Effective Diffusion Barrier Research Articles

The Interfacial Microstructure and Mechanical Properties of Diffusion-Bonded Joints of 316L Stainless Steel and the 4J29 Kovar Alloy Using Nickel as an Interlayer

316L stainless steel (Fe–18Cr–11Ni) and a Kovar (Fe–29Ni–17Co or 4J29) alloy were diffusion-bonded via vacuum hot-pressing in a temperature range of 850–950 °C with an interval of 50 °C for 120 min and at 900 °C for 180 and 240 min, under a pressure of 34.66 MPa. Interfacial microstructures of diffusion-bonded joints were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The inter-diffusion of the elements across the diffusion interface was revealed via electron probe microanalysis (EPMA). The mechanical properties of the joints were investigated via micro Vickers hardness and tensile strength. The results show that an Ni interlayer can serve as an effective diffusion barrier for the bonding of 316L stainless steel and the 4J29 Kovar alloy. The composition of the joints was 316L/Ni s.s (Fe–Cr–Ni)/remnant Ni/Ni s.s (Fe–Co–Ni)/4J29. The highest tensile strength of 504.91 MPa with an elongation of 38.75% was obtained at 900 °C for 240 min. After the width of nickel solid solution (Fe–Co–Ni) sufficiently increased, failure located at the 4J29 side and the fracture surface indicated a ductile nature.

GaP-interlayer formation on epitaxial GaAs(100) surfaces in MOVPE ambient

The challenge to embed a single monolayer of phosphorus during epitaxial gallium arsenide (GaAs) growth triggers numerous questions regarding practical preparation, effective analysis, and fundamental consideration of the resulting interlayers. Beyond better understanding of III-V heterointerface formation processes, precise interlayer incorporation may enable enhanced interface design, effective diffusion barriers, and advanced band structure engineering. We employ metalorganic vapor phase epitaxy (MOVPE) in various growth modes (continuous, with interruptions, pulsed, surface exchange) targeting the most abrupt incorporation of thinnest GaP films in the GaAs(100) matrix. The intensities of higher order interference fringes in high resolution X-ray diffraction (HR-XRD) serve as a measure of the effective GaPxAs1−x film thickness and P concentration, which is compared to compositional analysis based on scanning transmission electron microscopy (STEM). In situ reflection anisotropy spectroscopy (RAS) provided us with insights to the GaAs(100) surface configurations relevant during the P interlayer preparation.

Microstructure and intrinsic stress evolution during epitaxial film growth of an Ag0.93Al0.07 solid solution on Si(111); excessive planar faulting due to quantum confinement

The correlation of microstructural development and the kinetics of film growth has been investigated during the epitaxial film growth of an ultrathin binary Ag0.93Al0.07 solid solution on a Si(111)-7×7 surface at 300 K by the combination of high-resolution transmission electron microscopy, X-ray diffraction, scanning tunneling microscopy, low energy electron diffraction, and real-time in-situ stress measurements. Up to a film thickness of 6 ± 2 nm, epitaxial Ag0.93Al0.07 film growth is characterized by the strikingly extensive formation of planar faults parallel to the film/substrate interface, while at larger thickness the film grows practically defect-free. As revealed by real-time in-situ stress measurements, the extensive formation of planar faults at the very initial stage of growth is not driven by the reduction of the system's elastic strain energy but is rather caused by a striking thickness-dependence of the stacking-fault energy owing to a quantum size effect of the ultrathin metal alloy film, resulting in a frequent succession of fcc and hcp stackings of close-packed layers during the initial stage of film growth. The extensive development of planar faults at the initial stage of film growth (<6 ± 2 nm) is associated with the occurrence of a high density of kinks and corners at thereby atomically rough surface ledges, which strongly enhances the downward transport of adatoms from higher to lower terraces (interlayer mass transport) by a reduction of the effective diffusion barrier at the edge of surface steps and by increasing the driving force for adatoms to attach to the surface ledges. As a result, the epitaxial Ag0.93Al0.07 film initially grows in a 2D layer-by-layer type of growth and thus establishes atomically smooth film surfaces. For the practically planar-fault-free growth at thicknesses beyond 6 ± 2 nm, interlayer mass transport becomes distinctively limited, thereby inducing a transition from 2D to 3D type of film growth.

