Emm-important Questions.pdf

EMM- 2-Marks 1. S t a t e G i b b ' s p h a s e r u l e ? ( M a y 2 0 1 4 ) The Phase rule allows one to determine the number of degrees of freedom (F) or variance of a chemical system in equilibrium. This is useful foe interpreting phase diagrams. F=2+C–P Where, F = Number of degrees of freedom C = Number of chemical components P = Number of Phases in the system. 2. State Hume Rothery's rules for formation of substitutional solid solutions. To exhibit unlimited solid solubility, the solute and solvent elements should obey the following general rules of Hume Rothery. They are 1. Size factor: The atoms must be of similar size, with less than the 15% difference in atomic radius 2. Crystal structure: The materials must have the same crystal structure. 3. Valance: The atoms must have the same valence 3.Differentiate Isomorphous and Eutectic reactions. (May 2012) Isomorphous s ystem represents all alloys wherein the two metals have complete solubility in solid and liquid states. These s ystems form a loop t ype equilibrium diagram. e.x Cu-Ni; Au-Ag; Au-Ni etc. Eutectic reaction is defined as a phase transformation in which all the liquid phase transforms on cooling to two solid phases simultaneousl y. e.x Fe-C; Pt-Ag; Cu-Zn etc. 4. Define solid solution. Solid solution is a type of alloy in which the atoms of alloying elements are distributed in the base metal and both have similar crystal structure. The composition of alloying elements may vary but the structure should be similar to the base metal. e.x Ag-Cu; Cu-Zn; Fe-C etc. 5. Define substitutional and interstitial solid solution. (Nov 2010) Substitutional : Atoms of allo ying elements occup y the atomic sites of the base metal. Interstitial : Atoms of allo ying elements occup y the in terstitial sites of base metal. This t ype of solid is formed when atomic size of the allo ying element is much smaller as compared to that of the base metal.

6. What is quenching? List some of the quenching medium generally used in industries. (May 2014) Quenching is the rapid cooling of a workpiece to obtain certain material properties. It prevents low-temperature processes, such as phase transformations, from occurring by only providing a narrow window of time in which the reaction is both thermodynamically favorable and kinetically accessible. For instance, it can reduce crystallinity and thereby increasing the hardness of both alloys and plastics. When quenching, there are numerous types of media called quenchants. Some of the more common include: air, nitrogen, argon, helium, brine (salt water), oil and water. Experience shows that olive oil is particularly efficient as a good quench. 7.

Define critical cooling rate.(Nov 2012) It is the cooling rate which just avoids entering the pearlite and bainitic region. It can also be defined as the rate of coo ling necessary to just suppress the diffusion transformation and avoid the nose of T.T.T curve.

8 . D e f i n e h a r d e n a b i l i t y a n d c a s e d e p t h . (May 2012)(Nov 2014) Hardenability is defined as the ease with which a desired depth of hardness can be attained in steel. Case depth is the thickness of the hardened layer on a specimen. 9. Define recrystallisation. (N14) Recrystallization is a process by which deformed grains are replaced by a new set of undeformed grains that nucleate and grow until the original grains have been entirely consumed. Recrystallization is usually accompanied by a reduction in the strength and hardness of a material and a simultaneous increase in the ductility.

10. Write the importance of spheroidising annealing. (Nov 2011,May 2012) This heat treatment increases machinabilit y of steels and softens them. The microstructure after this treatment shows globules of cementite or carbides in the matrix of ferrite. This heat treatment is mainl y given to high carbon & alloy steels. 11. What is the effect of the grain size on the mechanical properties of the materials? (M14) Grain size has high influence on mechanical properties of material, viz. ductility, strength, toughness etc.. The fine grained structure has better mechanical properties as compared to coarse grain structure.

1 2 . W h a t i s c r e e p ? ( M 1 3 ) (N11) (M11) Creep is defined as the slow and progressive deformation of material with time under a constant stress at temperatures approximately above 0.4 Tm. Tm is melting point of material in ⁰K 13. What is S-N diagram? What is the significance of it? (M14) Fatigue test results are expressed in terms of stress (S) and the number of cycles required for failure (N).

1 4 . D i f f e r e n t i a t e b e t w e e n F a t i gu e a n d C r e e p t e s t s . ( N13 ) S .N o

F at i gu e t e st

C r ee p t e st

1 . In t hi s t es t , sp e ci m e n i s s ubj e ct ed t o fl u ct ua t i n g & c yc l i c s t r es s.

