Railways NTPC (Technical Ability) Materials Science

Materials Science

• Materials science is an interdisciplinary field which deals with the discovery and design of new materials. Though it is a relatively new scientific field that involves studying materials through the materials paradigm its intellectual origins reach back to the emerging fields of chemistry, mineralogy and engineering during the Enlightenment.
• It incorporates elements of physics and chemistry, and is at the forefront of Nano science and nanotechnology research. In recent years, materials science has become more widely known as a specific field of science and engineering.
• It is an important part of forensic engineering (the investigation of materials, products, structures or components that fail or do not operate or function as intended, causing personal injury or damage to property) and failure analysis, the latter being the key to understanding, for example, the cause of various aviation accidents.
• Many of the most pressing scientific problems that are faced today are due to the limitations of the materials that are available and, as a result, breakthroughs in this field are likely to have a significant impact on the future of technology.
• The material of choice of a given era is often a defining point. Phrases such as Stone Age, Bronze Age, Iron Age, and Steel Age are great examples.
• Originally deriving from the manufacture of ceramics and its putative derivative metallurgy, materials science is one of the oldest forms of engineering and applied science.
• Modern materials science evolved directly from metallurgy, which itself evolved from mining and likely) ceramics and the use of fire. A major breakthrough in the understanding of materials occurred in the late 19th century, when the American scientist Josiah Willard Gibbs demonstrated that the thermodynamic properties related to atomic structure in various phases are related to the physical properties of a material.
• Important elements of modem materials science are a product of the space race: the understanding and engineering of the metallic alloys, and silica and carbon materials, used in the construction of space vehicles enabling the exploration of space.
• Materials science has driven, and been driven by, the development of revolutionary technologies such as plastics, semiconductors, and biomaterials.
• A material is defined as a substance (most often a solid, but other condensed phases can be included) that is intended to be used for certain applications. There are a myriad of materials around us-they can be found in anything from buildings to spacecraft. Materials can generally be divided into two classes: crystalline and non-crystalline.
• The traditional examples of materials are metals, ceramics and polymers. [3] New and advanced materials that are being developed include semiconductors, nanomaterial's, biomaterials, etc.
• The basis of materials science involves studying the structure of materials, and relating them to their properties. Once a materials scientist knows about this structure-property correlation, he/she can then go on to study the relative performance of a material in a certain application.
• The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and the way in which it has been processed into its final form. These characteristics, taken together and related through the laws of thermodynamics and kinetics, govern a material's microstructure, and thus its properties.
• Materials science examines the structure of materials from the atomic scale, all the way up to the macro scale. Characterization is the way materials scientists examine the structure of a material.
• This involves techniques such as diffraction with x-rays, electrons, or neutrons, and various forms of spectroscopy and chemical analysis such as Raman spectroscopy, energy-dispersive spectroscopy (EDS), chromatography, thermal analysis, electron microscope analysis, etc
• Nanostructure deals with objects and structures that are in the 1-100 nm range. In many materials, atoms or molecules agglomerate together to form objects at the Nano scale. This leads to many interesting electrical, magnetic, optical and mechanical properties.
• In describing nanostructures it is necessary to differentiate between the number of dimensions on the Nano scale. Nano textured have one dimension on the Nano scale, i.e., only the thickness of the surface of an object is between 0.1 and 100 nm.
• Nanotubes have two dimensions on the Nano scale, i.e., the diameter of the tube is between 0.1 and 100 nm; its length could be much greater. Finally, spherical nanoparticles have three dimensions on the Nano scale, i.e., the particle is between 0.1 and 100 nm in each spatial dimension.
• The terms nanoparticles and ultrafine particles (UFP) often are used synonymously although UFP can reach into the micrometer range. The term 'nanostructure' is often used when referring to magnetic technology. Nano scale structure in biology is often called ultrastructure.
• Materials whose atoms/molecules form constituents in the Nano scale (i.e., they form nanostructure) are called nanomaterial's. Nanomaterial's are subject of intense research in the materials science community due to the unique properties that they exhibit.
• Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above \[25\,\,\times \] magnification. It deals with objects in from 100 nm to few cm.
• The microstructure of a material (which can be broadly classified into metallic, polymeric, ceramic and composite) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behavior, wear resistance, and so on. Most of the traditional materials (such as metals and ceramics) are micro-structured.
• The manufacture of a perfect crystal of a material is physically impossible. The microstructure of materials reveals these defects, so that they can be studied.
• Macrostructure is the appearance of a material in the scale millimeters to meters-it is the structure of the material as seen with the naked eye.
• Crystallography is the science that examines the arrangement of atoms in crystalline solids. Crystallography is a useful tool for materials scientists. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see macroscopically, because the natural shapes of crystals reflect the atomic structure.
• In addition, physical properties are often controlled by crystalline defects. The understanding of crystal structures is an important prerequisite for understanding crystallographic defects.
• Mostly, materials do not occur as a single crystal, but in poly-crystalline form. Because of this, the powder diffraction method, which uses diffraction patterns of polycrystalline samples with a large number of crystals, plays an important role in structural determination.
• Most materials have a crystalline structure. But, there are some important materials that do not exhibit regular crystal structure. Polymers display varying degrees of crystallinity, and many are completely non-crystalline.
• Glass as, some ceramics, and many natural materials are amorphous, not possessing any long-range order in their atomic arrangements. The study of polymers combines elements of chemical and statistical thermodynamics to give thermodynamic, as well as mechanical, descriptions of physical properties.
• To obtain a full understanding of the material structure and how it relates to its properties, the materials scientist must study how the different atoms, ions and molecules are arranged and bonded to each other.
• This involves the study and use of quantum chemistry or quantum physics. Solid-state physics, solid state chemistry and physical chemistry are also involved in the study of bonding and structure,
• Synthesis and processing involves the creation of a material with the desired micro/nanostructure. From an engineering standpoint, a material cannot be used in industry if no economical manufacturing method for it has been developed. Thus, the processing of materials u is very important to the field of materials science.
• Different materials require different processing/ synthesis techniques. For example, the processing of metals has historically been very important and is studied under the branch of materials science known as physical metallurgy.
• Currently, new techniques are being developed to synthesize nanomaterials such as graphene.
• When a part is subjected to a cyclic stress, also known as stress range (Sr), it has been observed that the failure of the part occurs after a number of stress reversals (N) even if the magnitude of the stress range is below the material's yield strength.
• Generally, higher the range stress, the fewer tile number of reversals needed for failure.
• There are four important failure theories: maximum shear stress theory, maximum normal stress the theory maximum strain energy theory, and maximum distortion energy theory.
• Out of these four theories of failure, the maximum normal stress theory is only applicable for brittle materials, and the remaining three theories are applicable for ductile materials.
• Of the latter three, the distortion energy theory provides most accurate results in majority of the stress conditions. The strain energy theory needs the value of Poisson’s ratio of the part material, which is often not readily available.