Features of Production and High-Temperature Oxidation of SHS Ceramics Based on Zirconium Boride and Zirconium Silicide

This article is devoted to the investigation into the combustion kinetics and mechanism of reaction mixtures in Zr–Si–B and Zr–B systems formed according to the forced SHS-pressing of compact ceramic materials, as well as to studying their heat resistance. It is shown that dependences of the combustion temperature and rate on the initial temperature (T0) for compositions in the Zr–Si–B system are linear; i.e., staging of chemical reactions of formation of zirconium diboride and disilicide remains invariable with an increase in T0. The values of effective activation energy of SHS process, which evidence the leading role of the reaction interaction of zirconium with boron and silicon in the melt, are calculated. Staging of chemical transformations in the combustion wave of the Zr–Si–B system is investigated: initially the ZrB2 phase is formed by crystallization from the melt, and then the ZrSi2 phase appears with a delay of 0.5 s; unreacted Si crystallizes after 1 s. The phase composition of synthesis products, in which the main component is ZrB2 diboride, and zirconium disilicide, Si, and ZrB12 boride are contained depending on the composition of the reaction charge, is investigated. Compact samples having high hardness and low residual porosity are fabricated according to forced SHS-pressing technology. High-temperature oxidation of SHS samples results in the formation of SiO2–ZrO2–B2O3 oxide films and ZrSiO4 complex oxide on their surface depending on the composition, which serve the effective diffusion barrier and lower the oxidation rate.

Diffusions of β-cyclodextrins in mucus studied by 19F diffusion NMR

β-Cyclodextrin (β-CD) based materials have been widely used as drug carriers for pharmaceutical applications. To understand the diffusion of β-CDs in mucus is important for selecting β-CD based drug carriers for applications targeting mucosal absorption because the surfaces of many biological membranes are covered with a highly viscous aqueous mucus layer which forms relatively effective diffusion barriers for drugs. In this study, 19F self-diffusion NMR technique has been applied to study the self-diffusions of β-CDs in mucus. The 19F NMR signals arose from 1-fluoroadamantane molecules entrapped in the cavities of β-CDs. The diffusive abilities of different β-CDs in mucus were assessed through analyzing the diffusion coefficients using the presented kinetic model, and Ogston’s and Renkin’s diffusion models for hydrogel systems. The kinetic results show that 2-hydroxypropyl-β-CD and 2-Carboxyethyl-β-CD have the smallest binding affinities to bovine submaxillary mucin and human nasal mucin among five tested β-CDs. The mesh sizes of the bovine submaxillary mucus at different concentrations and that of the human nasal mucus were evaluated using the diffusion models. We hope that this 19F diffusion method will be useful to study the diffusion of β-CD based materials in other biological systems.

Preparation and enhanced oxidation performance of a Hf-doped single-phase Pt-modified aluminide coating

A Hf-doped β-(Ni,Pt)Al coating was prepared by co-deposition of a Pt-Hf composite plating and successive aluminisation. Then, a distinct Hf-rich belt was formed internally between the outer additive (Ni,Pt)Al coating and interdiffusion zone. An isothermal oxidation test at 1100°C revealed a relatively lower oxidation rate constant and decreased oxide scale rumpling tendency for the Hf-doped coating during which the Hf-rich belt partly acted as an effective diffusion barrier. The unique addition of Hf into a β-(Ni,Pt)Al coating can delay the transitional oxidation period from transient alumina to stable one and postpone the degradation from β to γ'.

The Properties of HPMC:PEO Extended Release Hydrophilic Matrices and their Response to Ionic Environments.