In t hi s t es t , sp e ci m e n i s s ubj e ct ed t o co nst an t t e nsi l e s t r ess .

2 . Da t a o bt ai n e d b y f a t i gu e t e st a r e pl ot t e d on S - N cu r v e.

Da t a o bt ai n e d b y f a t i gu e t e st a r e pl ot t e d on c r ee p c ur ve .

3 . Gr a ph i s pl o t t ed b et we e n m ax i m um st r es s(S ) & no . of t est

Gr a ph i s pl o t t ed b et we e n c re e p de fo rm at i on o r st ra i n and t i m e .

c yc l es fo r f a i l u r e. ( N) 15. Define toughness. (N11) Toughness is the total amount of energy absorbed by the material before its failure. 16.

W h a t a r e s u p e r a l l o y s ? ( M a y1 4 )

A superalloy, or high-performance alloy, is an alloy that exhibits several key characteristics: excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion or oxidation. The crystal structure is typically facecentered cubicaustenitic. Examples of such alloys are Hastelloy, Inconel, Waspaloy, Rene alloys, Haynes alloys, Incoloy, MP98T, TMS alloys, and CMSX single crystal alloys. 17. W h a t i s p r e c i p i t a t i o n h a r d e n i n g ? ( N o v 1 0 , N o v 1 3 , N o v 1 4 ) Precipitation hardening, also called age hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and some stainless steels. In superalloys, it is known to cause yield strength anomaly providing excellent high-temperature strength. 18. What is inoculation? (Nov10) It is the best method of reducing the size & improving the distribution of graphite flakes by the addition of a mall amount of materials called as “inoculation”. The materials like calcium silicate, silicon carbide, metallic calcium, aluminium, titanium are combination of these materials. 19. What are the primary effects of chromium, and copper as alloying elements in steel? (May14) Chromium is added to the steel to increase resistance to oxidation. This resistance increases as more chromium is added. 'Stainless Steel' has approximately 11% chromium and a very marked degree of general corrosion resistance when compared with steels with a lower percentage of chromium. When added to low alloy steels, chromium can increase the response to heat treatment, thus improving hardenability and strength. Copper (0.1-0.4%): Most often found as a residual agent in steels, copper is also added to produce precipitation hardening properties and increase corrosion resistance. 2 0 . B r i e f a b o u t a n y t w o t yp e s o f p o l ym e r s . ( N 1 3 ) i a single

Li n e a r p o l ym e r – U n i t s j o i n e d t o g e t h e r e n d t o e n d t o f o r m long chain.

ii B r a n c h e d p o l ym e r – P o l ym e r s w i t h s i d e c h a i n s a t t a c h e d t o t h e main ones. 2 1 . W h a t a r e t h e a p pl i ca t i o n s o f P ol y S t yr e n e s? ( N 1 3 ) Used for low cost transparent mouldings such as CD cases, Ball p o i n t p e n s , t o ys e t c . 22.

W hat i s P ol ym eri z at i on? (N11) It i s defi n ed as t he process of form i ng l ar ge pol ym er b y l i n ki ng t o get her m onom ers. e.x wood, resi n, st arch, N yl on et c.

23. Distinguish polymer and ceramic with respect to mechanical and physical properties. (N10) Natural polymers are derived from plants & animals. Mechanical properties of polymers are low. Also polymers are light in weight. Ceramic is a compound formed by combination of in-organic and non-metallic materials. Ceramics are hard and brittle materials and used for high temperature applications. 24.

W hat are si al ons? S tat e t hei r appl i c at i ons.(M14) S i al on i s deri ved from t he i ngredi ent s i nvol ved such as si l i con, al um i ni um ox ygen & ni t rogen. It i s fo rm ed b y bl endi ng si l i c on ni t ri de wi t h di fferent propo rt i ons of al um i ni um ox i de, al um i ni um nit ri de & yt t ri um ox i de. Appl i cat i ons: i. Used for cut t i ng t oo l m at eri al s, wi re & t ube drawi n g di es, ro ck and coal cut t i n g equ i pm ent s et c.

