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Answer the following in brief. (20 marks) Discuss Scanning electron microscopy. The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. The signals that derive from electron-sample interactions reveal information about the sample including external morphology (texture), chemical composition, and crystalline structure and orientation of materials making up the sample.   Differentiate between SEM and FESEM. The difference between a FESEM and an SEM lies in the electron generation system. As a source of electrons, the FESEM uses a field emission gun that provides extremely focused high and low-energy electron beams, which greatly improves spatial resolution and enables work to be carried out at very low potentials . This helps to minimise the charging effect on non-conductive specimens and to avoid damage to electron beam-sensitive samples. What is AFM? The atomic force microscope (AFM) is ...

Write notes on the following (2 x 10) Binary system Binary phase diagrams are maps that represent the relationships between temperature and the compositions and quantities of phases at equilibrium, which influence the microstructure of an alloy. Phase diagram A phase diagram is a graphical representation of all the  equilibrium phases as a function of temperature, pressure,  and composition.  For one component systems, the equilibrium state of the  system is defined by two independent parameters (P and  T), (T and V), or (P and V). Pressure-temperature phase diagram for H₂O: Viscoelastic properties A viscoelastic material has the following properties: hysteresis is seen in the stress–strain curve stress relaxation occurs: step constant strain causes decreasing stress creep occurs: step constant stress causes increasing strain its stiffness depends on the strain rate or the stress rate  Ductile fracture Little or no plastic deformation in brittle fracture an...

Answer all questions Magnetic moment  The magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnets), permanent magnets, elementary particles (such as electrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc). Grain growth  Grain growth refers to an increase in the size of crystallites (grains) in a material at high temperatures.  Grain growth is due to an alteration of the internal energy of the molecular structure of a given metal, ceramic, or mineral.  Grain growth is typical in metals that have undergone annealing and other processes of surface modification.  Due to the destabilization of the molecular structures of metals due to grain growth, the probability of crevice, intergranular, and grain boundary corrosion is increased. Age hardening  ...

What is the angle between the directions [001] and [111 ] of cubic crystal? Hint:  What is the degree of freedom of a system of one component when the number of phases is two? F = 2 – 2 + 1 = 1. What is congruent transformation? Congruent transformation : It involves no change in composition (e.g., allotropic transformation such as α-Fe to γ-Fe or melting transitions in pure solids). Incongruent transformation: Here at least one phase changes composition (e.g. eutectic, eutectoid, peritectic reactions). Define devitrification. Devitrification, the process by which glassy substances change their structure into crystalline solids. This devitrification process is very slow, but over millions of years, a glass will form a completely crystalline mass; thus, the occurrence of very old glassy rocks is rare. What is mobility? We define Mobility in Physics as the measurement of the ease with which charged particles move through a solid material under the influence of an applied electr...

What is stress corrosion cracking (SCC)? Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected sudden failure of normally ductile metals subjected to tensile stress, especially at elevated temperatures in the case of metals.  SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments. The chemical environment that causes SCC for a given alloy is often one that is only mildly corrosive to the metal otherwise. Hence, metal parts with severe SCC can appear bright and shiny, while being filled with microscopic cracks. This factor makes it common for SCC to go undetected prior to failure.  SCC often progresses rapidly and is more common among alloys than pure metals. The specific environment is of crucial importance, and only very small concentrations of certain highly active chemicals are needed to produce catastrophic cracking, ofte...

If G = 130 GPa for a metal and Poisson's ratio = 0.3, calc ulate the value of E for the metal. Modulus of elasticity (E) = 45 MPa, and Poisson's ratio (μ) = 0.31   The relation between Elastic modulus and Poisson's ratio and Modulus of rigidity is given as:   E = 2G(1 + μ)     ⇒ 130 = 2 × G (1 + 0.3) From this, G = 50 GPa Stainless steels (an alloy of iron, a = 0.2867 nm) always can contain a huge amount of chromium. (a = 0.2885 nm). Explain. From the given lattice parameters (a) the corresponding radii for iron and chromium are 0.124 nm. and 0.125 nm which are nearly the same so can easily form the crystal bonding. Stainless steel contains about up to 11% chromium. Define isomorphous systems with examples. The term isomorphous system is related to phase diagram, isomorphic means having the same crystal structure or complete solubility for all compositions. The copper-nickel system is an example of an isomorphous system. A pure copper wire has been dra...

Why are cutting tools manufactured from high-carbon steel in preference to low or medium carbon? High carbon steels contain more carbon and are therefore harder both initially and after heat treatment. In most instances, the cutting tool must be harder than the material being cut. Suggest whether low, medium or high-carbon steel should be used for the following applications.  nails  ball bearings car bodies crankshafts heat-treatable machine parts drills Low High Low Medium Medium High. State whether the carbon contents below relate to low,  medium or high carbon steels. 0.29%  0.65% 0.87% 0.08% 1.32% 0.31% 0.59% Low High High Low High Medium Medium In which way does the normalising treatment differ from the annealing treatment.  The only difference between annealing and normalising treatments is the way in which they are cooled. Material that is being annealed is cooled in the furnace whilst normalising cooling is done in still air. Explain case hardening. Case...

