Ideal Work Of Adhesion Research Articles

Structure and energetics of ZrC(100)||c-ZrO2(001) interface: A combination of experiments, finite temperature molecular dynamics, periodic DFT and atomistic thermodynamic modeling

The oxidation process of ZrC is very important as it affects its initial excellent mechanical and physical properties. ZrC is an ultra-high temperature ceramic, but forms low refractory oxides at lower temperatures of 500–600 °C. To develop core/shell materials by coating the ZrC surface with another material that forms protective layers on ZrC and prevents it from oxidation (such as SiC), there is the need to study and characterize the oxidized layer surrounding ZrC particles. XPS, ToF-SIMS, TEM-ED and EDX analyses were used to investigate the covering oxidized layer, and polycrystalline ZrO2(mainly cubic phase) was identified. Some traces of the tetragonal phase are observed to be present as shells around the ZrC particles with a thickness of about 4 nm on the average. Periodic DFT was subsequently used to characterize the interface formed between ZrC(100) and c-ZrO2(001) phases. A strong interface was noticed mainly with charge transfer from Zr (c-ZrO2 side) at the interface to O and C (ZrC side) atoms at the interface. The interfacial properties are local to only the first and second layers of ZrO2, and not on the third and fourth layers of ZrO2, as Bader charge analysis revealed substantial charge transfer at the interface region with no charge redistribution in the second ZrO2 layer and subsequent bulk layers. The main physical quantity, ideal work of adhesion (Wad), used to characterize the interface, remains quite constant for all ZrO2 layers, and converges at three layers of ZrO2. The interfacial bonds formed are observed to be stronger than the free surfaces in the corresponding ZrC and c-ZrO2 used to generate the interface.

A model to partition the constituent element’s atomic energy in TiC crystal and to characterize the interface properties of α-Ti(0001)/TiC(111)

A periodic slab model was proposed to characterize the TiC(111)/α-Ti(0001) interface properties. The model provides an effective method to partition the total energy of TiC crystalline into its constituent element’s atomic energy by constructing a periodic TiC(111)/α-Ti(0001) interface structure with a specific atomic stacking sequence on the interface. The calculation result shows that Ti and C atom possess −116.65009 Ry and −12.06893 Ry in TiC crystal respectively, which is in good agreement with the TiC total energy of −128.71901 Ry, indicating a satisfactory accuracy better than ~10−4 Ry. The information of the constituent element’s atomic energy provides a direct solution to quantitatively characterize TiC(111) surface energy, or rather, the surface energy on an arbitrary crystallographic plane of TiC crystal. The calculated Ti- and C-terminated surface energies on TiC(111) surface are −0.154 J/m2 and 8.014 J/m2 respectively. Under the atomic configuration in the present periodic model, the Ti-Ti and Ti-C interface energies were calculated to be −1.705 J/m2 and −1.891 J/m2, respectively. The investigation on the ideal work of adhesion indicated that the Ti-Ti interface is the most vulnerable region in the TiC(111)/α-Ti(0001) interface structure on account of the weaker metallic bonding between the Ti-Ti atomic layers.

Adhesion strength and bonding mechanism of γ-Fe (111)/α-Al2O3 (0001) interfaces with different terminations

The ideal work of adhesion (Wad), interfacial energy (σ), charge density, charge density difference and partial density of states (PDOS) of the γ-Fe (111)/α-Al2O3 (0001) interface were studied by the first-principles calculations method. The results indicated that three types of interface between Al2O3 (0001) and Fe (111) surface were formed, which are single Al (Al1-terminated), double Al (Al2-terminated) and O (O-terminated). Each type of interface established different stacking sequences, including Hcp-, Hole- and Top-site. The calculation of Wad and σ showed that the stacking sequence of the interface significantly affected the bonding strength and stability. In the optimized stable structures, the stacking sequences of the maximum Wad corresponding to the Al1-, Al2- and O-terminated interfaces are Hcp (0.65 J/m2), Hcp (3.92 J/m2) and Top (9.30 J/m2), respectively. Notably, the maximum Wad for the O-terminated interface is much larger than that for Al1- and Al2-terminated interfaces, implying the O-terminated interface is the largest bonding strength in all interfacial structures. Furthermore, the electronic properties of the interfaces revealed that the order of electron concentration is O-＞Al2-＞Al1-terminated, which vividly reflects the differences in interactions at the interface. Also, the bonds of the Al1-terminated interface are mainly covalent and little metallic bonds, while the Al2-terminated interface performed not only a mixture of metallic and covalent features but also a certain degree of ionic characteristics. Compared to Al1/2-terminated interfaces, the covalent, ionic and metallic bonds are formed between Fe and Al/O for the O-terminated interface. Additionally, the type of chemical bond and the number of electron orbital hybrids at the interface are the fundamental reasons that affect the bonding strength of the interface.

