The fracture morphology of nickel-base superalloys tested in fatigue and creep-fatigue at 650 C

The fracture surfaces of compact tension specimens from seven nickel-base superalloys fatigue tested at 650 C were studied by scanning electron microscopy and optical metallography to determine the nature and morphology of the crack surface in the region of stable growth. Crack propagation testing was performed as part of an earlier study at 650 C in air using a 0.33 Hz fatigue cycle and a creep-fatigue cycle incorporating a 900 second dwell at maximum load. In fatigue, alloys with a grain size greater than 20 micrometers, HIP Astroloy, Waspaloy, and MERL 76, exhibited transgranular fracture. MERL 76 also displayed numerous fracture sites which were associated with boundaries of prior powder particles. The two high strength, fine grain alloys, IN 100 and NASA IIB-7, exhibited intergranular fracture. Rene 95 and HIP plus forged Astroloy displayed a mixed failure mode that was transgranular in the coarse grains and intergranular in the fine grains. Under creep-fatigue conditions, fracture was found to be predominantly intergranular in all seven alloys

Creep-fatigue behavior of NiCoCrAlY coated PWA 1480 superalloy single crystals

Single crystal specimens of a Ni base superalloy, PWA 1480, with a low pressure plasma sprayed NiCoCrAlY coating were tested in various 0.1 Hz fatigue and creep fatigue cycles both at 1015 and 1050 C. Creep fatigue tests of the cp, pc, and cc types were conducted with various constant total strain ranges employing creep dwells at various constant stresses. Considerable cyclic softening occurred as was evidenced particularly by rapidly increasing creep rates in the creep fatigue tests. The cycle time in the creep fatigue tests typically decreased by more than 80 percent at 0.5 N sub f. Though cyclic life did correlate with delta epsilon sub in a better correlation existed with sub f for both the fatigue and creep fatigue tests, and poor correlations were observed with either sigma sub max or the average cycle time. A model containing both delta sigma and delta sigma (sub in), N sub f = alpha delta sigma (sub in) beta delta sigma gamma, with best fit values of sigma for each cycle type, but the same values of beta and gamam, was found to provide good correlations. Life lines were not greatly different among the cycle types, differing only by a factor of about three. The cp cycle life line was lowest for both test temperatures, however among the other three cycle types there was no consistent ranking. For all test types failure occurred predominately by multiple internal cracking originating at pores. The strong correlation of life with delta sigma may reflect a significant crack growth period in the life of the specimens

Fatigue crack propagation of nickel-base superalloys at 650 deg C

The 650 C fatigue crack propagation behavior of two nickel-base superalloys, Rene 95 and Waspaloy, is studied with particular emphasis placed on understanding the roles of creep, environment, and two key grain boundary alloying additions, boron and zirconium. Comparison of air and vacuum data shows the air environment to be detrimental over a wide range of frequencies for both alloys. More in-depth analysis on Rene 95 shows at lower frequencies, such as 0.02 Hz, failure in air occurs by intergranular, environmentally-assisted creep crack growth, while at higher frequencies, up to 5.0 Hz, environmental interactions are still evident but creep effects are minimized. The effect of B and Zr in Waspaloy is found to be important where environmental and/or creep interactions are presented. In those instances, removal of B and Zr dramatically increases crack growth and it is therefore plausible that effective dilution of these elements may explain a previously observed trend in which crack growth rates increase with decreasing grain size

Isothermal and bithermal thermomechanical fatigue behavior of a NiCoCrAlY-coated single crystal superalloy

Specimens of single crystal PWA 1480 with group of zone axes (100) orientation, bare, or with NiCoCrAlY coating PWA 276, were tested in low cycle fatigue (LCF) at 650, 870, and 1050 C, and in simplified bithermal thermomechanical fatigue (TMF) tests between these temperatures. These tests were examined as a bridge between isothermal LCF and general TMF. In the bithermal test, an inelastic strain is applied at one temperature, T sub max, and reversed at T sub min. The out-of-phase (OP) test type imposing tension at T sub min and compression at T sub max received most study, since it was more damaging than the in-phase type. Specifically investigated were the effects of: inelastic strain range, the coating, delta T, T sub max, T sub min, and the environment

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. 3: Tension-compression anisotropy

