Thick Cr Research Articles

Influence of coating parameters on oxidation behavior of Cr-coated zirconium alloy for accident tolerant fuel claddings

The Cr coatings (4.5–9.0 µm-thick) with porous/columnar and dense/columnar microstructure were deposited on Zr alloy. Oxidation was performed at 900, 1050, 1200 and 1400 °C in steam to define the role of coating microstructure and thickness on oxidation behavior of Cr-coated Zr alloy. The activation energy for chromium oxidation decreases from 249 to 124 kJ/mol when the coating microstructure changes from dense to porous. Both coatings types are consumed by Cr-Zr interdiffusion resulting in the similar thickness of residual Cr. The Cr-Zr interdiffusion can prevent forming the Cr oxide film and cause direct oxidation of the alloy at 1400 °C.

Initial stages of oxide growth on AM stainless steel exposed to a supercritical CO2 environment

Wrought and additively manufactured (AM) 316 L stainless steel samples were exposed to a simulated Brayton cycle supercritical CO2 (sCO2) environment, at temperature of 450 °C and pressure of 76 bar in 99.999% CO2 for 2 weeks. The ground surfaces of wrought and AM 316 L specimens had average oxide thickness of 95 and 51 µm, respectively, composed primarily of Fe and Cr oxides. An as-printed AM 316 L sample was also exposed to the sCO2 environment and exhibited negligible oxidation during the 2-week exposure because of a thick Cr rich Mn silicate native oxide covering most of surface.

Fabrication of onion-like fullerene nanostructure film by electrochemical reduction

Onion-like fullerenes possess distinctive physical and chemical performance, and thus are believed to have great significance in theoretical study and engineering applications. In this exploratory research, we introduced a novel way, namely electrochemical reduction method performed in aqueous solution at room temperature and very low voltages, for preparing a film composed of onion-like fullerene nanostructures. The method was discovered by accident. During the preparation of thick Cr coating by electrodepositing from Cr (III) electrolyte, a layer of black film was found at the interface between the steel substrate and Cr coating. XPS analysis shows that the main element contained in the film is C. The results from Raman spectrum, HRTEM and SAED reveal that the carbonaceous film is composed of the nanostructures roughly having onion-like fullerene unit. This means with significant advantages has the potential to develop into a practical technique for fabricating carbonaceous films or coatings.

Microstructure evolution and adhesion properties of thick Cr coatings under different thermal shock temperatures

The effect of thermal shock temperatures of 1000 °C, 1100 °C, 1200 °C and 1300 °C on the microstructure evolution and adhesion properties of thick Cr coatings on Zr-4 alloy substrates are systematically studied. The results show that the Cr coating has excellent thermal shock resistance even at 1300 °C and still adheres well to the substrate after the thermal shock tests. The main reasons for the degradation of coating properties are the severe diffusion and migration of Cr and Zr at near-eutectic temperatures, while the formation of pores on the Cr2O3 layer may be related to the evaporation of volatile CrO2(OH)2 at the grain boundaries of the Cr2O3 oxides. In addition, the microstructural evolution of thick Cr coatings is also discussed in detail.

Evaporation of Ti/Cr/Ti Multilayer on Flexible Polyimide and Its Application for Strain Sensor.

A flexible Ti/Cr/Ti multilayer strain gauge have been successfully developed based on polyimide substrate. The pure Ti metal strain gauge have shown the hysteresis phenomenon at the relationship between resistance and strain during tensile test. The experimental results of multilayer strain gauge show that adding Cr interlayer can improve the recovery and stability of the sensing electrode. When the interlayer Cr thickness was increased from 0 to 70 nm, the resistance decreased from 27 to 8.8 kΩ. The gauge factor (GF) value also decreased from 4.24 to 2.31 with the increase in the thickness of Cr interlayer from 30 to 70 nm, and the hysteresis phenomenon disappeared gradually. The multilayer Ti/Cr/Ti film has feasible application for strain sensor.