First-principles calculation of the interface stability of 3C-SiC(111)/Mg(0001)

The first-principles plane wave pseudopotential method based on density functional theory was used to study four SiC(111)/Mg(0001) interface models, and the ideal work of adhesion, charge density distribution, charge density difference and Mulliken population of the four interface models were calculated. The calculation results show that the structure of four interface models has not changed significantly, except for the more or less decrease in the interface spacing after geometry optimization. The Center-site interface of the C-terminated has the largest work of adhesion and the smallest interface spacing, which is the most stable structure among the four models. The calculation of the electronic structure shows that interfacial bonding of these two terminated interfaces of Center-site is a mixture of covalent and ionic bonds.

First-principles calculations on the interface of the Al/TiC aluminum matrix composites

The Al-TiC composites with different TiC contents were synthesized by spark plasma sintering. The microstructure and tensile properties were investigated by the experimental tests. In order to theoretically clarify the properties of interface between the matrix and particles, the atomic structure, ideal work of adhesion (Wad) and electronic structure of Al/TiC interface were calculated by first-principles method based on the interfacial relationship between Al and TiC. For the crystal structures of Al(1 2 1)/TiC(1 1 1) interface, the Wad value of C-terminated Al(1 2 1)/TiC(1 1 1) interfaces were much larger than the Wad value of Ti-terminated Al(1 2 1)/TiC(1 1 1) interfaces. The charge density difference, Bader charges and density of state (DOS) analyses of Al(1 2 1)/TiC(1 1 1) interface suggested that the interfacial bonding was mainly attributed to the Al-C ionic bonding and covalent bonding, as well as the Al-Ti metallic bonding. The Al-C ionic bonding and covalent bonding was stronger than the Al-Ti metallic bonding.

Adhesion at cerium doped metal-ceramic α-Fe/WC interface: A first-principles calculation

Electronic structure, stability and bonding strength of α-Fe/WC interfaces between Ce-doped and undoped WC cermet coating were investigated by first-principles methodology based on density-functional theory (DFT). Based on the minimum mismatched lattices, the relatively stable interface that forms between WC (100) and bcc α-Fe (100) was employed to predict the atomic structure, bonding, and ideal work of adhesion. There are three possible positions which were defined as OT, MT, HCP, taking into account both C- and W-terminations. The sequence of structural stability tested in this paper was: MT > OT > HCP. After full relaxation, the results show that only the first and second layers of the interface have significant influence on the electronic structure between Fe and WC. The interaction of Ce elements at the interface is achieved by comparing the interface structure and electronic structure of the doped and undoped interfaces. Ce doped interface possesses a shorter interface distance (d0 = 0.09776 nm) and a larger interface energy (Wad = 8.98 J/m2) than undoped interface (Wad = 8.76 J/m2, d0 = 0.10134 nm).Charge density distribution and difference, and density of states were utilized to characterize the electronic properties and determine the interfacial bonding.The results demonstrate that strong covalent bonding existed in the undoped interface, while a mixed covalent/ionic bonding was formed at the Ce-doped interface.

Atomic structure, stability and electronic properties of S(Al2CuMg)/Al interface: A first-principles study

Interfacial models of Al2CuMg/Al were investigated by first-principles calculations based on density functional theory. Two types of Al2CuMg(001)/Al(021) interface structures were investigated in consideration of two different terminations for Al2CuMg(001) surface (Al-terminated and CuMg-terminated). The interaction of interfaces was analyzed by the optimized atomic structures. The ideal work of adhesion (Wad) of the Al2CuMg(001)/Al(021) interfaces was also calculated. The results show that the interface model with CuMg-terminated is more stable than that of Al-terminated. It is also demonstrated from the values of interfacial energy (γint) that the CuMg-terminated interface is more thermodynamically stable. The calculated electronic properties, including charge density distribution and density of states, reveal that there is a significant hybridization among the interfacial Cu 3d, Mg 3p and Al 3p states. It is the main reason why CuMg-terminated interface is more stable.

