Cr Interlayer Research Articles

Adhesion layers between piezoelectric and magnetostrictive layers in a MEMS magneto-sensor stack: Influence on the phase transformation of deposited Co/Fe multilayers to magnetostrictive CoxFe1−x phase

Magnetoelectric MEMS devices, such as magnetic field sensors, may be composed of a multilayer stack as a magnetostrictive layer, which is mechanically coupled to a piezoelectric film. Good adhesion and a stable rigid interface have to be maintained for such a sensor. Certain electric and magnetic properties, especially the magnetostriction, have to reach sufficiently high values, which can be achieved by selected phases or mixtures of phases. In this study, Co/Fe multilayers with varied bilayer periods are deposited onto AlN or Sc0.14Al0.86N coated Si substrates by DC magnetron sputtering with the optional insertion of a 5 nm thick adhesion layer of Cr or Zr to investigate its influence on the formation of the desired mixture of bcc and fcc Co0.7Fe0.3 phases, which are expected to yield a high magnetostrictive strain, after an RTA at 800 °C. A qualitative phase analysis is made by XRD in Bragg-Brentano geometry and shows that the bcc + fcc mixture can be achieved with a Cr interlayer. A sharp, void free, and undamaged interface for that case was observed in SEM images of cross sections prepared with FIB.

Effects of diamond/Al interface structure evolution on interfacial thermal conductance during the carbonization of the Cr interlayer

The correlation between the interface structure evolution and the interfacial thermal conductance (ITC) in diamond particles reinforced Al matrix (diamond/Al) composites has been largely unclear. Herein, diamond/Cr/Al nanolayered structures with the interlayers in different carbonization stages were prepared via magnetron sputtering and annealing treatment to simulate the interfaces in diamond/Al composites. As the annealing time increases, the formed Cr3C2 phase progressively grows from discrete particles to a continuous layer at the diamond/Cr interface, during which the thickness of the carbide layer gradually increases. The formation of Cr3C2 phase improves the interface bonding and provides a more convenient channel for the heat exchange of hot carriers between the interfaces. Accordingly, the ITCs of the samples gradually increases with the annealing time and reaches the maximum value of 436.66 MW/(m2·K) at 120 min due to the formation of a thin and continues Cr3C2 layer. However, considering high interfacial thermal resistance was introduced at the interface when the Cr3C2 interlayer is too thick, the ITC of the sample decreased to 321 MW/(m2·K) as the annealing time extended to 240 min. In addition, Al8Cr5 phase is generated at the Al/Cr interface, but its impact on the ITC of the samples is negligible due to the small amount.

High-Temperature Mechanical and Tribological Performance of W-DLC Coating with Cr interlayer on X40CrMoV5-1 Hot Work Tool Steel

High-Temperature Mechanical and Tribological Performance of W-DLC Coating with Cr interlayer on X40CrMoV5-1 Hot Work Tool Steel

Interlayer design for strong adhesion in the double-layer flexible copper clad laminate via HiPIMS deposition

By designing different interlayers (Al, Si/SixNy and Cr interlayer) and oxygen plasma pretreatment of the substrate, strong adhesion was realized for the double-layer flexible copper clad laminate on polyimide (PI) substrate via high power impulse magnetron sputtering (HiPIMS) technology. The microstructures and properties of Cu films on PI substrate were characterized by an X-ray powder diffractometer (XRD), X-ray photoelectron spectroscope (XPS), atom force microscopy (AFM), scanning electron microscope (SEM), nano-scratch test, scotch tape test and four-probe detector. With the introduction of interlayer and oxygen plasma pretreatment, the critical load of Cu film (300 nm thick) peaked at 43.5 mN and the sheet resistance ranged from 124 to 227 mΩ/sq. The oxygen plasma pretreatment resulted in the drastic oxidation to generate functional groups on the PI substrate surface, which contributed to the improvement of adhesion strength by chemical interaction in terms of the film with Si/SixNy or Cr interlayer. Besides, for the Cu film with Si/SixNy interlayer, the resistance against copper diffusion by the SixNy layer can also promote the enhancement of adhesion strength.