PART-B 1. (a) What are the properties and application of different types of Cast Iron? Explain in brief. (May 10,May 11)

Cast irons are generally coming under ferrous alloys with carbon contents above 2.14% to 6.7%. But in practice, most of the cast irons contain c arbon content between 3 & 4.5% and in addition other alloying elements. Grey cast iron Properties Grey cast irons are weak & brittle in tension. Tips of graphite flakes are sharp & pointed and are cause for stress concentration. Strength & ductility are high under compressive load. Have high resistance to wear. Ductile cast iron Properties These are stronger & ductile than the grey cast iron. They have properties approaching towards steel. Here the alloying elements were added to spheroidise carbon du ring slow cooling. These type of iron finds its applications in machine castings subjected to bending and vibrations and other applications where strength and ductility are important. White cast iron Properties Since more cementite is present, the white iron is very hard & brittle. They are unmachinable. They have very less ductile properties. They can be used only where hard & wear resistance surface is required like rolling mills.

Malleable cast iron Properties They have relatively high strength & appreciable ductility and malleability. It exhibits excellent machinability. It offers good shock resistance properties. This material is highly resistant to corrosion. It offers high strength and toughness.

. (b) Explain with a phase diagram of Eutectoid & Peritectic reaction.(NOV 11) Eutectoid reaction It is an isothermal reversible invariant reation in which a solid phase is converted into two or more intimately mixed solids on cooling. The reaction on heating & cooling gives, γ –solid

α solid + β solid

The in the eutectoid phase diagram indicating the composition of eutectoid and this temperature of transformation is known as eutectoid point. Examples for eutectoid systems are Cu -Zn; CU-Al; Al-Mn; Cu-Be etc. Another important example of eutectoid system occurs in the iron carbon system. In this austenite, a solid solution of carbon - γ iron decomposes into pearlite , an infinite mixture of alpha iron & iron -carbide. This reaction is basis for much of the heat treating of steels. On heating & coolig, γ (Solid)

α solid1 + Fe 3 C

Peritectoid Reaction

It is an isothermal reversible invariant reaction in which a solid phase reacts with a second solid phase to produce yet a third solid phase on cooling. The reaction on heating & cooling can be given as, γ –solid + β Solid

α Solid

2. With the help of neat sketch explain the two types of solid solution. ((May 2013, Nov 11, Nov2012) Solid solution

A solid solution is simply a solution in the solid state that consists of two or more elements atomically dispersed in a single phase structure. When two metals are melted together and crystallized , a single crystal structure may form. In the unit cell of this crystal, both the metal atoms are present in proportion to their concentration. Types of solid solution (i)

Substituitional solid solution a)Random b)Ordered

(ii) Interstitial solid solution Substitutional solid solution This type of solid solution is formed when some of the solvent atoms (base metal atoms) are replaced by solute atoms (alloying element atoms) in a crystal lattice. Substitutional solid solution occurs when the solute and solvent atoms are equal or approximately equal in diameters. Examples are Cu-Ni where Cu has radius of 1.28 A and Ni radius is 1.24. Both copper & Nickel have FC structure. The structure of the solvent is unchanged, but the lattice may be distorted by the presence of solute atoms, particularly if there is significant difference in atomic radii of the solute & solvent atoms. Random solid solution Here, the solute atoms do not occupy specific position but are randomly distributed in the lattice structure of the solvent. The concentration of the solute atoms vary throughout the lattice structure of the solvent. Ordered solution When the atoms of the solute material occupy similar lattice points within the crystal structure of solvent material, the solid solution is called ordered substitutional solid solution.

Interstitial solid solution Interstitial solution are formed when the solute atoms are very small in comparison with the solvent atoms. The solute atoms occupy the holes or interstices between he solvent atoms. In general carbon, nitrogen, hydrogen and boron having small atomic diameters form interstitial solid solutions with the base metal atoms.

3. Explain jominy test (or) End quench harden ability test with the help of the neat sketches. (April 2010, May 2011, May 2012, May 2013)

One standard procedure that is widely used to determine hardenability is the Jominy end-quench test. In this test a cylindrical specimen of diameter 25.44mm and length 100 mm is austenised (heated to austenite region) After removal from the furnace , it is qui ckly mounted in a fixture.The lower end is quenched by a jet of water of specified flow rate and temperature. Thus , the cooling rate is maximum at the bottom end and diminishes along the length of the specimen. After the specimen is cooled to room tempera ture , shallow flats 0.4 mm deep are ground along the specimen length. Rockwell hardness measurements are made for the first 50 mm along the flat. For the firt 12.8 mm , hardness readings are taken at 1.6 mm intervals and for the remaining 38.4 mm ,every 3 .2 mm. A hardenabilty curve can be drawn when hardness is plotted in y axis and the position from the quenched end in x axis as shown in fig 3 & fig.4. From this curve we can see that the quenched end is cooled most rapidly and exhibits the maximum hardnes s. 100 % martensite is formed at the quenched end. Cooling rate decreases with the distance from the quenched end and the hardness also decreases as shown in fig.4

