon dioxide (SiO2). The numerical results show that our proposed TE-pass polarizer has a remarkable performance with IL < 0.34 dB over 420 nm (PER > 23.5 dB) or 380 nm (PER > 30 dB) for the air cladding, and IL < 0.3 dB over 420 nm (PER > 25 dB) or 320 nm (PER > 30 dB) for the SiO2 cladding. The fabricated polarizer shows IL < 0.8 dB and PER > 23 dB for the bandwidths of 1.26-1.36 µm and 1.52-1.58 µm (other bandwidths were not measured due to the limited instrument in our research center, but it still covers the most important O-band and C-band).

High-Temperature Interdiffusion of Tantalum and Niobium with SiC for Processing Hybrid Metal/CMC Components

To ensure the leak tightness of SiC/SiC composites cladding, niobium and tantalum have been retained as liner/coating materials for their high melting point, ductility and weldability; however, their chemical compatibility at high temperatures towards SiC remains to be assessed. In the literature, large discrepancies in the composition of the reaction zone and the kinetics were noticed between some metallic liners and SiC. In this work, diffusion couple experiments between Nb and Ta with SiC and SiC/SiC were conducted at high temperatures (1050–1500 °C) to determine the diffusion paths and the reaction kinetics in order to estimate the lifetime of such coatings in nominal conditions. A detailed analysis of the interaction area was conducted as a function of temperature by a combination of experimental characterizations and thermodynamic calculations. No significant difference in the sandwich cladding materials was observed. The interfacial reactivity was found to be strongly higher than expected from literature data. C and Si were evidenced as the main diffusing species in the Nb/SiC and Ta/SiC systems. From the reaction layer thickness extrapolation in gas-cooled fast reactor operating conditions, niobium but especially tantalum have been approved as liner material in hybrid CMC/metal cladding materials from a chemical compatibility point of view.

Thermo-mechanical modelling to evaluate residual stress and material compatibility of laser cladding process depositing similar and dissimilar material on Ti6Al4V alloy

• 3D finite element modelling of laser cladding process has been developed to predict residual stress at clad, substrate and interface. • Effect of Similar and dissimilar materials on the development of residual stress during laser cladding. • Benchmarking the model with experimental results. • Laser materials interaction of alloy and ceramic materials, and their effect on generation of residual stress. • Use of commercial software for any material system to select appropriate clad materials with minimised residual stress. The formation of residual stresses due to thermo-mechanical effect and microstructural transformation in the Laser Cladding process predominantly affects the final product integrity and service life. A 3D finite element transient thermo-mechanical model has been developed to predict thermal profile and residual stress distribution for repair application of Ti6Al4V alloy using a moving heat source. Then the developed model was applied for the deposition of ceramic materials Al 2 O 3 and TiC on Ti6Al4V alloy substrate. The outcome of this model is to predict temperature distribution, cooling rate, melt pool depth, heat affected zone and residual stress. This study mainly highlights the thermal effect on the residual stresses for similar and dissimilar clad/substrate materials and suggests the suitable cladding material with minimum residual stress.

Microstructure Investigation of Mechanically Alloyed 316L-6Al-0.5Y2O3 Oxide Dispersion Strengthened Austenitic Steel Powder

Development of accident-tolerant fuel cladding (ATFC) materials for LWRs (Light Water Reactors) is being intensively carried out in many research centers in the world as the lesson-learned from the Fukushima Daiichi nuclear reactor power plant accident. One of the advanced high temperature materials which is intensively developed is Oxide Dispersion Strengthened (ODS) steel. The strengthened mechanism is generated by homogeneous dispersion of nano-meter sized ceramic oxide particles in the matrix of the steel which is done by mechanical alloying technique so called mechanosynthesis. Synthesis of an austenitic ODS steel powder of 316L with additional element of 6 wt.% aluminum and dispersion of nano-particles of 0.5 wt.% yttrium oxide (yttria: Y2O3) has been done. The aim of the research is to achieve a better performance of 316L austenitic steel as the proven material for power plant at elevated temperature by modified to become ODS austenitic steel with additional of aluminum. Mechanosynthesis was done using High Energy ball Milling (HEM) for 30 hours with BPR (Ball to Powder Ratio) of 10:1. Afterward, the sample was characterized using Scanning Electron Microscope-Energy Dispersive Spectroscope (SEM-EDS) and X-ray Diffraction (XRD) to analyze the microstructure characteristics. The results showed that the alloying between 316L and aluminum powders was formed. Furthermore, crystal grains and the particles of 316L-6Al-0.5Y2O3 steel powder was much smaller than as received 316L austenitic steel and aluminium powders. The particles size and element composition was homogeneously distributed. The results showed that the parameters of mechanical alloying for development of 316L-6Al-0.5Y2O3 ODS austenitic steel powder have reached the optimum condition.

Qualitative and quantitative analysis of neutron irradiation effects in SiC/SiC composites using X-ray computed tomography

Silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites are candidate materials for cladding of light water reactor (LWR) fuels. Loss of fission product gas retention due to the formation of microcrack networks is considered a potential failure mechanism for SiC/SiC-cladded fuels. In this study, a variety of SiC/SiC composite tubes were irradiated with and without an LWR-relevant radial heat flux in the High Flux Isotope Reactor, followed by detailed characterization with X-ray computed tomography (XCT). This first set of XCT data for neutron-irradiated samples confirmed that the internal stresses arising from a combination of temperature gradients and irradiation-induced swelling act as the primary driver for cracking. While the observed cracking patterns varied depending on the tube architectures, the sharp edges of relatively large pores were found to be the common stress concentrator. These findings are useful to help improve the design and manufacturing of SiC/SiC fuel claddings for reduced failure probability.