The effects of interlayer size and crystallinity on fatigue behavior of Cu/X (X= cr, amorphous CuZr) bilayers

In this work, interlayer (Cr vs amorphous CuZr) with various thicknesses ranging from 5 nm to 40 nm were utilized for 1000 nm-thick nanostructured Cu films on polyimide substrates. The effects of heterogeneous interface and interlayer thickness on the fatigue behavior of Cu/interlayer bilayers were investigated by in situ synchrotron X-ray diffraction, electrical resistance measurement, in combination with microstructural examinations. The results demonstrated that the fatigue tolerance highly depends on the thickness and constituent of interlayer. The fatigue lifetime monotonically increases as CuZr interlayer thickness increases, coupled to the yield stress. In contrast, the fatigue lifetime first increases and then decreases with increasing Cr interlayer thickness, reaching its maximum value at a thickness of 5 nm. The underlying mechanisms for this discrepancy can be elucidated in terms of heterogeneous constraint and interface voiding, both of which depend on the interlayer thickness.

Effect of arc-deposited diamond-like carbon (DLC) coating thickness on friction and size effects in high-speed micromilling of Ti6Al4V

Diamond-like carbon (DLC) can be considered one of the frontline coating materials for high-speed cutting tools owing to both abrasion resistance and solid lubricant properties. However, coating thickness increases the edge radius of the micro tools, which may result in adverse rubbing and plowing that need to be investigated. In this work, DLC coatings of 440, 640, and 1160 nm thicknesses with a ∼250 nm Cr interlayer are deposited on WC micro-end mills using a cathodic-arc system. DLC-coated surfaces exhibited enhanced tribological and mechanical properties compared to uncoated surfaces. Among the DLC-coated micro-end mills, the DLC-640 nm coated tool outperformed, manifesting the best machining performance by reducing friction and size effects together.

Effects of N doping on mechanical properties of Fe and interlayer adhesion of Fe with Cr, Ti, and Si: A spin-polarized density functional theory study

Interlayers between a substrate and a functional film are used extensively to tailor film adhesion and avoid failure induced by delamination. With nitrogen doping increasingly used to improve the surface properties of steel, how to select appropriate interlayers for high film adhesion on substrate remains elusive in theory. Using spin-polarized density functional theory computations, the authors investigated the effects of N doping on the mechanical properties of Fe and its adhesion with widely used Cr, Ti, and Si interlayers. The results showed that N atoms doped at the Fe octahedron center increased hardness by 30% under 4 wt. % N. N atom at Cr/Fe, Ti/Fe, Si/Fe interfaces interestingly increased the interlayer adhesion of Ti/Fe and Si/Fe, while reducing that of Cr/Fe. This behavior is attributed to competition between magnetic coupling and atomic bonding. For Cr/Fe with strong magnetic coupling, the reduction in adhesion was resulted from doped N that inhibited magnetic coupling at the interface. For Ti/Fe and Si/Fe with weak magnetic coupling, the formation of covalent bonds at the interface by the N atom increased interfacial adhesion. This study provides insights into the nitrogen doping of steel and the selection of proper interlayers for strong film-substrate adhesion.

Improved oxidation resistance of Cr/FeCrAl coating on Zr alloy in high-temperature steam environment

A new bi-layer Cr/FeCrAl coating was successfully fabricated on the Zr-4 plates through multi-arc ion plating in order to take advantage of the two materials of FeCrAl and Cr. The high-temperature steam oxidation behavior of the Cr/FeCrAl-coated Zr-4 at 1000–1200 °C was investigated and compared with that of bare and single-layer FeCrAl-coated Zr-4. Various analytical techniques including scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the microstructural and compositional analysis of the as-deposited and oxidized samples. Results indicated that the FeCrAl-coated Zr-4 could only withstand up to 1000 °C because of the severe FeZr interdiffusion. Whereas the introduction of the Cr interlayer effectively prevented fast FeZr interdiffusion and consequently improves the overall oxidation resistance of the Zr substrate below 1200 °C steam environment. After 1100 °C steam oxidation, the weight gain of the Cr/FeCrAl-coated Zr-4 was about 8 times and 2 times lower than that of the uncoated and FeCrAl-coated Zr-4 alloys, respectively. These facts make possible the use of FeCrAl coating on Zr cladding which has excellent high-temperature mechanical properties and oxidation resistance.

