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SELVAM COLLEGE OF TECHNOLOGY, NAMAKKAL – 637 003 DEPARTMENT OF MECHANICAL ENGINEERING YEAR/SEM: II/ IV Engineering Materials and Metallurgy (ME 2253) 2 Marks Question & Answers Unit – I CONSTITUTION OF ALLOYS AND PHASE DIAGRAMS PART – A 1. What is an alloy? A metal alloy, or simple an alloy, is a mixture of two or more metals or a metal (metals) and a non-metal (non-metals). 2. How many components are found in an alloy? Two or more components are found in an alloy. 3. What is meant by base meta
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  SELVAM COLLEGE OF TECHNOLOGY, NAMAKKAL – 637 003DEPARTMENT OF MECHANICAL ENGINEERING YEAR/SEM: II/ IV Engineering Materials and Metallurgy (ME 2253) 2 Marks Question & AnswersUnit – ICONSTITUTION OF ALLOYS AND PHASE DIAGRAMSPART – A1. What is an alloy?A metal alloy, or simple an alloy, is a mixture of two or more metals or a metal(metals) and a non-metal (non-metals).2. How many components are found in an alloy?Two or more components are found in an alloy.3. What is meant by base metal?In an alloy, the element which is present in the largest proportion is called the basemetal.4. What are alloying elements?In an alloy, all elements other than the base metal are called the alloying elements.5. Differentiate between substitutional and interstitial solid solution.In a substitutional solid solution, the solute atoms (impurities) substitute for parentsolvent atoms in a crystal lattice.In interstitial solid solution, the solute atoms fit in to the space between the solventor parent atoms.6. State Hume Rothery’s rules for formation of substitutional solid solutions.1. Size factor: The atoms must be of similar size, with less than a 15% difference inatomic radius (in order to minimize the lattice strain).2. Crystal structure: The materials must have the same crystal structure.3. Valence: The atoms must have the same valence.4. Electro negativity: The atoms must have approximately the same electronegativity.7. What are intermediate phases?If an alloying element is added in excess of the limit of solid solubility, a secondphase appears along with the primary solution. If the second phase differs in bothcrystalstructure and properties from primary solid solution, then it is known as an‘intermediate’phase.8. What are intermetallic compounds?  The compound formed by two or more metals in apparently stoichiometric proportionis called intermetallic compounds.9. What are electron compounds?If two metals consist of atoms more or less similar size but different valency, then thecompounds formed are called electron compounds.10. Define ‘phase’. What different kinds of phases are possible?A phase is defined as any physically distinct, homogeneous and mechanicallyseparable portion of a substance. Three different kinds of phases are solid, liquid andvapour.11. What is an equilibrium phase diagram?A phase diagram can be defined as a plot of the composition of phases as a functionof temperature in any alloy system under equilibrium condition.12. What are the advantages of the equilibrium diagrams?1. To show what phases are present at different compositions and temperature underequilibrium conditions.2. To indicate the equilibrium solid solubility of one element in other element.3. To indicate the temperature range over which solidification of a material occurs.4. To indicate the temperature at which different phases start to melt.13. State Gibb’s phase rule?Gibb’s phase rule is given byF=C-P+2Where,F=degrees of freedom of system or number of variables (such as temperature,pressure or composition) that may be changed independently without altering theequilibrium;C=number of components (usually elements or compounds) forming the system;andP=no of phases present in the system.14. What are cooling curves?Cooling curves are obtained by plotting the measured temperatures at equal intervalsduring the cooling period of a melt to a solid.15. What is liquidus line? A Solidus line? A solvus line?In a phase diagram, liquidus line is the line or boundary that separates liquid andliquid+solid phase regions.Solidus line is a line or boundary that separate solid and solid+liquid phase region.Solvus line separate single-phase solid regions from two-phase solid regions.16. What pieces of information can be obtained for each point in a phase