Al Si Bonds Research Articles

Promoting bonding strength between internal Al-Si based gradient coating and aluminum alloy cylinder bore by forming homo-epitaxial growth interface

The reliability of interface bonding strength between internal thermal sprayed coating and cylinder bore substrate causes special concern in the field of internal thermal spraying. In this study, a new approach is proposed to create a large area of metallurgical bonding at the coating-substrate interface by the design of Al-Si based gradient coating on A383 alloy cylinder bore. The internal coating comprises hypereutectic Al-Si-Cu-Fe top layer, near-eutectic Al-Si bond layer, and transition layers, which were fabricated by an advanced internal rotating plasma spraying technology. The tensile adhesive and interfacial indentation tests were conducted to investigate the adhesion properties of the coating. The crystallographic relationship of the bond layer-substrate interface was further investigated using the focused ion beam and high-resolution transmission electron microscopy. Results show that the Al-Si based gradient coating presents both desirable surface hardness (385.1 ± 46.6 HV0.025) and bonding strength (46.4–58.1 MPa). The tensile failure mode is the fracture at the subsurface of the top layer, without fracture at the coating-substrate interface. The superior bonding strength results from the formation of chemical interdiffusion (estimated thickness of 700–1500 nm) and homo-epitaxial growth at the interface. This study provides a framework for forming a reliable metallurgical bonding interface of internal thermal-sprayed coating.

Low-Valent Mx Al3 Cluster Salts with Tetrahedral [SiAl3 ]+ and Trigonal-Bipyramidal [M2 Al3 ]2+ Cores (M=Si/Ge).

Schnöckel's [(AlCp*)4 ] and Jutzi's [SiCp*][B(C6 F5 )4 ] (Cp*=C5 Me5 ) are landmarks in modern main-group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]+ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)3 ][WCA] ([WCA]- =[Al(ORF )4 ]- and [F{Al(ORF )3 }2 ]- ; RF =C(CF3 )3 ). The tetrahedral [SiAl3 ]+ core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also-due to its facile accessibility and high stability-provides a convenient preparative entry towards low-valent Si-Al clusters in general. For example, an elusive binuclear [Si2 (AlCp*)5 ]2+ with extremely short Al-Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge2 (AlCp*)5 ]2+ dication were also obtained and represent the first mixed Al-Ge cluster.

Mechanical and thermodynamic behaviors of AlSi2Sc2 under uniaxial tensile loading: A first-principles study

This study investigates the structural, mechanical, and thermodynamic behaviors of AlSi2Sc2 under uniaxial tensile loading by performing first-principles calculations based on density functional theory. The parameters of the lattice a and c were found to depend on the Al–Si and the Sc–Si bonds, respectively. Tensile stress–strain curves were used to obtain ideal tensile strengths of 16.1 GPa and 21.2 GPa along the a- and c-axes, respectively. The criteria for stability showed that the AlSi2Sc2 compound became mechanically unstable when the strain exceeded 0.1 and 0.3 along the a- and the c-axes, respectively. The polycrystalline elastic constants of AlSi2Sc2 decreased with increasing strain along both axes as well, as did its Debye temperature and minimum thermal conductivity. An analysis of its electronic structure indicated that the Al–Si bonds mainly originated from the hybridization of the Al-3p and the Si-3p states, whereas the Sc–Si bonds originated from the Sc-3d and Si-3p states.

Steel–Aluminum Hybrid Die Casting: Microstructures related to the applied Al–Si bond coating

The microstructure of a successfully applied Al–Si bond coating for the interconnection of cast aluminum alloy with a conventional steel substrate is analyzed in detail. The bond coating formed a 10–20 μm columnar Al layer which is attached to the steel substrate with an intermetallic layer (2–3 μm) during physical vapor deposition at approx. 853 K. Silicon grains precipitated in between the columnar Al layer and the intermetallic phases, giving rise to the ternary compounds on top of the IMC layer, whereas binary intermetallics were found in vicinity to the steel. Peculiarities of the crystallographic structural models of the observed intermetallics are discussed in light of the existing literature and are evaluated integrally using X-ray diffraction and locally by electron backscatter diffraction. The sequence of the phases of the bond coating and a resulting diffusion path is discussed on basis of the isothermal section of the ternary Fe–Al–Si phase diagram. After mechanical shear tests it was found that the applied bond coating did not detach from the steel substrate and instead failure was observed at the interface between columnar Al and cast Al or even within the microstructure the cast Al, proving the successful connection of the bond coating with the steel substrate.