Strong and durable fluorine-implanted targets developed for deep underground nuclear astrophysical experiments

Nine fluorine targets of various types were developed for the 19F(p, α)16O experiment to be performed at the Jinping Underground Nuclear Astrophysics Experiment (JUNA), China. Two targets were produced by evaporating CaF2 on Ta backings: one was produced by sputtering MgF2 on the Cr+Fe backings, and six were produced by implanting 20–80 keV 19F ions into pure Fe and Cu backings. Thin Cr protective layers were covered over these targets. We assessed each target’s stability by monitoring the γ-ray yields of the 19F(p, αγ)16O reaction over the well-known 340 keV resonance. Our results indicate that the traditional evaporated and sputtered targets exhibit 0.6%–6% deterioration (or 19F material loss) per Coulomb, while the implanted targets exhibit relatively small deterioration due to the proton beam bombardment. For the optimum target #8, the 19F target material loss is only approximately 0.05% per Coulomb proton beam bombardment, and such target is much more stable than the traditional targets. The fluorine depth distribution of the implanted target #8 was precisely analyzed by the atom probe tomography (APT) technique. The obtained depth distribution can well reproduce the experimental γ-ray yield curve. Furthermore, as test experiment, the 19F(p, αγ)16O cross section was measured with the implanted target #8 in a center-of-mass energy region of Ec.m. = 174–358 keV, which is consistent with the previous results. In conclusion, traditional fluorine targets produced with the evaporation and sputtering techniques are not suitable for the high-current experiment even with a protective layer. For the upcoming high-current JUNA experiment, this work offers an optimum target scheme: first, implanting 19F ions into the pure Fe backings with an implantation energy of 40 keV, and then sputtering a 50 nm thick Cr layer to further prevent the fluorine material loss.

Odd spin frustration in Cr(001) films thinner than three nanometers revealed by spin-polarized scanning tunneling microscopy

We have studied the surface structure and morphology of epitaxial Cr films on Au(001) substrate with Cr thickness (${d}_{\mathrm{Cr}}$) below 3 nm. We have characterized the films prepared under various growth conditions by using scanning tunneling microscopy and spectroscopy (STM/STS), low-energy electron diffraction, and Auger electron spectroscopy. The good growth conditions of the Cr(001) films, which have atomically flat terraces without surface segregation of Au and with distinct surface states, are obtained by the following two methods. (I) ${d}_{\mathrm{Cr}}=3$ nm film realized by two-step growth, i.e., first 1.5 nm of Cr deposited at room temperature ($\ensuremath{\sim}290$ K) and an additional 1.5 nm Cr deposition at 570 K and (II) ${d}_{\mathrm{Cr}}=1.5$ nm film by room temperature growth and subsequently post-annealing at 470 K. The magnetic imaging of (I) ${d}_{\mathrm{Cr}}=3$ nm Cr(001) film was performed by means of spin-polarized STM/STS. The observed magnetic image indicates that the topological antiferromagnetic (AF) order appears in a series of adjacent terraces and two types of spin frustration caused by screw dislocations lead to modifications of the topological AF order. One type of spin frustration is accompanied by narrow domain walls between two screw dislocations. The other type is a complex spin frustration caused by a cluster of an odd number of screw dislocations. The difference of the two types of spin frustration is explained through a micromagnetic simulation. We have also identified a large spin-frustrated area, consisting of a cluster of multiple number of screw dislocations.

Effects of alloying elements on surface oxides of hot–dip galvanized press hardened steel

The effects of steel alloying elements on the formation of the surface oxide layer of hot–dip galvanized press hardened steel after austenitization annealing were examined with various advanced microscopy and spectroscopy techniques. The main oxides on top of the original thin Al2O3 layer, originating from the primary galvanizing process, were identified as ZnO and (Mn,Zn)Mn2O4 spinel. For some of the investigated steel alloys, an additional non–uniform, several nanometer thick Cr enriched film was found at the Al2O3 layer. At a sufficiently high concentration, Cr can act as a substitute for Al during annealing, strengthening and regenerating the original Al2O3 layer with Cr2O3. Further analysis with secondary ion mass spectrometry allowed a reliable distinction between ZnO and Zn(OH)2.

Electroplating of Thick Hard Chromium Coating from a Trivalent Chromium Bath Containing a Ternary Complexing Agent: A Methodological and Mechanistic Study

