Material Science.pdf

Material Science

Laboratory Manual

SUNIL PANDEY

School of Engineering & TechnologyDepartment

ofMechanical and Automobile Engineering

Gurgaon, Haryana

Formerly (Institute of Technology and Management)

Name _______________________________________________

Roll No. ______________________________________________

Branch_______________________________________________

Section ______________________________________________

ITM University

Material Science Laboratory Manualii

Published by:

SCHOOL OF ENGINEERING & TECHNOLOGYDepartment of Mechanical and Automobile EngineeringITM UniversityGurgaon

Lab Manual is for internal circulation only.

Copyright Reserved

No part of this manual may be reproduced, used,stored without prior permission.

Eighth EditionJanuary, 2012

Printed by:

ABC PRESS A-21/12, Naraina Indl. Area, Ph-II, New Delhi-28Tel: 25896768 E-mail: [email protected] Web: www.abcpress.in

Material Science Laboratory Manual iii

PREFACE

A strong need was felt to lay down the instructions and procedures in a clear and systematic manner andstandardize the format for recording of observations for the practical work undertaken by the students inthe laboratories. Its a matter of pride to ring out a comprehensive manual for Material Science laboratory.It would enable the students to read, assimilate, understand the requirements and perform the practicalwork independently. It would serve a two fold purpose- eliminate spoon- feeding and help develop ananalytic mind, which is a very essential requirement for the engineering students. Practical applicationsof the concepts/ principles have also been covered for meaningful understanding of the students.

Detailed instructions on performing ten experiments, as prescribed by ITM University, have been includedin this manual. General instructions on conduct of experiments in the lab, writing up the book, etc. aregiven in the introductory pages. At the end of each experiment some selected questions are given tocheck the understanding of the subject and space provided to write the answers. These questions willalso prepare the students for viva-voce during the final university examination.

It is hoped that this book will be of great assistance to the students and provide the necessary guidancefor conducting the university prescribed experiments of Material Science Lab in the correct manner andenhance their knowledge on the subject. The author would be too glad to receive any constructivecriticism/ suggestions for any further improvements in the book.

The authors express deep gratitude to the Governing Body-ITMU for providing constant encouragementand motivation in this direction. Sincere thanks are also due to, Prof. K.K. Chaudhary, HOD-Mechanical& Automobile Engineering for his contribution, valuable guidance from time to time and continuous supportin writing this manual.

AuthorITM University, Gurgaon

January, 2012

Material Science Laboratory Manualiv

LIST OF EXPERIMENTS

S. No. Content Page No.

1. General Instructions 1-2

2. Detail of Experiments 3-52

2.1 Experiment No. 1 3-9Study of Crystal Structures

2.2 Experiment No. 2 10-15Study of Metallurgical Microscope and SpecimenPolishing Machines

2.3 Experiment No. 3 16-18Study of Heat treatment Furnace and Thermocouple Pyrometer

2.4 Experiment No. 4 19-24Study of Crystal Imperfections

2.5 Experiment No. 5 25-28Micro structural Examination of Heat treated Specimen

2.6 Experiment No. 6 29-33Performance of heat treatment Process

2.7 Experiment No. 7 34-41

Study of Chemical Corrosion and its Prevention

2.8 Experiment No. 8 42-44Creep behavior of Materials

2.9 Experiment No. 9 45-48Study of Various Types of Plastics

2.10 Experiment No. 10 49-52Study of Thermosetting Plastics

3. Notes & Comments 53-64

Material Science Laboratory Manual 1

GENERAL INSTRUCTIONSTo make laboratory experiments safe and effective, each student should follow the given instructions.

Safety1. High voltage source in the laboratory should be handled properly under the guidance of lab assistant,

as it may cause a serious accident.

2. Avoid loose clothes, shirts should be properly tucked, skirts with extra flares should be avoided,slippers are not allowed, shoes with rubber soles are recommended for mechanical worklaboratories.

3. Make sure that all power sources are off during set-up of machines.

4. Keep safe distance from moving parts of machines.

5. Follow the instruction given by the instructor

6. In case of operating furnace, dont touch the inside parts of furnace.

7. failure to obey instructions may result in being expelled from the lab.

Attendance1. All students are required to attend and contribute adequately while performing experiments in the

group.

2. All students must write satisfactory report for each lab experiments.

3. Failure to be present for an experiment will result in losing entire marks for the corresponding lab.

4. All students are supposed to attend only their group of experiment assigned at the beginning ofthe lab.

Preparation of Lab Report1. Before coming to the laboratory, each student must read and review appropriate experiment to be

conducted on the subsequent turn.

2. Record your experiment observations and sample calculations carefully.

3. Each student is required to write a neat and clean report for the experiment conducted.

4. Reports are due one week after the completion of the experiment.

5. Each report shall be submitted with all necessary instructions, sample calculations, graphs, anddiscussion over data and graph.

6. weightage will be given for discussion over results and graphs.

7. Questions give at the end of each experiment have to be answered appropriately with in the spaceprovided in the manual.

8. Students should remain prepare for the viva-voce on any turn.

Material Science Laboratory Manual2

How to Plot a Graph1. Before drawing a graph between two observed variables it is necessary to know the nature of

expected theoretical graph.

2. Decide which parameter to be considered on X axis and which one on the Y-axis. (parameterwhich is under the control of the student is generally kept over X axis)

3. Selection of appropriate scales for the two variables should be chosen such that it appears assquare graph.

4. Points plotted should be joined such that it appears smooth and near to the theoretical nature ofthe curve. It is not necessary to join all points on the graph. Average graph is always advisable,instead of point.

3Material Science Laboratory Manual

Experiment No. 1 Name__________________________________ Roll No. ____________ Group No. ____________ Date _________________ Marks/Grade ___________ Facultys Signature___________________

Object Study of crystal structures.

Equipment required Charts, models of crystal structures.