FIRST-PRINCIPLE INVESTIGATION ON THE BONDING MECHANISM OF THE SILICON PARTICLES ON THE COPPER FOIL IN COLD SPRAYING

For lithium–ion batteries, the composite silicon-based electrodes can prevent from losing electrical contact and hence retain the capacity over many cycles. To uncover the adhesion mechanism on the interface formed by the copper foil and the thin silicon coatings during the cold gas dynamic spraying (CGDS) at the microscopic level, the first-principle calculations are performed to investigate the interface properties between them. The ideal work of adhesion, fracture toughness and the interface electronic properties are analyzed. It is found that all the atoms on the interface have vertical displacements, and covalent and ionic bonds are formed between the interfacial Cu and Si atoms which increases the bonding strength. However, the ideal work of adhesion on the interface is lower than one of the Cu bulk and Si bulk, so that fracture would be easier to take place on the interface.

AFM measurements of adhesive forces between carbonaceous particles and the substrates

Graphite dust is carbonaceous particles generated during operation of High Temperature Gas-Cooled Reactors (HTR). Graphite dust resuspension is the key behavior associated with HTR source term analyses and environmental safety assessment. The adhesive force is the key factor that determines the resuspension rate. The present study used an atomic force microscope (AFM) to measure the adhesive force between a single carbonaceous particle and the substrate. The measurements were performed on mica, graphite IG110 and Inconel 800H. The prepared “probe cantilevers” were mesocarbon microbeads (MCMB), fuel element debris from HTR-10 and graphite NBG18. The equivalent work of adhesion was derived from the measured adhesive force and calculated based on substrate profile approximation and the JKR theoretical model. The measured work was smaller than the ideal work of adhesion, most likely due to the rough particle morphology and the rough substrate surface. Additionally, a shape factor imposes a constraint on the lateral deformation of the particles. Furthermore, surface roughness could reduce the adhesive force some depending on the particle size. Once the particle was too small to be trapped into a trough, the adhesive force would not be further reduced.

Theoretical calculations on the adhesion, stability, electronic structure and bonding of SiC/W interface

Abstract The β-SiC(1 1 1)/α-W(1 1 0) interfaces were studied by first-principles calculations based on density functional theory (DFT). The ideal work of adhesion (Wad) and interface energy (γint) were calculated for six different interfacial structures, taking into account both Si- and C-terminations of β-SiC(1 1 1) surfaces, and three different stacking sequences. The interfacial electronic structures including charge density distribution and difference, and density of states (DOS) were simulated to determine the nature of SiC/W bonding. The results show that the Si-terminated top-site interface is the most stable interface, yielding the highest Wad and the lowest γint. During the optimization, the Si-terminated top-site interface will transform into the center-site structure, resulting in the interaction among the interfacial W and Si atoms, and subinterfacial C atoms. In addition, the calculated interface energies show that an interdiffusion layer will form on the SiC/W interface. The experimental results also have verified the existence of an interdiffusion layer on the SiC/W interface in a CVD-SiC fiber.

Formation of aluminides on Ni-based superalloy 690 substrate, their characterization and first-principle Ni(111)/NiAl(110) interface simulations