Single crystal superalloy specimens with various crystallographic directions along their axes were tested in compression at room temperature, 650, 760, 870, and 980 deg C. These results are compared with the tensile behavior studied previously. The alloy, Rene N4, was developed for gas turbine engine blades and has the nominal composition 3.7 Al, 4.2 Ti, 4 Ta, 0.5 Nb, 6 W, 1.5 Mo 9 Cr. 7.5 Co, balance Ni, in weight percent. Slip trace analysis showed that primary cube slip occurred even at room temperature for the 111 specimens. With increasing test temperature more orientations exhibited primary cube slip, until at 870 deg C only the 100 and 011 specimens exhibited normal octahedral slip. The yield strength for octahedral slip was numerically analysed using a model proposed by Lall, Chin, and Pope to explain deviations from Schmid's Law in the yielding behavior of a single phase Gamma prime alloy, Ni3(Al, Nb). The Schmid's Law deviations in Rene N4 were found to be largely due to a tension-compression anisotropy. A second effect, which increases trength for orientations away from 001, was found to be small in Rene N4. Analysis of recently published data on the single crystal superalloy PWA 1480 yielded the same result

NiAl-based approach for rocket combustion chambers

A multi-layered component, such as a rocket engine combustion chamber, includes NiAl or NiAl-based alloy as a structural layer on the hot side of the component. A second structural layer is formed of material selected from Ni-based superalloys, Co-based alloys, Fe-based alloys, Cu, and Cu-based alloys. The second material is more ductile than the NiAl and imparts increased toughness to the component. The second material is selected to enhance one or more predetermined physical properties of the component. Additional structural layers may be included with the additional material(s) being selected for their impact on physical properties of the component

Cell Imaging with Fluorescent Bi-Metallic Nanoparticles

Last decades various imaging techniques have been applied in biological and biomedical research, such as magnetic resonance imaging, different types of tomography, fluorescence/bioluminescence, ultrasound, as well as multimodality approaches. Fluorescence imaging, especially in combination with nanoscale materials, is a very prospective tool for experiments in vivo and clinical applications due to its high temporal and spatial resolutions. Fluorescent nanoparticles (NPs), having ability to interact with biomolecules both on the surface of and inside the cells, may revolutionize the cell imaging approaches for diagnostics and therapy. In our investigation we report about new method of cell imaging with fluorescent bi-metallic NPs synthesized by chemical reduction of the relevant ions. As the model of living organism, the cells of yeast Hansenula polymorpha were used. All NPs in minimal concentration (up to 0.05 mM) was proved to be non-toxic for yeast cells. The NPs and NPs-modified cells were characterized with the methods of UV-VIS spectroscopy, scanning electron microscopy, atom force microscopy, transmission electron microscopy and fluorescence microscopy. The bimetallic NPs, possessing the stable fluorescence in solution and inside the cells, allow to observe the phenomenon of NPs transferring from parental to daughter cells through at least three generations followed by releasing from the modified cells. The fluorescent NPs synthesized being small, non-toxic and fluorescent was shown to be perspective tool for cell imaging

Isolation and characterization of mutated alcohol oxidases from the yeast Hansenula polymorpha with decreased affinity toward substrates and their use as selective elements of an amperometric biosensor

<p>Abstract</p> <p>Background</p> <p>Accurate, rapid, and economic on-line analysis of ethanol is very desirable. However, available biosensors achieve saturation at very low ethanol concentrations and thus demand the time and labour consuming procedure of sample dilution.</p> <p>Results</p> <p><it>Hansenula polymorpha </it>(<it>Pichia angusta</it>) mutant strains resistant to allyl alcohol in methanol medium were selected. Such strains possessed decreased affinity of alcohol oxidase (AOX) towards methanol: the K_Mvalues for AOX of wild type and mutant strains CA2 and CA4 are shown to be 0.62, 2.48 and 1.10 mM, respectively, whereas V_maxvalues are increased or remain unaffected. The mutant AOX alleles from <it>H. polymorpha </it>mutants CA2 and CA4 were isolated and sequenced. Several point mutations in the AOX gene, mostly different between the two mutant alleles, have been identified. Mutant AOX forms were isolated and purified, and some of their biochemical properties were studied. An amperometric biosensor based on the mutated form of AOX from the strain CA2 was constructed and revealed an extended linear response to the target analytes, ethanol and formaldehyde, as compared to the sensor based on the native AOX.</p> <p>Conclusion</p> <p>The described selection methodology opens up the possibility of isolating modified forms of AOX with further decreased affinity toward substrates without reduction of the maximal velocity of reaction. It can help in creation of improved ethanol biosensors with a prolonged linear response towards ethanol in real samples of wines, beers or fermentation liquids.</p

Новий спектрофотометричний мeтод за використання лакказних нанозимів для аналізу адреналіну в фармацевтичних препаратах