Investigate the extended release behaviour of compacts containing mixtures of hydrophilic HPMC and PEO in hydrating media of differing ionic strengths. The extended release behaviour of various HPMC:PEO compacts was investigated using dissolution testing, confocal microscopy and magnetic resonance imaging, with respect to polymer ratio and ionic strength of the hydrating media. Increasing HPMC content gave longer extended release times, but a greater sensitivity to high ionic dissolution environments. Increasing PEO content reduced this sensitivity. The addition of PEO to a predominantly HPMC matrix reduced release rate sensitivity to high ionic environments. Confocal microscopy of early gel layer development showed the two polymers appeared to contribute independently to gel layer structure whilst together forming a coherent and effective diffusion barrier. There was some evidence that poorly swollen HPMC particles added a tortuosity barrier to the gel layer in high ionic strength environments, resulting in prolonged extended release. MRI provides unique, non-invasive spatially resolved information from within the HPMC:PEO compacts that furthers our understanding of USP 1 and USP 4 dissolution data. Confocal microscopy and MRI data show that combinations of HPMC and PEO have advantageous extended release properties, in comparison with matrices containing a single polymer.

Highly Enhanced TMR Ratio and Δ for Double MgO-Based p-Mtj Spin-Valves with Top Co2Fe6B2 Free Layer By Nanoscale-Thick Iron Diffusion-Barrier

Recently, perpendicular spin-transfer-torque magnetic-random-access-memory (p-STT MRAM) has intensively been researched as a promising memory cell of overcoming the physical scaling limit of less than 10 nm in current dynamic-random-access-memory (DRAM) because of its fast write time (~10 ns), non-volatile memory operation, and low power consumption. A p-STT MRAM cell consists of a selective device and a perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valve. CoFeB/MgO based p-MTJ spin-valves have been widely researched. In particular, for tera-bit-level integration, they require a high tunneling-magneto-resistance (TMR) ratio (> 150%) for a sufficient write/erase margin, high thermal stability (Δ) (> 74) for a 10-year data retention-time, and a low switching current (J c) (~1x102 MA/cm2) for low power consumption at the back end of line (BEOL) temperature of 400oC for p-STT-MRAM cells1. Recently, a Ta based double MgO-based p-MTJ spin-valve structure has been attractively proposed to achieve simultaneously a high TMR ratio and high thermal stability2. However, it has been extremely difficult to achieve a TMR ratio of >100% at 400oC (BEOL) because of Ta diffusion into the MgO tunneling barrier degrading the (100) crystallinity3. Thus, in this study, we designed a novel double MgO-based p-MTJ spin-valve with a top CoFeB free layer using W as a nanoscale-thick capping layer, spacer layer, and bridging layer by inserting a nanoscale-thick b.c.c. crystallized Fe diffusion-barrier between the W capping layer and the MgO capping layer, as shown in Fig. 1(a). First, we investigated the effect of this Fe diffusion barrier on the TMR ratio in a double MgO-based p-MTJ spin-valve with a top Co2F6B2 free layer ex-situ annealed at 400oC. Then, we examined the mechanism by which the Fe diffusion barrier enhances the TMR ratio by using current-in-plane tunneling (CIPT) at room temperature, the anisotropy energy density and thermal stability calculation by estimating the PMA magnetic moment. The TMR ratio was strongly dependent on the Fe diffusion-barrier thickness; i.e., it rapidly increased from ~131% to ~154% when the thickness increased from 0 to ~0.30 nm and it considerably decreased from ~154% to ~134% when the thickness increased from ~0.30 nm to ~0.66 nm. Thus, the TMR ratio peaked at a specific nanoscale Fe diffusion-barrier thickness, i.e., ~154% at ~0.30 nm, as shown in Fig. 1(b). Two kinds of the PMA structure, i.e., the PMA structure without a Fe diffusion barrier and with 0.30-nm thick Fe diffusion-barrier, were prepared to estimate the anisotropy energy and thermal stability. The anisotropy energy density (~0.31 erg/cm2) peaked at a specific effective thickness of the upper Co2Fe6B2 free layer (~0.67 nm) for the PMA structure without a Fe diffusion barrier; otherwise, it (~0.35 erg/cm2) peaked at a specific effective thickness of the upper Co2Fe6B2 free layer (~0.83 nm) for the PMA structure with 0.30-nm thick Fe diffusion barrier, as shown in Fig. 1(c). These result indicate that the insertion of a 0.30-nm-thick Fe diffusion barrier between the W and MgO capping layer could enhance the anisotropy energy density at a higher effective thickness of the upper Co2Fe6B2 free layer. Furthermore, thermal stability (Δ) was calculated. The Δ (33.8)peaked at a specific effective thickness of the upper Co2Fe6B2 free layer (~0.67 nm) for the PMA structure without a Fe diffusion barrier; otherwise, it (38.0) peaked at a specific effective thickness of the upper Co2Fe6B2 free layer (~0.83 nm) for the PMA structure with 0.30-nm thick Fe diffusion barrier, as shown in Fig. 3(b). These result indicate that the insertion of a 0.30-nm-thick Fe diffusion barrier between the W and MgO capping layer would increase the of the upper Co2Fe6B2 free layer approximately 15% since the ~0.30-nm thick Fe diffusion-barrier plays an excellent a role of the diffusion barrier of the W atoms ex-situ annealing at 400oC. In our presentation, we will report the mechanism by which thickness of the Fe diffusion barrier influence the TMR ratio was revealed by examining the static magnetization behavior, (100) bcc crystallinity, depth profile of the atomic composition of the spin-valves, the dead-layer thickness and thermal stability calculation, and the strain at the interface between the W capping and MgO tunneling barrier layer by theoretical calculation. * This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2014R1A2A1A01006474) and the Brain Korea 21 PLUS Program in 2014. Reference [1] H. Honjo et al., Symp. VLSI Tech. T160-161 (2015) [2] Y. Tomczak et al., Appl. Phys. Lett. 108, 042402 (2016) [3] Y. Takemura et al., Nanotecknology. 26, 195702 (2015) Figure 1

