Defence Metallurgical Research Laboratory

Nanostructured materials have gained importance in recent years due to their significantly enhanced properties. In particular, electrochemistry has a special role in producing a variety of nanostructured materials. In the current review, we discuss the superiority of electrochemical deposition techniques in synthesizing various nanomaterials that exhibit improved characteristics compared with materials produced by conventional techniques, as well as their classification, synthesis routes, properties and applications. The superior properties of a nanostructured nickel coating produced by electrochemical deposition are outlined. The properties of various nanostructured coating materials produced by electrochemical techniques are also described. Finally, the importance of nanostructured coatings in industrial applications as well as their potential in future technologies is emphasized.

A remarkably high saturation magnetization of ∼0.4μB∕Fe along with room temperature ferromagnetic hysteresis loop has been observed in nanoscale (4–40nm) multiferroic BiFeO3 which in bulk form exhibits weak magnetization (∼0.02μB∕Fe) and an antiferromagnetic order. The magnetic hysteresis loops exhibit exchange bias and vertical asymmetry which could be because of spin pinning at the boundaries between ferromagnetic and antiferromagnetic domains. Interestingly, both the calorimetric and dielectric permittivity data in nanoscale BiFeO3 exhibit characteristic features at the magnetic transition point. These features establish the formation of a true ferromagnetic-ferroelectric system with a coupling between the respective order parameters in nanoscale BiFeO3.

In this paper, we report the signature of spin gapless semiconductor (SGS) in CoFeMnSi that belongs to the Heusler family. SGS is a new class of magnetic semiconductors which have a band gap for one spin subband and zero band gap for the other, and thus are useful for tunable spin transport based applications. We show various experimental evidences for SGS behavior in CoFeMnSi by carefully carrying out the transport and spin-polarization measurements. SGS behavior is also confirmed by first-principles band-structure calculations. The most stable configuration obtained by the theoretical calculation is verified by experiment. The alloy is found to crystallize in the cubic Heusler structure (LiMgPdSn type) with some amount of disorder and has a saturation magnetization of $3.7\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{f}.\mathrm{u}.$ and Curie temperature of \ensuremath{\sim}620 K. The saturation magnetization is found to follow the Slater-Pauling behavior, one of the prerequisites for SGS. Nearly-temperature-independent carrier concentration and electrical conductivity are observed from 5 to 300 K. An anomalous Hall coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection data have yielded the current spin-polarization value of 0.64, which is found to be robust against the structural disorder. All these properties strongly suggest SGS nature of the alloy, which is quite promising for the spintronic applications such as spin injection as it can bridge the gap between the contrasting behaviors of half-metallic ferromagnets and semiconductors.

This paper compares the applicability of a few theoretical models for determining effective elastic moduli, using published experimental data on ceramic materials in a porosity range of 0–40% and on a cellular material with a porosity of about 90%. As the experimental data for the effective Poisson's ratio involve a large scatter, a set of numerical experiments using the finite element method was carried out to obtain the variation of the effective Poisson's ratio with porosity. These variations show that the effective Poisson's ratio approaches 0.25 with increasing porosity, irrespective of the material Poisson's ratio. The effect of pore shapes on the effective elastic moduli and the Poisson's ratio has also been analyzed using FEM.

The heat treatable aluminum–copper alloy AA2014 finds wide application in the aerospace and defence industry due to its high strength-to-weight ratio and good ductility. Friction stir welding (FSW) process, an emerging solid state joining process, is suitable for joining this alloy compared to fusion welding processes. This work presents the formulation of a mathematical model with process parameters and tool geometry to predict the responses of friction stir welds of AA 2014-T6 aluminum alloy, viz yield strength, tensile strength and ductility. The most influential process parameters considered are spindle speed, welding speed, tilt angle and tool pin profile. A four-factor, five-level central composite design was used and a response surface methodology (RSM) was employed to develop the regression models to predict the responses. The mechanical properties, such as yield strength (YS), ultimate tensile strength (UTS) and percentage elongation (%El), are considered as responses. Method of analysis of variance was used to determine the important process parameters that affect the responses. Validation trials were carried out to validate these results. These results indicate that the friction stir welds of AA 2014-T6 aluminum alloy welded with hexagonal tool pin profile have the highest tensile strength and elongation, whereas the joints fabricated with conical tool pin profile have the lowest tensile strength and elongation.