Name two important ceramic insulators with their properties. Porcelain is the most frequently used material for insulators. Insulators are made of wet, processed porcelain. The fundamental materials used are a mixture of feldspar (35%), china clay (28%), flint (25%), ball clay (10%), and talc (2%). Toughened glass is also frequently used for insulators. The melted glass is poured into a mould to form the shell. Dipping into hot and cold baths cools the shells. Write the scientific names of the following polymers with one of their typical use: Teflon, ABS. Teflon: PTFE (polytetrafluoroethylene) ABS: Acrylonitrile - Butadiene - Styrene Teflon-PTFE is a Polytetrafluoroethylene used in GoreTex and nonstick cookware, and also as a high-frequency, high-temperature dielectric/insulator for electrical wires and coaxial cables.  ABS is an ideal material wherever superlative surface quality, colour fastness and lustre are required. ABS is a two-phase polymer blend. A continuous phase of sty...

Suggest one suitable material for each of the following purposes with justifications: File cabinet Water tap Manhole cover Garden chair Glass cutter A suitable material is Steel, board   brass   cast iron    Wrought iron, concrete, bamboo, timber    Low alloy steel Atomic radii of two metal atoms are 0.128 nm and 0.133 nm respectively. Find out whether they form a solid solution, and if they form, state what type of solid solution it is. They will form substitutional solid solutions because the sizes of atoms are nearly the same. Atomic radii of two metal atoms are 0.1278  nm (Cu) and 0.1431 nm (Al) respectively. Find out whether they form a solid solution, and if they form, state what type of solid solution it is. Only 20% of copper atoms can be replaced by aluminium because there is a substantial difference in size.   Write down the slip plane and slip direction (one plane and one direction) of Nickel (only Miller indices). How ma...

A brass plate contains a steel screw and it is being used in a marine environment. Which of the two metals would corrode faster and why? The steel is on the higher side of the Galvanic series as compared to brass, so it will corrode faster. What is the weight % of carbon in low carbon steel? The percentage of carbon in low carbon steel is 0.05 to 0.3. What is carburizing? Carburizing is the diffusion or impregnation of carbon on the surface. Whether duralumin is wrought or cast alloy? It is a wrought alloy. Name at least two mechanisms of plastic deformation. Slip and Twinning. The key difference between slip and twinning is that during a slip, all atoms in a block move the same distance whereas, in twinning, the atoms in each successive plane in a block move through different distances that are proportional to their distance from the twinning plane. Which of the two main mechanisms of plastic deformation requires greater shear stress to deform. Slip If you wound annealed MS and copper...

If we test a cast-iron sample in tensile mode, will there be any appreciable plastic deformation? Why? Very small plastic deformation is associated with the tensile test of C.I. because it is brittle. For which type of fracture, the direction of crack motion is very nearly perpendicular to the direction of the applied tensile stress? The direction of crack propagation is nearly perpendicular to applied tensile stress in Brittle fracture.  Which alloying element is most important to make steel corrosion-resistant and what is the minimum percentage of this element required? To shape steel corrosion-resistant chromium is added with a minimum of 0.7%. Every plastic is polymer but every polymer may not be plastic. Is it true? Justify. The statement is true.  All polymers are not plastics, but all plastics are polymers. For instance, cellulose is a polymer; but, it cannot be processed in the same way as a plastic material unless it is modified. Polymers can exist organically or be c...

Cup and cone type of fracture is characteristic of which type of material? Cup and cone fracture is characteristic of moderately ductile material. The formation of the cup and cone fracture surface occurs in stages. Initially, as a result of the tensile load, the material stretches and experiences plastic deformation. Beyond some point, the material will begin to neck . Which two parameters constitute a slip system? Slip plane and slip direction constitute slip system. What is the essential difference between a brittle fracture and a ductile fracture? Little or no plastic deformation in brittle fracture and large plastic deformation in ductile fracture. Is it possible to determine stress in a body without measuring corresponding strain? Yes by measuring force and area. What is the essential difference between thermoplastic and thermoset polymers? Thermoplastic polymer softens on heating while thermosetting sets or hardens. What are the three stages of creep deformation? Decreasing rate...

What is the main objective of normalizing as a heat treatment process? In normalizing there is complete phase re-crystallization and the fine grain structure is obtained. It is a type of heat treatment applicable to ferrous metals only. In the normalizing process, the material is heated to an elevated temperature and after that, it is cool back by placing it in contact with air at room temperature. This process of cooling metal with air is called air quenching. What is the maximum solubility of carbon in iron? The maximum solubility of carbon in iron is 2 %. How are resistivity and conductivity related? The conductivity of reciprocal of resistivity and has units  ohm -1  m -1 Why does the resistivity of copper increase due to the presence of solute atoms? The solute atoms cause lattice distortion, these imperfections, cause irregularities in electric fields within the metal and decrease the mean free path thus reducing the mobility of electrons, thereby increasing the res...

Why is cast iron used as a material for machine tool beds? Cast iron has good machinability, stable dimensions and has got the property of damping vibrations in machines tools. When does Hook’s law appear to fail? Hooke’s law states that within the elastic limit, for elastic deformation, stress is proportional to strain. This does not hold in the case of elastomers like rubber whose stress-strain behaviour is not linear in their elastic range.  Define the term "dislocation". It is a type of line imperfection in a crystal in which positions of planes of atoms are missing or misaligned. These may be edge type or screw type.  What are the units of the surface energy of a grain boundary? Ergs/cm 2  or dynes/cm. When is grain boundary shear possible in metals? Grain boundary shear is possible only at temperatures above 0.5 T m  where T m  is the melting point of the metal expressed in absolute scale. Give two examples of heat-resisting alloys. Researchers have discov...