Theory Crystals posses a periodicity that produces long range order. By this we mean that the local atomic arrangement is repeated at regular intervals million of times in the three dimensional space. Crystal systems are the geometries of crystal variation in the axial angles and in the relative size of a, b and c dimensions lead to seven crystal systems.

The crystal systems broadly classified as 1. Cubic systems 2. Non cubic systems

1. Unit cell The atomic order in crystalline solids indicates that small groups of atoms form a repetitive

pattern. Thus, in describing crystal structures, it is often convenient to subdivide the structure into small repeat entities called unit cells. Unit cells for crystal structures are parallelepipeds or prisms having three sets of parallel faces; one is drawn within the aggregate of spheres as shown in fig. 1.1c.

Three relatively simple crystal structures are found for most of the common metals: face centered cubic, body centered cubic, and hexagonal closed packed.

2. Face- centered cubic crystal structure The crystal structure found for many metals has a unit cell of cubic geometry, with atoms

located at each of the corners and centres of all the cube faces. It is aptly called the face centered cubic (FCC) crystal structure. Some of the familiar metals having this crystal structure are copper. Aluminum, silver, and gold ( see Table 1.1) Fig. 1.1a also shows a hard sphere model for the FCC unit cell, whereas in fig. 1.1b the atom centres are represented by small circles to provide a better perspective of atom positions. The aggregate of atoms in fig. 1.1c represents a section of crystal consisting of many FCC unit cells. These spheres or ion cores touch one another across a face diagonal; the cube edge length a and the atomic radius R are related through

A = 2 R 2

4 Material Science Laboratory Manual

Figure 1.1a Figure 1.1b

For the FCC crystal structure, each corner atom is shared among eight unit cells, whereas a face

centered atom belongs to only two. Therefore, one eight of each of the eight corner atoms and one half of each of the six face atoms, or a total of four whole atoms, may be assigned to a given unit cell. This is depicted in fig. 1.1a, where only sphere portions are represented within the confines of the cube. The cell comprises the volume of the cube, which is generated from the centers of the corners atoms as shown in fig. 1.1b

3. Body- centered cubic crystal structure Another common metallic crystal structure also has a cubic unit cell with atoms located at eight

corners and a single atom at the cube center. This is called a body centered cubic (BCC) crystal structure. A collection of spheres depicting this crystal structure is shown in Fig. 1.2a, whereas Figures 1.2b is diagrams of BCC unit cell with the atoms represented by hard sphere and reduced models, respectively. Center and corner atoms touch one another along cube diagonals, and unit cell length a and atomic radius R are related through

a = 4R/ 3

Figure 1.2a Figure 1.2b

Chromium, iron, tungsten, as well as several other metals listed in Table 1.1 exhibit a BCC

structure. Two atoms are associated with each BCC unit cell: the equivalent of one atom from the eight

corners, each of which is shared among eight unit cells, and the single center atom, which is wholly contained within its cell. in addition, corner and center atom positions are equivalent. The coordination no. for the BCC crystal structure is 8; each center atom has as nearest neighbors its eight corner atoms. Since the coordination no. is less for BCC than FCC, so also is the atomic packing factor for BCC lower 0.68 versus 0.74.

4. Hexagonal closed - packed crystal structure Not all metals have unit cells with cubic symmetry; the final common metallic crystal structure

to be discussed has a unit cell that is hexagonal. Fig 1.3a shows a reduced sphere unit cell for this structure, which is termed hexagonal close- packed (HCP); an assemblage of several HCP unit cells is presented in Fig. 1.3b the top and bottom faces of unit cell consist of six atoms that


form regular hexagons and surround a single atom in the center. Another plane that provides three additional atoms to the unit cell is situated between the top and bottom planes. The atoms in this midplane have as nearest neighbor atoms in both of the adjacent two planes. The equivalent of six atoms is contained in each unit cell; one sixth of each of the 12 top and bottom face corner atoms, one half of each of the 2 center face atoms, and all the 3 midplane interior atoms.

Figure 1.3a Figure 1.3b The coordination no. and the atomic packing factor for the HCP crystal are the same as for

FCC: 12 and 0.74 respectively. The HCP metals include cadmium, magnesium, titanium, and zinc; some of these are listed in Table 1.1.

Table 1.1

5. Crystal systems Since there are many different possible crystal structures, it is sometimes convenient to divide

them into groups according to unit cell configurations and / or atomic arrangements. One such scheme is based on the unit cell geometry, that is, the shape of the appropriate unit cell parallelepiped without regard to the atomic positions in the cell. Within this frame work, an x, y, z, coordinate system is established with its origin at one of the unit cell corners; each of the x, y, and z axes coincides with one of the three parallelepiped edges a, b, and c, and the three interaxial angles , , and . These are indicated in Fig. 1.4, and are sometimes termed the lattice parameters of a crystal structure.


Figure 1.4

On this basis there are found crystals having seven different possible combinations of a, b, and c, and , , and, each of which represents a distinct crystal system. These seven crystal systems are shown in Table 1.2.

Table 1.2


Questions Q.1 What is the difference between atomic structure and crystal structure? Ans. Q.2 What is the difference between crystal structure and a crystal system? Ans. Q.3 Explain why the properties of crystalline materials are most often isotropic? Ans.


Q.4 Define following terms i) Body centered cubic structure. ii) Face centered cubic structure. iii) Hexagonal closed packed structure. Q.5 Give the name of various crystal systems? Ans.


Q.6 Give the examples of BCC, FCC, and HCP?



Object Study of metalurgical microscope and specimen polishing machine 1. To understand the construction and working of a metallurgical microscope. 2. To understand the construction and working of a specimen polishing machine.

Equipment required An optical microscope, a specimen polishing machine, specimens

Theory 1. Metallurgical microscope A metallurgical microscope is used to reveal the details of a metallic material composed of tiny

particles to be seen normally with unaided eye. Since the visible radiation cannot penetrate even a very thin film (metallic specimen) the study of structure with this microscope is carried out by using reflected light.