Fluorocarbon Oil Reinforced Triple Emulsion Drops.

Fluorocarbon oil reinforced triple emulsion drops are prepared to encapsulate a broad range of polar and non-polar cargoes in a single platform. In addition, it is demonstrated that the fluorocarbon oil within the emulsion drop acts as an effective diffusion barrier, as well as a non-adhesive layer, enabling highly efficient encapsulation and retention of small molecules and active biomolecules in microcapsules.

Efficiency enhancement of CIGS compound solar cell fabricated using homomorphic thin Cr2O3 diffusion barrier formed on stainless steel substrate

It is known that the efficiency of flexible Cu(In,Ga)Se2 (CIGS) solar cells fabricated on stainless-steel (STS) substrates deteriorates due to iron (Fe) and Cr impurities diffusing into the CIGS absorber layer. To overcome this problem, a nanoscale homomorphic chromium oxide layer was formed as a diffusion barrier by thermal oxidation on the surface of STS substrates for 1min at 600°C in oxygen atmosphere. By TEM and grazing-incidence X-ray diffraction (GIXRD), it was confirmed that the formed oxide layer on surface of STS substrates was a Cr2O3 layer. It was found that the formed homomorphic Cr2O3 thin layer of about 15nm thickness was an effective diffusion barrier to reduce impurity diffusion into the CIGS layer by secondary ion mass spectroscopy (SIMS). In contrast to the efficiency of CIGS solar cell without homomorphic Cr2O3 diffusion layer is 8.6%, whereas with diffusion barrier it increases to 10.6% because of impurities such as Fe and Cr from the STS substrate into the CIGS layer. It reveals that the layer formed on the surface of STS substrate by thermal oxidation process plays an important role in increasing the performance of CIGS solar cells.

