Showing papers on "Quenching published in 1997"

Polymer-Supported Quenching Reagents for Parallel Purification

Abstract: The preparation of polystyrene−divinylbenzene-supported derivatives of tris(2-aminoethyl)amine and methyl isocyanate are described. These polymeric reagents are used to quench excess reactants and remove known impurities from the crude reaction products obtained from the solution-phase, parallel syntheses of ureas, thioureas, sulfonamides, amides, and pyrazoles. In conjunction with the use of other polymeric reactants during the course of a reaction, the addition of polymer-supported quench reagent(s) at the conclusion of the reaction allows isolation of the desired product by a single filtration and evaporation of solvent. The mechanical simplicity and efficiency of this methodology make possible the rapid, parallel purification of crude reaction products obtained via solution-phase syntheses, regardless of whether the intended product is a single compound or a mixture of compounds, and hence offers an attractive alternative to solid-phase organic synthesis in the practice of combinatorial chemistry.

Quenching Processes in Hydrogen-Bonded Pairs: Interactions of Excited Fluorenone with Alcohols and Phenols

Abstract: In order to clarify mechanisms of excited state interactions in hydrogen-bonded pairs, we have studied the kinetics of dynamic quenching of singlet and triplet fluorenone by a series of alcohols, phenols, and related compounds, in which hydrogen-bonding power, redox potential, and acidity are systematically varied. In addition, effects of solvent basicity or polarity and deuteration help identify the role of hydrogen-bonding in physical or chemical quenching processes. Alcohols and weak acids, with high oxidation potentials, do not quench the triplet, but quench the singlet at rates which parallel hydrogen-bonding power. This is attributed to a physical mechanism, involving vibronic coupling to the ground state via the hydrogen bond. This is much stronger in the excited state than in the ground state, and provides efficient energy dissipation in the radiationless transition. Phenols, with hydrogen-bonding power comparable to that of the alcohols but with much lower oxidation potentials, quench both single...

Quenching of spontaneous emission via quantum interference

Abstract: A four-level atom, driven by a coherent field, is considered. We show that under certain conditions complete quenching of spontaneous emission is possible. Hence the population inversion on some specific atomic transitions can be created using a very weak incoherent pumping. We investigate the physics of the effect using bare and dressed states. The proposed scheme may be useful, in principle, for generation of high-frequency and/or high power laser light.

Structure and Chemistry of Interfaces in Si3N4 Ceramics Studied by Transmission Electron Microscopy