Insight into mechanical and thermodynamic properties of Al2Si2La and Al2Si2Pr from first-principles calculations

The crystal structures, stability, mechanical behaviors, thermodynamic properties and electronic structures of Al2Si2La and Al2Si2Pr compounds have been investigated by means of first-principles calculations. It is revealed from formation enthalpies that Al2Si2La exhibit much more thermodynamically stability. According to the results of elastic constants, Al2Si2Pr has stronger incompressibility, stronger shape deformation resistance and higher stiffness. It can be concluded from Debye temperature and minimum thermal conductivity that Al2Si2Pr and Al2Si2La exhibit nearly the same thermal conductivity. Electronic structures results demonstrate that the Al–Si bonds in Al2Si2La and Al2Si2Pr are attributed to the hybridization of Al 3s state, Al 3p state and Si 3p state, while RE–Si bonds are the contribution of Si 3p state and La 5d or Pr 4f state in Al2Si2La and Al2Si2Pr, respectively.

Thermal Barrier Coatings for Molybdenum Produced Using Nanopowders

The molybdenum is one of the most important refractory metals used in aerospace industry. The main disadvantage of Mo is low oxidation resistance at elevated temperature and the using of protective coatings is necessary. In present article the new types of protective coatings produced by slurry method were developed. The slurries contained Al nanopowder and Si powder as well as non-organic binder (H2CrO4 and water). After immersion and drying the samples with slurries were heat treated at 1000°C in Ar atmosphere. The thickness of obtained coatings was in range 10-20 μm. The presences of phases form Mo-Al as well Mo-Si systems was analyzed using scanning electron microscopy. The developed coatings were used as a bond coat for ceramic layer produced by plasma spray physical vapour deposition method (PS-PVD). In this process the columnar ceramic layer contains yttria stabilized zirconia (YSZ) was obtained wit thickness above 100 μm. The obtained results showed that it is possible to obtain TBC coating on molybdenum contained Al-Si bond coat and outer YSZ ceramic layer. The proposed coating can be used in aerospace applications.

Structure and stability of vacancy–solute complexes in Al–Mg–Si alloys

This study investigates the structure and stability of vacancy–solute complexes in Al–Mg–Si alloys using first-principles calculations along with the prediction of initial structures using multiple linear regression analysis. In Al–Mg and Al–Si binary alloys, vacancy–solute complexes become unstable when more than five solute atoms are combined with a vacancy, due to the repulsive interactions between adjacent atom pairs. In Al–Mg–Si alloys, the formation energy of the vacancy–solute complexes continues to decrease as the number of solute atoms increase. The stability of vacancy–solute complexes mainly arises from the Mg–Si bonds formed with the increasing number of solute atoms. The combination of inward displacement of the Mg atoms and outward displacement of the Si atoms accommodates the increase in the number of Mg–Si bonds. Owing to short range repulsive interatomic interactions, Mg–Mg bonds cannot be formed in vacancy–solute complexes of Al–Mg–Si alloys. However, Si–Si bonds are a preferable alternative to enhance stability in vacancy–solute complexes, despite their decreased strength compared with Mg–Si, Al–Mg, and Al–Si bonds. The concentration of Si atoms in the vacancy–solute complexes is always larger than that of Mg atoms at finite temperatures. The stability of the Si-rich composition originates from the difference between the Si–Si and Mg–Mg interactions in the vacancy–solute complexes.

