Cr Layer Research Articles

Residual stress and thickness effects on fracture behavior of trilayer films during uniaxial loading

The effects of residual stress and film thickness on crack evolution in metallic trilayers deposited on polyimide substrate have been investigated during uniaxial tensile loading. Four different systems, consisting of Mo/Cu/Cr layers deposited on polyimide, with nominal thicknesses of 100/100/100 or 100/500/100 nm, were developed using two physical vapor deposition techniques, resulting in opposite as-deposited high residual stress for the top Cr layer (about +2.7 GPa versus -2.6 GPa). First, it was found that the higher the compressive residual stress of the top Cr layer and the thickness of the middle Cu layer, the higher the critical strain to initiate crack propagation in the trilayer film system. Second, it was found that the higher the compressive residual stress of the top Cr layer and the thickness of the middle Cu layer, the lower the maximum crack density in the trilayers. The maximum crack density in the thicker system with Cr in a tensile residual stress was similar to the maximum crack density in the thinner system with the Cr top layer in a compressive residual stress.

Relationship between bonding strength and surface roughness in low-temperature bonding of glass for micro/nanofluidic device

The bonding of glass substrates is an important process in the fabrication of glass micro/nanofluidic devices. In this study, the influence of the surface roughness of glass substrates after low-temperature bonding is investigated. It is found that plasma etching can be used to control the surface roughness to the range 2–9 nm. Substrates with a roughness of 5 nm or less can be bonded. The pressure capacity of devices tends to decrease with increasing surface roughness. A pressure capacity of 500 kPa or higher is obtained with a surface roughness of 2 nm or less. This criterion for bonding conditions can be applied to roughness formed by other methods (e.g. via a Cr layer). The proposed approach will facilitate the design and fabrication of glass micro/nanofluidic devices, especially those that complicated fabrication processes or embedding of multiple materials.

Fabricating a MnCo coating to improve oxidation resistance and electrical conductivity of Crofer22H alloy as SOFC interconnect

The oxidation kinetic behavior of Crofer22H alloy at 700–800 °C was investigated. Due to the high oxidation rate exhibited at 800 °C, the xCr-MnCo dual-structured spinel coating was prepared by magnetron sputtering. The element diffusion behavior of the coating/alloy system was changed by control the formation of Cr layer with different thicknesses on the surface. Appropriately increase the thickness of Cr barrier layer can effectively hinders the Fe outward diffusion and improve the antioxidant performance. Fe doped into Mn–Co spinel increased the electron hopping in the crystal structure. Higher electron hopping and thin Cr2O3 layer reduced the electron resistance.

Microstructure and Wear Resistance of Fe3Al Coating on Grey Cast Iron Prepared via Direct Energy Deposition

In this study, the potential of Fe3Al coating material as an environmentally friendly alternative to coatings containing critical elements for brake discs was investigated. A buffer layer of Cr–Mo steel (Ferro 55) that was about 500 µm thick was applied on a gray cast iron disc to enhance the coating quality and prevent the formation of hot cracks during solidification. The microstructural analysis of the cross-section of the coating showed that the buffer layer diffused into the Fe3Al coating, forming a combination of Fe3Al, Fe, and Fe3AlC0.5 phases. The tribological properties of the Fe3Al-coated disc were evaluated using pin-on-disc tests against two different copper-free friction materials extracted from commercial brake pads. The wear results show a coefficient of friction comparable to that of an uncoated disc (≈0.55), but with a reduction in particulate matter (PM) emissions, which decreased from 600 to 476 #/cm3. The last issue is an interesting aspect that is gaining increasing importance in view of the upcoming international standards.

Increasing the thermal stability of a Cr/Sc multilayer by nitriding

The effect of nitridation of Cr, Sc or both layers in the ultrathin multilayer structure Sc/Cr on the intermixing of thin Cr and Sc layers, as-deposited and after annealing at different temperatures were considered in details. The processes of passivation by nitrogen and synthesis in nitrogen medium of chromium and scandium layers are also compared. It was established that during passivation process the nitrogen interacts with surface of scandium film forming a ScNx compound and does not interact at all with the chromium layer. A net scavenging of nitrogen is observed in the case of CrNx/Sc system, while in the Sc/CrNx system the interaction of scandium with nitrogen gas before chromium layer deposition with formation of some amount of ScNx is added.Based on theoretical analysis of the effect of nitriding the system and detailed analysis carried out by photoelectron spectroscopy a multilayer system [Sc/CrNx]300 was synthesized and analyzed at different temperatures of annealing. Analysis of X-ray diffraction data showed that the sample consists of X-ray amorphous layers, the crystallinity of which practically does not change with increasing temperature. The results show that the [Sc/CrNx]300 system with small nitrogen content is very resistant to elevated temperatures up to 450 °C.