Despite a plethora of materials suggested for spintronic applications, a new class of materials has emerged, namely spin gapless semiconductors (SGS), which offers potentially more advantageous properties than existing ones. These magnetic semiconductors exhibit a finite band gap for one spin channel and a closed gap for the other. Here, supported by electronic-structure calculations, we report evidence of SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (prototype LiMgPdSn) structure but exhibiting chemical disorder (${\mathrm{DO}}_{3}$ structure). CoFeCrGa is found to transform from SGS to half-metallic phase under pressure, which is attributed to unique electronic-structure features. The saturation magnetization $({M}_{S})$ obtained at $8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ agrees with the Slater-Pauling rule and the Curie temperature $({T}_{C})$ is found to exceed $400\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Carrier concentration (up to $250\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and electrical conductivity are observed to be nearly temperature independent, prerequisites for SGS. The anomalous Hall coefficient is estimated to be $185\phantom{\rule{0.16em}{0ex}}\mathrm{S}/\mathrm{cm}$ at $5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Considering the SGS properties and high ${T}_{C}$, this material appears to be promising for spintronic applications.

High strength aluminium alloy AA7075 (Al–Zn–Mg–Cu) is a precipitate hardenable alloy widely used in the aerospace, defense, marine and automobile industries. Use of the heat treatable aluminium alloys in all these sectors is ever-increasing owing to their excellent strength-to-weight ratio and reasonably good corrosion resistance. The shortage in corrosion resistance, however, usually poses negative concern about their reliability and lifetime when they service in the variable marine environments. These alloys also exhibit low weldability due to poor solidification microstructure, porosity in fusion zone and lose their mechanical properties when they are welded by fusion welding techniques. Friction stir welding (FSW) is a reliable technique to retain the properties of the alloy as the joining takes place in the solid state. The welds are susceptible to corrosion due to the microstructural changes in the weld nugget during FSW. In this work, the effect of post weld treatments, viz., peak aging (T6) and retrogression & reaging (RRA), on the microstructure, mechanical properties and pitting corrosion has been studied. Friction stir welding of 8 mm-thick AA7075 alloy was carried out. The microstructural changes of base metal and nugget zone of friction stir welds were studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. Tensile and hardness test of base metal and welds has been carried out. Pitting corrosion resistance was determined through dynamic polarization test. It was observed that the hardness and strength of weld were observed to be comparatively high in peak aged (T6) condition but the welds showed poor corrosion resistance. The resistance to pitting corrosion was improved and the mechanical properties were maintained by RRA treatment. The resistance to pitting corrosion was improved in RRA condition with the minimum loss of weld strength.

The development of high-temperature titanium alloys has contributed significantly to the spectacular progress in thrust-to-weight ratio of the aero gas turbines. This paper presents an overview on the development of high-temperature titanium alloys used in aero engines and potential futuristic materials based on titanium aluminides and composites. The role of alloy chemistry, processing, and microstructure, in determining the mechanical properties of titanium alloys is discussed. While phase equilibria and microstructural stability consideration have restricted the use of conventional titanium alloys up to about 600 C, alloys based on TiPl (or,), E,AINb (0), TiAl (y), and titaniumltitanium aluminides-based composites offer a possibility of quantum jump in the temperature capability of titanium alloys.

The aluminium alloy AA2219 (Al–Cu–Mg alloy) is widely used in the fabrication of lightweight structures with high strength-to-weight ratio and good corrosion resistance . Welding is main fabrication method of AA2219 alloy for manufacturing various engineering components. Friction stir welding (FSW) is a recently developed solid state welding process to overcome the problems encountered in fusion welding . This process uses a non-consumable tool to generate frictional heat on the abutting surfaces. The welding parameters, such as tool pin profile, rotational speed , welding speed and axial force , play major role in determining the microstructure and corrosion resistance of welded joint. The main objective of this work is to develop a mathematical model to predict the corrosion resistance of friction stir welded AA2219 aluminium alloy by incorporating FSW process parameters. In this work a central composite design with four factors and five levels has been used to minimize the experimental conditions. Dynamic polarization testing was carried out to determine critical pitting potential in millivolt , which is a criteria for measuring corrosion resistance and the data was used in model. Further the response surface method (RSM) was used to develop the model. The developed mathematical model was optimized using the simulated annealing algorithm optimizing technique to maximize the corrosion resistance of the friction stir welded AA2219 aluminium alloy joints .