Kinetics Tuning of Li-Ion Diffusion in Layered Li(NixMnyCoz)O2

Understanding and further designing new LiNixMnyCozO2 (NMC) (x + y + z = 1) materials with optimized transition metals contents is an important way to meet high power density applications for rechargeable Li batteries (LIBs). Using ab initio calculations combined with experiments, we investigate the kinetics of Li-ion diffusion vs. selection of advantage paths and their effective diffusion barriers depended on activation energies and Li-slab space in NMC materials systematically. It is found that Li-ions tend to choose oxygen dumbbell hopping (ODH) at the early stage of charging (delithiation), and tetrahedral site hopping (TSH) begins to dominate when more than 1/3 Li-ions are extracted. Apart from this, in both ODH and TSH, the Li-ions surrounded by nickel (especially with low valence state) are more likely to diffuse with low activation energy and form an advantage path. The Li slab space, which also contributes to the effective diffusion barriers, is found to be closely associated with the delithiaton process (Ni oxidation) and the contents of Ni, Co, and Mn. Therefore, the kinetics of Li-ion diffusion in layered NMC materials can be tuned by the Li content (delithiation process) as well as the different contents of Ni, Co, and Mn in NMC materials. Based on these discovers, we finally propose that developing Li[Ni0.5Mn0.5]1-xCoxO2 (0 < x ≤ 0.33) system is a most promising way to further optimize the performance of NMC materials. Figure 1

Microstructural Evolution of Cu/Solder/Cu Pillar-Type Structures with Different Diffusion Barriers

Microstructural evolution of the Cu/solder/Cu pillar-type bonding structures with a reduced solder volume subjected to thermal aging at 423 K to 473 K(150 °C to 200 °C) was investigated. In a bonding structure employing a Ni single layer as the diffusion barrier, solder was consumed with formation of the Ni3Sn4 phase at the bonding interfaces due to an usual Sn/Ni interfacial reaction. However, an unusual Sn/Cu reaction occurred with formation of the Cu6Sn5 (and Cu3Sn) phase on the periphery of the Cu pillar due to out-diffusion of Sn toward the pillar periphery. Consumption of solder was accelerated by the above two reactions which led to the formation of a continuous gap in the bonding structure. Employment of a thicker Ni layer plus a Cu cap layer as the diffusion barrier in the bonding structure effectively blocked out-diffusion of Sn toward the periphery of the Cu pillar and therefore retarded the gap formation. The retardation effect was attributed to an increment of diffusion distance on the pillar periphery due to an effective diffusion barrier composed by Ni and thicker Cu-Sn (Cu6Sn5 + Cu3Sn) phase layers. Detailed phase identification and microstructural evolution in the bonding structures were also investigated using scanning electron microscopy and transmission electron microscopy.

Effects of TaN Diffusion Barrier on Cu-Gate ZnO:N Thin-Film Transistors

The effects of TaN Cu diffusion barrier in Cu-gate ZnO:N thin-film transistors (TFTs) were studied. Bias stress tests were performed on Cu-gate TFTs with atomic layer deposited Al2O3 and HfO2 gate insulators. The mobility, the threshold voltage, and the reliability were significantly improved by applying a TaN diffusion barrier at the interface between the Cu gate and the gate insulator. The reduction in Cu diffusion by the diffusion barrier is a key process that increases device stability and results in improved oxide TFT performance.