Nanozymes, which have high enzyme-like activity of natural enzymes, are very promising for analytical purposes, in particular, for the development of methods for sensitive, quantitative detection of practically important analytes – biomarkers of common diseases or pharmaceutical products. Recently, it has been reported that artificial enzymes with laccase-like activity or “nanolaccases (nLacs),” can serve as catalytic elements for the creation of sensitive methods for catecholamines. Our work aimed to obtain laccase-like nanozymes and characterize and demonstrate their suitability for spectrophotometric adrenaline (AD) analysis. In this article, we report on preparing five hexacyanoferrate nanoparticles (HCF NPs) that possess laccase-like activity, particularly, Co-HCF, Ni-HCF, Mn-HCF, Zn-HCF, and Cu-HCF. Among the investigated nLacs, Cu-HCF was selected and characterized. It was shown that Cu-HCF reveals the highest activities, is stable in various pH conditions in the range 3.0–6.5, and has satisfactory stored stability. A new spectrophotometric method for the quantitative detection of AD was created using the selected nLacs. The linearity of the proposed method is in the range from 5 μM to 50&nbsp;μM (0.66–11 μg/ml), and the limit of detection is 1.5 μM (0.33 μg/ml), which is lower than that catalyzed by native laccase (1.15 μg/ml). The proposed method was tested on the real samples of pharmaceuticals, and the obtained data agree with the data declared by the producer. The resulting nLacs have great potential for use in catalysis of mimetics, environmental restoration, and sensor design. Thus methods, the obtained Cu-HCF has great potential application in spectrophotometric and biosensor method for analysis of biologically active toxic compounds in surface waters.Нанозими (НЗ), що володіють високою ферментоподібною активністю природних ензимів, є сьогодні дуже перспективними для аналітичних цілей, зокрема для розроблення методів високочутливої кількісної детекції практично важливих аналітів – біомаркерів поширених захворювань або фармацевтичних продуктів. Недавні дослідження повідомляють, що штучні ферменти з псевдолаказною активністю або “нанолакази” можуть служити каталітичним елементом для створення чутливих методів аналізу катехоламінів. Метою нашої роботи було отримати лаказоподібні-нанозими, охарактеризувати та продемонструвати їх придатність для спектрофотометричного методу аналізу адреналіну (АД). В цій статті ми повідомляємо про отримання п’яти типів гексаціанофератних наночастинок (HCF НЧ), які володіли лакказною активністю: Сo-HCF, Ni-HCF, Mn-HCF, Zn-HCF та Cu-HCF. Серед досліджуваних “нанолаказ, нЛак” було відібрано Cu-HCF НЗ, які мали найвищу активність, були стійкі в різних умовах, таких як рН 3,0–6,5, висока солоність та зберіганні активності протягом шести місяців. За використання відібраних нЛак, було створено новий спектрофотометричний метод кількісного визначення АД. Його лінійність зберігається в межах 5–50 мкмоль (0,66–11 мкг/мл), а порогова чутливість – 1,5 мкмоль (0,33 мкг/мл), що є нижче, ніж каталізується істиною лакказою (1,15 мкг/мл). Цей метод з Cu-HCF НЗ апробували на реальних фармацевтичних зразках, що містять АД, і одержані дані добре корелюють із результатами, заявленими виробником. Таким чином, отримані НЗ Cu-HCF мають великий потенціал до застосування спектрофотометричних та біосенсорних методах аналізу для виявлення біологічно активних токсичних сполук у поверхневих водах

Lactic acid as a systemic product and biomarker of physical load

This paper presents an up-to-date review of research data on the specific features of lactic acid metabolism and its role as an effector of vital regulatory mechanisms. Lactic acid is an alpha-hydroxy monocarboxylic acid. Physical loads of submaximal intensity and some diseases can cause dramatic increase of lactic acid content in the body fluids. The excessive lactate is removed from the working muscle and either metabolized by other tissues or excreted from the human body. Alteration of the lactate-pyruvate balance is one of the main markers of the development of cardiac hypertrophy and failure. The redistribution of lactate between the cells producing it and the cells that metabolize it is vital to maintain a stable pH level in tissues and hold lactate in the body since this compound is an important energy source as well as an effector of important regulatory mechanisms. The quantification of lactate is used to assess general physical capabilities of the human body, the intensity of physical load and the rate of recovery in physical rehabilitation. Specialized proteins, which refer to the group of monocarboxylate transporters, are involved in lactate excretion and absorption by cells. The presence of various types of transporters in cell membranes that differ in affinity to lactate and the direction of transport ensures a rapid redistribution of lactic acid throughout the body and regulates the intensity and direction of its metabolism according to the physiological needs. Efficient transfer and redistribution of lactate between different tissues of the body is essential, given the participation of lactate in several important regulatory mechanisms. As an effector, lactate is involved in the regulation of angiogenesis, differentiation of myosatellitocytes, regeneration of muscle fibers, polarization of macrophages and the course of inflammatory processes. Besides, lactate participates in epigenetic mechanisms of muscle tissue metabolism regulation. Therefore, lactate is one of the key metabolites in the human body