This study describes the relative effect on the permanent magnet characteristics viz. remanence (Br), intrinsic coercivity (Hci), Curie temperature (TC), and rectangularity of the intrinsic demagnetization curve, when Al, Cu, Ga, and Nb are added individually to NdFeB. Each elemental addition causes significant improvement in Hci but the level of improvement differs from one additive element to the other. The addition of Nb is favored over other elements for realizing maximum enhancement in Hci and rectangularity of the demagnetization curve. The microstructural features of the sintered samples of NdFeB with elemental addition show the formation of a new phase, in addition to the phases (φ,η, and Nd-rich) generally found in the ternary sample. The factors influencing the permanent magnet characteristics of sintered samples are the distribution of the Nd-rich phase in the intergranular region, the size and distribution of the minor phases at the grain junctions, the formation and distribution of new phases due to alloying addition, and the solubility of the dopant element in various phases coexisting in the sample.

The strength-to-weight ratio offered by AA6XXX alloys and their enhanced mechanical properties have become crucial criteria for their use in light weight military vehicles, rockets, missiles, aircrafts, and cars, used for both defence and civil purpose. The focus of this review paper is to put together the latest knowledge available from various sources on alloy design, industrial processing, development of properties, and potential use of AA6XXX alloys. The direct chill (DC) cast AA6XXX wrought alloys which are subsequently processed by fabrication process like hot working, cold working, process annealing, and age hardening heat treatments are the foci of this review though designation section also contains the designations of cast alloys to provide the reader a broad overview on designation. World-wide accepted designations are briefly tabled along with their alloying elements. The effects of the alloying elements which are generally used for AA6XXX wrought alloys are discussed incorporating their interactions during wrought AA6XXX alloy fabrication. The significance of the alloying and also the processing to develop the certain properties and the underlying strengthening mechanisms are discussed. The frequent and versatile uses of these AA6XXX alloys for the structural applications both in defence and civil purpose are put forth.

We report the structure, magnetic property, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to crystallize in the cubic Heusler structure (prototype LiMgPdSn) with considerable amount of DO3 disorder. Thermal analysis result indicated the Curie temperature is about 750 K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 ± 0.01 was deduced using point contact andreev reflection measurements. The temperature dependence of electrical resistivity has been fitted in the temperature range of 5–300 K in order to check for the half metallic behavior. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.

A tandem absorber of TiAlN∕TiAlON∕Si3N4 is prepared using a magnetron sputtering process. The graded composition of the individual component layers of the tandem absorber produces a film with a refractive index increasing from the surface to the substrate, which exhibits a high absorptance (0.95) and a low emittance (0.07). The tandem absorber is stable in air up to 600°C for 2h, indicating its importance for high temperature solar selective applications. The thermal stability of the tandem absorber is attributed to high oxidation resistance and microstructural stability of the component materials at higher temperatures.

INTRODUCTION TO FRACTOGRAPHY Dimple Rupture Cleavage Fatigue Intergranular PHYSICAL METALLURGY OF TITANIUM ALLOYS Introduction Application of Titanium Alloys Effect of Alloying Elements Types of Titanium Alloys Alpha (alpha) Alloys Near alpha Alloys alpha + ss Alloys Metastable ss Alloys Beta Alloys Titanium Aluminides The Microstructure of Titanium Alloys Conventional Titanium Alloys Titanium Aluminides CHEMICAL COMPOSITIONS ALPHA ALLOYS NEAR-ALPHA ALLOYS ALPHA + BETA ALLOYS BETA ALLOYS TITANIUM ALUMINIDES Ti3Al-Based Alloys TiAl-Based Alloys CASE STUDY: FAILURE INVESTIGATION REPORT OF IMI 550 HIGH-PRESSURE COMPRESSOR (HPC-I) AERO ENGINE BLADE Introduction Investigation Chemical Analysis Microstructure Fractography Stress-Concentration Effects of a Notch Analysis of the Deposits Conclusion References Index