Trivalent chromium electroplating is considered a greener alternative to hexavalent chromium electroplating. However, the electrochemical reduction of Cr(III) in aqueous solution is extremely unstable and the thickness of the coating can hardly grow beyond 10 μm, which limits its industrial applications. We herein report a trivalent chromium bath containing a ternary complexing agent, which yields bright and uniform chromium coatings with thickness exceeding 30 μm, as well as high hardness and corrosion resistance. The electroplating behaviors and first principal calculations reveal that the Cr(II) intermediate plays a vital role in sustained electroplating in Cr(III) baths. The composition of complexing agents has a profound effect on the geometry and electron accepting ability of the Cr(II) complex ions. The failure to grow thick Cr coating is attributed to the accumulation of inactive hydroxo-bridged complexes. In the bath with ternary complexing agent, the Cr(II) complex ions are dsp3 or dsp2 hybridized with high electron affinity, which can be readily reduced to metallic Cr. The bath also shows a strong competitive ligand-binding effect that renders Cr(II) to preferentially bind with an organic ligand rather than a hydroxy ligand. Furthermore, the planar geometry of dsp2 hybridization does not favor the formation of hydroxo-bridged complexes because of the steric hindrance effect. The above merits of the ternary complexing agent lead to sustained electroplating, and thick Cr coatings are obtained.

Nanoscale stress distributions and microstructural changes at scratch track cross-sections of a deformed brittle-ductile CrN-Cr bilayer

In order to interpret the mechanical response of thin films subjected to scratch tests, it is necessary to elucidate local stress distributions and microstructural changes accompanying deformation across the scratch track area. Here, 50 nm synchrotron cross-sectional X-ray nanodiffraction and electron microscopy are used to characterize nanoscale multiaxial residual stress gradients and irreversible microstructural-morphological changes across a brittle-ductile film consisting of 1.2 and 2 μm thick CrN and Cr sublayers. The experimental results reveal a complex alternation of the original columnar grain microstructure and a formation of pronounced lateral and depth stress gradients, which are complemented by a finite element model. After scratching, steep gradients of in-plane, out-of-plane and shear stress distributions were revealed, ranging from −6 to 1.5 and − 1.5 to 1.5 GPa in CrN and Cr, respectively, which are furthermore correlated with microstructural changes and residual curvatures. The scratch test results in intergranular grain sliding and the formation of nanoscopic intragranular defects within CrN, while Cr sublayer's thickness reduction and pile-up formation are accompanied by a bending of columnar crystallites and localized plastic deformation. In summary, the quantitative stress data elucidate the stabilizing role of the Cr sublayer, which suppresses the bilayer's catastrophic fracture during scratch tests.

Interface evolution of Cr/Ti multilayer films during continuous to discontinuous transition of Cr layer

Cr/Ti multilayers with moderate to low bi-layer thickness have been deposited by Ion beam sputtering system and have been investigated thoroughly by specular grazing incidence X-ray reflectivity (GIXR) and diffused X-ray scattering (both in coplanar and non-coplanar configurations) measurements. The investigation is important for development of Cr/Ti soft X-ray multilayer mirrors for “water window” applications in the wavelength regime of 2.2–4.4 nm. Initially few multilayers have been deposited and the highest reflectivity at first Bragg peak positions of the GIXR plots have been obtained for the Cr layer to bi-layer thickness ratio of 0.4. Subsequently, keeping the ratio fixed a set of five samples with bi-layer thickness varying from 3.8 nm to 2.1 nm have been prepared. For the all five ML samples reported in this communication, Ti layer thickness is greater than 1.3 nm, however, the Cr layer thickness varies from 1.5 to 0.8 nm in the above range of bi-layer thickness and it undergoes continuous-to-discontinuous transition. Cr films undergo significant change in morphology as the thickness changes and thus the interfaces are also evolved differently. Analysis of the diffused X-ray scattering data shows that interface imperfection of Ti-on-Cr interfaces is dominated by interface diffusion at low Cr thickness (discontinuous) regime and by interface roughness at high Cr thickness (continuous) regime, while in case of Cr-on-Ti interfaces, interface roughness dominates throughout the whole thickness regime. For the sample with highest bi-layer thickness of 3.8 nm high Bragg peak reflectivity value close to the ideal case is obtained manifesting high thickness uniformity, very low interface imperfection and high vertical correlation length across the interfaces for this sample which is also confirmed by cross-sectional Transmission Electron Microscopy. A 50 bi-layer sample prepared with the above bi-layer thickness shows high reflectivity of 5.6% at 2.84 nm water window soft X-ray wavelength.