Vapor Phase Self-Assembled Monolayers for CMOS BEOL Barrier Layers

As the Back - End - of - Line (BEOL) Interconnects are scaling down to nanometer regime with multiple levels of metallization , need for ultra thin diffusion barrier layers arise. Self assembled monolayer (SAM) is an ideal solution to satisfy the requirement of an ultra thin barrier layer to avoid Copper difussion. However, wet chemical processes are preferably avoided in Complimentary - Metal - Oxide - Semiconductor (CMOS) fabrication process. Accordingly , a novel technique to form SAM of Zinc (||) tetraphenyl hydroxy porphyrin (ZnTPPOH) in vapor phase on Inter - Layer Dielectric (ILD) materials is developed in present work to suit the industry process flow and be integreable in CMOS fabrication. The vapor phase SAM formation of ZnTPPOH is investigated employing different techniques and studies from simple contact angle measurements, spectroscopic measurements such as x-ray photoelectron spectroscopy (XPS) , fourier transform infrared spectroscopy (FTIR) , Ultra Violet - Visible Spectroscopy (UV - Vis) , and the atomic force microscopy (AFM) , etc. The vapor phase SAM of ZnTPPOH was formed on different ILD materials such as Black Diamond , Hydrogen silsesquioxane , etc and also on Silicon dioxide substrates. Selective formation of SAM in vapor phase was studied using different substrates such as Gold , Copper , etc . The vapor phase SAM was incorporated in Metal - Oxide - Semiconductor Capacitor (MOSCAP) structure. Copper was used as metal and the Vapor phase SAM was formed on Oxide / ILD materials so as to sandwich between the Copper and ILD, to repel and isolate the Copper in order to avoid any diffusion of Copper into the ILD materials. Capacitance - Voltage (CV) measurements , Current - Voltage characterization were done under bias and temperature stress on the MOSCAP devices to investigate the electrical performance of MOSCAP device and efficiency of ZnTPPOH vapor phase SAM as a barrier layer. Similarly blanket MOSCAP stack was formed and subjected to temperature stress and the extent of copper diffusion was investigated using (SIMS). Scanning electron microscopy (SEM) and scotch tape tests were done to observe improvement in adhesion of Copper to the ILD materials. The vapor phase SAM process was optimized and devloped to suit the CMOS technology and demonstrated as an effective copper diffusion barrier layer for interconnects. This technique opens up a whole new set of opportunities to scale down the barrier layer thickness. Integrating such bottom-up approach within the CMOS fabrication process would make scaling to 7nm and beyond possible where interface layers, dielectrics, and semiconductor films will be on a molecular level. Figure 1

Laser cladding of SiC multilayers for diamond deposition on steel substrates

It is well-known that growth and adhesion of polycrystalline diamond coating directly on steel are both problematic. To solve these issues, interlayers are needed. For the present study, diamond film was deposited on steel with intermediate barrier of silicon carbide (SiC). In addition, laser cladding process produced interlayer. Diamond films were grown by Hot Filament Chemical Vapor Deposition (HFCVD). During laser cladding process, SiC was partially dissociated and so, formation of FeSi was observed. Just 1-layer SiC was enough to grow diamond film since the iron is no longer free to migrate to the surface during the CVD deposition. Nevertheless, the high residual stress formed at the interface, during the reactor cooling, produces fragmentation of the diamond film grown with 1-layer SiC on the steel. To overcome the disadvantage, we propose to create SiC multilayers in an effort to reduce the influence of steel thermal expansion coefficient. Detailed characterization of the SiC interlayer, FeSi phase and diamond coating, are discussed based on X-ray Diffraction, Scanning Electron Microscopy and Raman Spectroscopy. Results showed that the presence of FeSi, formed by SiC dissociation, was the main reason for diffusion barrier effectiveness. Further, the use of SiC multilayers efficiently relaxed the high thermal stress.

Lithium intercalation and diffusion in TiO2 nanotubes: a first-principles investigation.

Titanium dioxide nanotubes have attracted considerable attention because of their excellent photoelectric and electrochemical performance in lithium-ion batteries (LIBs). Precise intercalation sites and controllable diffusion paths are very important for the structures and transport properties of TiO2 nanotubes. Based on first-principles calculations, herein, we discuss these parameters. The results indicate that TiO2 nanotubes with 2-coordinate oxygen vacancies could effectively improve the immigration ability of Li ions. The effective diffusion barriers (0.53 eV) between the outer and inner surfaces suggest a potential material for application in Li-ion barriers.