A process for the fabrication of high-quality and near-net-shaped superconducting specimens of (Y-123) with uniformly distributed fine (Y-211) is discussed. The process involves the fabrication of 211 preforms by conventional ceramic routes such as uniaxial and isostatic pressing, injection moulding and slip casting, and pressureless infiltration basically from a reservoir containing liquid phases. A compact of 123 or 123 rich in liquid phases(s), acting as a source of liquid phases, is placed in contact with the 211 preform, and heated above the peritectic temperature of 123. The liquid from the source compact infiltrates the 211 filler and the peritectic reaction occurring between the preform material (211) and the matrix (liquid phases) during slow cooling from the peritectic temperature results in the growth of 123 with uniformly distributed fine 211 particles. We have also demonstrated that the present process can be extended to the fabrication of other rare earth (RE) superconductors where a solid solution of the kind occurs due to comparable size of the RE and Ba atoms, by choosing the RE = Gd system as an example. Herein the advantages and bounds of the process are reviewed; the effect of various cooling rates on the growth kinetics of 123 and the resulting macro- and microstructures are discussed. Fabrication of composites containing fine and very uniformly distributed Ag is also demonstrated by the process. Comparisons are made between the characteristics of the samples produced in the present process and the existing melt texturing process. The utility of the process is demonstrated by the fabrication of a three-dimensional component - a hollow cylinder.

The structure of orthorhombic (α″) martensitic phase of Ti–8Nb, Ti–12Nb, and Ti–16Nb alloys has been investigated using Rietveld refinement of x-ray diffraction data. The chemical analysis data have been used to determine the site occupancy of initial models. A limit of the Wyckoff positions has been proposed based on the symmetry of the Cmcm space group, which allows the movement of atoms without breaking the space group symmetry. This has also been incorporated in the initial models of experimental alloys, and accordingly Wyckoff positions have been refined. It has been observed that the atoms move along the Y-axis (parallel to the b-axis) and the movement of atoms increases with increase in Nb concentration. The formation of orthorhombic (α″) phase has been explained based on the movement of atoms along the Y-axis. This in turn breaks the hexagonal symmetry and forms an orthorhombic phase.

Industrial applications of aluminium and its alloys are restricted because of their poor tribological properties. Thermal spraying, laser surfacing, electron beam welding are the most widely used techniques to alter the surface morphology of base metal. Preliminary studies reveal that the coating and layering of aluminium alloys with ceramic particles enhance the ballistic resistance. Furthermore, among aluminium alloys, 7075 aluminium alloy exhibits high strength which can be compared to that of steels and has profound applications in the designing of lightweight fortification structures and integrated protection systems. Having limitations such as poor bond integrity, formation of detrimental phases and interfacial reaction between reinforcement and substrate using fusion route to deposit hard particles paves the way to adopt friction stir processing for fabricating surface composites using different sizes of boron carbide particles as reinforcement on armour grade 7075 aluminium alloy as matrix in the present investigation. Wear and ballistic tests were carried out to assess the performance of friction stir processed AA7075 alloy. Significant improvement in wear resistance of friction stir processed surface composites is attributed to the change in wear mechanism from abrasion to adhesion. It has also been observed that the surface metal matrix composites have shown better ballistic resistance compared to the substrate AA7075 alloy. Addition of solid lubricant MoS2 has reduced the depth of penetration of the projectile to half that of base metal AA7075 alloy. For the first time, the friction stir processing technique was successfully used to improve the wear and ballistic resistances of armour grade high strength AA7075 alloy.

Graphene–Fe ₃ O ₄ (G–Fe ₃ O ₄ ) composite was prepared from graphene oxide (GO) and FeCl ₃ ·6H ₂ O by a one-step solvothermal route.

Abstract This work presents the influence of machining parameters on surface roughness (SR) and material removal rate (MRR) of high strength armor steel using wire cut electrical discharge machining (WEDM). Tests have been carried out with six process parameters: pulse-on time, pulse-off time, wire feed, flushing pressure, spark voltage, and wire tension. Taguchi's technique has been employed for experimental investigation. Results show that pulse-on time, pulse-off time, and spark voltage are significant variables to MRR and surface roughness (SR). The confirmation experiments have also been conducted to validate the results obtained by the Taguchi technique. Keywords: ANOVAElectrical discharge machiningMaterial removal rateSurface roughnessTaguchi's technique

Project cost is most sensitive to its schedule. The construction project environment comprising dynamic, uncertain, but predictable, variables such as weather, space congestion, workmen absenteeism, etc., is changing continuously, affecting activity durations. The reliability of project duration forecast can be enhanced by an explicit analysis to determine the variation in activity durations caused by the dynamic variables. A computer model is used to simulate the expected occurrence of the uncertainty variables. From the information that is collected normally for a progress update of the tactical plan and by simulating the project environment, the combined impact of the uncertainty variables is predicted for each progress period. By incorporating the combined impact in the duration estimates of each activity, the new activity duration distribution is generated. From these activity duration distributions, the probability of achieving the original project completion time and of completing the project at any other time is computed.