Potentials of intermetallics for high temperatures were realized in the early 1900s. But initial attempts from time to time failed due to inadequate ductility as well as poor high-temperature creep strength exhibited by the intermetallic phases. From these early attempts three main ideas germinated. First, addition of ternary elements can improve properties of intermetallic phases dramatically. Second, introduction of new phases not only can change properties but also allow tailoring of the microstructure according to the demand of the application requirements. Third, combining brittle phase along with a ductile matrix it is possible to develop a composite material that encompasses the inherent limitations of the intermetallic phases. Based on these points, a new series of alloys and phases were developed. These recent developments and innovations are summarized in this chapter. The first part of the chapter is devoted to various intermetallic phases, which are under active consideration, and the second part of the chapter is focused on the development of refractory metal-based alloy and high-entropy alloy systems.

Borides, carbides, and nitrides are usually synthesized under extreme conditions. Temperature, pressure, atmospheric/surrounding environment, and heat-treatment processing are important parameters to get pure phase. Synthesis temperature range covers from a low (say 200°C) to a high temperature (2000°C). Pressure under hot/cold pressing is an important parameter in making different phases and stoichiometry. For preparation of nitrides, atmospheric/surrounding environment such as N2, NH3, and N2/H2 are required; and for preparation of carbides, methane, ethane, propane, and urea, C/CO/CO2/H2 are required; and boric acid or boron trioxide for preparation of borides has to be maintained. Heat-treatment effect such as quenching from high to low temperature and fast/slow heating is also important in production of unusual phases and tailoring of properties. Suitable precursors used during synthesis help in getting stoichiometric compounds. Their crystal structure and bonding can be characterized by many techniques including X-ray diffraction (XRD), neutron scattering/diffraction, extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Raman/infrared spectroscopy, electron energy loss spectroscopy (EELS), and X-ray fluorescence (XRF). Stoichiometry can be determined by chemical analysis and inductively coupled plasma mass spectrometry (ICP-MS). In transition metal nitrides and carbides, N/C atoms usually occupy interstitial sites of host metal lattice, whereas B atoms do not occupy interstitial sites in transition metal borides. Microstructure can be investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), atomic/magnetic force microscopy (AFM/MFM), etc. Samples with different particle sizes from micron to nanometer can be produced by varying heat-treatment procedures. Usually, borides, carbides, and nitrides have very good thermal conductivity but poor electrical conductivity. Some of them show superconductivity with Tc from 1 to 39K (e.g., MgB2). Their hardness varies from soft to hard and can be comparable with diamond. The unusual high magnetic moment in Fe16N2 is observed as compared to pure iron. These materials have good thermal and chemical stability because of high melting points and covalent bonding character. They are used in many applications such as interconnector, electrical insulator, hard material, cutting tools (e.g., WC), bearing in motors, gas turbines, car engine parts, cantilevers in AFM, protective coating agents, diamagnetic sample holder (e.g., BN, SiNx) in vibrating sample magnetometer and nuclear magnetic resonance (NMR), magnetic material, superconducting material, etc. They have aesthetic applications such as appearance of gold color after coating of material with TiN. Also, they are used as catalysts or support for catalyst in catalysis. They have extraordinary stability in H2 atmosphere. In view of the high neutron absorption cross-section, the boron carbides are used in nuclear reactors as control rods, shielding, and shutdown pellets.

The mechanical behavior of materials is directly related to their microstructure. Materials that undergo severe plastic deformation (SPD), i.e., von Mises strain in excess of 2, result in an ultrafine-grained (UFG) microstructure with length scales less than a micrometer and in some cases within the 100nm limit to make it nanocrystalline. This chapter discusses severe plastic deformation of metallic materials—the various methods of achieving severe plastic deformation, the phenomena of microstructural refinement, the subsequent mechanical properties, and finally some current applications and industrial products. Severe plastic deformation is achieved by repetitive cyclic plastic deformation processes such that the overall dimensions of the workpiece remain unchanged after each deformation cycle. Some common techniques such as equal channel angular pressing, high-pressure torsion, and multiaxial forging are discussed here. The general process of grain refinement through severe plastic deformation is discussed with thoughts on the role that dynamic recrystallization process plays in grain refinement, which includes continuous, discontinuous, and geometric dynamic recrystallization. It is due to this change in microstructure that the mechanical behavior of these UFG materials becomes interesting. How the refinement of microstructural length scales in materials affect their mechanical properties such as strength, ductility, strain rate sensitivity, fatigue, and superplasticity are discussed. Finally, components produced by SPD and their applications are discussed.