Abstract: Interfaces in liquid-phase sintered Si3N4 materials were investigated employing both analytical and high-resolution transmission electron microscopy techniques (AEM, HREM). Owing to the sintering process that involves the addition of metal oxides to the Si3N4-starting powder, densified materials are composed of Si3N4-grains and amorphous as well as partly crystalline secondary phases. Most Si3N4 ceramics contain continuous, thin interlayers of residual glass along grain boundaries. HREM studies in conjunction with electron energy-loss spectroscopy (EELS) focused on the characterization of these grain-boundary films. A comparison between the diffuse dark field, the Fresnel fringe and the high-resolution lattice imaging technique revealed the latter technique to be most accurate in order to determine intergranular film width quantitatively. Depending on the interface composition, HREM imaging revealed conspicuous differences in film thickness. However, with a given batch composition each as sintered material is characterized by a constant film width within ±0.1nm. Crystallization of secondary phases can alter the interface chemistry and thus change intergranular film thickness. The latter result is in line with the variation of interfacial film widths before and after oxidation. Owing to cation outward diffusion, a thinning of the interlayer was observed. In contrast, with increasing impurity-cation concentration at the interface, first a thinning and furtheron a widening of the intergranular film was observed. Si3N4 materials with only SiO2 present at interfaces showed a film thickness of 1.0nm, independent of glass volume fraction. Apart from cations, the influence of anion segregation at Si3N4-grain boundaries was studied. Fluorine was found to markedly affect the mechanical response of the material. Owing to a lowered cohesive interface strength, as a consequence of F-segregation at grain boundaries, intergranular fracture was predominantly monitored. Moreover, in comparison to undoped specimens, anion-doped samples revealed markedly higher creep rates, which are related to a decrease in the apparent grain-boundary viscosity, as elaborated from internal friction measurements.In addition to the characterization of internal interfaces at room temperature, microstructures at high service temperatures were studied by rapid cooling Si3N4 materials from high temperatures. Quenching a MgO-doped Si3N4 from 1350°C produced no observable variation in the grain-boundary film thickness. A substantial increase and a non-uniform width of the amorphous films was, however, observed when rapidly cooling from temperatures of about 1420°C. Specimens quenched from higher temperatures or longer residence times above the eutectic temperature again revealed an equilibrium thickness that was slightly wider compared to the film widths observed in the material slowly cooled down to room temperature.By studying a MgO-doped Si3N4 that was exposed for about 14, 000h to 1100°C, the question was addressed as to whether internal grain-boundary films are actually stable and can sustain a long-term exposure to high testing temperatures. It is shown that, apart from other microstructural changes induced during high-temperature exposure, the grain-boundary structure was fundamentally altered and depleted grain boundaries were formed. Moreover, the characteristics of interfaces, observed in Si3N4/SiC microstructures obtained by the pyrolysis and subsequent crystallization of organometallic precursors, are briefly discussed. Here, similar to the long-term exposure experiment, complex interface structures without the presence of continuous grain-boundary films were observed. In brief, the content of this

Quenched-in vacancies in B2-structured intermetallic compound FeAl

Abstract: The concentrations of quenched-in vacancies retained in B2 intermetallic compound Fe1-cAlc were obtained as functions of composition (0.39 < c < 0.51) and quenching temperature (773–1273 K) from lattice constant and density measurements. Obtained vacancy concentration indicates rather gradual increase with composition in lower Al content region, while it increased rapidly as the composition approaches to stoichiometric composition. Further, the data for slow-cooled (1 K min−1) samples showed that retained vacancy concentration is higher than that for samples annealed at and quenched from 773 K. Observed lattice constant for each composition decreases linearly with vacancy concentration, which is interpreted in terms of atomic size effect. From changes in vacancy concentration with quenching temperature, apparent vacancy formation energies were estimated. The relation between vacancy concentration and microhardness was also examined. Present results of dependency of lattice constant on heat treatment condition confirm the hardening effect due to retained vacancy. Further, the proposed linear relation of hardness to the square root of vacancy concentration is supported by the present study.

Deformation, fracture, and mechanical properties of low-temperature-tempered martensite in SAE 43xx steels

Abstract: Uniaxial tensile tests were performed on 4330, 4340, and 4350 steels in the as-quenched (AQ) condition and after quenching and tempering at 150 °C, 175 °C, and 200 °C for times of 10 minutes, 1 hour, and 10 hours, respectively. Strength parameters decreased and ductility parameters increased continuously with increasing tempering. Mechanical properties are presented as a function of tempering conditions and steel carbon content, and hardness and ultimate strength changes are given as a function of Hollomon—Jaffe tempering parameters. All tempered specimens, except for some lightly tempered 4350 specimens, deformed plastically through necking instability and failed by ductile fracture. The stresses required for the ductile fracture, estimated from an analysis of the interfacial stresses at particles in the neck at fracture, showed no systematic variation with carbon content or tempering conditions despite significant variations in deformation and strain hardening. The AQ specimens of the 4340 and 4350 steels, and some of the lightly tempered 4350 steels, failed by brittle mechanisms. The deformation and fracture of the low-temperature-tempered 43xx steels are discussed in terms of the changes in fine structure, namely, the formation of transition carbides and a rearranged dislocation substructure that evolve from an AQ martensitic substructure consisting of dislocations with and without carbon atom segregation.

