A pseudo-binary interdiffusion study in the β-Ni(Pt)Al phase

Interdiffusion study is conducted in the Ni-rich part of the β-Ni(Pt)Al phase following the pseudo-binary approach. Interdiffusion coefficients over the whole composition range considered in this study increases with increase in Pt content, which is in line with the theoretical study predicting the decrease in vacancy formation and migration energy because of Pt addition. The trend of change in diffusion coefficient with the increase in Ni and Pt contents indicates that Pt preferably replaces Ni antisites.     

Observation of phase separation in magnetron sputter-deposited Al–Cu thin films

The microstructures of Al–1.8 to 92.5?at.% Cu thin films prepared by radiofrequency (13.56?MHz) cathodic magnetron sputtering have been investigated by X-ray diffraction (XRD) and transmission electronic microscopy (TEM). A phase separation occurs in films of nominal Al–66.64?at.% Cu composition, consisting of a fcc Al solid solution phase, a fcc Cu solid solution phase and an unexpected sc Cu₃Al ordered phase with a Cu₃Au structure and a lattice parameter of about 0.36?nm.     

Epitaxial decagonal thin films on crystalline substrates

Al-Cu-Fe-Cr quasicrystalline thin films were grown on atomically flat Al 2 O 3 sapphire (0001) substrates by single-target magnetron sputtering followed by annealing. A decagonal phase with the tenfold axis A 10 parallel to the substrate surface normal was observed. The epitaxial decagonal film had two different unique orientations: a twofold P axis A 2P and a twofold D axis A 2D parallel to of the substrate. These two configurations were explained using a coincidence reciprocal lattice planes model for the interface energy. We show that this classic approach for crystal-crystal epitaxy can be applied to quasicrystal-crystal systems.     

Reversible phase transition in vanadium oxide films sputtered on metal substrates

Vanadium oxide films, deposited on aluminium (Al), titanium (Ti) and tantalum (Ta) metal substrates by pulsed RF magnetron sputtering at a working pressure of 1.5 x10^?2 mbar at room temperature are found to display mixed crystalline vanadium oxide phases viz., VO₂, V₂O₃, V₂O₅. The films have been characterized by field-emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy, and their thermo-optical and electrical properties have been investigated. Studies of the deposited films by DSC have revealed a reversible-phase transition found in the temperature range of 45–49 °C.     

Structures of Ti2(Ni,V) in crystalline and quasicrystalline phases

Abstract

A new criterion for the classification of quasicrystalline structures is proposed. A quasicrystal with composition close to a Frank-Kasper phase, which consists exclusively of tetrahedra, should belong to the i((Al, Zn)₄₉Mg₃₂) class whereas one with composition close to that of the crystal, which consists of both tetrahedra and octahedra, should belong to the i(A1MnSi) class. The Ti₂(Ni, V) building block consists of four icosahedra and a truncated tetrahedron. Replacing the eight carbon atoms of a diamond unit cell with this building block produces the Ti₂(Ni, V) crystal. Placing a distorted Ti₂(Ni, V) building block on a threefold axis of an icosahedrally symmetric point group and operating on it by this point group gives a double Mackay icosahedron. It can be concluded that the Ti₂(Ni, V) and α-AlMnSi quasicrystals are isomorphic structures since Ti₂(Ni, V) and α-A1MnSi crystals consist of both tetrahedra and octahedra.     

Sol-gel-hydrothermal growth of oxide thin films at low temperatures

Lead zirconate titanate (PZT) (Pb(Zr_0.52Ti_0.48)O₃) and barium titanate (BaTiO₃) thin films have been successfully prepared using a novel sol-gel- hydrothermal (SG-HT) technique at low temperatures, which involves a combination of the conventional sol-gel process and a hydrothermal method. Highly (111)-oriented PZT thin films with a single perovskite phase and polycrystalline BaTiO thin films with well developed crystallites were obtained at a processing temperature as low as 160⁰C. The microstructural characteristics demonstrate that the SG-HT-derived PZT and BaTiO₃ thin films with good crystallinity and surface morphology are converted from the amorphous phase to the desired perovskite phase on platinum-coated and bare silicon substrates at a low processing temperature of 100-200 C. These results suggest that the SGHT technique, which is of great significance because of its low processing temperature, will become a potential and promising process for fabricating PZT, BaTiO₃ and other oxide thin films.     