Materials play a crucial role in various nuclear technologies. Fission reactor–based technologies involve application of materials such as nuclear fuel, control rod in encapsulating and diluting spent nuclear fuel and as prospective candidates for transmuting/burning long-lived radionuclides in fast reactors and even in futuristic accelerator-driven subcritical systems. Materials used in these applications face an extreme environment of radiation. Thus one of the critical requirements for a material to be used in any of these applications is its ability to resist any kind of structural, chemical, and morphological modifications under the influence of radiation. Interaction of radiation with materials, primarily, causes point defects, which at high temperatures agglomerate into line defects like dislocations and voids. These lead to detrimental effects like phase transformations, including amorphization, segregation of atoms and hence changes in the chemistry, thermal properties (decreased thermal conductivity), swelling, etc. These eventually may cause failure of the structural component in use. The major damage producing radiation in the nuclear environment includes neutrons, primary knock-on atoms created by neutrons, fission fragments (70–120MeV Ga-Gd ions), α-particles, α-recoils, and β-particles. In some applications such as nuclear waste immobilization, accumulation of radiation damage takes place over prolonged timescales. Irradiating materials with accelerated ion beams has been a popular and a favored method of imparting damage selectively and assessing it over practical duration of time. This chapter provides an outline of different sources of radiation and interaction of radiation with materials significant from the point of view of nuclear energy applications. Some specific aspects like effect of structure and powder properties on radiation stability of complex oxides of nuclear relevance are also discussed. Basic understanding of the herein-mentioned factors would aid the development of a new generation of radiation-tolerant materials.

This chapter deals with the state of materials under extremely high pressure and at extremely high temperatures. The high pressure (several megabars) and temperatures (millions of degrees) that will be dealt with in this chapter, such as those present in stars, can be achieved in a laboratory only using high-powered lasers. Such high-density, high-temperature matter is an excellent source of X-rays, which could be broadband or monochromatic, and of long (several ns) or ultrashort (few hundreds of fs) duration, depending on the laser pulse duration. The isochoric heating of matter (heating matter to a very high temperature at constant volume) can be achieved using ultrashort pulse lasers. Ultrashort pulse lasers can produce energetic protons, neutrons, and ions, and can also be used to accelerate electrons to GeV energy. All these aspects are discussed in this chapter.

Vapor pressure data at ultrahigh temperatures (5000K) are required for refractory materials, especially for nuclear fuel materials, because these data are important input parameters to carry out analysis of consequences of any off-normal events in liquid-metal–cooled fast-breeder reactors (LMFBRs). Conventional experimental techniques used to measure the vapor pressures below 2500K cannot be used at very high temperatures (>3000K) because of limitations arising from the need for a suitable sample container and difficulties in generation of very high temperatures. One way of avoiding these problems is to use a dynamic pulse-heating technique. Of the different methods, the laser pulse-heating technique is advantageous. We have developed a laser-induced vaporization–mass-spectrometry system and studied the vaporization behavior of nuclear fuel materials such as UO2, UC, and ThO2, and other technologically important materials such as graphite and Si3N4 at very high temperatures.

Rapid industrialization demands development of materials with better performance characteristics. When a material is subjected to an application, it is going to experience different conditions/environments, including, for example, high pressure, high temperature, hostile chemical environments, high mechanical stress, etc. Among the ones mentioned herein, the hostile chemical environment is a very important aspect. The nature and extent of interaction of a particular environment with a material and how it influences its physicochemical properties decide the hostile nature of the environment and this forms the subject matter of this chapter. In the beginning of this chapter, different hostile environments and their origins are described briefly. This is followed by synthesis and characterization of a variety of materials including stainless steel, nitrides, oxides, carbides, silicates, polymers, resins, etc. Important properties of these materials and how they vary upon interaction with different environments are discussed in detail. Techniques to monitor the extent of interaction of hostile environment with different materials are also discussed in this chapter. Along with this, the mechanism by which certain materials maintain their integrity and stability when exposed to different hostile chemical environments is also addressed.