Effects of He and Ni ion irradiation on the ZrO2/Cr composite coating on Zr1Nb alloy

ZrO2/Cr composite coating has been irradiated by 2.8 MeV He and 38 MeV Ni ions at 350 °C. Similar extents of grain-growth and partial healing of microcracks have been identified in the ZrO2 layer of both irradiated samples. The monoclinic to tetragonal transformation of ZrO2 and the formation of an amorphous (Zr,Cr)O phase at the ZrO2/Cr interface is identified in the Ni-irradiated sample. Large amounts of dislocation loops and small cavities are observed in the Cr layer while significantly less loops are found in the ZrO2 layer in both samples. The irradiation processes also cause significant growth of surface Cr oxides.

In-situ TEM investigation of defect evolution in FeCrAl during post-irradiation annealing

Aiming to newly-developed FeCrAl alloys for accident-tolerant fuels (ATF) in light water reactors (LWR), an in-situ investigation of scan transmission electron microscopy (STEM) observation and annealing was performed in order to understand the evolution of radiation-induced defects (RID) and the Cr segregation during elevating the temperature. In this study, the FeCrAl alloys were irradiated with 6Mev Au+ ions up to a dose of 10 dpa at 400 °C, and the RID in depth of 1 μm were assess by in-situ TEM during annealing. A Cr layer, the dislocation loop raft and Cr-decorated dislocation loops were formed in the near-surface region I. Cavities, Cr-rich precipitates were formed in the interior region II. By calculating thermal equilibrium vacancies theoretically, the cavity formation is ascribed to the surface effect of the foil and the damage of TEM electrons. Shrinkage of some loops could be ascribed to produced vacancies. Formations of the raft and Cr-decorated loops are due to the strain or stress constructed by the surface C species or damages when annealing below 500 °C. The pronounced Cr-rich precipitates during 550–600 °C are due to the Cr atomic segregation initiated by vacancies via a long-time recovery towards low-energy sites. This work indicates the defect-caused stress profile is important for the Cr segregation.

Cross-sectional transmission electron microscopy studies of Si coated heat-treated stainless steel with improved optical absorption for solar thermal applications

Heat-treatment of stainless steel substrate is reported to improve absorptance due to an increase in roughness along with the formation of surface oxides. Depositing a thin Si layer on stainless steel prior to the heat-treatment results in the formation of islands of nano-micrometer sizes with gaps between them which helps in improving absorptance. Cross-sectional Transmission Electron Microscopy studies are required to understand the development of the surface structures and improved optical properties. The cross-sectional bright- and dark-field Transmission Electron Microscopy images showed the presence of a bright Si-rich region where small nanocrystalline islands were embedded. On top of this layer, larger nanocrystalline protrusions were observed. Energy Dispersive X-ray analysis and Selected Area Diffraction data showed that the substrate elements diffuse out through the Si layer forming smaller islands of various Fe-Cr-Mn-based silicides in the Si layer and islands of Fe, Cr, and Mn-based silicides and oxides at the surface. The High-Resolution Transmission Electron Microscopy images showed that the islands are nanocrystalline in nature and are embedded in a Si-rich amorphous region. The absence of O in the Si-rich layer in SAD data was observed. Also, from the top layer EDX data, Fe peak intensity was found to be higher than Cr peak intensity. These observations indicate that the presence of the Si layer helps in reducing the inward diffusion of O into the substrate, thus preventing internal oxidation. Also, this Si layer prevents the Cr from forming a continuous Cr oxide layer and instead forms mixed oxide/silicide islands which enhance optical properties. Similar studies in the heat-treated substrate without a Si layer showed the presence of sharp-angled nanocrystalline structures of Fe-Cr-based oxides and smooth-angled nanocrystalline structures of Fe-Mn-based oxides on the surface.

Welding reinforcement between silica glass and stainless steel using nanosecond fiber laser with chromium interlayer

Modern manufacturing industries need high strength and stable joint between glass and steel. Laser welding is an efficient technique to meet the requirement, but strength still needs to be improved. In this work, a welding reinforcement method of Cr addition was proposed to improve shear strength. The two materials were added with Cr metal film and Cr3+ solution in the interface, and welded by an nanosecond fiber laser. A maximum shear strength of 41.4 MPa was obtained, 40 % higher than that without Cr addition. The surface morphology and elemental distribution of the welds were observed. With Cr addition, the elemental diffusion in the interface was extended. Fe-O-Si and Cr-Si bonds were greatly increased in the welds. And microcracks were significantly reduced. In addition, the Cr layer also reduced the adverse effects caused by the different thermal expansion, making it more reliable in various industrial production fields.