Formation of decagonal and approximant phases in the Al-Ni-Ru system

Al-Ni-Ru alloys with a wide composition range have been synthesized and examined by X-ray and electron diffraction experiments. In this system, two types of decagonal (d) phases are formed, namely basic-type and superlattice-type d phases. Annealing experiments have shown that the basic-type d phase is stable at high temperatures and that its single-phase region is located in a small composition range around Al 75 Ni 15 Ru 10 . On the other hand, the superlattice-type d phase is metastable and has been found to form only in the samples before annealing. Besides the d phases, a high-order crystal approximant phase with lattice parameters a = 99.5 Å and b = 84.6 Å has been found. The structural relation between the approximant phase and the d phase is discussed in terms of a phason tensor.     

Crystal structure of the ξ phase in the Al-Si-Mg-Fe system studied by electron channelling

We have re-examined the structure of the ~ phase in a quaternary alloy previously found to have the composition Al 8 Si 6 Mg 3 Fe. Electron probe microanalysis shows that the composition of the phase is actually Al 9 Si 5 Mg 3 Fe and, based on this new chemical formula, we propose a revision of the atomic positions which does not require any substitutional disorder within the hexagonal crystal unit cell with space group P ¥ 62 m (no. 189). These Wyckoff positions are as follows: for Al, 6i and 3f; for Si, 4h and 1b; for Mg, 3g; and for Fe, 1a. Results from electron channelling experiments are consistent with these new positions while ruling out those previously reported in the literature.     

The orientation and temperature dependences of dislocation velocity in Ni 3 Al single crystals

The average velocities of screw dislocations in Ni 3 Al single crystals have been directly measured as a function of resolved shear stress (RSS) and orientation in the temperature domain of the flow stress anomaly using the etch-pit technique. The velocity was found to be extremely sensitive to the RSS in all cases. In contrast with ordinary metals, the screw dislocation velocities in Ni 3 Al show anomalous behaviour; under a constant RSS, the velocities decrease dramatically with increasing temperature. Furthermore, the velocities and the tension-compression asymmetry of the velocities depend on the orientation of applied stress.     

Multilayered phase formation after high-fluence implantation of nickel into aluminium

The formation of crystalline and amorphous layers has been observed in Al crystals after 5MeV Ni implantation up to a fluence of 7.6 10 17 Ni atomscm -2 . The layers are structured into sublayers perpendicular to the implantation direction with sharp interfaces between the phases and almost symmetrically arranged to both sides of the maximum of the implantation profile. The sublayers of thickness of the order of 100nm were analysed by transmission electron microscopy. They consist of polycrystalline Al 3 Ni, crystalline Al 3 Ni precipitates and small amorphous zones, depending on the local Ni implantation concentration.     

Work function dependence on the thickness and substrate of carbon contamination layers by Kelvin probe force microscopy

The contact potential difference (CPD) between carbon contamination (CC) layers and the several substrates on which they were deposited has been measured as a function of the film thickness by means of Kelvin probe force microscopy (KPFM). The observed CPD trends may be divided into three categories:

2. an increase, or decrease, in CPD with thickness up to a saturation value with sign inversion with respect to the substrates (Al and Si);

3. an oscillation with no sign inversion (substrates, gold and platinum);

4. an oscillation through sign inversion (palladium substrate).

Effects (ii) and (iii) seem to be typical of CC, since they have not been observed for other materials, including evaporated carbon. Several possible causes of the above two effects are examined, but a satisfactory interpretation has not been found yet. The sensitivity of KPFM is such that CC layers 10 nm thick are easily visible, whereas they are hardly detectable by topography.     