Irradiation, be it ions or electrons or neutrons, pumps in ∼108J/mol of energy into the host lattice, which manifests as atomic displacements and microchemical modifications. Irradiation drives a system far from equilibrium, leading to many surprising phenomena, unheard of during thermal activation. The atomic displacements evolve with time, into various defect configurations, which alter the diffusion kinetics and energetics of the irradiated lattice. Such changes during electron or ion irradiation have been utilized as “phase tunable strategy” for tailoring photonic nanomaterials with almost atomic precision. The basic understanding of new phenomena during ion/cluster or molecular ion irradiation has opened up new possibilities for nanodevice fabrication. However, the microstructural changes in engineering materials during neutron irradiation invariably lead to degradation of materials in a fission/fusion reactor, which has provided the major impetus to the study of materials under irradiation since the 1970s. The development of basic concepts and their confirmation by simulated and limited in-reactor experiments was the trend in the last century. This chapter discusses the developments, mainly in the 21st century. The current trend is to develop advanced materials for Generation IV fission and fusion reactor systems, based on the rich in-reactor data generated and multiscale modeling methods being developed. The current status of the field is presented in the review in the following sequence: the rationale behind considering irradiation as an extreme situation, differences in the interaction of various incident beams, defect dynamics, irradiation-enhanced diffusion and segregation, radiation-induced phase transformations, and consequent impact on properties. Despite the current in-depth understanding, challenges exist in predicting materials behavior when exposed to 14MeV neutrons with copious amount of helium and hydrogen, as in fusion situations. Hence, it becomes necessary to evolve joint international materials programs, which would open up new opportunities.

There is an impending need for light-weight, high-strength materials for the development of structural components for construction, infrastructure, wind energy, automobile, and space applications. Polymer nanocomposites have been envisaged to have unique advantages in such applications as they offer very high specific stiffness at low cost. They overcome limitations imposed on traditional structural materials through their intrinsic characteristics and a variety of combinatorial approaches. Polymer nanocomposites essentially consist of a polymer phase in which nanofillers are uniformly dispersed. The nanofillers have at least one dimension in the range of 1–50nm, allowing a significant increase in the interfacial area, and in the case of anisotropic fillers, their aspect ratio is many times higher than their conventional analogues. Such characteristics entail an efficient load transfer mechanism and lead to high reinforcement of polymer matrix at a much lower loading of the filler. Owing to their exceptionally high specific strength and high aspect ratio, nanofillers such as carbon nanotubes, nanoclays, graphene, nanocrystalline cellulose, and boron nitride tubes have shown exceptional reinforcement effect in different polymer matrices. Nanocomposites synthesis, however, demands proper selection of nanofiller and polymer matrix, stabilization of the achieved dispersion, interface modification, desired orientation, and packing of the dispersed phase. The chapter describes the technological aspects of polymer nanocomposites with a specific reference to micromechanics, morphology, and interfacial interactions. A detailed account of thermoplastics, elastomers, and thermosets has been presented with a brief discussion on important nanofillers and interface modification techniques. Few recent examples of novel polymer nanocomposites that displayed exceptionally high mechanical properties have also been discussed.

Tribology is an important and interesting aspect of mechanical engineering especially pertaining to the machining and drilling industries. Different types lubricants have been developed, ball bearings designed, and advanced technologies invoked to reduce the wear and tear of machines during their operation. An important approach involves coating of the surface of the relevant parts of the machines such as tool tips, drill beats, ball bearings, piston barrels, etc. with coatings of suitable materials having excellent tribological properties. Coatings of a large number of materials including alumina, silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, titanium nitride, boron nitride, diamond and diamond-like carbon or composites of these materials show promise of being used as protective hard coatings. This chapter provides a brief overview of the mode of deposition, tribology, and prospective fields of applications of a few of these materials with special emphasis on hard coatings of alumina, diamond, and diamond-like carbon.