N. Eswara Prasad

Aluminium Alloys for Aerospace Applications

This chapter starts with a brief overview of the historical development of aerospace aluminium alloys. This is followed by a listing of a range of current alloys with a description of the alloy classification system and the wide range of tempers in which Al alloys are used. A description is given of the alloying and precipitation hardening behaviour, which is the principal strengthening mechanism for Al alloys. A survey of the mechanical properties, fatigue behaviour and corrosion resistance of Al alloys is followed by a listing of some of the typical aerospace applications of Al alloys. The Indian scenario with respect to production of primary aluminium and some aerospace alloys, and the Type Certification process of Al alloys for aerospace applications are described. Finally there is a critical review of some of the gaps in existing aerospace Al alloy technologies.

C/C and C/SiC Composites for Aerospace Applications

This chapter deals with different aspects of the carbon fibre-reinforced carbon composites (C/C) and carbon fibre-reinforced silicon carbide composites (C/SiC), especially for aerospace applications. The reinforcement and matrix materials and the process technologies developed for these composites are discussed. Typical mechanical and thermal properties at room and high temperatures are also presented, together with some actual and potential aerospace applications. Some products developed in India are also included.

Facile reduction of para-nitrophenols: catalytic efficiency of silver nanoferns in batch and continuous flow reactors

The catalytic efficiency of silver-nanoferns (Ag-NFs) decorated on carbon microfiber surfaces has been investigated. The Ag-NFs were grown on carbon microfibers employing electrodeposition technique using an electrolytic solution of aqueous silver nitrate and boric acid. The structure of grown Ag-NFs has nanoscaled sub-branches of sizes ≤50 nm that could be controlled by applied voltage and electrodeposition time. Using a specially designed home-made glass reactor, the catalytic efficiency of the Ag-NFs grown over carbon microfibers (cAg-NF) has been measured and tested for a model catalytic reaction of para-nitrophenol reduction mediated by sodium borohydride, both in batch and continuous flow modes of operation. The cAg-NFs have shown excellent catalytic activity with a normalized rate constant κ = 3.42 s−1 g−1. The reusability for the cAg-NFs has been observed up to seven cycles of operation without much degradation in the catalytic efficiency. The integrated c-Ag-NF catalyst system and the designed reactors are simple and can be easily incorporated for facile effluent treatment or in other applications where catalytic reduction may be required.

Low cycle fatigue resistance of Al–Li alloys

AbstractLow cycle fatigue (LCF) resistance data from binary Al–Li, ternary Al–Li–Cu, and quaternary Al–Li–Cu–Mg alloys have been compiled and discussed. The LCF resistance is measured in terms of the variation of the number of reversals to failure 2N fwith the plastic strain amplitude Δɛ p /2 as well as a modified average plastic strain energy per cycle (ΔW p )modified , obtained at different applied total strain amplitudes (Δɛ t /2). The data show the effects of microstructural features, namely dominant strengthening precipitates and the degree of recrystallisation as well as crystallographic texture. Lithium content, when in excess of 2·5 wt-%in aluminium decreases the low cycle fatigue resistance the most. The degree of aging, the degree of recrystallisation, and the degree of texture also influence the LCF resistance; among which the effect of the degree of aging is the most pronounced. The effects of lithium content in aluminium solid solution and strengthening precipitates obtainable by the change i...Abstract Low cycle fatigue (LCF) resistance data from binary Al–Li, ternary Al–Li–Cu, and quaternary Al–Li–Cu–Mg alloys have been compiled and discussed. The LCF resistance is measured in terms of the variation of the number of reversals to failure 2N fwith the plastic strain amplitude Δɛ p /2 as well as a modified average plastic strain energy per cycle (ΔW p )modified , obtained at different applied total strain amplitudes (Δɛ t /2). The data show the effects of microstructural features, namely dominant strengthening precipitates and the degree of recrystallisation as well as crystallographic texture. Lithium content, when in excess of 2·5 wt-%in aluminium decreases the low cycle fatigue resistance the most. The degree of aging, the degree of recrystallisation, and the degree of texture also influence the LCF resistance; among which the effect of the degree of aging is the most pronounced. The effects of lithium content in aluminium solid solution and strengthening precipitates obtainable by the change in the Li/Cu ratio are found to be marginal. Based on a modified total cyclic plastic strain energy till fracture, it is shown that most of the Al–Li alloys exhibit degradation in their LCF resistance in both hypotransition (higher fatigue lives) and hypertransition (lower fatigue lives) regions. Such degradation is attributed to the combined effects of mechanical fatigue, strain localisation through dislocation–precipitate interaction, environmental effects, and finally strain localisation through the high angle grain boundaries. In comparison with the currently used 2XXX and 7XXX series aluminium alloys, Al–Li alloys require substantial improvement before they can be considered for fatigue critical applications.

Ceramic Matrix Composites (CMCs) for Aerospace Applications

Ceramic materials have excellent properties, but are brittle and the strengths are highly variable. Particulate reinforcements give isotropic properties, but only marginal improvement in toughness. Continuous reinforcements improve the ceramic materials both in terms of fracture toughness as well as strength variability. The processing of ceramic matrix composites and improving the required properties with the available reinforcements is an emerging technology that is finding new critical applications.