2. Specimen Polishing machine I t is used after rough polishing of the specimen over fine emery papers. Polishing is necessary

to ensure a perfectly flat specimen surface without any scratches. A shiny mirror like surface is required after polishing the specimen so as to get proper microstructure.

Constructional details & operation 1. Metallurgical microscope The constructional features of simple microscope are shown in fig.1.It consists of a body tube

which carries an objectives turret below and an eyepiece above , with a plane glass vertical illuminator above objective. The incident light from a source encased in the illuminator tube attached to a body tube at right angles to it strikes the plane glass at 45. Part of this light is reflected down on to the specimen through one of the objectives arranged in line with the body tube. The rays are returned by reflection passing to eye again through objective, plane glass and eye piece. The arm supporting the body tube carries at the upper portion a coarse adjustment , consisting of a rack & pinion device and a fine adjustment to facilitate final focussing of an object. These adjustments operate on the body tube which contains a draw tube by means of which distance between eyepiece and object can be varied.

The important parts of a metallurgical microscope are described here-


Figure 2.1 Microscope

2. Objective It is a combination of lens nearest to the specimen. The objective makes a primary real image of

object. In microscope under study four objectives lens of magnifying power as 5x, 10x, 45x and 100x are attached to an objective lens turret. This turret can be rotated for desired magnification.

3. Eyepiece Eyepiece is so called because it is nearest to eye. A removable eyepiece is fitted to an

adjustable draw tube. The two eyepieces available are marked 10x and 15x.

3. Illuminator Its function is to light up the surface of the specimen under examination. It has a light source an

operator diaphragm (iris) and a plane glass reflector. A horizontal beam of light from light source is reflected downwards by the plane reflector and through the objective piece on surface of the specimen. A certain amount of this incident light is reflected from the specimen surface which passes through the objective and the eyepiece. The aperture diaphragm (iris) controls the angular aperture of the cone of light rays which is used to illuminate the specimen and form the image. The optimum opening of the diaphragm depends on the objective lens being used.


Figure 2.2 Metallurgical Microscope

4. Magnification It is the ratio of image size to the object size. In metallurgical microscope , a magnification

1500 ( written as 1500x ) is practical upper limit .The magnification of a microscope is the product of the objective and eyepiece magnification.

Specimen Polishing Machine Figure below shows the schematic arrangement of machine. It is used after rough polishing of the specimen over fine emery papers. Polishing is necessary to ensure a perfectly flat specimen surface without any scratches. A shiny mirror like surface is required after polishing the specimen so as to get proper microstructure. This machine consists of a cast iron disc mounted at end of a vertical shaft. The shaft is driven by an electric motor through pulley and belt arrangement. The RPM of disc available are 900.A fine cloth is stretch over the top surface of the disc and is held in position with the help of a ring clamp. When in working, a fine abrasive powder suspended in water is applied to cloth on revolving disc. The cloth is kept supplied with suspension from a cylindrical container held above the disc. Alternatively an abrasive paste may be frequently applied to the cloth on the disc while supply of water may be regulated by the cylindrical container to the disc. A pvc tube brings the liquid from the cylindrical container, regulated by a cork, to the top surface of the disc. While polishing the specimen is held firmly in hand with a gentle pressure against the cloth on the revolving disc. This is maintained so far a period as will permit mirror like finish on the surface of specimen. Thereafter specimen is washed with water and cleaned dry with alcohol. Care is taken not to touch the polished


surface with fingers, otherwise finger prints may be produced on that surface requiring repolishing of the surface.

Procedure 1. Use of lowest power objective is initially made for focussing the specimen. 2. The coarse focussing control is used to lower the body tube until the low power objective is

about 5mm above the specimen. 3. Looking through the eyepiece specimen is brought into appropriate focus by raising the

objective with the help of coarse adjustment. 4. Look carefully on whole surface of specimen by moving it under the objective over the stage

and select the areas which warrant more complete study at higher magnification. 5. Raise the body tube and bring the high power objective piece into place. 6. Watch the microscope tube carefully from the side of the stage and bring the objective very

close to specimen. Be careful that the objective lens does not touch the specimen at any time otherwise scratches may be produced on the lens damaging it permanently.

7. Bring the specimen into sharp focus by raising the body tube with only fine adjustment.


Questions Q.1 What is the importance of polishing? Ans. Q.2 Give different types of polishing? Ans. Q.3 Give names of different types polishing pastes? Ans.


Q.4 Give names of different parts of metallurgical microscope? Ans. Q.5 What is etching and what is its importance? Ans. Q.6 What are the etchants used in etching process? Ans.



Object Study of Heat treatment Furnace and Thermocouple Pyrometer

To understand the construction and working of a heat treatment furnace and thermocouple pyrometer.

Equipment Required An electrically heated muffle type heat treatment furnace and a thermocouple pyrometer.

Theory 1. Heat treatment furnace A muffle furnace is so constructed that it provides a chamber known as muffle, separate from

the heating element chamber of furnace, in to which metal piece to be heated is placed. An electrically heated muffle furnace used in laboratory purpose. The muffle, made of Fire clay is provided with a door at front opening. The door can be operated with a steel strip and job to be heated can be loaded in to muffle of furnace. The door can be turned back to its close position. In the center of door, there is a peep hole covered by a swing type lid. By turning away the lid inside of furnace can be viewed. The furnace has asbestos lining between its outer steel casing and fire brick walls, so as to minimize the loss of heat from the furnace to its surroundings. The temperature of the furnace is indicated by a thermocouple pyrometer. The temperature can be read on the indicating dial of this pyrometer fitted on the top of the rear of the furnace. It can read up to 990C when furnace is working. At its front near its bottom, the furnace is provided with a knob of temperature controlling device. The pointer on the knob moves on a circular scale when the knob is turned. The temperature required to be attained by the furnace, for particular heat treatment operation, can be set by moving knob pointer to the particular marking on the circular scale. Near the temperature control knob there are two indicating lights one on each side of knob. One of this light is green and other is red. The green light is meant to indicate the coming of electric supply. The red light glows when set temperature has actually been attained inside the muffle.