Modelled and measured residual stresses in plasma sprayed thermal barrier coatings

Abstract: Thermal barrier coatings consisting of a NiCrAlY bond coating and a 1.4 mm thick partially stabilised zirconia top coating were air plasma sprayed onto grit blasted nickel-base substrates. Two samples were produced using different amounts of external cooling during spraying of the top coatings. The residual stress profiles in the samples were measured after each manufacturing process step with a layer removal technique. A finite element model including a thermal analysis and a stress-strain analysis of the deposition was developed to model the origin of the thermal stresses and to verify the measured residual stresses. The main components for the residual stresses in the sprayed coatings were identified as stresses developing during the rapid cooling of individual droplets (quenching stresses) and stresses formed during cooling from deposition temperature to room temperature. The quenching stresses were predicted to be low and tensile in the top coating, due to stress relaxation by formation of vertical microcracks. During cooling to room temperature, compressive stresses were superimposed on the top coating quenching stresses. The final residual stresses were predicted to be compressive in the top coating. This was confirmed by measurements (−15 MPa). In the bond coating, no stress relaxation by microcracking was observed and the residual stresses were found to be tensile (~100 MPa). In the substrate, compressive residual stresses reaching −200 MPa were found in a zone to a depth of 0.3, mm into the substrate. The stresses were found to have originated during the grit blasting of the substrates prior to bond coating deposition. A correlation between modelled inelastic strain and measured densities of vertical microcracks in the top coating was obtained. High values were found close to the bond coating, which were correlated to a low substrate temperature during spraying of the top coating material.

Reactive thermal plasmas: ultrafine particle synthesis and coating deposition

Abstract: Thermal plasmas jets produced by d.c. arcs or RF discharges at pressures close to atmospheric pressure are characterized by the high temperatures (between 6000 and 14 000 K ) of heavy species and high velocities (between 100 and 2500 m s’1) of plasma flow. They can be used either for their physical properties, i.e. acceleration and melting of solid particles (in the diameter range 10‐100 mm) to spray thick coatings (from 0.1 mm to a few millimetres), or for their reactive properties. When reagents are introduced in the plasma stream, they are transformed in highly reactive radicals and/or atoms in excited states. These reactive species can form a coating with high deposition rates (~100 m mh ’1) due to the steep gradients in the boundary layer plasma‐substrate: this process is called thermal plasma-assisted chemical vapour deposition (PCVD). Without substrate and using adequate quenching, they can also form ultrafine particles, the size of which is controlled (with diYculty) by temperature during the quenching process. These PCVD processes can be used to form new chemical species on the surface of solid and molten particles in flight in the plasma jets, or on the resulting splats and between the successive passes to produce coatings with dispersed hard phases (reactive plasma spraying). It is also possible to agglomerate reactive particles (e.g. carbon and metal ) a few micrometres in diameter, to achieve exothermic reactions within the particles in flight and spray carbide coatings in air. This paper presents our knowledge in these fields as follows: (1) the main characteristics of plasma d.c. and RF torches, transferred arcs and the injection of reagents and/or quenching gases; (2) the modelling problems of reactive gas flow injection; boundary layer close to the substrate; ultrafine particle synthesis with the corresponding experimental results obtained for PCVD coatings; thin film deposition by flash evaporation and ultrafine particle synthesis; and (3) the reactive plasma spraying achieved either by spraying agglomerated particles (in the 10‐50 mm size range) where self-propagating high-temperature synthesis occurs, or by mixing a reactive gas with the plasma jet. © 1997 Elsevier Science S.A.