Effect of Amino Multi Walled Carbon Nanotubes Reinforcement on the Flexural Properties of Neat Epoxy

The effect of amino multi-walled carbon nanotubes (MWCNTs) on the flexural properties of epoxy/ nanocomposites was studied. Sonication technique was employed for dispersion of amino MWCNTs in epoxy. The properties of both neat epoxy and nanocomposites extensively studied by using three point bend test and scanning electron microscopy. From the experimental results, it was found that reinforcement with carbon nanotubes improved the flexural properties, namely (a) flexural modulus, (b) flexural strength, (c) nonlinear deformation and (d) total flexural toughness.

Effect of aging on work hardening behaviour of cold rolled Nimonic C-263 alloy

Abstract Experimental true stress–true strain data of Nimonic C-263 alloy in solution treated as well as aged condition have been analysed using different flow relationships. Ludwigson relationship provides the best fit of the data for all the conditions investigated. The transition in macroscopic flow behaviour of the alloy with plastic strain, in solution treated condition, can be correlated with the transition in deformation mode from low strain regime to high strain regime. Although aging does not appear to alter the macroscopic flow behaviour, it causes a considerable change in flow parameters of the Ludwigson relationship and substructural evolution. On the other hand, the effect of sheet thickness is marginal. The flow data of the aged alloys fitted according to Ludwigson model not only yield a unique set of flow parameters for each aging condition but also exhibit a systematic trend with aging time. The transition in macroscopic flow behaviour of the alloy with strain, in aged conditions, can be correlated with a change in dislocation mechanism from dislocation–precipitate interaction at lower strains to dislocation–dislocation interaction at higher strains leading to formation of a dense dislocation tangled networks in the matrix regions surrounding the precipitates. The alloy in both solution treated and aged conditions exhibits three fairly distinct stages of strain hardening. The strain hardening rate decreases in regime I, remains constant in regime II and begins to fall again in regime III. Furthermore, it is observed that the alloy specimen with longitudinal orientation (L, i.e. parallel to rolling direction), exhibits marginally highest strain hardening rates, while specimens with long transverse orientation exhibit lowest strain hardening rates both in solution treated and aged conditions. However, for all other in-plane orientations (i.e. L+30°, L+45° and L+60°), the strain hardening rate data are fairly very close and lie in between those of longitudinal and long transverse orientations.

Processing, structure and flexural strength of CNT and carbon fibre reinforced, epoxy-matrix hybrid composite

Advanced materials such as continuous fibre-reinforced polymer matrix composites offer significant enhancements in variety of properties, as compared to their bulk, monolithic counterparts. These properties include primarily the tensile stress, flexural stress and fracture parameters. However, till date, there are hardly any scientific studies reported on carbon fibre (Cf) and carbon nanotube (CNT) reinforced hybrid epoxy matrix composites (unidirectional). The present work is an attempt to bring out the flexural strength properties along with a detailed investigation in the synthesis of reinforced hybrid composite. In this present study, the importance of alignment of fibre is comprehensively evaluated and reported. The results obtained are discussed in terms of material characteristics, microstructure and mode of failure under flexural (3-point bend) loading. The study reveals the material exhibiting exceptionally high strength values and declaring itself as a material with high strength to weight ratio when compared to other competing polymer matrix composites (PMCs); as a novel structural material for aeronautical and aerospace applications.

Low cycle fatigue and creep–fatigue interaction in short fibre reinforced aluminium alloy composite

Abstract The high temperature low cycle fatigue resistance and the creep–fatigue interaction (CFI) behaviour in terms of the effects of prior fatigue exposure on the subsequent creep behaviour are evaluated and reported for a short alumina fibre (Saffil) reinforced aluminium alloy (Al–12Si–CuMgNi) matrix composite at 623 K. The prior fatigue to study the CFI behaviour was imparted in the form of low cycle fatigue loading in a fully reversed, total strain controlled loading up to a quarter of fatigue life at a total strain amplitude of 0·006 (the plastic strain amplitude at half-life is 0·004), corresponding to a plastic strain energy per cycle value of 0·46 MJ m–3. Subsequently, isothermal tensile creep tests were conducted at 623 K to evaluate the minimum creep rate, rupture time and strain to failure as a function of applied creep stress. Also examined were the fracture features as well as the nature and extent of damage that occurs during low cycle fatigue and creep–fatigue loading. The results obtained on the composite material are compared with those of the matrix aluminium alloy to bring out the effects of reinforcement. The results showed that the reinforcement causes significant loss in high temperature low cycle fatigue resistance in terms of fatigue ductility and cyclic energy parameters. Prior fatigue loading was seen to cause a small but consistent decrease in the creep resistance, which is attributed to the combined effects of mechanical loading and microstructural damage from prior fatigue loading.

Nickel-Based Superalloys

Nickel-based superalloys are an exceptional class of structural materials for high temperature applications, particularly in the challenging environment of the turbine sections of aircraft engines. Continued improvements in the properties of these materials have been possible through close control of chemistry and microstructure as well as the introduction of advanced processing technologies. Surface modification by application of coating technology concurrent with the introduction of directional structures and then single crystals, has extended the useful temperature range of superalloys. Further improvements are likely with the development and implementation of tools for alloy design, microstructure-process evolution, and mechanical-property modelling. To date, six generations of single crystal (SC) nickel-based superalloys have been developed with improved creep properties and phase stability. Therefore it appears that the evolution of advanced nickel-based superalloys is a never ending process, and their replacement in turbine engine applications seems to be impossible at least for a few more decades. The present chapter is a brief review of various aspects pertaining to chemical composition, heat treatment, microstructure, properties and applications of both cast, and wrought alloys as well as the evolution of advanced cast nickel-based superalloys.