Control of spin orientation in antiferromagnetic NiO by epitaxial strain and spin–flop coupling

A ferromagnet/antiferromagnet (FM/AFM) Fe/NiO bilayer was grown using molecular beam epitaxy on MgO(001) and Cr buffered MgO(001) substrates. X-ray linear dichroism measurements showed a dominating out-of-plane component for the NiO spins in Fe/NiO/MgO and an in-plane spin direction for NiO layers grown on the Cr buffer. Furthermore, systematic studies on the magnetic properties of Fe/NiO grown on the wedge-shaped Cr buffer revealed a continuous strain-induced spin reorientation transition from out-of-plane to in-plane NiO spin directions when the Cr thickness increased from 0 nm to 3.5 nm. The analysis of the in-plane magnetic structure of NiO in Fe/NiO/Cr showed a pronounced uniaxial anisotropy in thin AFM layers. The AFM spins are perpendicular to the Fe spins due to spin–flop interaction. These results demonstrate the feasibility of using strain and coupling with FMs to manipulate spin structures in NiO.

Spin-Hall magnetoresistance in Ta/Cr/YIG trilayers with different Cr thicknesses

We report an investigation of spin-Hall magnetoresistance (SMR) in Ta/Cr/Y3Fe5O12 (Ta/Cr/YIG) trilayers with different thicknesses of the Cr inserted layer. The Ta/Cr/YIG film with a 1-nm-thick Cr layer shows a maximum SMR of 4.2×10-4 at 100 K, which is an order of magnitude larger than that previously reported in the Ta/YIG or Cr/YIG systems. The enhancement of SMR in the Ta/Cr/YIG is ascribed to the strong spin–orbit coupling (SOC) effect of both Ta and Cr and the anti-oxidation protection by the Ta coating. A negative SMR different from the conventional SMR is found for the Ta/Cr/YIG with the Cr thicknesses of 3 and 6 nm at the temperature below 100 and 260 K, respectively, which suggests the occurrence of the spin-flop coupling between the antiferromagnetic Cr and ferromagnetic YIG moments. Both the anisotropic magnetoresistance (AMR) and the anomalous-Hall resistance (AHR) indicate an induced ferromagnetism of Cr which is likely due to the spin-flop transition or the uncompensated magnetic moments. Our results suggest that the 3d transition metal Cr can be used as a spin current generator, and the antiferromagnetic structure of Cr can be employed to regulate the transport of spin current.

Effect of the Flow Velocity on the Corrosion Behavior of UNS S41426 Stainless Steel in the Extremely Aggressive Oilfield Environment for the Tarim Area

Effect of flow velocity on the passive film and pitting corrosion behavior of UNS S41426 stainless steel (SS) under the extreme oilfield environment was investigated using different techniques such as microscopy, nanoindentation, and electrochemical techniques. The experimental results show that the corrosion rate of UNS S41426 SS increased with velocity. The increase in flow velocity decreased the thickness and content of amorphous Cr(OH)3 (s) in the film. This in turn increased the density of phase boundary, resulting in a higher defect density. Thus, the UNS S41426 SS film became susceptible to breaking. Furthermore, the pitting had a higher susceptibility to grow to a larger size both in the vertical and horizontal directions with the increase in flow velocity.

A thermodynamic and kinetic study of the formation and evolution of corrosion product scales on 13Cr stainless steel in a geothermal environment

The formation and evolution of corrosion product scales on 13Cr stainless steel at 200 °C and various CO2 partial pressures were investigated. Scanning electron microscope was used to show the physical nature of the scales formed at 0.27 MPa CO2. The thin non-uniform layer was identified as FeCr2O4 by Raman Spectroscopy with a thick Cr(OH)3 layer being determined at 2.85 MPa CO2. These results provide a guide to understanding the mechanisms of CO2 corrosion for 13Cr stainless steel exposed to high temperature and pressure and demonstrate the influence of thermodynamics and kinetics on the formation and evolution of the corrosion products.

Optimization of Single-Step UV Exposure for Fabrication of Integrated Optical Device by Imprinting

In this paper, a single ultra-violet exposure for multi-height structure was used to fabricate an optical-fiberintegrated planar lightwave circuit (PLC) splitter using a thermal imprinting technique. The 1 × 8 tapered multimode PLC splitter was designed with a trench at a depth of 50 μm and a variable width ranging from 50 μm to 690 μm for the insertion of waveguide and fiber structures measuring 125 μm × 87.5 μm in order to minimize insertion loss. Photolithography with a Cr layer and bottom anti-reflection coating (BARC) was utilized to fabricate a multi-height photoresist structure, and the effect of the thick Cr layer and BARC on the geometry was investigated. Scanning electron microscopy of the fabricated structures showed that a Cr thickness of 50 nm and BARC provided the ideal geometry with a minimal undercut and sidewall roughness. Based on the characterization of the imprinted splitter, the average value and uniformity of optical loss between the channels were 10 dB and less than 0.42 dB, respectively.