Effect of mechanical stress on the absorption band tail of cubic boron nitride thin films synthesized by inductively coupled radio-frequency plasma chemical vapour deposition

Thin films of cubic boron nitride were deposited on silica and Si substrates by inductively coupled radio-frequency plasma chemical vapour deposition (IPCVD) technique using a B₂H₆?+?N₂?+?Ar gas mixture. Cubic phase formation was confirmed by glancing-angle X-ray diffraction studies, which showed reflections up to (311). Fourier-transform infrared (FTIR) spectra also indicated the predominantly cubic nature of the deposited films. The optical properties of the films were studied in the wavelength range 200–1000?nm. Both direct and indirect transitions were found to be present. Mechanical stress in the grain-boundary region of the films seems to contribute significantly to the optical absorption below the band gap. The intercrystalline barrier height (E _b) and the trap state density (Q _t ) were obtained from an analysis of the effects of grain boundaries on the optical properties of the samples.     

Friction and wear behaviour of Inconel 718 alloy fabricated by selective laser melting after heat treatments

ABSTRACT

The effect of heat treatments (solution and double aging) on friction and wear behaviour of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) were studied. After heat treatment of solution and double aging, the friction and wear of the alloy have been improved. The worn surfaces of heat-treated IN718 alloy became smoother, and micro-ploughing became shallower. After solid solution hearting, a portion of the Laves phase ((Ni, Fe, Co)₂(Nb, Ti, Mo)) dissolves into the matrix, after which the γ″ phase (Ni₃Nb) andthe equilibrium phase of the δ phase (Ni₃Nb) precipitates during double ageing. After solution and double aging, nano-scale γ′ (Ni₃(Al, Ti)) and γ″ phases distribute homogeneously in the matrix, which improves the material hardness and wear resistance of the SLMed IN718 alloy.     

site determination of dilute Cu in beta-phase NiAl by 63Cu nuclear magnetic resonance and X-ray emission channelling patterns

A sharply bimodal lattice site distribution of dilute Cu in both Ni-deficient and Al-deficient beta-phase Ni-Al alloys has been observed in the 63Cu nuclear magnetic resonance (NMR) spectra. These NMR results are correlated with results derived from incoherent channelling patterns (ICPs) formed by variations in characteristic X-ray emission as a function of incident fast electron orientation. Statistical analysis of ICP data, generated near a 210 zone axis, indicates that Cu occupies substitutional sites; Cu is exclusively on the Al sublattice sites in the Al-deficient alloy, whilst the partition ratio of Ni : Al sublattice sites for Cu in the Ni-deficient alloy is about 80 : 20. Comparison of ICP contrast from Cu X-ray emission with ICPs from the host lattice enables the two peaks in the 63Cu NMR spectrum to be individually identified as originating from Cu on Ni sublattice sites, and from Cu on Al sublattice sites. The respective NMR line intensities from the Ni-deficient alloy yields a Ni : Al sublattice site occupancy ratio which is in good agreement with the partitioning ratios derived from channelling patterns     

Structure of a phase induced with Xe-ion irradiation-implantation in γ-TiAl

A phase transformation in γ-TiAl intermetallic alloy was found to be induced with 50keV Xe-ion irradiation-implantation at doses larger than 2.2 x 10¹⁸ ions m^-2 at room temperature. The structure and the chemical composition of the induced phase were investigated with high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The zones of the induced phase have sizes up to about several tens of nanometres. The phase has a hexagonal structure with a = 0.286 nm and c = 0.462nm. The crystallographic orientation relationship between the phase (P) and the gamma-TiAl matrix is (001)_P//(111)_γ and \[100]_P//[011]_γ. The \[Al]/[Ti] atomic composition ratio in the phase is analysed to be 56/44, slightly different from that of the matrix, 51/49. These results suggest that the induced phase is an Al solid solution of α-Ti alloy phase, which has different structural parameters and chemical composition from those of the reported phase. It is suggested that the size of the ions is important in the phase transformation.     