First-principles study on the diffusion dynamics of Al atoms on Si surface

<sec>Density functional theory is used to calculate the adsorption and diffusion behavior of Al atoms on clean, H-terminate, Cl-terminate Si(100) and Si(111) surfaces. The most stable position of Al atom adsorption and the diffusion path are different on Si(100) surface terminated by different methods. On the surface of clean Si(100), the <i>Tr</i> site is the most stable site for Al atom with an adsorption energy of 4.01 eV, and the <i>H</i> and <i>M</i> sites are the sub-stable stable sites with the adsorption energies of 3.51 eV, and 3.63 eV, respectively. When the Al atom is adsorbed at the <i>Tr</i> site on the clean Si(100) surface, it bonds with the Si atom to destroy the Si—Si bond in the dimer. Therefore Al is easily adsorbed at the <i>Tr</i> site of the trench and diffuses in a zigzag pattern along the trench. On the H-terminate and Cl-terminate Si(100) surface, Si—Si bonds in the dimer column are changed from cross to parallel. Al is easily adsorbed at the <i>H</i> position at the top of the dimer column, and diffuses along the line at the top of the dimer. The differential charge density shows that the Al atom transfers electrons to the Si atoms on the surface, and the surface H-terminate and Cl-terminate weaken the interaction between Al atoms and Si, and reduces the diffusion energy barrier of Al atoms. </sec><sec>The Si(111) surface terminated by different methods has the same stable position (<i>T</i><sub>4</sub> site) for the adsorption of Al atoms. When Al atom adsorbs at the <i>T</i><sub>4</sub> site on the clean Si(100) surface, it bonds to Si atom, which located at the three <i>T</i><sub>1</sub> site, then Al atom is firmly fixed by the three Al—Si bonds with a bond length of 2.55 Å. Thus Al atom can has the largest adsorption energy and form the most stable state at the <i>T</i><sub>1</sub> site. With the diffusion and migration of Al atom, the bond between Al atom and the <i>T</i><sub>1</sub> site in the opposite direction appears to be broken. When Al atom migrating to the saddle point position is the most unstable. Here Al atom bonds to the Si atoms of the two adjacent <i>T</i><sub>1</sub> sites to form a bond with a length of 2.49 Å, which is 0.06 Å shorter than the initial Al—Si bond (2.55 Å). What’s more, the diffusion energy barrier of Al atom at this position is 0.65 eV, which impede Al atom to diffuse and migrate. When Al atom migrates to the <i>H</i> site, it rebonds to the three Si atoms on the adjacent surface and forms a bond with a length of 2.52 Å, which is 0.03 Å shorter than the Al—Si bond (2.55 Å) at the initial position. On the H-terminate and Cl-terminate Si(111) surface, Al atom doesn’t bond with Si atom for the H or Cl saturates the dangling bonds on the Si surface. The Si(111) surface terminated by different methods has the same stable position for adsorption of Al atoms. The diffusion paths of Al atoms are similar, and they are easy to be adsorbed to the top position (<i>T</i><sub>4</sub> site) of the second Si atom, and the path along <i>T</i><sub>4</sub> to <i>H</i><sub>3</sub> is diffused. Similarly, the H-terminate or Cl-terminate of Si(111) surface weakens the electron transfer between Al and Si atoms and reduces the diffusion energy barrier of Al atoms. Regardless of the Si(100) or Si(111) surface, the H-terminate and Cl-terminate Si surfaces are effective in reducing the diffusion barrier of Al atoms.</sec>

First-Principles Investigation on Type-II Aluminum-Substituted Ternary and Quaternary Clathrate Semiconductors R8Al8Si128 (R = Cs, Rb), Cs8Na16Al24Si112

Structural and vibrational properties of the aluminium-substituted ternary and quaternary clathrates R8Al8Si128 (R = Cs, Rb), Cs8Na16Al24Si112 are investigated. The equilibrium volume of R8Si136 expands when all Si atoms at the 8a crystallographic sites are replaced by Al. Formation of the Al–Si bond is thus anticipated to correlate with decreased guest vibration modes. Underestimation of the predicted lattice phonon conductivity κL (1.15 W m−1 K−1) compared to a previous experiment (1.9 W m−1 K−1) in Cs8Na16Si136 is thought to arise from our evaluation on the phonon mean free path λ using the “scattering centers” model. Accordingly, we expect that the “three-phonon” processes dominate the determination of the phonon relaxation time, leading to a more reasonable λ in the R8Al8Si128 system. Additionally, the “avoided-crossing” effect causes no appreciable difference in the sound speed for acoustic phonons in this framework. Starting with configuration optimization about aluminium arrangements in Cs8Na16Al24Si112, the calculated lattice parameter agrees well quantitatively with the experiment. The reduced Uiso of Cs from this calculation is anticipated to be primarily related to temperature-dependent quartic anharmonicity. Meanwhile, the predicted κL for Cs8Na16Al24Si112 remains not sensitive to the Al arrangement on 96g Wyckoff sites.