Studying the Effect of Cr and Si on the High-Temperature Oxidation-Resistance Mechanism of Hot Stamping Steel

The surface of hot stamping steel is severely oxidized during heating, holding, and transfer from the heating furnace to the stamping die in the production of traditional automotive parts. Coating-free hot stamping steel with Cr and Si elements exhibits excellent oxidation resistance during hot stamping without the protection of a surface coating. This paper investigates the oxidation behavior of three types of hot stamping steel at 800–1200 °C. The results show that although Cr-Si hot stamping steel performs excellently short-term (≤7.5 min) for oxidation resistance, its long-term (≥15 min) or high-temperature (≥1100 °C) oxidation resistance is much lower than that of the conventional hot stamping steel 22MnB5, affecting the production and surface quality control of the new coating-free Cr-Si hot stamping steel. By analyzing the oxidation kinetics and characterizing the structure of oxide layers in hot stamping steel, it was found that the structural change in the Cr and Si element enrichment layer between the oxide scale and the substrate varied in oxidation performance at different temperatures. When the oxidation temperature was below 1000 °C, the solid Cr and Si enrichment layer acted as a barrier to prevent the diffusion of Fe ions. When the oxidation temperature exceeded 1100 °C, the molten Cr and Si enrichment layer effectively adapted to the substrate and avoided blistering. Meanwhile, Fe2SiO4 penetrated the Fe oxide layer along the grain boundary and became a rapidly diffusing channel of Fe ions, contributing to a significant increase in the oxidation rate.

Composition-mediated abnormal phase evolution in Ta-W films with Cr buffer layers

With the monotonically increasing of W from 0 to 20 at. % in Ta-W films with Cr buffers, an abnormal phase evolution of α-Ta→β-Ta→α-Ta was found, which is due to the breaking and rebuilding of α-Ta nucleation. A small amount of W addition could disturb the epitaxial growth of α-Ta on Cr layers by refining the nucleus size. Nevertheless, as a completely miscible system, Ta-W solid solutions are preferred to possess the α-Ta structure. With the increasing W content, the nucleation barrier of α-Ta is correspondingly lower, facilitating the rebuilding of α-Ta growth. The effect of phase evolution competes with that of solid solution strengthening in the controlling mechanism of Ta-W hardness. The hardness of the sample with low W contents is largely influenced by the proportion of β-Ta, while the solid solution strengthening effect is more pronounced in high W.

Effect of alloying (Cr, Mo, and V) on corrosion behaviors of API-grade steel in CO2-saturated aqueous solutions with different pH

The corrosion behaviors of steels alloyed with Cr, Mo, and V were examined in two different solution chemistries: near-neutral (pH 6) and weakly acidic (pH 4.5) solutions saturated with CO2. In near-neutral solutions, Cr alloying hindered the formation of a stable corrosion scale on the surface, reducing the corrosion resistance compared to conventional low-carbon steel. On the other hand, the alloyed steel exhibited higher corrosion resistance in acidic solutions. In contrast to the conventional carbon steel, which had a single scale of crystalline FeCO3 scale on its surface, a more stable bi-layer of corrosion scale consisting of an inner layer of amorphous Cr(OH)3 and an outer layer of crystalline FeCO3 was developed on the alloyed steel. This was attributed primarily to the increased thermodynamic stability of Cr(OH)3 with an increase in Cr contents at this solution pH. Moreover, the increase in Cr with Mo addition resulted in a refinement of FeCO3 on the outer surface through increased hydrolysis reactions leading to a decrease in the local pH on the steel surface. Furthermore, adding V, even in minute quantities contributed to an increase in Cr-enrichment in the inner scale by suppressing M7C3 precipitation and leaving more Cr in the solid solution.

Nonvolatile magnetization switching in a single-layer magnetic topological insulator

Magnetization in a ferromagnetic layer could be manipulated by the spin-orbit torque whose generation commonly relies on the spin-orbit coupling from the adjacent heavy-metal layer within the bilayer. The fact that the magnetic topological insulator possesses both the ferromagnetic order with perpendicular anisotropy and inherent spin-orbit coupling inspires to realize such a torque-induced magnetization switching without forming any heterostructure with other materials. Here, only using a single layer of magnetically-doped topological insulator Cr:(Bi,Sb)2Te3, we realize a magnetization switching only by applying a large dc current. Assisted by the magnetic history, such a switching behaves nonvolatile under zero field but becomes volatile otherwise, as consistently shown by magnetoelectric transports and magneto-optical Kerr effect measurements. Static and quasistatic current are found to be equivalent for the switching. We propose that this switching may associate with the torque resulted from the spin-orbit coupling and the compositional asymmetry in the Cr-profile of the single layer.