Preparation of amorphous NiCoB alloys and the effect of cobalt on their hydrogenation activity

Abstract: The bimetallic amorphous alloys Ni Co B were prepared by the chemical reduction of the solution containing both nickel and cobalt salts with aqueous potassium borohydride. Those samples were thoroughly characterized by ICP, BET, DSC, XRD, EXAFS, XPS, TEM and TPR. Superior to the rapid quenching techniques, the content of Co in Ni Co B alloys could be adjusted in a wide range by changing the initial concentration of cobalt salt in the solution. The catalytic activities of the asprepared materials were measured through the hydrogenation of benzene under moderate pressure in liquid phase. By comparing with the activities of the corresponding pure Ni B, Co B and their mixture as well as the Ni Co B amorphous alloys with different contents of Co, both the inhibiting and promoting effects of Co on the hydrogenation activities in Ni Co B amorphous alloys have been observed and discussed according to the amount of the effective metal in the alloys and their structural characters, especially their surface properties.

Electric field effect on luminescence efficiency in 8-hydroxyquinoline aluminum (Alq3) thin films

Abstract: Electric field-induced luminescence quenching in thin films made from common organic electroluminescent material of aluminum (III) 8-hydroxyquinoline (Alq3) is reported. The dependence of luminescence quenching on excitation wavelength and electric field is attributed to field-assisted hopping separation of charge in localized excited states. The effect extrapolated to high electric fields can reduce the luminescence yield by as much as 60% limiting electroluminescence quantum efficiency in high-field-driven light emitting diodes based on the Alq3 emitter.

Mechanical alloying of highly processable glassy alloys

Abstract: Glasses are generally produced from the undercooled liquid state by rapid quenching methods or quasi-statically at slow cooling by the effective control of heterogeneous nucleation sites. For metallic systems the latter method recently has led to the development of multicomponent metallic glasses with large glass forming ability and a wide supercooled liquid region before crystallization. Large-scale bulk samples of such alloys can be produced by conventional casting techniques. Alternatively, glass formation can be achieved by solid-state processing without passing through the liquid state. This crystal-to-glass transition is observed when a sufficiently high energy level is reached and kinetic conditions prevent the establishment of equilibrium. Hence, mechanical alloying as a special form of solid-state reaction technique and subsequent consolidation of the resulting powders above the glass transition temperature can be used to prepare bulk metallic glasses via the powder metallurgy route. The glass formation and the thermal stability of mechanically alloyed glassy alloys are compared with data for melt quenched samples showing that basically the same glassy state can be reached approaching it from the liquid or the solid state. Special emphasis is given to the glass forming ranges achievable by the different techniques and to the influence of impurities. Results for consolidated bulk samples are presented and compared with data for cast bulk specimens.

Experimental and Computational Study of the Quenching of Carbon Steel

Abstract: An investigation of the quenching of 1080 carbon steel cylinders has been carried out to determine the validity of a quenching process model for carbon steels. The process model included a description of the austenite-pearlite and austenite-martensite transformations in carbon steels, temperature-dependent material properties, and an elastic-plastic stress analysis. The model was simulated using the finite element method (FEM). An experimental study of the quenching of 1080 steel cylinders in water and two types of polymeric quenchants has also been carried out. The temperatures at three points within the cylinder during quenching were measured using thermocouples. The hardness and residual stress distributions along a cross-section of the quenched cylinders were determined using a Rockwell hardness test and an X-ray diffraction technique, respectively. The temperature-time histories, residual stress, and hardness distributions predicted from the FEM simulation of the quenching model were found to be in good agreement with the corresponding measurements. The quenching process simulation described in the study appears to be a promising tool for the design of heat-treatment process parameters for carbon steels.

A novel method for uniform dispersion of the rare earth ions in SiO2 glass using zeolite X

