1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Superalloys: Fundamentals and Applications

The chemical, physical, and mechanical characteristics of nickel-based superalloys are reviewed with emphasis on the use of this class of materials within turbine engines. The role of major and minor alloying additions in multicomponent commercial cast and wrought superalloys is discussed. Microstructural stability and phases observed during processing and in subsequent elevated-temperature service are summarized. Processing paths and recent advances in processing are addressed. Mechanical properties and deformation mechanisms are reviewed, including tensile properties, creep, fatigue, and cyclic crack growth. I. Introduction N ICKEL-BASED superalloys are an unusual class of metallic materials with an exceptional combination of hightemperature strength, toughness, and resistance to degradation in corrosive or oxidizing environments. These materials are widely used in aircraft and power-generation turbines, rocket engines, and other challenging environments, including nuclear power and chemical processing plants. Intensive alloy and process development activities during the past few decades have resulted in alloys that can tolerate average temperatures of 1050 ◦ C with occasional excursions (or local hot spots near airfoil tips) to temperatures as high as 1200 ◦ C, 1 which is approximately 90% of the melting point of the material. The underlying aspects of microstructure and composition that result in these exceptional properties are briefly reviewed here. Major classes of superalloys that are utilized in gas-turbine engines and the corresponding processes for their production are outlined along with characteristic mechanical and physical properties.

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Nickel-Based Superalloys for Advanced Turbine Engines: Chemistry, Microstructure and Properties

To evaluate the antibacterial activity of 21 plant essential oils against six bacterial species. The selected essential oils were screened against four gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris) and two gram-positive bacteria Bacillus subtilis and Staphylococcus aureus at four different concentrations (1:1, 1:5, 1:10 and 1:20) using disc diffusion method. The MIC of the active essential oils were tested using two fold agar dilution method at concentrations ranging from 0.2 to 25.6 mg/ml. Out of 21 essential oils tested, 19 oils showed antibacterial activity against one or more strains. Cinnamon, clove, geranium, lemon, lime, orange and rosemary oils exhibited significant inhibitory effect. Cinnamon oil showed promising inhibitory activity even at low concentration, whereas aniseed, eucalyptus and camphor oils were least active against the tested bacteria. In general, B. subtilis was the most susceptible. On the other hand, K. pneumoniae exhibited low degree of sensitivity. Majority of the oils showed antibacterial activity against the tested strains. However Cinnamon, clove and lime oils were found to be inhibiting both gram-positive and gram-negative bacteria. Cinnamon oil can be a good source of antibacterial agents.

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In vitro antibacterial activity of some plant essential oils.

Chitosan based edible films and coatings: A review

Structures in Other Domains The methodology of structural analysis discussed in this article has been applied beyond the narrow realm of natural language syntax that we have discussed in this article. Within the study of language, similar methods of analysis have been pervasively applied to the study of sounds (phonology), words (morphology), and meanings (semantics), yielding a range of of abstract structural representations whose properties bear considerable explanatory burden. There are a wealth of cases in each of these domains analogous to those discussed here, though space prevents us from going in these (see Akmajian, Demers, Farmer and Harnish 1995 for a traditional overview, and Jackendo 1994 for one more focused on connections with cognitive science). Additionally, these representations have shed substantial light on the processes of language acquisition and language change. It has been found that variation in the types of sentences that are used, whether during the course of children's acquisition of their native languages or in the centuries-long periods of linguistic change, are best characterized not as super cial and haphazard alterations, but rather in terms of parametric modi cations to the fundamental underlying grammatical rules and constraints. Moving outside the domain of language, one application of these same methods has been in the study of music cognition. Just as the representations of linguistic theory arise out of an attempt to model speakers' intuitions about well-formedness and possible meanings of the sentences of their

Structural analysis

Antimicrobial activity of cinnamon and clove oils under modified atmosphere conditions

Creep of CMSX-4 superalloy single crystals: effects of rafting at high temperature

On the kinetics of rafting in CMSX-4 superalloy single crystals

Creep of CMSX-4 superalloy single crystals: effects of misorientation and temperature

The structure of the a〈112〉 dislocation ribbons in CMSX-4 single crystal superalloy crept at 750°C and 750 MPa has been characterised using transmission electron microscopy. Calculations are performed which confirm that the macroscopic creep deformation occurring under these conditions, i.e. the accumulation of primary creep, is principally a result of the movement of the ribbons through the γ/γ′ structure. Emphasis is placed on clarifying the factors which control the movement of the fault: it appears that the rate controlling step is the entry of the final a/3〈112〉 dislocation into the γ′ phase, which has the effect of removing the superlattice extrinsic fault. Further observations suggest that the a/2〈110〉 dislocations play a vital role not only in nucleating the ribbons, but also in terminating their long-range movement through the microstructure. It is proposed that this latter effect results in the breakdown of primary creep and thus the transition to secondary ‘steady-state’ creep.

Nirundorn Matan

Papers

Antimicrobial activity of cinnamon and clove oils under modified atmosphere conditions

Creep of CMSX-4 superalloy single crystals: effects of rafting at high temperature

On the kinetics of rafting in CMSX-4 superalloy single crystals

Creep of CMSX-4 superalloy single crystals: effects of misorientation and temperature

The role of stacking fault shear in the primary creep of [001]-oriented single crystal superalloys at 750°C and 750 MPa