Surface Plasmon Resonance Sensor Based on Waveguides Inscribed in No-Core Fiber

We present a surface plasmon resonance (SPR) refractive index sensor based on femtosecond laser inscribed waveguides in a no-core fiber sandwiched between two sections of single mode fibers. The waveguides inscribed have a trapezoidal structure which consists of three sections: two slant waveguides to direct light out and back into the core of single mode fiber and a straight waveguide close to and in parallel with the surface of no-core fiber. A thin layer of Cr+Ag is coated on the surface of NCF to cover the straight waveguide region. The device is compact and has good mechanical robustness. The experimental results obtained show that the device has a refractive index sensitivity of ~3234 nm/RIU in the refractive index range of 1.34-1.37, and is expected to have practical applications in the fields of bio-medicine and environmental monitoring.

Cold recycling mix design approach targeting permanent deformation resistance

Cold recycling technology offers a sustainable construction pathway for pavements with a potential of recycling up to 100% of the existing in-situ materials. This study introduces a new approach to design emulsion-based cold recycling mixtures. The proposed mix design approach channels the design efforts to optimize the mixture’s components and evaluate its long-term performance. The elements of the proposed design include altering aggregate gradation to achieve optimum packing; a method to selecting an optimum moisture content that is derived from both liquid components in the mixture; and selecting the residual asphalt content based on the mixture’s resistance to permanent deformation. To evaluate the reliability of the proposed mix design method, an optimum mixing water content was derived for an optimum RAP gradation. The effect of varying the emulsion content while keeping the mixing water content constant was evaluated on the mixture’s volumetrics, strength, and permanent deformation behavior. A conventional triaxial compression stress path was applied on samples compacted with several residual asphalt contents. The triaxial test results were compared with results obtained from Hamburg Wheel Tracking Test and Asphalt Pavement Analyzer rutting device. The increase in residual asphalt content at optimum mixing water content led to a systematic increase in strength and reduction in voids that stabilizes as the content increases. The permanent deformation experiments showed the importance of imposing a deformation criterion to select the residual asphalt content in the mix design stage. Additionally, the triaxial repeated load tests demonstrated the importance of using anticipated stress states to characterize permanent deformation resistance which cannot be captured by simple performance tests. Representative stress states in the CR layer should be taken into account during the mix design stage where higher stresses are anticipated in the recycled layer.

Large damping-like torque and efficient current-induced magnetization reversal in Ti/Tb–Co/Cr structures

Seeking the magnetic heterostructures with large current-induced torque efficiency is currently one of the core hotspots in spintronics. In this work, we report the large and composition-dependent damping-like (DL) torque in the structure consisting of light metal Cr and Ti layers and a ferrimagnetic Tb–Co layer. The DL torque efficiency in the structures reaches a maximum (around −0.55) as the Tb content in the Tb–Co layer is in the range of 0.15–0.18. This composition-dependent behavior is different from that observed in the usual heavy-metal/ferrimagnetic structures. We also demonstrated the efficient current-induced magnetization reversal in these structures with a low threshold current density down to 8×1010 A/m2. In comparison, only very low efficiency values of −0.06 and −0.086 are obtained in the Ti/Co/Cr and Ti/Tb–Co/SiN control samples, respectively, suggesting that the large DL torque in the Ti/Tb–Co/Cr structures may originate from the orbital Hall effect in the Cr metal. By fitting the Cr layer thickness dependence of the torque efficiency with a simple orbital current diffusion model, we obtained an effective orbital Hall angle of −0.57±0.02 for the Ti/Tb0.85Co0.15/Cr samples. This work demonstrated the possibility to enhance the orbital torque effect by using the magnetic layer containing the element with strong spin–orbit coupling.