Chemical effects on periodicity and structure of decagonal phases in Al-Ni- and Al-Co-based alloys

Abstract

The structures of decagonal phases in binary Al-Ni and Al-Co systems and ternary Al₇₀Ni _x TM_1?x(TM = Co, Rh or Ir) alloys have been studied by electron diffraction. In the Al-Co system, the periodicity of the decagonal phase is 1.6 nm in Al₈₀Co₂₀, and 0.8 nm in Al₇₆.₅Co_23.5 and Al₇₂Co₂₈, suggesting that the stacking rule between Al and Co atoms is different along the c axis for the three alloys. In the ternary systems, diffuse streaks and periodicity systematically vary with the atom substitution of Co for Ni and Ir for Ni, indicating that Ni, Co and Ir atoms play different roles in the decagonal phase and exhibit various sorts of chemical order with Al atoms.     

Anisotropic BaTiO3 thin films grown on MgO-buffered R-plane sapphire

Epitaxial BaTiO₃ thin films grown on MgO-buffered R-plane-cut Al₂O₃ substrates show a non-uniform distribution of planar defects. Transmission electron microscopy allows the determination of the distributions of planar defects with respect to the Al₂O₃ substrate. The BaTiO₃ film, the MgO buffer and the Al₂O₃ substrate have an orientation relationship of [100]_BaTiO3//[100]_MgO//[1120]_Al2O3, (010)_BaTiO3//(010)_MgO//(1104)_Al2O3 and (001)_BaTiO3//(001)_MgO// ≈ (1102)_Al2O3 (about 5°; deviation). Under the above relationship, most of the {111} stacking faults occur on (111) and (111) planes, that is two of four sets of {111}_BaTiO3, whereas cracks in the BaTiO₃ film (and MgO buffer) are situated on the (100) planes. The anisotropic distribution of planar defects is regarded as a consequence of an anisotropic stress in the films generated during their fabrication.     

Roughening kinetics of reactively sputter-deposited Ti-Al-N films on Si(100)

The roughening kinetics of Ti_{1? x} Al _x N (0?x? 1) films 600 nm thick synthesized by reactive dc magnetron sputtering on Si(100) substrates has been investigated by atomic force microscopy (AFM). The quantification of surface roughening was achieved by calculation of both vertical root-mean-square roughness and lateral correlation lengths of the film surface using the height-height correction functions of measured AFM images. For all the Ti_{1? x} Al _x N films, a steady roughness exponent α = 0.94 ± 0.03 was determined. The evolution of the surface topography as a function of Al concentration is discussed in terms of the competition between surface diffusion and shadowing instability during sputter deposition.     

Cluster formulae for alloy phases

Composition formulae for alloy phases are developed using first-neighbour coordination polyhedra plus their connections. The resultant cluster formulae [cluster](glue atom) _x , similar to molecular formulae for chemicals, contain key structural and composition information on the alloy phases. As examples, Al–Ni–Zr alloy phases are analysed with the objective of revealing cluster formula properties such as the principal cluster, the cluster phase and the definition of complex alloy phases.     

Heterophase polydomain structure and metal-semiconductor phase transition in vanadium dioxide thin films deposited on (1010) sapphire

Vanadium dioxide (VO₂) thin films deposited on ₍1010₎ sapphire are composed of two mixed monoclinic phases, namely M1 and M2. The M1 phase is unstable because of the existence of a larger misfit strain in the ₍102₎ VO₂ film. The reduction of misfit strain in the film favours the formation of the M2 phase. The X-ray diffraction and pole figure results show that both M1 and M2 phases are well aligned with the substrate and both contain twinned structures. Therefore, the microstructure of the film can be regarded as being a transversely modulated heterophase polydomain. A higher electrical resistivity ratio of the semiconductor phase to the metallic phase (rho_s/rho_m) can be achieved only in single-phase VO₂ thin films, either the M2 or M1 phase. Phase mixing degrades the ratio of rho_s/rho_m. The film with a single M2 phase exhibits a lower transition temperature of 58 C without any degradation of the rho_s/rho_m ratio.