Ni-based superalloy 690 substrates were pack aluminized in a low Al-containing pack at 1273K for 4h in argon atmosphere. Scanning electron microscopy with energy dispersive X-ray analysis along the cross section of aluminized specimen revealed the formation of multilayer. The uppermost layer consisted of NiAl type phase (~45μm), while adjoining one composed of (NiCr)Al and (NiCr)2Al types layer (~25μm) and subsequently Cr-rich layer (~35μm) adjacent to substrate. Al-content was found to increase while moving from Cr-rich layer towards outer layer. Cross-sectional transmission electron microscopy confirmed the formation of NiAl layer on the topmost surface and revealed the formation of nanoparticles of nickel aluminide on the uppermost surface. Microhardness was found to vary from 624 to 157 Vickers hardness number along the cross section of aluminized substrate indicating high, intermediate and low values for NiAl, Cr-rich layer and substrate, respectively. To evaluate the adherence of multilayer, scratch test was performed along the cross section of aluminized substrate at a constant load level of 2N at ambient temperature. For aluminides, a decrease in friction coefficient with the decrease in Al-content was noticed. Cr-rich layer showed lowest friction coefficient, while its variation was little for substrate. Aluminide layers indicated lower penetration depth than the substrate, whereas no penetration was recorded for Cr-rich layer. Scratched surface did not reveal any peeling off either at the multilayer or layer/substrate interface indicating their good adherence. Aluminized specimens showed good overall oxidation resistance at 1273K in air due to the formation of α-Al2O3. First-principle spin-polarized calculations on Ni(111)/NiAl(110) interface indicated strong adhesion (Ideal work of adhesion, Wad (ideal)=3684mJ/m2; lowest bound value) arising from strong metallic Ni d Ni d interaction and covalent Ni d Al p mixing of states.

The simulation of adhesion, stability, electronic structure of W/ZrB2 interface using first-principles

The optimal electronic structure of W(110)/ZrB2(001) interface was investigated using first-principles based on density functional theory. The ideal work of adhesion (Wad) and interface energy (γ) was calculated for six different interfacial structures, taking into account both Zr- and B-terminations of the boride. The interfacial electronic structure including charge density distribution, states of density (DOS), and Mulliken population was simulated to determine the nature of metal/boride bonding. The results showed that the most stable interface geometry is B-termination, in accord with other theoretical observations. Meanwhile, the adhesion strength of the metal/ceramic interfaces is closely related to the atomic type at the surface layer of the ceramic.

Adhesion of TiC/Fe Cermet Interface with C Vacancy: A First-Principles Study

This work focus on the effects of C vacancy on wetting of Fe to TiC/Fe at the cermet interfaces. We do the whole work using the first-principles density functional theories. The ideal work of adhesion of the pure interface is not big enough, comparing with the expeimental value. Our calculations suggest that the C vacancy at the interface is a very important factor for interface banding of TiC/Fe cermet composite. An adequate quantities of C vacancies at the interface can improve the wetting of TiC/Fe interfaces.

Interfacial fracture toughness of transition metal nitrides

Interfacial fracture toughness is one of the key parameters in assessing and controlling the quality and performance of multiple-layer hard protective coatings. This paper reports on a study of interfacial fracture toughness of transition metal nitrides using ab initio density functional theory (DFT) calculations. Five transition metal nitrides, TiN, CrN, ZrN, VN and HfN, were selected for this study. The interfaces between these nitrides were constructed, and the ideal work of adhesion W ad and Young's modulus E along (100) and (110) orientations for these nitrides were calculated. On the basis of calculated W ad and E, the interfacial fracture toughness K IC was evaluated. The trends of interfacial fracture toughness were analyzed for two specific orientations (100) and (110). It is proposed that interfacial fracture toughness may be used as guidance for the development of multi-layer coatings for either wear or erosion protection.

Structure, bonding, and adhesion at the ZrC(1 0 0)/Fe(1 1 0) interface from first principles

We report a pseudopotential-based density functional theory (DFT) investigation of the interface between ZrC and bcc Fe. ZrC is a potential candidate for a protective coating for ferritic steels because of its favorable physical, chemical, and mechanical properties. Here we predict the atomic structure, bonding, and ideal work of adhesion ( W ad ideal) of the interface formed between the most stable surfaces of ZrC and bcc Fe, namely, the ZrC(1 0 0)/Fe(1 1 0) interface. Bulk properties of ZrC and bcc Fe, calculated for calibration of the DFT approximations involved, are in good agreement with experiment. Further, all the low-index surfaces of ZrC and bcc Fe are observed to retain near ideal bulk termination, as observed experimentally. Stabilities of both ZrC and bcc Fe surfaces follow their respective packing density sequence, i.e., (1 1 0) < (1 1 1) < (1 0 0) for ZrC and (1 1 1) < (1 0 0) < (1 1 0) for bcc Fe. Based on surface energy values, we estimate that the critical stress required for crack propagation in bcc Fe to be at least 30% larger than in ZrC. The ZrC(1 0 0)/Fe(1 1 0) interface is well lattice-matched (≈1.7% strain) producing a fairly smooth interface with little structural relaxation. Bonding at the interface consists of covalent C p–Fe d mixing and some metallic Zr d–Fe d interactions. As the coating grows, decreases in inter-metallic bonding, coupled with increased intraceramic interactions, weaken the interfacial bonding. While a monolayer of ZrC is tightly bound to an Fe substrate ( W ideal=3.05 J/m 2), the adhesion decreases upon film thickening, with the asymptotic value of W ad ideal reached for 4 ML of ZrC (∼2.3 J/m 2). This interface strength is sufficiently high that it may survive as a coating for steels in extreme environments, though it is much smaller than the minimum energy required for fracture of either ZrC or Fe.