diagram?Using a phase diagram, one can obtain at least the following three information.1. The phases that are present, 2. The composition of each phase, and3. The amount of each phase present.17. What is tie-line?A tie line is simply an isothermal line drawn through point of consideration, extendingacross the two-phase region and terminating at the phase boundary lines on either side.  18. What is the lever-law calculation and what information can it provide?Opposite arm of leverPhase fraction= ----------------------------Total length of tie lineOpposite arm of leverand phase percentage = --------------------------- × 100Total length of tie lineUsing the lever law calculations, one can compute the phase fraction and the phasepercentage.19. What is mean by invariant reaction?The eutectic reaction is also called an invariant reaction since it occurs underequilibrium conditions at a specific temperature and alloy composition that cannot bevaried.20. Differentiate between eutectic and eutectoid reactions.Eutectic reaction is given byCoolingLiquidSolid 1 + Solid 2HeatingEutectoid reaction can be written asCoolingLiquidiron (Austenite) + Fe 3 C (Cementite)Heating21. Distinguish between peritectic and peritectoid reactions.The peritectic reaction can be written asCoolingLiquid + Solid 1Solid 2HeatingThe peritectoid reaction can be written asCoolingSolid 1 + Solid 2Solid 3Heating22. What do you understand by ‘allotropy of iron’?Allotropy refers to the possibility of existence of two or more different crystalstructures for a substance depending upon temperature.23. Define: ferrite and austenite.Ferrite is a primary solid solution based on iron having BCC structure. Maximumsolubility of carbon in iron is 0.025% carbon at 723°C, while its solubility at roomtemperature is only about 0.008%.Austenite is a primary solid solution based on iron having FCC structure. Themaximum solubility of carbon in FCC iron is about 2% at 1140°C.24. Define: Cementite and Pearlite?  Cementite is the name given to the carbide of iron (Fe 3 C). It is the hard, brittle,intermetallic compound of iron with 6.69% of carbon.Pearlite is the eutectoid mixture of ferrite (87.5%) and cementite (12.5%). It isformed when austenite decomposes during cooling. It contains 0.8% of carbon.25. Define: martensite, and bainite?Martensite is the super saturated solid solution of carbon in iron. It is formed whena steel is very rapidly cooled from the austenitic state.Bainite is a decomposition product of austenite, consisting of an aggregate of ferriteand carbide. Bainite has hardness in between the hardness of pearlite and martensite.26. Why is the iron-carbon equilibrium diagram usually not shown beyond 6.67%carbon?This is because in practice, all steels and cast irons have carbon contents less than6.67 wt% C.27. What is steel?The ferrous alloy having the carbon composition ranging from 0.008 to 2% is knownas steel.28. What is meant by eutectoid, hypoeutectoid, hypereutectoid steels?Steels that contain 0.8% C (the eutectoid amount of carbon) are called eutectoidsteels.Steels having less than 0.8% C are known as hypoeutectoid steels.Steels having more than 0.8% C are known as hypereutectoid steels.29. How do cast irons differ from steels in terms of carbon content?Composition from 0.008% to 2% carbon represent steel and those above 2% carbonrepresent cast iron.30. Distinguish between hypoeutectic and hypereutectic cast irons.Cast irons that contain less than 4.3% C are termed as hypoeutectic whereascastirons that contains more than 4.3% C termed as hypereutectic.Unit – IIHEAT TREATMENTPART – A1. Define the term ‘heat treatment’.Heat treatment may be defined as an operation or combination of operations involvingheating and cooling of a metal/alloy in solid state to obtain desirable properties.2. What are the purposes of the processing heat treatments?1. To relieve internal stresses. 2. To improve machinability. 3. To refine grain size.4. To soften the metal. 5. To improve hardness of the metal surface.6. To improve mechanical properties (like tensile strength, hardness, ductility, etc.)3. List the various stages of a heat treatment process.Stage 1: Heating a metal/alloy beyond the critical temperature.Stage 2: Holding at that temperature for a sufficient period of time to allow necessarychanges to occur.
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