4. Explain the different types of mechanical properties and mechanism of plastic deformation by slip and twinning. (May 2010, Nov 2011, Nov 2012, May 2013) (16)

5. Explain briefly about charpy impact test.

Charpy impact test In this test, certain mass is released from some distance above the impact point which strikes the specimen. Charpy test is conducted on te same impact testing machine. In charpy test, the weight of the pendulum is 20.932 kg and the length of the arm is 0.825m. For charpy impact test the pendulum is released from an angle of 140 ⁰. In this test, a standard specimen which is square prism of size 10mm x 10mm x 55mm, V-notched at the centre is used. In some cases, key hole notch or U -notch is also used. Testing procedure 1. The specimen is placed in the vice of the anvil. 2. The pendulum hammer is raised to known standard height depending on the type of specimen to be tested. 3. When the released, its potential energy is converted into kinetic energy just before it strikes the specimen. 4. Now the pendulum strikes the specimen. It may be noted that the izod specimen is hit above the v-notch and the charpy specimen will hit behind the V-notch. 5. The pendulum after rupturing the specimen, rises on the other side of the machine. 6. The energy absorbed by the specimen during breaking is the weight of the pendulum times the difference in two heights of pendulum on either side of the machine. 7. Now the energy, the notched impact strength, in foot -pounds or metre-kg is measured from the scale of the impact testing machine.

6. What do you understand by polymerization? With the help of suitable examples, Compare and contrast the process of addition polymerization and

condensation polymerization. (16)

(May2013)

Polymerisation It is defined as the process of forming large polymer by linking together the monomers. E.x wood, resin, starch, Nylon etc 7. What are the properties and Application of PVC, PET, PP and PC? Explain.

a) PVC (May 2013, Nov 2011) Properties i) ii) iii) iv)

Normally rigid, but may be made flexible with plasticizers Often copolymerized. Susceptible to heat distortion. Have good flame, electrical, chemical, oil, abrasion and weather resistance.

Applications i) ii) iii)

Used in furniture, water proof coatings, bags & folders,gaskets. Floor coverings, pipe, phonograph records. In industries used for corrosion resistance coat for metals.

b) PET P ol yet h yl ene t e raph t hal at e al so known a s pol yest e r i s a l i ne ar pol yest e r m ade b y t he condensat i on pol ym eri z at i on of et h yl ene gl ycol and t erapht ha l i c aci d. C haract e ri st i cs i. The y ar e hi gh st r en gt h, hi gh st i ffness t herm opl ast i cs. ii. The y ar e produc ed a s fi bres, as t ransp ar ent t hi n fi l m s and as m oul di ng m at eri al s. i i i . The y poss ess ex cel l ent fat i gu e & we ar s t rengt h. i v. The y can b e rei nfo r ced wi t h gl ass fi bre. v. The y poss ess good r esi st ance t o hum i di t y, a ci ds, gre ase, oi l s & sol vent s.

Appl i cat i ons i)

Fi bres, phot o gr aphi c fi l m s, recordi n g t a pes, bever a ge cont ai ners , soft dri nks bot t l es, el ect ri c al conne ct or s part s for dom est i c goods and aut om ot i ve com ponent s.

(c) PP (Polypropylene) (May 2012) Properties i) ii) iii) iv) v) vi)

Resistance to heat distortion. Excellent electrical properties & fatigue strength. Chemically inert & relatively inexpensive Poor resistance to UV light. More stiff & stronger than polyethylenes. Good chemical & thermal resistance.

Applications i) ii) iii) iv)

Sterlizable bottle Packaging fil TV cabinets Luggage

(d) PC (Polycarbonate) Properties i) ii) iii) iv) v)

They They They They They

are dimensionally stable have low water absorption quality. are transparent. have very good impact resistance and ductility. have low fatigue & wear resistance.

Applications i) ii)

Safety helmets, goggles, lenses, light fittings etc. Head lamp mouldings, kettle mouldings, instrument casings & machine housings, kitchen wares etc.