Abstract: A novel method for uniform dispersion of the rare earth ions in SiO2 glass is presented. Nd doped SiO2 laser glass has been made by aluminum co-doping to avoid quenching due to Nd clustering. Previous works with aluminum co-doping were passive methods because uniform dispersion of the rare earth ions in SiO2 glass depended only on aluminum co-doping effect. Concentration quenching of Nd laser glass is explained by cross-relaxation process and depends on Nd-Nd distance in the glass. The shorter the Nd-Nd distance the stronger is quenching, so the distance should be greater than some minimum. Homogeneous rare earth doped SiO2 glass is achieved by a modified sol-gel method using zeolite X. Zeolite X (Na86[(AlO2)86 · (SiO2)106] · 264H2O, faujasite-type structure) is a suitable material because Nd ions are selectively exchanged at the D6R segment structure in zeolite X, and the distance between Nd ions in the D6R 0.88 nm. This distance is three times larger than the critical range of cross-relaxation process which causes quenching. If the Nd-Nd distance is kept at 0.88 nm, the ratio of cross-relaxation probability to radiative decay probability will be 0.23%. Quantum yield is an adequate quantity for confirming uniform dispersion of the rare earth ions in Nd doped laser media. For a newly prepared Nd doped SiO2 glass using zeolite X, quantum yield increased to 50 ± 3.4% at 1.0 wt%, while an ordinary produced one was 7 ± 0.5%.

Bulk amorphous metallic alloys: Synthesis by fluxing techniques and properties

Abstract: Bulk amorphous alloys having dimensions of at least 1 cm diameter have been prepared in the Pd-Ni-P, Pd-Cu-P, Pd-Cu-Ni-P, and Pd-Ni-Fe-P systems using a fluxing and water quenching technique. The compositions for bulk glass formation have been determined in these systems. For these bulk metallic glasses, the difference between the crystallization temperature T{sub x}, and the glass transition temperature T{sub g}, {Delta}T = T{sub x} - T{sub g}, ranges from 60 to 1 10 K. These large values of {Delta}T open the possibility for the fabrication of amorphous near net-shape components using techniques such as injection molding. The thermal, elastic, and magnetic properties of these alloys have been studied, and we have found that bulk amorphous Pd{sub 40}Ni{sub 22.5}Fe{sub 17.5}P{sub 20} has spin glass behavior for temperatures below 30 K. 65 refs., 14 figs., 3 tabs.

Thermal Conductivity of Quasicrystals and Associated Processes

Abstract: Quasicrystals (QCs) exhibit unusual physical properties that are significantly different from those of crystalline materials and are not expected for alloys consisting of normal metallic elements. Opposite to conventional metallic alloys, their thermal conductivity and diffusivity are unusually low (with a positive temperature coefficient)—practically that of an insulator—which is atypical for materials containing about 70-at.% aluminum. Moreover the thermal conductivity decreases when the structural perfection is improved. One observes a low, if any, electronic contribution to the heat capacity and thus a vanishing density of electronic states at the Fermi level.The origin of this unexpected behavior was first attributed to the existence of a deep pseudogap at the Fermi level with a localization tendency of electrons near the Fermi level.However experimental evidence led to an alternative approach related to the structure of quasicrystals. In QCs, well-defined atomic clusters form self-similar subsets of the structure over which electronic and vibrational states are expected to extend. According to the inflation symmetry of the icosahedral structure, the so-called recurrent localization effects may then explain the conduction behavior and other striking features of quasicrystals (e.g., brittleductile transition at high temperature, corrosion resistance, low friction, high hardness).In the following, we first present the main thermal properties of quasicrystalline alloys compared to those of conventional materials with an emphasis on the variation of the thermal conductivity with temperature. The combination of such peculiar conduction, mechanical, and tribological properties gives the quasicrystalline alloys a technological interest for applications where superficial thermal and mechanical conditions are of prime importance. This is illustrated with two examples involving a QC coating on a base Al substrate: (1) thermal insulation for which a low conductivity is needed and (2) quenching heat-transfer modification due to a low-effusivity superficial effect. These processes are then explained in the third part of this article in terms of the cluster-modes delocalization mechanism responsible for the low conductivity of the quasicrystals.

