Surface Layers Of Single Crystals Research Articles

Effect of ultrasonic shot peening on surface integrity and fatigue performance of single-crystal superalloy

• Ultrasonic shot peening applied to improve fatigue performance of single crystal alloys. • Notch fatigue limit after peening increased to higher than the oringinal smooth fatigue limit. • Three anti-fatigue mechanisms: (1) machining marks elimination; (2) surface nanoscale sub-crystalline structure; (3) deformation promotion of casting micro-pores. We investigated the effect of ultrasonic shot peening on the surface integrity and fatigue properties of single-crystal superalloys. The results show that ultrasonic shot peening significantly reduces the surface roughness of single-crystal specimens and improves surface finishing. The surface hardness increases by 49 %, reaching more than HV660. At the same time, the microstructural analysis illustrates that the single-crystal surface layer after ultrasonic shot peening forms a nanoscale refined sub-crystalline structure that rotates along the [110] axis. It significantly improves the mechanical properties of the surface metal. The originally existing round casting micro-pores are elongated along the [001] axis, forming a willow shape - elliptical shapes from the surface inward, reducing the stress concentration of the casting micro-pores perpendicular to the [001] axis. Combining the above three modification effects, the fatigue limit of the single-crystal notched Kt = 3 sample at 650 ℃ strengthened by ultrasonic shot peening is 94.2 % higher than that of the as-received notched sample, and 17.4 % higher than that of the smooth sample.

Room-temperature sub-band gap optoelectronic response of hyperdoped silicon

Room-temperature infrared sub-band gap photoresponse in silicon is of interest for telecommunications, imaging and solid-state energy conversion. Attempts to induce infrared response in silicon largely centred on combining the modification of its electronic structure via controlled defect formation (for example, vacancies and dislocations) with waveguide coupling, or integration with foreign materials. Impurity-mediated sub-band gap photoresponse in silicon is an alternative to these methods but it has only been studied at low temperature. Here we demonstrate impurity-mediated room-temperature sub-band gap photoresponse in single-crystal silicon-based planar photodiodes. A rapid and repeatable laser-based hyperdoping method incorporates supersaturated gold dopant concentrations on the order of 10(20) cm(-3) into a single-crystal surface layer ~150 nm thin. We demonstrate room-temperature silicon spectral response extending to wavelengths as long as 2,200 nm, with response increasing monotonically with supersaturated gold dopant concentration. This hyperdoping approach offers a possible path to tunable, broadband infrared imaging using silicon at room temperature.

The effect of He+, O+, B+, and Cd+ implantation on the surface structure of magnesium oxide substrates for HTSC films

The surface structure and the morphology of polished MgO(100) substrates after ion implantation and laser annealing are studied. It is shown that ion implantation, combined with subsequent laser annealing, modifies the surface of the MgO(100) substrate, producing a single-crystal surface layer. According to electron diffraction analysis data, this layer is continuous only in case of Cd+ implantation.

Investigations of the magnetic structure of the surface and volume of aluminum-substituted Sr-M type hexaferrites

The magnetic structure of the surface layer of single crystals of hexagonal ferrites of the type Sr-M (SrFe12O19) in which some iron ions are replaced by diamagnetic Al ions is investigated, in direct comparison with the magnetic structure in the bulk of the sample, by the method of simultaneous gamma, x-ray, and electron Mossbauer spectroscopy. It is found that under conditions of diamagnetic dilution of the magnetic lattice of hexagonal ferrites of the type Sr-M by Al ions, a layer ~200 nm thick in which the orientation of the magnetic moments is not collinear with the direction of the moments in the bulk of the sample is observed on the surface of SrFe10.2Al1.8O19 crystals. Thus a “transitional” surface layer has been observed on macroscopic ferromagnetic crystals.

Characterization of the magnesium diffused lithium mobate surface layer by gixrd

Characteristics of MgO-rich layer in the magnesium diffused lithium niobate single crystal surface layer are investigated with the conventional X-ray diffraction and glancing-incidence X-ray diffraction. It is found that the MgO-rich layer is composed of an unknown compound and MgNb2O6. The MgNb2O6 is in the surface layer of MgO-rich layer, the unknown compound is in the subsurface layer beneath the MgNb2O6. The compounds have apparent preferred orientation

An XPS study of Mg overlayers on a Mo(100) surface

Ultra-thin Mg films supported on a Mo(100) surface have been studied using X-ray photoelectron spectroscopy. It is shown that the Mg(2p) and Mg(1s) binding energies decrease with an increase in Mg overlayer coverages. In addition, the Mg(2p) binding energy for a monolayer Mg film on a Mo(100) surface is higher than that of a single-crystal Mg(0001) surface. These differences in the core-level binding energies of the atoms in a monolayer, a multilayer and a single-crystal surface layer are explained in terms of the coordination number and the charge transfer at the Mg/Mo interfaces.