Low-temperature bonding between F82H and Cr assisted by metastable Cr interlayers applied by pulsed laser deposition

The joining of F82H and pure Cr metal has been demonstrated at temperatures as low as 798 K, assisted by the prior application of a thin metastable Cr interlayer to both bonding surfaces using pulsed laser deposition. Bonded F82H/Cr interfaces were characterised by SEM-EDS and TEM analysis, with respect to diffusion behaviour, chemical composition and microstructure. At higher bonding temperatures, an interface layer formed on the Cr side of the joint, which was rich in M23C6, though its structure and thickness was different depending on whether Cr interlayers were applied. As the bonding temperature was decreased stepwise, the interface layer thickness reduced to a minimum of ∼60 nm and appeared to adopt a film-like structure. Although the chemical composition of the thinner interface layers could not be determined, they were most likely M23C6 in a film-like form, which subsequently formed particles, and then columns, as the bonding temperature and interface layer thickness increased. Hardness around the interface increased as compared with the bulk F82H and Cr, though the peak hardness value decreased as the interface thickness decreased. The hardness of bulk F82H and Cr was similar before and after bonding at all temperatures, suggesting little impact on mechanical properties. Diffusion of Cr into F82H and Fe into Cr was not detected at any of the conditions tested, and the original tempered lath martensite microstructure of F82H appeared to have been retained.

Patterned Adhesion Layer Enables Rugged Pd-MIS Hydrogen Sensors.

Rugged Pd-metal-insulator-semiconductor (Pd-MIS) hydrogen sensors for detecting charge-exchange particles in fusion reactors have been constructed by utilizing a novel patterned adhesion layer. Poor adhesion at the interface between Pd and SiO2 is a common failure mode for Pd-MIS devices, severely limiting the Pd thickness and their usefulness as hydrogen sensors. The mechanical integrity of the Pd coatings is of particular importance in magnetic fusion energy research where the Pd-MIS diodes are used to measure hydrogen charge-exchange neutral fluence at the wall in tokamaks. In this application, particularly thick Pd contacts are desirable to prevent damage caused by high-energy particles; however, such thick Pd coatings are prone to mechanical failure due to blistering and wire bond detachment during construction or operation. A continuous Ti or Cr adhesion layer is not possible for this application since it would interfere with H uptake at the SiO2 interface, which is essential for the device to generate a response. In this work, we demonstrate that a patterned Cr interlayer substantially improves adhesion while still providing access for hydrogen to reach the SiO2-Pd interface.

Effect of Cr ion etching on the structure and properties of TiAlN-coated cemented carbide

In this paper, YG8 cemented carbide substrate was treated with Cr ion etching at different bias voltages followed by deposition of TiAlN coating on it based on the cathodic arc technique. The effects of Cr ion etching at different bias voltages on morphology, roughness, elemental composition of the surface of substrate and residual stress, as well as on the growth, microstructure, adhesion and frictional properties of the coating were investigated. After Cr ion etching, the roughness of cemented carbide surface was improved with a significant reduction of residual stresses. At a − 200 V bias voltage, a Cr interlayer was formed on substrate surface, which increased the roughness and improved the match of mechanical properties between substrate and coating, resulting in an increase in adhesion between coating and substrate from 50 N to 73 N. At an etching bias voltage of −800 V, etching effectively refined the coating grains and improved the hardness of the coating. The TEM cross section images of the coating showed that TiAlN coating was epitaxially grown on the etched substrate, which benefited adhesion of coatings to substrate. With increment of etching bias voltage, wear resistance of the coated cemented carbide tends to increase, and its major wear mechanisms are abrasive wear and adhesive wear.

Fatigue tolerance of nanostructured Cu/interlayer bilayers: Tuned by heterogeneous interface

In this paper, interlayers with different characteristics (crystalline Cr vs amorphous CuZr) were used for nanostructured Cu films adherent to polyimide substrates. Impact of heterogeneous interface on the fatigue behavior was investigated by using microstructural examinations in combination with molecular dynamics simulations. It is revealed that the Cr interlayer deteriorated the fatigue property of Cu films because of the formation of voids at the Cu/Cr interface during cyclic loading. By contrast, the CuZr interlayer improved the fatigue performance of Cu films, which can be attributed to the strengthened constraint effect on dislocation motion and the excellent interface compatibility associated with the absorption of dislocations. These findings provide new insight in tailoring the interlayers to achieve optimized performance for nanostructured Cu/interlayer bilayers as extensively applied in microelectronics field.