Figure 3.1 Muffle Furnace


2. Thermocouple pyrometer It is a temperature measuring Instrument that is being widely used these days for determining

temperature in many modern furnaces. Figure indicates the construction and working of the thermocouple pyrometer. The instrument makes use of the principle of thermo-electric effect. Two wires of dissimilar metal are twisted together at one end and a circuit is completed by connecting the other ends to a sensitive voltmeter. Then, due to thermoelectric effect, an e.m.f. is induced if the twisted end is heated. The voltmeter scale is calibrated in terms of temperature of the heated end. The twisted end is called Hot Junction. The ends connected to sensitive voltmeter, which remains at room temperature, are known as cold junction. The amount of current flowing in the circuit depends on the difference of temperature between the these junctions and type of metal wire used. Slight variations in cold junction temperature are not of much importance when the instrument is used for measurement of temperature of the furnaces. The hot junction is enclosed in a protective sheath, which is a porcelain tube. The two metal wires are insulated from each other for rest of the length except for the joints. The hot junction along with its protective sheath is placed inside the furnace through the hole for the measurement of temperature while the temperature indicating unit (cold junction)is securely placed on the outside of the furnace. Leads take the connection from the thermocouple wires to the indicating units terminals, acting as cold junction, Some useful wire combinations for this instruments are

Thermocouple Composition ( % ) Temperature Range Copper- constantan Cu=55 , Ni = 45 Up to 300C

Iron -Constantan Ni=60, Cr= 15, Mn= 2 , Fe=rest

Up to 750 C

Chromel - Alumel Ni =94.5, Mn= 2.5, Al=2,Si=1 Up to 1200C Platinum-Platinum/rhodium - Upto 1450C

Questions Q.1 What Do you Mean by Muffle Furnace? Ans.


Q.2 Explain the constructional detail of Furnaces? Ans. Q.3 What is the function of pyrometer? Ans. Q.4 What type of pyrometer you have studied? Ans.



Object Study of crystal imperfection.

Equipment required Charts of crystal imperfection.

Theory As we know crystals posses long range order and unit cell is a module that repeated identically. But the world is not perfect. Crystals sometimes contain atoms that are in wrong place or there may be missing atoms or foreign atoms.

In many situations, we can use these irregularities advantageously to develop useful and desired properties. For example one boron atom among 100 billion unit cells of silicon doubles the conductivity of otherwise pure silicon.

The imperfections are classified as -

Structural: a) Point, b) Boundaries, c) Linear, d) 3-D Compositional: a) Substitutional, b) Interstitial

Constructional Details Structional imperfections 1a) Point defect: When imperfections such as atoms vacancies involve the absence of one or a few atoms, we call them point defect. Such defects can be a result of imperfect packing during the original crystallization, or they may be arising from thermal vibrations of the atoms at elevated temperature.

Figure 4.1 Figure 4.2


1b) Dislocations- Line defects: A dislocation is a linear or one dimensional defect around which some of the atoms are misaligned. One type of dislocation is represented in Fig. 4.3 an extra portion of a plane of atoms, or half plane, the edge of which terminates within the crystal. This is termed as edge dislocation; it is linear defect that centers around the line that is defined along the end of the extra half- plane of atoms. This is sometimes termed the dislocation line, which, for the edge dislocation in fig.4.3, is perpendicular to the plane of the page. Within the region around the dislocation line there is some localized lattice distortion.

Figure 4.3

The atoms above the dislocation line in fig. 4.3 are squeezed together, and those below are pulled apart; this is reflected in the slight curvature for the vertical planes of atoms as they bend around this extra half- plane. The magnitude of this distortion decreases with distance away from the dislocation line ; at positions far removed , the crystal lattice is virtually perfect. Sometimes the edge dislocation in fig. 4.3 is represented by the symbol , which also indicates the position of the dislocation line. An edge dislocation line may also be formed by an extra half plane of atoms that is included in the bottom portion the crystal; its designation is a.

Another type of dislocation, called a screw dislocation, exists, which may be thought of as being formed by a shear stress that is applied to produce the distortion shown in fig. 4.4a: the upper front region of the crystal is shifted one atomic distance to the right relative to the bottom portion. The atomic distortion associated with a screw dislocation is also linear and also along a dislocation line, line AB in fig. 4.4b.

Figure 4.4a


Figure 4.4b

Most dislocations found in crystalline materials are probably neither pure edge nor pure screw, but exhibit components of both types; these are termed mixed dislocations.

1c) Interfacial defects: Interfacial defects are boundaries that have two dimensions and normally separate regions of the materials that have different crystal structures and / or crystallographic orientations. These imperfections include external surfaces, grain boundaries, twin boundaries, stacking faults, and phase boundaries.

1d) External surfaces: One of the most obvious boundaries is the external surface, along which the crystal structure terminates. Surface atoms are not bonded to to the maximum no. of nearest neighbors, and are therefore in high energy state than the atoms at interior positions. The bonds of these surface atoms that are not satisfied give rise a surface energy, expressed in units of energy per unit area (J/ m2). To reduce this energy, materials tend to minimize, if at all possible, the total surface area.

1e) Grain boundaries: Another interfacial defect, the grain boundary the boundary separating two small grains or crystals having different crystallographic orientations in polycrystalline materials. A grain boundary is represented schematically from an atomic perspective in fig. 4.5. Within the boundary region, which is probably just several atom distances wide, there is some atom is mismatch in a transition from the crystalline orientation of one grain to that of an adjacent one.

Figure 4.5


Various degrees of crystallographic misalignment between adjacent grains are possible (fig.4.5). When this orientation mismatch is slight, on the order of a few degrees, then the term smallangle grain boundary is used. These boundaries can be described in terms of dislocation arrays. One simple smallangle grain boundary is formed when edge dislocations are aligned in the manner of fig. 4.6. This type is called a tilt boundary; the angle of misorientation is also indicated in fig. 4.6. When the angle of misorientation is parallel to the boundary, a twist boundary results, which can be described by an array of screw dislocations.