Structure, bonding, and adhesion at the ZrC(100)/Fe(110) interface from first principles*1

We report a pseudopotential-based density functional theory (DFT) investigation of the interface between ZrC and bcc Fe. ZrC is a potential candidate for a protective coating for ferritic steels because of its favorable physical, chemical, and mechanical properties. Here we predict the atomic structure, bonding, and ideal work of adhesion ( W ad ideal ) of the interface formed between the most stable surfaces of ZrC and bcc Fe, namely, the ZrC(1 0 0)/Fe(1 1 0) interface. Bulk properties of ZrC and bcc Fe, calculated for calibration of the DFT approximations involved, are in good agreement with experiment. Further, all the low-index surfaces of ZrC and bcc Fe are observed to retain near ideal bulk termination, as observed experimentally. Stabilities of both ZrC and bcc Fe surfaces follow their respective packing density sequence, i.e., (1 1 0) < (1 1 1) < (1 0 0) for ZrC and (1 1 1) < (1 0 0) < (1 1 0) for bcc Fe. Based on surface energy values, we estimate that the critical stress required for crack propagation in bcc Fe to be at least 30% larger than in ZrC. The ZrC(1 0 0)/Fe(1 1 0) interface is well lattice-matched (≈1.7% strain) producing a fairly smooth interface with little structural relaxation. Bonding at the interface consists of covalent C p–Fe d mixing and some metallic Zr d–Fe d interactions. As the coating grows, decreases in inter-metallic bonding, coupled with increased intraceramic interactions, weaken the interfacial bonding. While a monolayer of ZrC is tightly bound to an Fe substrate ( W ideal =3.05 J/m 2 ), the adhesion decreases upon film thickening, with the asymptotic value of W ad ideal reached for 4 ML of ZrC (∼2.3 J/m 2 ). This interface strength is sufficiently high that it may survive as a coating for steels in extreme environments, though it is much smaller than the minimum energy required for fracture of either ZrC or Fe.

Density Functional Study of the Aluminum—Graphite Interface

Our group has previously performed a series of ab initio calculations to study the atomic structure, ideal work of adhesion, Wad, and bond character of several aluminum—ceramic interfaces. Periodic interfaces were used where the thicknesses of both the Al and ceramic slabs were previously converged with respect to surface energy. Using a plane-wave density functional code with the local density and generalized gradient approximation, our past calculations find the Wad is proportional to the surface energies of the mating materials, and the degree of polarity in the ceramic surface. Our calculations compare favorably with available experimental work of adhesion values of liquid Al on graphite, and Al on Al2O3. We investigated interfacial geometries after atomic relaxation, and interfacial bonding via plots of charge density, charge density difference, the electron localization function, and the projected density of states. In this paper we focus on our preliminary results for the aluminum—graphite interface.