In Situ Ramp Anneal X-ray Diffraction Study of Atomic Layer Deposited Ultrathin TaN and Ta1-xAlxNy Films for Cu Diffusion Barrier Applications

Ultrathin TaN and Ta1-xAlxNy films with x = 0.21 to 0.88 were deposited by atomic layer deposition (ALD) and evaluated for Cu diffusion barrier effectiveness compared to physical vapor deposition (PVD) grown TaN. Cu diffusion barrier effectiveness was investigated using in-situ ramp anneal synchrotron X-ray diffraction (XRD) on Cu/1.8 nm barrier/Si stacks. A Kissinger-like analysis was used to assess the kinetics of Cu3Si formation and determine the effective activation energy (Ea) for Cu silicidation. Compared to the stack with a PVD TaN barrier, the stacks with the ALD films exhibited a higher crystallization temperature (Tc) for Cu silicidation. The Ea values of Cu3Si formation for stacks with the ALD films were close to the reported value for grain boundary diffusion of Cu whereas the Ea of Cu3Si formation for the stack with PVD TaN is closer to the reported value for lattice diffusion. For 3 nm films, grazing incidence in-plane XRD showed evidence of nanocrystallites in an amorphous matrix with broad peaks corresponding to high density cubic phase for the ALD grown films and lower density hexagonal phase for the PVD grown film further elucidating the difference in initial failure mechanisms due to differences in barrier crystallinity and associated phase.

Metal-boride phase formation on tungsten carbide (WC-Co) during microwave plasma chemical vapor deposition

Strengthening of cemented tungsten carbide by boriding is used to improve the wear resistance and lifetime of carbide tools; however, many conventional boriding techniques render the bulk carbide too brittle for extreme conditions, such as hard rock drilling. This research explored the variation in metal-boride phase formation during the microwave plasma enhanced chemical vapor deposition process at surface temperatures from 700 to 1100°C. We showed several well-adhered metal-boride surface layers consisting of WCoB, CoB and/or W2CoB2 with average hardness from 23 to 27GPa and average elastic modulus of 600–730GPa. The metal-boride interlayer was shown to be an effective diffusion barrier against elemental cobalt; migration of elemental cobalt to the surface of the interlayer was significantly reduced. A combination of glancing angle X-ray diffraction, electron dispersive spectroscopy, nanoindentation and scratch testing was used to evaluate the surface composition and material properties. An evaluation of the material properties shows that plasma enhanced chemical vapor deposited borides formed at substrate temperatures of 800°C, 850°C, 900°C and 1000°C strengthen the material by increasing the hardness and elastic modulus of cemented tungsten carbide. Additionally, these boride surface layers may offer potential for adhesion of ultra-hard carbon coatings.

Formation of Cr2O3 Diffusion Barrier Between Cr-Contained Stainless Steel and Cold-Sprayed Ni Coatings at High Temperature

A novel approach to prepare a coating system containing an in situ grown Cr2O3 diffusion barrier between a nickel top layer and 310SS was reported. Cold spraying was employed to deposit Ni(O) interlayer and top nickel coating on the Cr-contained stainless steel substrate. Ni(O) feedstock was prepared by mechanical alloying of pure nickel powders in ambient atmosphere, acting as an oxygen provider. The post-spray annealing was adopted to grow in situ Cr2O3 layer between the substrate and nickel coating. The results revealed that the diffusible oxygen can be introduced into nickel powders by mechanical alloying. The oxygen content increases to 3.25 wt.% with the increase of the ball milling duration to 8 h, while Ni(O) powders maintain a single phase of Ni. By annealing the sample in Ar atmosphere at 900 °C, a continuous Cr2O3 layer of 1-2 μm thick at the interface between 310SS and cold-sprayed Ni coating is formed. The diffusion barrier effect evaluation by thermal exposure at 750 °C shows that the Cr2O3 oxide layer effectively suppresses the outward diffusion of Fe and Cr in the substrate effectively.

Accelerated Bonding of Magnesium and Aluminum with a CuNi/Ag/CuNi Sandwich Interlayer by Plasma-Activated Sintering

Plasma-activated sintering (PAS) has been applied, for the first time, to join magnesium and aluminum using a CuNi/Ag/CuNi sandwich structural interlayer. A cleaning effect and high efficient plasma heating mode in PAS have contributed to forming a strong interfacial diffusion bond under low temperature 673 K (400 °C) and short dwell time (0.6 ks). The designed interlayer provides a diffusion barrier effect and an enhanced physical contact between the interfaces. Strong bonding has been achieved without forming the brittle Mg-Al intermetallics.