Cracking failure analysis due to fatigue of the Ti-6Al-4V alloy coated with SiC layer and Cr interlayer deposited by magnetron sputtering

This work aimed to study the effects of coating a thin film of Silicon Carbide and chromium interlayer on the fatigue behavior of Ti-6Al-4V alloy and the correspondent failure evaluation. In the characterization of the layer, the roughness, thickness, and adhesion were determined. Uniaxial fatigue tests were performed under R = 0.1 and the fracture surfaces and corresponding failure mechanisms were observed and identified by SEM, respectively. In the specimens coated using the DC source the number of cycles to failure of the fatigue was increased. The fracture surfaces showed that the crack initiation occurred in the internal regions of the specimens and not superficially. In this case, the layer remained adhered to the specimens even after the tests, showing the effectiveness of the film. In specimens coated using the HiPIMS source, the number of cycles to failure decreased, the cracks were mostly superficial, and the deposited film showed low adhesion after the tests. It proved to be ineffective, worsening the material fatigue behavior.

Cr-containing diamond-like carbon coatings deposited on 316 stainless steel substrates: Characterization and interfacial fracture toughness measurements

A series of Cr-containing hydrogenated amorphous carbon (a-C:H:Cr) coatings were deposited onto 316 stainless steel (316SS) substrates using inductively coupled plasma assisted reactive sputter deposition. Elemental Cr interlayers with different thicknesses of 100, 200, and 300 nm were deposited between a-C:H:Cr and 316SS. Detailed composition, structure, and mechanical behavior characterization of deposited a-C:H:Cr/Cr/316SS specimens were performed. Fracture toughness values of the a-C:H:Cr layer, the Cr layer, and the a-C:H:Cr/Cr/316SS interfacial regions were measured by bending of microcantilever beams with focused ion beam milled pre-notches in-situ a scanning electron microscope. Measured fracture toughness of a-C:H:Cr/Cr/316SS interfacial regions exhibits an approximately linear correlation with the area fraction of the fracture surface occurring in the Cr interlayer, indicating that the interfacial fracture toughness depends on the detailed path of crack propagation and suggesting that interfacial toughness can be engineered through materials design of the interfacial region.

Controlling interfacial composition and improvement in bonding strength of compound casted Al/steel bimetal via Cr interlayer

The fabrication of Al/steel bimetal with a good metallurgical interface is always a great challenge, particularly for the improvement of bonding strength due to the inevitably extensive formation of brittle Al–Fe intermetallic compounds (IMCs) at the interface. Therefore, in this work, the electroplated Cr coating with thickness of 5 μm was firstly used as the interlayer of Al/steel bimetal to suppress Al–Fe IMCs and further improve the interfacial bonding strength. Al/steel bimetal was prepared by compound casting combined with a hot-dip aluminizing process. The results showed that the interface of Al/steel bimetal with Cr interlayer contained an unmolten Cr coating and a reaction layer, in which the latter consisted mainly of Al13Cr4Si4, Al5Cr, Al-rich solid solution and CrSi2 phases. Besides, the morphology of these new Al–Cr–Si and Al–Cr phases was granular rather than the tongue-shaped of Al–Fe phase and the polygonal blocky of Al–Fe–Si phase. Both the microstructure characterization and kinetics calculation results revealed that the application of Cr interlayer could avoid the contact between Fe atoms from steel side and Al atoms from Al alloy side, thereby suppressing the formation of brittle Al–Fe phases at the interface. Moreover, the reaction layer showed a lower nano-hardness than that of without Cr interlayer. With assistance of Cr interlayer, Al/steel bimetal with maximum shear strength of 115.5 MPa was obtained and the interface failed through the Al alloy side. The morphology characteristic and lower nano-hardness of these new phases, the composite structure consisting of Al–Cr–Si and Al–Cr layer together with the Al-rich solid solution layer greatly contributed to the enhancement of the interfacial strength for the Al/steel bimetal.