Triplet quenching by onium salts in polar and nonpolar solvents

Abstract: The triplet quenching of several sensitizers (thioxanthone (TX), 2-chlorothioxanthone (CTX), xanthone (X), benzophenone (BP), pyrene (PY), benzil (BZ), and phenothiazine (PT)) was investigated with lipophilic substituted onium salts (iodonium I(1) and sulfonium salts S(1)) in benzene, n-heptane, and mixtures of these. Moreover, the triplet quenching of these sensitizers was also studied in acetonitrile with onium salts I(2) and S(2) with a similar pattern of substitution to the lipophilic salts. Using the determined half-wave reduction potential of the onium salts, one can show that an efficient triplet quenching by electron transfer is possible with the exception of BP and BZ. The quenching constants obtained fit the theoretical Rehm-Weller plot. The quality of the fit is better in acetonitrile than in n-heptane. Using TX and CTX cation radicals are detectable, which support a triplet quenching by electron transfer. Nevertheless, the triplets of BP and BZ were also efficiently quenched by the onium salts. The quenching reaction by sulfonium salt is hardly influenced from the polarity of the solvent used. However, the iodonium salt shows a strong dependence on the polarity: for instance in benzene the rate is one order of magnitude higher than in n-heptane. Moreover, the magnitude of triplet quenching in benzene is for the iodonium salt one order higher than for the sulfonium salt. Surprisingly, we found (with exception of PT and PY) in n-heptane no strong differences in quenching between iodonium and the sulfonium compounds.

Deposition-induced photoluminescence quenching of tris-(8-hydroxyquinoline) aluminum

Abstract: Ca, Ag, and Ge atoms quench the photoluminescence (PL) of an organic thin film, tris-(8-hydroxyquinoline) aluminum (Alq3), a model organic material for organic light emitting diodes. The observed PL quenching behavior was similar for all three elements, independent of their metallic nature. Due to strong interactions at the Ca/Alq3 interface, the quenching was much less effective at submonolayer coverages. We have also observed that proper oxidation of Ca at the Ca/Alq3 interface can significantly recover the quenched luminescence of Alq3.

The X-ray determination of the amounts of the phases in samples of isotactic poly(propylene) quenched from the melt at different cooling rates

Abstract: A new procedure for the determination of the amounts of phases in samples of isotactic poly(propylene) quenched at different cooling rates from the same melted polymer is described. According to the procedure, all the patterns corresponding to the same quenching series are simultaneously analyzed for the amounts of phases so that reliable phase fractions relative to the different samples of the series are achieved. The analysis of the results points out that for increasing cooling rates above 30°C/s a remarkable increase of the mesomorphic phase settles, mainly at the expense of the α-monoclinic one.

Method and apparatus for carburizing, quenching and tempering

Abstract: Method and apparatus for carburizing, quenching and tempering workpieces, by which the step of carburizing can be incorporated into a machining and manufacturing process to be performed by an on-line machining and manufacturing system as one stage thereof, and by which high-quality treatment or processing can be achieved without occurrences of variation in quality among heat-treated products. In this apparatus, a preheating chamber (2), six carburizing chambers (5a to 5f), a cooling chamber (6), a reheating chamber (7), a quenching chamber (8) are placed around an intermediate chamber (4) having a transport device (12). Further, a high-frequency induction heating technique is used for heating each of major ones of the treatment or processing chambers. Moreover, a plasma carburizing method is performed in the carburizing chambers. Furthermore, workpieces, which are successively carried into this apparatus through a machining and manufacturing line, are assigned and distributed to the chambers, respectively, and are then treated or processed therein. Thus, the process of carburizing, quenching and tempering can be performed without stagnation.

Initial stages of γ2 precipitation in an aged Cu-Al-Ni shape memory alloy

Abstract: Effect of ageing on martensitic transformation in a low-temperature Cu-Al-Ni shape memory alloy was investigated by calorimetry and transmission electron microscopy. Shifts of the transformation temperatures were followed and the microstructural observations with special attention to the early stages of precipitation of the γ 2 phase were done on samples annealed for 30 min between 175 and 325 °C. The most remarkable structural features in the as-quenched β 1 phase are prismatic dislocation loops with Burgers vectors in 〈100〉 directions, which were formed by coalescence of excess vacancies. Most probably, some off-stoichiometric Al atoms segregated to the plane of the loops during quenching, thus predetermining the places where the first coherent precipitates of the equilibrium γ 2 phase form upon ageing. Stresses and concentration changes in the close vicinity of the precipitates can facilitate the nucleation of martensite and, consequently, raise the M s temperature. However, an unambiguous explanation of the observed increase of the A s temperature has not been found. In the later stages of precipitation, rows of relatively large γ 2 particles arranged along 〈100〉 directions may act as effective obstacles to the motion of the phase interfaces and impede the martensite transformation.