7376. Investigation of the dependence of the secondary processes in channeling on the location of impurity atoms in the near surface layers of single crystals: P A Aleksandrov and L I Ognev, Nucl Instrum Meth Phys Res, B51, 1990, 273–277

The sol–gel method was used to prepare two families of organic/inorganic hybrids incorporating europium triflate, classed as di-urethanesils and aminosils. A siliceous network to which short polyether chains are covalently bonded through urethane linkages, composes the di-urethanesil host. A siliceous network containing pendant amine terminated propyl chains, forms the aminosils. The xerogels were investigated by photoluminescence, particularly the local interaction between the Eu3+ ions and the host matrix. The Eu3+ local coordination was modelled in terms of a local-field perturbation representing the ion’s nearest ligands interaction potential. While for the aminosils the Eu3+ ions occupy one low-symmetry local site—crystal-field strength of ca. 760.5 cm−1 and 5D0 lifetime of 0.6–0.7 ms—two local Eu3+ environments with distinct point symmetry group, 5D0 lifetimes (ca. 0.2–0.3 and 1.4–1.8 ms, respectively) and covalent nature—crystal-field strengths of ca. 540 and 740–780 cm−1, respectively—were identified in the di-urethanesils.

Investigation of the dependence of the secondary processes in channeling on the location of impurity atoms in the near surface layers of single crystals

A method of investigating the effect of the distribution of atoms in the surface layers (down to depths $ ̌ 200 A ̊ ) of perfect single crystals on the orientation dependences of the Auger yield under irradiation by a fast electron beam ( E p ≲ 100 keV) modulated in depth in the course of channeling is developed. The determination of the concentrations of impurity atoms, with allowance for their positions in the crystal lattice, needs the solution of two coupled systems of linear equations. The impurity atoms are assumed in this case to form no clusters and to occur in the matrix sites or interstitials.

X-ray standing waves in the Laue case – location of impurity atoms

Impurity-atom fluorescence excited by X-ray standing waves in the Laue case of X-ray diffraction has been investigated experimentally and theoretically. Possibilities for location of impurity atoms in the bulk and the surface layer of single crystals are discussed. The experiments were carried out on silicon crystals of different thicknesses doped with germanium. The general approach for calculation of the fluorescence-yield angular curves has been developed. In the case of the uniform distribution of impurity atoms in the bulk of a crystal and also in the case of the kinematical X-ray diffraction on a thin surface layer, analytical expressions can be used.

Distribution of the effective Debye temperature in the surface layers of single crystals of the FeNi System

Distribution of the effective Debye temperature in the surface layers of single crystals of the FeNi System

Surface fatigue life of CBN and vitreous ground carburized and hardened AISI 9310 spur gears: Townsend, D.P. and Patel, P.R.

We investigated the effect of ultrasonic shot peening on the surface integrity and fatigue properties of single-crystal superalloys. The results show that ultrasonic shot peening significantly reduces the surface roughness of single-crystal specimens and improves surface finishing. The surface hardness increases by 49 %, reaching more than HV660. At the same time, the microstructural analysis illustrates that the single-crystal surface layer after ultrasonic shot peening forms a nanoscale refined sub-crystalline structure that rotates along the [110] axis. It significantly improves the mechanical properties of the surface metal. The originally existing round casting micro-pores are elongated along the [001] axis, forming a willow shape - elliptical shapes from the surface inward, reducing the stress concentration of the casting micro-pores perpendicular to the [001] axis. Combining the above three modification effects, the fatigue limit of the single-crystal notched Kt = 3 sample at 650 ℃ strengthened by ultrasonic shot peening is 94.2 % higher than that of the as-received notched sample, and 17.4 % higher than that of the smooth sample.

Evolution of a dislocation structure in the surface layers of single crystals during high-temperature annealing

The dislocation structure of KCl crystals annealed in a forevacuum has been shown to display a nonmonotonic variation of the density of dislocations in the direction from the surface. Our experiments and estimates showed that the observed redistribution of dislocations near the surface is due to the diffusion of impurities from the atmosphere and the generation of dislocations in the diffusion zone.

The method of integral characteristics in X-ray diffraction studies of the structure of the surface layers of single crystals

A further development is presented of the integral-characteristics method which is suggested in an earlier work for investigating the damage localized in surface layers of single crystals by X-ray diffraction technique. In the case of ion implantation with a small irradiation dose a generalization of the model for a disturbed layer is suggested which assumes the flux density of incident particles to be insufficient for damaging all the crystal surface. Recommendations for the practical application of the method are also given. The method is used to study a disturbed layer structure of silicon single crystals irradiated with ions of argon, phosphorus, and boron. Die Integral-Charakteristik-Methode, die in einer fruheren Arbeit zur Untersuchung des in der Oberflachenschicht eines Einkristalls lokalisierten Damage mittels Rontgenbeugungstechnik vorgeschlagen wurde, wird weiter entwickelt. Fur den Fall von Ionenimplantation mit geringer Bestrahlungsdosis wird eine Verallgemeinerung des Modells fur eine gestorte Schicht vorgeschlagen, die annimmt, das die Flusdichte der eindringenden Teilchen nicht fur eine Schadigung der gesamten Kristalloberflache ausreicht. Empfehlungen fur die praktische Anwendung der Methode werden ebenfalls gegeben. Die Methode wird zur Untersuchung der gestorten Schichtstruktur von Siliziumkristallen benutzt, die mit Argon- Phosphor- und Borionen bestrahlt wurden.

The effect of removal of the surface layers of single crystals of tungsten during static deformation on their mechanical properties

The effect of removal of the surface layers of single crystals of tungsten during static deformation on their mechanical properties