Effect of chromium doping on the structure and mechanical properties of anti-wear TiB2 coatings

TiB2-based coatings have been intensively developed due to their physical and mechanical properties, including excellent thermal stability and high hardness with good abrasion and corrosion resistance, which appear to be the most beneficial in industrial application. Previous investigations have shown that doping TiB2 with W, Ni and C can significantly reduce residual stresses and improve adhesion, making these coatings ideal on tools to machining aluminum alloys. The aim of this study was to analyze the effect of an Cr interlayer on the durability (adhesion) of the fabricated Ti1−xCrxB2 (x = 0; 0.03; 0.06; 0.10) films and determine the influence of Cr on their microstructure and mechanical properties. The structural characterization of Ti1−xCrxB2 coatings was carried out using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and atomic force microscopy. To investigate the mechanical properties, nano-scratch and—hardness tests (NST, NHT) were performed, and fracture toughness of the substrate layer systems was determined. The use of an adhesive layer of pure Cr increased the adhesion of the coatings to the substrate. It is shown that the changes in Cr content not only affect the microstructure, mainly by decreasing the crystallite size (column width), but also the texture (preferred film orientation) and phase composition. The addition of chromium also has an effect on the mechanical properties of TiB2 films by reducing their hardness and Young’s modulus and increasing their fracture toughness (KIC).

Silver films on glass with very thin chromium adherence interlayers; reflectance and adherence at film-glass interface

Silver (Ag) thin films deposited on glass are proficient in their visible range reflectance at both Ag/air and Ag/glass interfaces. However, the film adherence onto glass is feeble due to a surface free energy disparity between the materials. Issues such as peeling, pitting, and detaching of Ag films on glass used as mirrors and prisms in various optical instruments are common. Very thin and intermittent adherence interlayers of chromium (Cr), titanium (Ti), etc, between Ag and glass resolves the issues to a substantial level. With least possible net surface area of the interlayer and a sufficient adherence of the film system the reflectance at the film/glass interface may be affected only insignificantly. This study presents an adherence optimization of Ag thin films on glass using very thin Cr interlayer with an attempt to retain its Ag/glass interface reflectance at useful levels. Adherence layers of Cr at various thicknesses from 0.4 nm to 5.0 nm and overlayer Ag films around 120 nm on silica glass were deposited by thermal evaporation in vacuum. Then the adherence and reflectance of the film system at the glass interface were evaluated using Scratch and Scotch Tape Tests and UV–visible spectrophotometric measurements. Amount and distribution of the intermittent adherence layers have been evaluated by energy dispersive X-ray photoelectron spectroscopy. 0.7 nm thick intermittent chromium interlayer between the pure silver film and the glass were found to be useful as resolving the adherence issues with a loss about 4–5% in reflectance.

Effective diamond deposition on Ti:sapphire with a Cr interlayer via microwave plasma chemical vapor deposition

In this work, a diamond film was deposited on a Ti:sapphire substrate to improve the thermal performance by using a Cr interlayer.

A Comparative Investigation of Mechanical Properties of TiB2/Cr Multilayer Film by Indentation

Alternating TiB2-dcMS and Cr-HiPIMS layers are used to fabricate TiB2/Cr multilayer films. Introducing a 5-nm-thick Cr interlayer deposited under a substrate bias of −60 V produces slight increases in both film hardness and elastic modulus. The TEM observation indicates that the Cr grains favor epitaxial growth on the TiB2 interlayer, forming a coherent TiB2/Cr interface. This improves hardness. Mechanic measurement by using AFM illustrates that the coherent interface increases the elastic modulus of the Cr up to ~280 GPa, which is significantly higher than bulk material.

Effect of Cr interlayers on texture and magnetic properties of FeSi films with micrometer thickness

Magnetised soft ferromagnetic films with micrometer thicknesses can be used as π-flippers in spin-echo small-angle neutron scattering instruments. An FeSi film with a total thickness of 2000 nm separated by Cr interlayers (each 10 nm thick) was fabricated using direct-current magnetron sputtering. The thickness of each FeSi layer was 100 nm between adjacent Cr interlayers. Hysteresis loop measurements were performed to characterise the magnetic properties of the FeSi films. X-ray diffraction measurements, high-resolution transmission electron microscopy, and selected-area electron diffraction were used to characterise the texture. Results demonstrated that the saturation magnetisation of the FeSi film separated by Cr interlayers was higher and its coercivity was lower than those of the FeSi film separated by Ta interlayers because of different texture of FeSi layer. The FeSi film separated by Cr interlayers featured FeSi (210) and FeSi (221), and the Cr interlayers presented Cr (110). The FeSi layer between the Cr interlayers demonstrated structural coherency with the upper FeSi layer, and continuity of the lattice fringes from the Cr grains to the FeSi layers was observed. Therefore, degradation in the soft magnetic properties of FeSi films can be prevented by the insertion of Cr interlayers.