Crystallization and glass formation in 50Li2O·50Nb2O5 and 25Li2O·25Nb2O5·50SiO2

Abstract: Quenching of 50Li 2 O·50Nb 2 O 5 melt was investigated with X-ray diffraction (XRD) and surface morphological analysis. Glass formation of 25Li 2 O·25Nb 2 O 5 ·50SiO 2 and devitrification of LiNbO 3 from the 25Li 2 O·25Nb 2 O 5 ·50SiO 2 glass system were studied using DTA, XRD and electrolysis techniques. High quench rate yields smaller crystal grain size, lower crystallinity and more LiNbO 3 crystal dendritic growth than the slow quenching. Three-fold symmetry was observed and a preferred crystallographic orientation of [0001] was confirmed for the quenched surfaces of LiNbO 3 . High Li + mobility was observed in 25Li 2 O·25Nb 2 O 5 ·50SiO 2 glass. By firing the 25Li 2 O·25Nb 2 O 5 ·50SiO 2 at 800°C, glass ceramics of LiNbO 3 –SiO 2 can be prepared.

Process of making fibers

Abstract: An apparatus and process for producing meltblown fibers employs a coflowing primary cold air flow and secondary hot air flow in a meltblowing nozzle. The primary cold air flow provides the majority of the force used to attenuate the polymer stream into fibers, while a secondary hot air flow shrouds the die tip and prevents premature quenching.

High surface pressure resistant steel parts and methods of producing same

Abstract: High surface pressure resistant steel parts and their producing methods are disclosed. These steel parts are useful as gears, cams, bearings and similar high-strength compact steel articles which are required to have wear resistance and strength to withstand fatigue in rolling or rolling-slipping applications. In a steel part formed according to the invention, a fine nitride and/or carbonitride having at least an average grain size of 0.3 μm or less is dispersed in the contact surface structure; a multi phase structure composed of martensite, which is divided into extremely fine pieces, forming a disordered shape, by the nitride and/or carbonitride, is formed; and a carbide having a grain size of 3 μm or less is dispersed to increase the hardness of the surface. Such a steel part is produced by carrying out carbonitriding or carburization/carbonitriding so as to precipitate extremely fine AIN, using nitrogen permeating from the surface and by carrying out quenching or quenching/tempering, starting from a temperature region where the parent phase is austenite

Influence of severe plastic deformation on aging effect of Al-Zn-Mg-Cu-Zr alloy

Abstract: The influence of severe plastic deformation (SPD) on aging effects in commercial strongly alloyed Al-Zn-Mg-Cu-Zr alloy was studied. The effect of natural and artificial aging was studied after application of three different processing schemes: (1) usual quenching; (2) SPD in the starting state; (3) SPD at once after quenching. It was shown that SPD process leads to formation of nanocrystalline structure ( d z = 70 nm) providing a high strength state. The attained value of microhardness equal to 2800 MPa is a record and exceeds a correspondent value obtained by traditional methods by a factor of 1.5–2.0.

Optical quenching of photoconductivity in GaN photoconductors

Abstract: The observation of optical quenching of photoconductivity in GaN photoconductors at room temperature is reported on. Three prominent quenching bands were found at Ev+1.44, 1.58, and 2.20 eV, respectively. These levels are related to three hole traps in GaN materials based on a hole trap model to interpret the quenching mechanism. The responsivity was reduced about 12% with an additional He–Ne laser shining on the photoconductor.