Figure 4.6

Twin boundaries A twin boundary is a special type of grain boundary across which there is a specific mirror lattice geometry ; that is , atoms one side of the boundary are located in mirror image positions of the atoms on the other side ( fig. 4.7 ) .The region of material between these boundaries is appropriately termed as a twin. Twins result from atomic displacements that are produced from applied mechanical shear forces (mechanical twins), and also during annealing heat treatments following deformation (annealing twins).

Figure 4.7

Twinning occurs on a definite crystallographic plane and in a specific direction, both of which depend on a crystal structure. Annealing twins are typically found in metals that have the FCC crystal structure, while mechanical twins are found in BCC and HCP metals.


Questions Q.1 Give names of different types of defects found in crystals? Ans. Q.2 What are point defects? Give their types also? Ans. Q.3 Define dislocations? Give their types also? Ans.


Q.4 Define following terms- 1. Dislocation line. 2. Edge dislocation. 3. Line dislocation. 4. Vacancy 5. Divacancy 6. Schottky defect 7. Frenkel defect



Object Micro structural Examination of Heat Treated Specimen

To prepare specimens of heat treated steel for micro analysis and study their microstructure.

Equipment Required 1. Specimens of the steel being heat treated (annealed, normalized, hardened tempered) 2. Specimen cutting machine 3. A set of fine emery papers no. 100, 150, 320,400,600 4. Flat glass plates 5. Fine polishing powder or paste of diamond dust, alumina, chromic oxide or magnesia,etc. 6. Glass slides 7. Plasticizer or any other suitable fixing cement 8. Echants: a) Natal 2 % nitric acid conc. In absolute methyl or ethyl alcohol for etching

annealed or normalized steel b) 10 % solution of HCl in alcohol etching hardened steel. 9. Porcelain dish for echants 10. Distilled water 11. Ethyl alcohol or methyl alcohol

Theory Microscopic examination is the study of microstructure of materials under a microscope at large magnification. The structure so observed is called microstructure definite thorough only qualitative relationship exists between the structure of a metal observed in an optical microscope and certain properties of metal. In microanalysis shows that the variations in alloy properties are due to variations in chemical compositions and conditions of treatment. The application of white light in optical microscope allows the structure of metals to be observed at general magnification of a few 10 to 2000- 3000. The useful magnification , however cannot exceed 1500 because of light diffraction with such a magnification , it is possible to detect element of structure not less than 0.2 m in size , which is in most cases sufficient for determination of the size of the majority of phase present in alloy. Thus the method of microscope can be used with success for observation of structure of many metallic alloys.

Polishing of specimen surface for microscopic study is done to prepare a smooth , deformation or distortion free surface for giving a clear two dimensional view of the microstructure present . But the polished surface of a uniform specimen appears bright without any detail under the microscope , it is necessary to impart unlike appearances to the constituents. This is accomplished by selectively corroding or etching the polished surface.


Procedure Preparation of specimen for examination The surface of the specimen to be examined requires elaborate preparation.

This includes the following steps:

Specimen cutting: Specimen of a size which can be handed is first obtained by cutting. This operation is finely accomplished with the help of an abrasive wheel of a specimen cutting machine. The cutting should proceed at such a speed and with the use of coolant that the original condition of material is not changed.

Preliminary polishing: With the help of preliminary polishing the deformation caused by grinding while cutting specimen has to be completely removed. For this purpose, the specimen surface has to be polished on progressively finer dry or wet emery papers. This paper is placed on a flat board or glass plate. The polishing is done by the movement of the specimen on the emery paper in one direction only. In changing to the next fine paper, the direction of polishing is kept at right angles to the previous one. The polishing is carried out to next when polish marks introduced by the previous papers just disappears. The specimen is then cleaned in water and alcohol and is to be given final polishing.

Final polishing: The specimen has given final polishing on the revolving disc of a polishing machine. The disc is revolving at high speed is covered with sylvet, broad cloth chiffon or pure silk cloth , holding in suspension in water a fine grade of powder or paste. The surface of the specimen to be polished is held gently against this revolving cloth. The specimen after polishing on the revolving disc should be free from all scratches and should present the appearance of a polished mirror.

Etching: The finally polished specimen is then thoroughly washed with water and dried with alcohol. The specimen, with its polished surface upwards, is immersed in etching solution contained in a small porcelain disc. The specimen surface should be watched from time to time and the specimen is removed from the etchant when its grain structure is just visible to the unaided eye, of course it requires some practice then the etched specimen is thoroughly washed with water and dried with alcohol.

Microscopic Examination Fix the specimen on a glass slide with plasticine. Then place it on the microscopic stage. Level the etched surface with the help of a leveling device then focus the specimen and note down the microscopic structure of different specimen one by one .

Precautions 1. While cutting the specimen for microstructure study the speed of cutting and coolants supply

should be such as to avoid any change in original condition of material. 2. For preliminary polishing, the emery paper should place on a flat board or glass plate. 3. For preliminary polishing, the direction of polishing of the specimen is kept at right angle to the

previous one. The polishing is carried out to next paper when polish marks introduced by previous one disappear.

4. Never touch the polished surface to avoid appearing of finger prints on it. Otherwise re-polishing is required.

5. While polishing hold the specimen firmly in hand and do not allow it to revolve in the hand.


6. While performing final polish on the specimen, applied polishing paste suspension frequently to the cloth on the revolving disc. Keep the cloth wet through controlled supply of water on it, when using the paste.

7. Make use of cleaned distilled water for various operation involved in the experiment. 8. Avoid scratches in the microscopic lenses. 9. Keep polishing surfaces and microscope properly covered after use.

Questions Q.1 What do you understand by microstructure analysis? Ans. Q.2 What is importance of rough polishing and final polishing? Ans.


Q.3 Which etchant is used in etching process? Ans. Q.4 What is importance of microscopic examination? Ans.



Object To perform the following heat treatment processes of steel specimen.