Hydrogen release at metal-oxide interfaces: A first principle study of hydrogenated Al/SiO2 interfaces

The Anode Hydrogen Release (AHR) mechanism at interfaces is responsible for the generation of defects, that traps charge carriers and can induce dielectric breakdown in Metal-Oxide-Semiconductor Field Effect Transistors. The AHR has been extensively studied at Si/SiO2 interfaces but its characteristics at metal-silica interfaces remain unclear. In this study, we performed Density Functional Theory (DFT) calculations to study the hydrogen release mechanism at the typical Al/SiO2 metal-oxide interface. We found that interstitial hydrogen atoms can break interfacial AlSi bonds, passivating a Si sp3 orbital. Interstitial hydrogen atoms can also break interfacial AlO bonds, or be adsorbed at the interface on aluminum, forming stable AlHAl bridges. We showed that hydrogenated OH, SiH and AlH bonds at the Al/SiO2 interfaces are polarized. The resulting bond dipole weakens the OH and SiH bonds, but strengthens the AlH bond under the application of a positive bias at the metal gate. Our calculations indicate that AlH bonds and OH bonds are more important than SiH bonds for the hydrogen release process.

Making and Breaking Bonds in Superconducting SrAl4–xSix (0 ≤ x ≤ 2)

We explored the role of valence electron concentration in bond formation and superconductivity of mixed silicon–aluminum networks by using high-pressure synthesis to obtain the BaAl4-type structural pattern in solid solution samples SrAl4–xSix where 0 ≤ x ≤ 2. Local ordering of aluminum and silicon in SrAl4–xSix was evidenced by nuclear magnetic resonance experiments. Subsequent bonding analysis by quantum chemical techniques in real space demonstrated that the strong deviation of the lattice parameters in SrAl4–xSix from Vegard’s law can be attributed to the strengthening of interatomic Al–Al and Al–Si bonds within the layers (perpendicular to [001]) for 0 ≤ x ≤ 1.5, followed by the breaking of the interlayer bonds (parallel to [001]) for 1.5 < x ≤ 2 and leading to the structural transition from the BaAl4 structure type with three-dimensional anionic framework at lower x values to the two-dimensional anion of the BaZn2P2 structure type with increasing x values. Low-temperature measurements of the resisti...

DFT modeling of plasma-assisted atomic layer deposition for Si(110) passivation: formation of boehmite-like chains as γ-Al2O3 precursors

One accelerated computational route to elaborate a Si(110)/γ-Al2O3 interface model passivated via plasma-assisted atomic layer deposition is proposed. The final oxidation step corresponds to a junction of a slab with a γ-Al2O3 fragment after two O → Al or three O → Al → O atomic deposition steps over a basic Si(110) surface. The sizes of both Si(110)/γ-Al2O3 components were selected to lead to a minimal mismatch while atomic coordinates were optimized using DFT with periodic boundary conditions. The extent of Si(110) passivation after each deposition step was studied by analyzing the geometry of the atoms (to detect the under-coordinated defects) and by assigning the band structure and projected densities of the s- and p-states (to detect structural defects, with distorted bond lengths and angles). The formation of boehmite-like chains with higher (octahedral) Al coordination without Al–Si bonds in the Si(110)/SiOX/AlOY interface is particularly discussed. Examples of models with a passivated interface (using or not the junction with γ-Al2O3 fragment) were obtained together with a list of typical defects.