First‐principles study of metal/nitride polar interfaces: Ti/TiN

AbstractWe have examined the optimal interface structure, ideal work of adhesion and bonding character of polar Ti(110)/TiN(111) interfaces by first‐principles density‐functional plane‐wave pseudopotential calculations. Both Ti‐ and N‐terminated interfaces, including six different interface structures, were calculated. The interface structure for each termination, continuing the TiN crystal structure across the interface, has the largest work of adhesion. Although both terminations yield substantial adhesion energies in the range 3–7 J m−2, the N‐terminated interface is ∼4 J m−2 stronger than the Ti‐terminated interface. Analysis of the interfacial electronic structure shows that the Ti‐terminated interface is a mixed strong, metallic and weak covalent character, whereas the N‐terminated interface is a polar covalent bond similar to the Ti/TiC interface. Further study of the separation of the optimal interface shows that the cleavages will never fracture at the interface due to the strong bonding, which is consistent with the experimental results. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Structure, bonding, and adhesion at the TiC(100)/Fe(110) interface from first principles

Metal carbide ceramics offer potential as protective coatings for steels. Here we report a pseudopotential-based density functional (DFT) investigation of one such coating, wherein we predict the atomic structure, bonding, and the ideal work of adhesion (Wadideal) of the interface between a TiC(100) coating and a bcc Fe(110) substrate. Calibration of the DFT approximations used yields TiC and Fe bulk properties in reasonable agreement with experiment. Subsequent characterization of the low-index TiC and Fe surfaces reveals that all surfaces retain near bulk termination, in agreement with experiment. Stabilities of both TiC and Fe surfaces increase with their packing densities, i.e., (110)&amp;lt;(111)&amp;lt;(100) for TiC and (111)&amp;lt;(100)&amp;lt;(110) for bcc Fe. We estimate that the minimum critical stress required for crack propagation in bcc Fe is 27% larger than that in TiC. The TiC(100)/Fe(110) interface exhibits a lattice mismatch of ∼2.1%, leading to a smooth interface with only a small structural relaxation, except for the ultrathin 1 monolayer (ML) coating. A mixture of metallic and covalent bonding dominates across the interface, due to significant C p-Fe d interaction and somewhat less pronounced Ti d-Fe d mixing; the latter is found to decrease with increasing coating thickness, but reaches a saturation value for 3-ML-thick coating. The asymptotic value of Wadideal for the TiC(100)/Fe(110) interface is predicted to be ∼2.56 J/m2 and is reached for a 3-ML-thick coating of TiC on Fe. This interface strength is considerably smaller than the energy required for cracking TiC or Fe, but may still be strong enough to survive as a coating for steel in extreme environments.

Adhesion, atomic structure, and bonding at theAl(111)/α−Al2O3(0001)interface: A first principles study

We have performed a series of ab initio calculations to determine the atomic structure, ideal work of adhesion $({\mathcal{W}}_{\mathrm{ad}\mathrm{}}),$ and bonding character of the $\mathrm{Al}(111)/\ensuremath{\alpha}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}(0001)$ interface. Six candidate interface geometries were considered, including Al and O terminations of the oxide. Minimization of the Hellman-Feynman forces resulted in substantial changes to the atomic structure of the metal near the interface, wherein some atoms adopted positions consistent with a continuation of the oxide's Al-sublattice crystal structure across the interface. Consequently, the lowest-energy structures (i.e., having the largest ${\mathcal{W}}_{\mathrm{ad}\mathrm{}})$ are those that facilitate this ``oxide extension'' mechanism. By applying several methods of analysis we have thoroughly characterized the electronic structure and have determined that Al-O bonds constitute the primary interfacial bonding interaction. These bonds are very similar to the cation-anion bonds found in the oxide bulk and are mainly ionic, yet maintain a small amount of covalent character. In addition, there is evidence of metal-cation bonding at the optimal Al-terminated interface. Taking into account recent theoretical and experimental evidence suggesting an Al termination of the clean oxide surface, our calculations predict ${\mathcal{W}}_{\mathrm{ad}\mathrm{}}=1.36{\mathrm{J}/\mathrm{m}}^{2}$ [local density approximation (LDA)] and 1.06 ${\mathrm{J}/\mathrm{m}}^{2}$ [generalized gradient approximation (GGA)] for the optimal Al-terminated structure, which are in good agreement with the experimental value of 1.13 ${\mathrm{J}/\mathrm{m}}^{2}$ as scaled to 0 K. These values are approximately an order of magnitude smaller than what is found for the optimal O-terminated interface: 10.70 ${\mathrm{J}/\mathrm{m}}^{2}$ (LDA) and 9.73 ${\mathrm{J}/\mathrm{m}}^{2}$ (GGA). Although cleavage preferentially occurs at the interface for the Al termination, strong bonding at the O-terminated interface favors cleavage within the metal.