1) Hardening 2) Annealing 3) Normalizing 4) Tempering

Material and Equipment Electrically heated muffle furnace complete with temperature control and thermocouple pyrometer, three specimen of steels(rod about 25mm dia. say 0.6% carbon), quenching bath of brine (with 10% sodium chloride in water), Rockwell hardness tester, a pair of tongs, number punches and a hand hammer, an emery paper, a smooth file and a bench vice.

Theory HEAT Treatments steel may be defined as an operation or combination of operations involving the heating and cooling of a steel piece to some specified temperature and rates in its solid state for the purpose of obtaining certain required structures and properties in it for particular applications.

Hardening It is that heat treatment process which increases the hardness of a steel piece by heating it to a certain high temperature and then cooling it rapidly to room temperature.

Annealing It is that heat treatment process which softens an already hardened steel piece by heating it to a certain high temperature and then by cooling it very slowly to room temperature. This process refines grain structure, softens the steel, improves its mach inability and restores its ductility. It also removes internal stress.

Normalising It is that heat treatment process which mainly removes internal stresses caused and refines grain structure by heating a hardened or cold worked steel to certain high temperature and then cooling it in a still air environment to room temperature. It does not soften the steel to the extent , it is done by annealing and also it does not restore ductility as much as it is done by annealing.

Tempering It is a process of imparting toughness at the cost of its hardness to an already hardened piece of steel by reheating to a certain temperature and then cooling it rapidly. The temperature of heating depends on toughness to be imparted and hardness to be reduced.


Procedure File a 4mm wide flat along some length of the specimens and punch over them numbers 1, 2, 3 respectively. Measure the Rockwell cone hardness number of each of the specimen and record it in the observation chart, drawn on left hand page of the note book. Take at least three readings of hardness on each specimen to facilitate calculation of satisfactory average value.

Hardening Consult the iron carbon equilibrium diagram as shown in

Figure 6.1

Figure 6.1 for 0.6% carbon steel (i.e. steel specimen and note its upper critical temperature which is about 750 C. Adding 50 C to this temperature, gives temperature 800 C to which this specimen is to heated for hardening, annealing and normalizing. Therefore set the furnace to a temperature of 800C and switch it on. Load the specimen in the furnace. After the furnace reaches the set temperature of 800C along the specimens, let the specimens remain at that temperature for about 10 minutes. Then take the specimens out from the furnace one by one by gripping firmly by a pair of tongs and quench them in the brine. The quenching should be endwise to the length of rod specimens and the specimen should be stirred well in brine while held in tongs. After quenching all the specimens, take them out from the brine, wipe them dry with cloth and rub off the scale by means of an abrasive paper. Measure again their Rockwell cone hardness at three different places on them and record their respective readings in the observation chart. Find out the average value of hardness of these reading.


Figure 6.2 T-T-T Diagram for various cooling rate

Annealing Now for annealing the specimen marked 1 , put it into the furnace at 800C (as shown in 6.3) and let it attain that temperature. Then hold it at that temperature for a further period of 35 minutes (i.e. about 3 min for each mm of the section thickness from center of section to outside) . Therefore take out the specimen by means of a pair of dry tongs and bury it in a heap of ashes so that it cools down at a very slow rate. After the specimen has reached the room temperature it is cleaned of scaling on it. Its hardness is measured at three different places on its length and recorded in observation chart and average value is calculated.

Normalising For normalizing the specimen marked 2, put it into the furnace at 830C (as shown in 6.3) and let it attain that temperature. Thereafter allow it to hold at that temperature about another 10 min. Then take out the specimen with help of dry tongs and place it in still air over a fire brick or on dry floor. After its cooling down, remove scaling on its surface with an abrasive paper, its hardness is measured at three different places on its length and recorded in observation chart and average value is calculated.


Figure 6.3

Tempering For tempering at 300C the hardened steel specimen marked 3, first polish the surface of specimen with the help of an emery paper. After the surface reaches this temperature, load the specimen in it. Observe the color of the specimen surface. As soon as the color of oxide scaling appears on the specimen surface (indicating a temperature of 300C) remove it from the furnace with help of tongs and quench it in the brine bath. Take out the specimen from the brine as it cools down, wipe its surface dry with cloth and clean it . Then test its hardness is measured at three different places on its length and recorded in observation chart and average value is calculated.

Calculations Specimen No. Rockwell Hardness

No. Before Heat Treament

Process Rockwell After Heat Treament

1 Hardening 2 Hardening 3 Hardening

Hardened

Specimen No. Rockwell Hardness

No. Before Heat Treament

Process Rockwell After Heat Treament

1 Annealing 2 Normalising 3 Tempering

(AT 300C )


Precautions 1. Avoid overheating of specimens. 2. Always use dry pair of tongs while taking out or loading specimens in the furnace. 3. To avoid distortion of specimen to possible extent, quench them endwise to their length. 4. Test the hardness of specimen after cleaning it. 5. Be careful that the hardness should be taken at three places on the surface of specimen and

these places should not be close to each other.

Questions Q.1 Define Heat Treatment Process. Ans. Q.2 Write the procedure and effect of following Heat Treatment Processes. 1. Annealing 2. Normalizing 3. Hardening 4. Tempering



Object Study the chemical corrosion and its protection.

Equipment Required Charts and models.

Theory Corrosion Corrosion is the process of surface deterioration of metals and related materials. Figure shows the corrosion reaction schematically. The two reactions (oxidation and reduction) may proceed adjacently or separately but must occur simultaneously. Corrosion may stop if

1. The electrical connection is disturbed 2. The cathode reactants are depleted. 3. The anode products are saturated.

Anode reaction All metals are subjected to the oxidation reaction by different extents. For example Zinc and Copper Zn Zn 2+ + 2 e - _________ (1) Cu Cu 2+ + 2 e - _________ (2)

Both released electrons are lead to an electrical potential, the value of which cannot be measured in isolation. However a standard voltage difference between the two reactions can be measured when the metals are in 1 molar solution of their own salts at 25 C (shown in fig.). In an open circuit, that voltage difference is 1.1V. If electrical contact is made, the voltage difference is removed because electrons move from zinc to copper (the current is in opposite direction). Thus reaction (1) proceeds with zinc becoming anode. Reaction (2) is reversed and copper atoms are reduced from the1 molar solution of Cu 2+ ions, Zinc is corroded at the anode: Copper is plated onto the cathode.