Band structures and optical properties of Al-doped α-Si3N4: theoretical and experimental studies

The band structures and optical properties for Al-doped α-Si3N4 have been studied combining theoretical calculations and experimental measurements. The geometry and band structures for substitutional and interstitial Al defective α-Si3N4 models have been calculated based on density functional theory. The results indicate that the location and composition of the intermediate energy level in the band gap are affected by the partial atomic environment around the Al atoms and the characteristics of Al–N and Al–Si bonds. The maximum energy gap is observably decreased to 1.99 eV because of the appearance of intermediate energy levels in the band gap for interstitial Al defective α-Si3N4. Moreover, the energy gaps deduced from the measured absorption and photoluminescence spectra of the as-prepared Al-doped α-Si3N4 sample are in good agreement with the calculated results. The significant improvement in the optical properties by doping Al makes silicon nitride a potential visible light emitting material.

Structural and electronic properties of a single Si chain doped zigzag AlN nanoribbon

The first-principles projector-augmented wave (PAW) potentials within the density function theory (DFT) framework have been used to determine the geometry structures and electronic properties of the zigzag edge AlN nanoribbons (ZAlNNRs) doped with a single Si chain under generalized gradient approximation (GGA). The average Al–Si, Si–Si, Al–N, Si–N, Al–H and N–H bond lengths are 2.39, 2.16, 1.83, 1.74, 1.59 and 1.03Å, respectively. Pure 7-ZAlNNR is an indirect semiconductor with a large band gap of 2.235eV, while a semiconductor to metal transformation is taken place after a single Si chain substituting for a single Al–N chain at various positions. In pure 7-ZAlNNR, the HVB and LCB are mainly attributed to the edge N and Al atoms, respectively, while in a single Si chain substituting doped 7-ZAlNNR, the HVB and LCB are mainly attributed to the Si atoms. The Al–N, Al–H and Al–Si bonds are ionic bond, the Si–Si and Si–H bonds are covalent bond, the N–H and N–Si bonds are covalent bond modified ionic bond.

Joule-Heating-Induced Damage in Cu-Al Wedge Bonds Under Current Stressing

Copper wires are increasingly used to replace gold wires in wire-bonding technology owing to their better electrical properties and lower cost. However, not many studies have been conducted on electromigration-induced failure of Cu wedge bonds on Al metallization. In this study, we investigated the failure mechanism of Cu-Al wedge bonds under high current stressing from 4 × 104 A/cm2 to 1 × 105 A/cm2 at ambient temperature of 175°C. The resistance evolution of samples during current stressing and the microstructure of the joint interface between the Cu wire and Al-Si bond pad were examined. The results showed that abnormal crack formation accompanying significant intermetallic compound growth was observed at the second joint of the samples, regardless of the direction of electric current for both current densities of 4 × 104 A/cm2 and 8 × 104 A/cm2. We propose that this abnormal crack formation at the second joint is mainly due to the higher temperature induced by the greater Joule heating at the second joint for the same current stressing, because of its smaller bonded area compared with the first joint. The corresponding fluxes induced by the electric current and chemical potential difference between Cu and Al were calculated and compared to explain the failure mechanism. For current density of 1 × 105 A/cm2, the Cu wire melted within 0.5 h owing to serious Joule heating.

Phase Range of the Type-I Clathrate Sr8AlxSi46–x and Crystal Structure of Sr8Al10Si36

Samples of the type-I clathrate Sr(8)Al(x)Si(46-x) have been prepared by direct reaction of the elements. The type-I clathrate structure (cubic space group Pm3n) which has an Al-Si framework with Sr(2+) guest atoms forms with a narrow composition range of 9.54(6) ≤ x ≤ 10.30(8). Single crystals with composition A(8)Al(10)Si(36) (A = Sr, Ba) have been synthesized. Differential scanning calorimetry (DSC) measurements provide evidence for a peritectic reaction and melting point at ∼1268 and ∼1421 K for Sr(8)Al(10)Si(36) and Ba(8)Al(10)Si(36), respectively. Comparison of the structures reveals a strong correlation between the 24k-24k framework sites distances and the size of the guest cation. Electronic structure calculation and bonding analysis were carried out for the ordered models with the compositions A(8)Al(6)Si(40) (6c site occupied completely by Al) and A(8)Al(16)Si(30) (16i site occupied completely with Al). Analysis of the distribution of the electron localizability indicator (ELI) confirms that the Si-Si bonds are covalent, the Al-Si bonds are polar covalent, and the guest and the framework bonds are ionic in nature. The Sr(8)Al(6)Si(40) phase has a very small band gap that is closed upon additional Al, as observed in Sr(8)Al(16)Si(30). An explanation for the absence of a semiconducting "Sr(8)Al(16)Si(30)" phase is suggested in light of these findings.

