Development of Low-Oxide MCrAlY Coatings for Gas Turbine Applications

Advanced high-energy plasma systems are being used to achieve the benefits of the high-velocity oxy-fuel (HVOF) system without losing the inherent advantages of plasma for coating of gas turbine parts. MCrAlY coatings play a very important role in the performance and reliability of gas turbine components. One of the important considerations for next generation of gas turbines, which have more demanding conditions and need to withstand ever increasing operating temperatures, is that they should possess very low oxygen content levels in the coating. Low oxygen content coatings are applied by the expensive low-pressure plasma spray (LPPS)/vacuum plasma spray (VPS) technique for critical components in aero- and land-based gas turbines. This work deals with the development of low-cost LPPS equivalent coatings (having low oxygen content) using the high-energy high-velocity plasma spray (HEHVPS) gun and inert gas shroud. A comparison has also been made with CoNiCrAlY coatings by HVOF.     

Indigenous design and development of a micro-pulse lidar for atmospheric studies

A sophisticated micro-pulse lidar (MPL) has been designed and developed for the study of the atmospheric boundary layer (ABL) and clouds. The developed MPL uses a low energy pico-second pulsed Nd:YAG laser at 532 nm. The conventional receiver optic is used along with a photomultiplier tube in single photon detection mode. Stanford Research Systems' multi-channel scalar (MCS) is used with a personal computer for data acquisition. Due to the short laser pulse and a fast MCS, a spatial resolution of 0.75 m has been achieved. The control circuit has been designed to sense telescope cover status (open or closed) to avoid any mistakes in dark count and background data acquisition. The complete control software and Graphical User Interface (GUI) has been developed in Visual Basic. The lidar system has been tested both for its functionality to detect the variation in ABL and cloud height and also for its capability to acquire continuous night-time data without user interaction. In this article the design details and some preliminary results are discussed.     

A G protein gamma subunit-like domain shared between RGS11 and other RGS proteins specifies binding to Gbeta5 subunits

Regulators of G protein signaling (RGS) proteins act as GTPase-activating proteins (GAPs) toward the alpha subunits of heterotrimeric, signal-transducing G proteins. RGS11 contains a G protein gamma subunit-like (GGL) domain between its Dishevelled/Egl-10/Pleckstrin and RGS domains. GGL domains are also found in RGS6, RGS7, RGS9, and the Caenorhabditis elegans protein EGL-10. Coexpression of RGS11 with different Gbeta subunits reveals specific interaction between RGS11 and Gbeta5. The expression of mRNA for RGS11 and Gbeta5 in human tissues overlaps. The Gbeta5/RGS11 heterodimer acts as a GAP on Galphao, apparently selectively. RGS proteins that contain GGL domains appear to act as GAPs for Galpha proteins and form complexes with specific Gbeta subunits, adding to the combinatorial complexity of G protein-mediated signaling pathways.     

Viscoelastic properties of hollow glass particle filled vinyl ester matrix syntactic foams: effect of temperature and loading frequency

Viscoelastic properties of hollow particle-reinforced composites called syntactic foams are studied using a dynamic mechanical analyzer. Glass hollow particles of three different wall thicknesses are incorporated in the volume fraction range of 0.3–0.6 in vinyl ester resin matrix to fabricate twelve compositions of syntactic foams. Storage modulus, loss modulus, and glass transition temperature are measured and related to the microstructural parameters of syntactic foams. In the first step, a temperature sweep from ?75 to 195 °C is applied at a fixed loading frequency of 1 Hz to obtain temperature dependent properties of syntactic foams. In the next step, selected four compositions of syntactic foams are studied for combined effect of temperature and loading frequency. A frequency sweep is applied in the range 1–100 Hz and the temperature is varied in the range 30–140 °C. Time–temperature superposition (TTS) principle is used to generate master curves for storage modulus over a wide frequency range. The room temperature loss modulus and maximum damping parameter, Tanδ, are found to have a linear relationship with the syntactic foam density. Increasing volume fraction of particles helps in improving the retention of storage modulus at high temperature in syntactic foams. Cole–Cole plot and William–Landel–Ferry equation are used to interpret the trends obtained from TTS. The correlations developed between the viscoelastic properties and material parameters help in tailoring the properties of syntactic foams as per requirements of an application.     

Novel defects in Al–Pd–Fe complex metallic alloys: A micromechanical modelling approach

Transmission electron microscopy investigations have revealed that in the face centred complex metallic alloy of C₂–Al–Pd–Fe, the dislocations mediating plastic flow are decorated by localized regions of body centred structure in the compressive part of their strain field thus forming composite defects. We calculated the properties of these defects using a micromechanical model. The Eshelby method was employed to estimate the energies involved in the formation of such defects in the face-centred C₂ phase. We could reproduce the experimentally observed features of the defects in terms of their size and spatial configuration. The model describes a unique mechanism of a non-equilibrium defect, i.e., a dislocation, being stabilized by the formation and interaction with another non-equilibrium defect, i.e., a nanometre sized inclusion of different structure.     

Phonon dynamics of plutonium chalcogenides and pnictides

We have investigated the phonon dynamics of the plutonium compounds (PuX; X = S, Se, Te, As, and Sb) by using rigid ion (RIM) and breathing shell models (BSM), later includes breathing motion of the electrons of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of electron-phonon interactions. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report the one phonon density of states and first time calculated the lattice specific heat for these compounds.     

Steady-state creep of orthotropic rotating disks of variable thickness

Creep analysis of orthotropic rotating disks with variable thickness has been carried out for secondary stage of creep. Norton's power law of creep is employed to derive general expressions for stresses and strain rates in the disks. These expressions have been utilized to find stress and strain rate distributions for disks with the following types of thicknesses - (i) constant thickness, (ii) linearly varying thickness, and (iii) hyperbolically varying thickness. The numerical computations to study the effects of anisotropy and the profile of the disks on stresses and strains have been carried out employing the method of successive approximations. Five different cases of anisotropy have been considered. Selecting a certain type of material anisotropy and an optimum profile for the disk may result in a better design for the turbine disks.