Figure 7.1: Electrochemical reactions associated with Corrosion of Zinc in an acid solution

The anode supplies electrons to the external circuit, conversely the cathode receives electrons from the external circuit. This definition is appropriate for corrosion, batteries, electroplating, cathode- ray tubes, and all other electronic devices in which the current flows. All corrosion occurs at the anode. (Electroplating on to the cathode is corrosion in reverse)

The voltage differences could be measured between all possible pairs of metals in the manner just described. However the most common practice is to use the

H2 2 H+ + 2e -

as the reference reaction for another anode reactions, as shown in figure, iron is more reactive (more anodic) than is hydrogen to the extent that the potential difference is 0.44 V. The equations of the table are for anodic reactions, are all called half cell reaction. As we noted, the standard electrode potential of table require an electrolyte i.e. a 1 molar solution (250C). The actual potential varies with concentration and temperature according to NERNST RELATIONSHIP as

= 298 + (KT / n) (In C) (3)

Where 298 is the standard electrode potential at 298 K (250C) as, listed in the table.


Figure 7.2: Standard Hydrogen reference half -cell Concentration C is expressed as moles per liter (i.e. molar). Since the constant K is 86.1 X 10-6 ev / K, equation (3) can be condensed to

= 298 + (0.0257 / n) (In C) (4)

Where n = no. of electrons released

Cathode Reaction The electron released from anode can be consumed in other than copper reaction, as follows (Electroplating) Mm+ + me- M0 (Hydrogen evolution) 2H+ + 2 e - H2 (Hydrogen formation) O2 + 2H2O + 4 e - 4 (OH-) (Water formation) O2 + 4H+ + 4 e - 2H2O Each of these cathode half cells reactions consumes electrons; each is the reverse of one of the anode half cell reactions in table. We readily see the corrosion product when iron corrodes and OH- ions are formed because the iron ions combine with the OH- ions to produce Fe (OH) 3 which is ordinary red iron rust.

Hydrogen Gas, 1 atmospherics Pressure


Table 7.1: The Standard emf Series

Galvanic Corrosion Cells we can categorize corrosion couples called galvanic cells, in three separate groups 1. Composition cells 2. Stress cells 3. Concentration cells

Composition Cells It may be established between any two dissimilar metals. In each case the metal lower in the electromotive series, as listed in table, acts as a anode. For example on a sheet of galvanized steel, the zinc coating acts as an anode and protects the underlying iron if the surface is not completely covered because the exposed iron is the cathode and does not corrode. Conversely, a tin coating on sheet iron or steel provides protection only for as long as the surface of steel is completely covered. If the surface coating is punctured, the tin becomes the cathode w.r.t. iron which acts as the anode. The galvanic couple that results produces corrosion of the iron. Very localized corrosion can result. Other examples of galvanic couples are

1. Steel screws in brass marine hardware 2. Pb-Sn solder around copper wire 3. A steel propelled shaft in bronze bearing

Stress Cells They dont involve compositional difference, rather they involve dislocations, grain boundaries, and highly stressed regions.


Concentration Cells They arise from the differences in electrolyte compositions. According to NERNST equation, an electrode in a dilute electrolyte is anodic w.r.t. a similar electrode in a concentrated electrolyte. As given by the following equation.

Cu Cu 2+ + 2 e -

The concentration cell accentuates corrosion, but it does so where the concentration of the electrolyte is lower. Oxidation type concentration cells are more important. When oxygen in the air has access to a moist metal surface, corrosion is promoted. However the most marked corrosion occurs in the part of the cell with an oxygen deficiency. Corrosion may be accelerated in apparently inaccessible place such as cracks or crevices and under accumulations of dirt or other surface contamination because these oxygen deficient areas serve as anodes.

Figure 7.3: Corrosion between two riveted Sheets


Corrosion Control We can minimize corrosion by isolating the metal surface from its environment. A layer of paint, a nickel-plated surface, and a vitreous enamel coating separate the metal from the electrolyte. Examples are shown in fig.4 Corrosion can be restricted if galvanic couples are avoided.

The unlike metals, which of course have different electrode potentials, may be insulated from each other.

Figure 7 .4: galvanic protection of steel as provided by a coating of Zinc

Galvanic Protection We can achieve service protection against corrosion in some applications by arranging for the product to be cathode, like in galvanized steel. Several adaptations of these Sacrificial Anoded are shown in fig. They can be replaced after the anode has been spent.

Figure 7.5 Cathodic protection of a) an underground pipeline using a magnesium sacrificial anode and

(b) an underground tank using an impressed current


Questions Q.1 Define corrosion? Give name of different types of corrosion? Ans. Q.2 What are the different causes of corrosion? Ans.


Q.3 How corrosion can be protected? Given name of different methods to control corrosion? Ans. Q.4 Define stress cells, concentration cells, composition cells? Ans.



Object To study creep behavior of materials.

Equipment Required Specimen, creep testing machine, scale.

Theory A typical creep test consists of subjecting a specimen to a constant load or stress while maintaining the temperature constant; deformation or strain is measured and plotted as a function of elapsed time. Most tests are constant load type , which yield information of an engineering nature ; constant stress tests are employed to provide a better understanding of the mechanisms of creep.