Adsorption of Al on the Si(0 0 1) surface

The first-principles calculations have been presented to study the adsorption of aluminum (Al) on the Si(0 0 1)(2×1) surface. We have investigated the optimized geometries and electronic structures of the adatom–substrate system. The adsorption energy of the system has been calculated. The most stable adsorption sites were consequently determined to be HH site and T3+T4. It is shown that the Si–Si dimer is asymmetric on the reconstructed bare surface and become symmetric upon Al adsorption. In addition, the bond length of Si–Si was found to be considerably elongated in the adsorption system. It is found that the work function change obtained in our work is different from other previous results on the adsorption of alkali metals on the Si(0 0 1) surface. In order to investigate the relative stability of phases at different coverages, the surface formation energy of the adsorption system was calculated. To shed light on the nature of the Al–Si bond and the character of silicon surface, the density of states (DOS) and difference charge density of the system were evaluated.

First-principles computational tensile test on a Na-segregated Al grain boundary with an Siadditive and an intergranular embrittlement suppression mechanism

We have performed a first-principles computational tensile test (FPCTT) on anNa-segregated Al grain boundary (GB) with an Si additive. We show that the Si additivein the GB greatly increases both the tensile strength and the toughness of theNa-segregated Al GB. We demonstrate that the final GB fracture is dominated bythe breaking of interfacial stronger Al–Si bonds according to the bond evolutionwith increasing strain. Based on the Na-induced Al intergranular embrittlementmechanism explored before and the present calculation results, we propose aGB-strengthening mechanism by adding a strengthening element such as Si for Alalloy to suppress the intergranular embrittlement by an Na impurity. Such anintergranular embrittlement suppression mechanism can explain the experimentalobservations.

First-principles calculations of β″-Mg 5Si 6/α-Al interfaces

The metastable β″-Mg 5Si 6 phase is often the most effective hardening precipitate in Al-rich Al–Mg–Si alloys. Two important factors that control the precipitate morphology are the strain energy and the interfacial energy between the precipitate and the matrix. By means of a first-principles supercell approach and density functional theory calculations, we have studied the interfacial properties between β″-Mg 5Si 6 and α-Al. We carefully construct a large number of interfacial cells in order to elucidate preferred interfacial terminations and orientations, as well as atom alignment and intermixing across the interface. Each of the low-energy interfaces we found possesses two key attributes: a high number of Al–Si bonds across the interface, and a face-centered cubic topological alignment of atoms across those interfaces. Our first-principles results yield quantitative values for the interfacial energies, lattice mismatches and strain energies that can be used in future predictions of precipitate morphologies as a function of size.

Ab initio molecular dynamics study on the formation process of Al layers on Si(001) surface

To clarify the early stage of the Al formation process on the Si(001) surface, we conduct ab initio molecular dynamics calculations of the precipitation of Al atoms on to the Si surface based on the pseudopotential plane wave basis method. We examine two candidate structures of the first Al layer, where the Al dimers are between Si dimer rows: Al dimers perpendicular (case A) and parallel (case B) to Si dimers. In case A, the distance between the first and the second layers is shorter than that between the (111) planes in an Al crystal. Results show that the charge density of the Al–Al bonds is 0.03–0.04 au−3 and that of the Al–Si bonds is 0.06 au−3. The bond lengths are 0.27 nm, which are almost the same as those in the Al single crystal. Al atoms precipitated after the formation of the two layers can move onto the surface. In case B, the first layer of Al atoms are arranged on a groove between the Si dimer rows and form bonds with the Si dimers, where the charge population of the bonds is similar to that in case A. These results suggest that dense layers of Al can be formed on the surface.