Combined x‐ray reflectivity and grazing incidence x‐ray fluorescence study of Ta/Cr/Pt thin film stacks

AbstractThe Ta/Cr/Pt three‐layer system can be used as a planar x‐ray waveguide, that is to say it can guide an x‐ray beam inside its chromium layer. This property comes from the difference in density and hence in optical index between the two “heavy” or cladding tantalum and platinum layers and the “light” or guiding chromium layer. The waveguide will be efficient provided the layers are a few nanometers thick and that the interfaces are as sharp as possible. To control the quality of the stack, we combine grazing incidence x‐ray fluorescence (GIXRF) and x‐ray reflectivity (XRR) measurements on a series of Ta/Cr/Pt samples, whose only difference is the thickness of the Cr layer. The three considered samples have been deposited by magnetron sputtering and their designed structures are: Ta (8 nm)/Cr (5, 10, and 15 nm)/Pt (14 nm)/Si substrate. The combination of XRR and GIXRF tightens constraints on the parameters used to simulate the stack: thickness, roughness, composition, and density of the layers and their interlayers. For each sample we used six GIXRF curves obtained from three different characteristic x‐ray lines (Ta Lα, Cr Kα, and Pt Lβ2,15) excited at three different incident photons energies (6.25, 10, and 12 keV) as well as one XRR curve obtained at 6.25 keV. The XRR‐GIXRF combined analysis demonstrates that the Ta/Cr/Pt structure is too simplistic and that it is necessary to introduce some interlayers at the top and bottom of the stacks to obtain a reliable agreement between the experimental and simulated GIXRF and XRR curves.

Magnetic properties of [Co/Cr]n/IrMn and [Fe/Pt]n/IrMn multilayers

Magnetic interactions of [Co/Cr]n/IrMn and [Fe/Pt]n/IrMn multilayers grown by magnetron sputtering were investigated by ferromagnetic resonance (FMR) and magnetometry. The phenomenological model used to determine the magnetic anisotropies parameters from the FMR data also revealed the presence of a rotatable anisotropy in the samples studied. The rotatable anisotropy field in [Co/Cr]n/IrMn multilayers can be associated to antiferromagnetic coupling between the Co and Cr layers, while in the case of [Fe/Pt]n/IrMn multilayers, the polarization of Pt atoms may account for the negative rotatable anisotropy.

Effect of Volatile Species on Chemical Vapour Deposition of SiO2 During Corrosion of Chromia- and Alumina-Formers

Silicon-bearing vapour at low pressure was used to deposit SiO2 during exposure of pure chromium, Fe-30Cr (wt.%) and Kanthal APM alloy to an Ar-10H2O-0.1HCl mixture (vol.%) at 650 °C. Pure Cr formed porous chromia blades on top of a polycrystalline Cr2O3 scale containing SiO2. A model Fe-30Cr alloy formed a scale consisting of a thick, amorphous (Cr,Si)Ox outer layer and a thin, polycrystalline Cr2O3 inner layer. Kanthal alloy formed a thin scale containing a Si-rich oxide outer layer and an inner layer of Fe, Cr, and Al oxides. Amorphous (Cr,Si)Ox nodules formed locally on top of (Cr,Fe)23C6 precipitates at the Kanthal surface.

Construction of Cr coatings with different columnar structure on Zircaloy-4 alloys to optimize the high-temperature steam oxidation behavior for accident tolerant fuel claddings

To optimize the oxidation behavior of chromium-coated Zircaloy-4 alloys under 1200 °C high-temperature steam for accident tolerant fuel (ATF) claddings, Cr coatings with different columnar structure are constructed by changing bias voltage using high power impulse magnetron sputtering and corresponding microstructure, mechanical and high-temperature steam oxidation properties are studied systematically. With the bias voltage increase from 0 V to − 150 V, the microstructure of Cr coatings changes from porous columnar structure to compact columnar structure. Especial for bias voltage is − 90 V, the tiny compact grains uniform distribute on the surface micrographs and optimal compact columnar structure are observed on the cross-section micrographs. The hardness and elastic modulus of as-prepared Cr coatings increase firstly and then decrease, the hardness of Cr coatings with optimal compact columnar structure is 8.65 GPa, which is elevated ∼2.28 times than Cr coatings with porous columnar structure. 1200 °C high-temperature steam oxidation test results show an interesting phenomenon that the thickness of Cr layer reduces initial and then increase with the exposure time prolong from 1 h to 4 h. The main steam oxidation mechanism, in the early oxidation stage, is formation the compact Cr2O3 oxide layer. Then, with the exposure time extend, the reduction reaction plays the significant part for steam oxidation mechanism, which is consumption of outmost Cr2O3 oxide layer and formation of subsurface Cr layer. The construction of Cr coatings with compact columnar structure and relevant oxidation mechanism are expected to offer a new idea for improving 1200 °C steam oxidation resistance of chromium-coated Zircaloy-4 alloys.