Fig. 8.1 is a schematic representation of the typical constant load creep behavior of metals. Upon application of load there is an instantaneous deformation, as indicated in the fig, , which is mostly elastic. The resulting creep curve consists of three regions, each of which has its own distinctive strain time feature. Primary or transient creep occurs first, typied by a continuously decreasing creep rate; that is, the slope of curve

Figure 8.1

diminishes with time .This suggests that the material is experiencing an increase in creep resistance or strain hardening- deformation becomes more difficult as the material is strained. For secondary creep, sometimes termed steady- state creep, the rate is constant; that is, the plot becomes linear. This is often the stage of creep that is of the longest duration. The constancy of the creep rate is explained on the basis of a balance between the competing processes of strain hardening and recovery, recovery being the process whereby a material becomes softer and retains its ability to experience deformation.


Finally, for tertiary creep, there is an acceleration of the rate and ultimate failure. This failure is frequently termed rupture and results from micro structural and / or metallurgical changes; for example, grain boundary separation ,and the formation of internal cracks, cavities, and voids.

For metallic materials most creep tests are conducted in uniaxial tension using a specimen having the same geometry as for tensile tests. On the other hand, uniaxial compression tests are more appropriate for brittle materials; these provide a better measure of the intrinsic creep properties inasmuch as there is no stress amplification and crack propagation, as with tensile loads. Compressive tests specimens are usually right cylinders or parallelepipeds having length- to- diameter ratios ranging from about 2 to 4 . For most materials creep properties are virtually independent of loading direction but depends on stress and temperature as shown in figure 8.2

Figure 8.2

Questions Q.1 What do you mean by Creep? Ans.


Q.2 Explain the working of material during three different phases of creep Ans. Q.3 What is the effect of increasing / decreasing stress/ or Temperature on the Creep behavior of

Materials. Ans. Q.4 Cite some Real world Example, where Creep play a significant Role Ans.



Object To study the various types of plastics and their properties.

Equipment Required Models, Charts and Tables

Theory Plastics are mould able organic resins. They are formed in plastic state either during or after their transition from a low molecular weight with chemical to a high molecular weight solid material .Some of their important properties are :

1. Good toughness 2. Light in weight and posses good strength and rigidity 3. Resistant corrosion and action of chemicals 4. Posses property of low moisture absorption 5. Heat resistance, colorbility, weather ability, etc.

Constructional Details The main types of plastics 1. Thermosetting Resins

Figure 9.1. Cross linked and Network Molecular structures.

2. Thermoplastic , amorphous 3. Thermoplastic, crystallites


Figure 2. Schematic representation of mer and chain structures.

The properties of various types of plastics are given in table:


TABLE 9.1

Questions Q.1 Define Plastics Ans.


Q.2 What is differences between Themoplastics and thermo setting materials? Ans. Q.3 Name few examples of thermoplastic and thermo setting materials. Ans. Q.4 What do you mean by degree of crystalline in plastics. Ans. Q.5 What do you mean by Network polymer? Ans.



Object To study thermosetting plastics.

Equipment Required Specimen, creep testing machine, scale

Theory Thermosetting plastics, once their shape has been made by casting or by plastic flow at elevated temperature, will no longer melt or flow on reheating. Polymerization has occurred by strong network bonds (cross linking) produced by catalysis or by the application of heat or pressure and these strong bonds keep the material from remelting when reheating is attempted. This material will char burn or in some cases sublime, thermosetting material cannot be recycled.

Thermosetting plastics have a structure that is characterized by three-dimensional network of molecules. The thermosetting materials usually require more expensive fabrication process. From the property standpoint thermosetting plastics are usually more brittle than thermosetting plastics. They are generally rigid. Most thermosetting are harder than thermoplastics materials, and they are usually not used without some type of reinforcement or filler.

Constructional Details The main families are- 1. Phenolics 2. Unsaturated polyesters 3. Urea

Pnenolics These are the oldest families of thermosetting plastics, dating back to the 1870. This family of polymers is based on the presence of a ring structure alcohol, phenol, with the following formula.

Various processes obtain based polymers the starting material for phenolic, but mostly it comes from petroleum distillates (benzene and propylene). Phenolic moulding and laminating resins formed by the reaction of phenol with formaldehyde (CH2O), contain the following monomer. These monomers form a rigid network structure, which in turn forms a hard rigid plastic. The first commercial PF polymers were introduced in the early part of this century under the trade name BAKELLITE, widely used for compression moulded electrical parts such as switches, distributor caps, and the like, because these have good electrical properties, low moisture absorption, and relatively high use temperature (about 204 C). The major fault of this family of thermosetting plastics is that they are relatively brittle.


Phenolics represent the largest tonnage of thermosetting resins. The high usage comes from applications that are not visible to the casual observer. They are used in

1. Adhesives in plywood 2. Adhesives for fiber glass insulation 3. Binders for brake and clutch friction material 4. Electrical circuit boards 5. Electrical outlets, switches, boxes, etc. 6. Binders in foundry cores

Urea Formaldehyde (UF) They are used for electrical devices, circuit breakers, switches, and the like. Technical applications include use as additives to papers and for construction adhesives.

The urea do not have the U.V. resistance hence they cannot be used outdoors. They are lower in cost.

Unsaturated Polyesters (UP) The term polyester is analogous to the term steel in metals. Some of the cellulosics are polyesters. They are of two groups in this category.

1. The thermosetting resins 2. The thermoplastic polyesters


Esters are the reaction product of the combination of an organic acid and an alcohol. The most important polyesters from the standpoint of engineering materials are the polyesters resins used as resin matrix reinforced composites.

The general purpose polyester resin used for boats, fishing poles, antos, and the like usually contains an esters produced by the reaction of ethylene glycol (alcohol) and maleic acid. This ester is unsaturated, that is, it is capable of bonding to other polymers because of available bonding sites (at carbon double bonds)

The ethylene glycol maleate polyester is reacted with styrene manomer, and the result is essentially a copolymer. There is a bright future for this family. It is used in boats, recreation and construction as well as in transportation.

Questions Q.1 What do you mean by thermosetting Plastics? Ans. Q.2 What type of bonding makes thermoplastics irreversible for moulding? Ans.


Q.3 List and Explain the main Families of Thermosetting plastics Ans. Q.4 Explain the importance of Phenolic resins. Ans.


Notes/Comments Introduction:

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