Metallurgical Soldering of Duplex CrN Coating in Contact with Aluminum Alloy

Coatings deposited by physical vapor deposition (PVD) significantly reduce the wear of high pressure die casting tools; however, cast alloy soldering still has a strong negative effect on production efficiency. Although a lot of research has been already done in this field, the fundamental understanding of aluminum alloy soldering toward PVD coatings is still scarce. Therefore, in this work the performance of CrN duplex coatings with different roughness is evaluated by a modified ejection test performed with delayed (DS) and conventional casting solidification (CS). After the ejection tests, sample surfaces and layers were subjected to comprehensive characterizations of their morphological and chemical characteristics. Considerably lower values of the ejection force were recorded in DS experiments than in CS experiments. Surface roughness played an important role in the CS experiments, while samples with different surface topographies in the DS experiments performed in a similar fashion. The decrease in the ejection force, observed in DS tests, is attributed to the formation of a thick Cr–O layer on CrN coating which reduced soldering and sliding friction against thick Al–O casting scale. The Cr–O layer formed in DS experiments suffered from diffusion wear by cast alloy. The observed oxidation phenomena of nitride coatings may be utilized in a design of non-sticking coatings.

Microstructure and high-temperature steam oxidation properties of thick Cr coatings prepared by magnetron sputtering for accident tolerant fuel claddings: The role of bias in the deposition process

Thick Cr coatings sized ∼27 μm were deposited on Zr-4 substrates by magnetron sputtering to improve the high-temperature oxidation resistance of Zr alloys for accident tolerant fuel claddings. The effects of the bias on the microstructure, mechanical properties and high-temperature oxidation resistance of the thick Cr coatings were investigated systematically. Oxidation tests showed that the Cr coatings with a bias of −50 V exhibit excellent oxidation resistance after steam oxidation at 1200 °C for 120 min, and can be used as an accident-tolerant fuel candidate material. The mechanism of high-temperature oxidation was also discussed in detail.

X-ray mirror figure correction by differential deposition and off-line metrology.

The surface figure error of a hard X-ray mirror was improved by combining differential deposition and off-line metrology tools. Thin Cr layers were deposited on flat substrates by DC magnetron sputtering. The substrates were moved in front of a beam-defining aperture. The required velocity profile was calculated using a deconvolution algorithm. The Cr thickness profiles were measured directly using hard X-ray reflectivity data. The surface figure was characterized using conventional visible-light metrology instrumentation (long trace profiler) before and after the deposition. The method converges quickly, and after two iterations the mirror surface figure had improved by a factor of 7. The surface roughness evolves with increasing Cr thickness and deteriorates the quality of subsequent multilayer coatings. The mirror curvature can change upon coating, which complicates the interpretation of the surface metrology data. In this context, the role of layer stress is discussed. Potential improvements of the process are also proposed.

Nanoscale lift-off process using field emission scanning probe lithography

Nanoelectronics manufacturing requires an ongoing development of lithography and also encompasses some “unconventional” methods. In this context, the authors use field emission scanning probe lithography (FE-SPL) to generate nanoscaled electronic devices. For the generation of future novel quantum devices, such as single-electron transistors or plasmonic resonators, patterning of features in the sub-10 nm regime as well as a defined metallization is necessary. In terms of metallization, the authors take advantage of the well-known lift-off process for creating narrow gap junctions. Narrow gap electrodes have found wide approval in the formation of narrow gap junctions and can be employed for the investigation of the electrical properties of molecules. In the lift-off process presented here, two sacrificial layers (50 nm polymethylglutarimide and 10 nm calixarene) have been deposited and patterned by FE-SPL. Subsequently, the sample was treated with tetraethyl-ammonium hydroxide in order to ensure an undercut. Afterward, a layer of 10 nm thick Cr has been deposited on top and finally the sacrificial films have been removed, leaving behind only the chromium film deposited directly on the substrate. In this work, the authors will present the utilization of novel active cantilevers with diamond coated silicon tips for FE-SPL purposes in order to generate chromium metal features by lift-off for the generation of future quantum devices. In this context, they will present the integration of an ultrananocrystalline diamond (UNCD) layer deposited on the tip of an active silicon cantilever. Electron emission and FE-SPL capabilities of UNCD coated silicon tips are evaluated. The authors demonstrate a reliable fabrication scheme of sub-15 nm coplanar narrow gap metal electrodes.