Parul Institute of Engineering & Technology, Limda Department of Mechanical Engineering Subject: Material Science & Metallurgy

Transcription

1 Practical No. 01 Types of Engineering Materials To understand types, properties, requirements & selection of materials for engineering application. Within the scope of material science the engineering materials may be classified into the metals, ceramics polymer & composites Metals: metals are elements substances that readily give up electrons to form metallic bonds and conduct electricity. When two more metals are melted together to form a new metals whose properties are quite different from those of the original metals it is called alloy. Metals possess specific properties like plasticity, strength, luster, hardness, malleability, stiffness. Ceramics: These are materials consisting of phases. A phase is physically separated and chemically homogeneous constituent of materials.ceramics are compounds of metallic and non metallic elements.common ceramics are rocks, minerals glass, fireclay & abrasives Polymer: These materials are carbon compounds. These usually consists of carbon chemically combined with hydrogen, oxygen or other non metallic substance they are solids composed of long molecular chains. Plastics PVC, PTEE are main example of polymer. THEORY: Material property is a qualitative or quantitative measure of response of materials to externally imposed conditions like force and temperature. Some important properties are physical, mechanical, electrical, thermal, magnetic, optical k7 technologically properties. To selection of materials for main criteria is properties of materials, performance requirement.material reliability, safety, disposability and recycling and reuse of materials, processing of materials, economical factor.. 1) Define material sciences & metallurgy, 2) Explain the classification of engineering materials. 3) Explain requirement of engineering materials. 4) Explain different properties of materials in brief 5) Enlist criteria for selection of materials for engineering applications with examples 1) Introduction to materials science& metallurgy: Dr.G.H.Upadhyay 2) materials science& metallurgy: O. P. Khanna

2 Practical No. 02 Study of Metallurgical Microscope To be acquainted with the Operation, Construction, application and capabilities of a Metallurgical Microscope. The Metallurgical Microscope is one of the important tools for Metallurgist. It helps revealing the microstructure of the materials in details, which in turn will help Metallurgist to analyze the properties and behavior of the material under study. Biological Microscope differs from Metallurgical one in a way that the later employs reflection of light for illumination compared to former which uses transmission of light for the same. Metallurgical Microscope has two distinct optical systems, namely, Objective and Eyepiece. Combination of both of these will render the magnified virtual image of the same under observation. For effective handling of the Microscope, it is essential that the Metallurgists should know the working principle of the microscope and fundamental terminology related with basic optical systems. PRINCIPLE: A beam of light from appropriate source is incident on to the surface of specimen through the objective. A certain amount of this incident light reflected from the specimen surface and magnified while passing through the objective and the eyepiece and will form enlarged image of the illuminated area. RAY DIAGRAM: Before a horizontal beam of light from some appropriate source is diverted by means of a plane glass reflector, it passes through a condensing lens. This reflected light beam now passes through the objectives and incident on the specimen surface. As the surface of the

3 specimen is polished and it is opaque in nature it reflects most of the light rays. This reflected light once again passes through the objective lens system and forms an enlarged primary real image. The size of primary image depends upon the relative distances at which object and image are existing from the objective. The position of that image beyond the objective depends upon (1) focal length of the objective & (2) the distance between the plane of object and the front focus point of objective. The primary image, formed by the objective in conjunction with the field length of the eyepiece is placed by focusing the microscope such that it is located at the focal point or within focus distance of the lens of the eyepiece. If now entrance pupil of eye is made to coincide with the exit pupil of the eyepiece the eye lens in conjunction with the cornea lens of the eye will form an unreversed and erected second real image on the eye retina. Due to response of human brain to excitation of the retina it will appear to be existing in space at approximately 250mm from the observer. Since this third image has no existence it is known as virtual image and it will appear to be inverted and reversed. When a particular combination of objective and eyepiece is used with proper tube length the total magnification is equal to the product of the magnification of the objective and the eyepiece. (N.B. The above explanation is based on the assumption that the eyepiece being used is of huygenian type. If the eyepiece being used were positive type then the primary image would have been formed solely by the objectives only.) Parts of Metallurgical Microscope 1) Halogen Lamp: It is used as a light source. This light source is especially suitable for color photomicrography. 2) Intensity Variation Knob: Intensity of halogen lamp can be adjust by this knob. 3) Aperture Diaphragm: It is placed in front of the lamp or condenser. Used to control resolving power, contrast and depth of the focus. 4) Filters: They are required to modify the light for optimum visual examination or photomicrography. Green filters are used for observation and blue filters are used for photography. 5) Plane Glass Reflector: Used to divert the horizontal beam of light coming from light source onto the specimen. It also transmits the reflected light from the specimen to eye-piece. 6) Objective: It forms the primary image in conjunction with the field lens of eyepiece. It collects as much light as possible coming any point on the specimen and combines this light to form the image. The Numerical aperture is a measure of the light collection capability of the objective. 7) Stage/Mounting table: It is used to hold the specimen. Separate knob is provided for X-Y movement of the table. 8) Focusing (Fine & Coarse): From these one can move the stage of the microscope up and down in respective type for getting clear image. 9) Eyepiece: It forms the second optical system. They are used to enlarge the primary image formed by the objective. 10) Trinocular Head: This is a part of microscope in which one can attach any system like CCD camera and get image on computer. 11) CCD camera: CCD stands for "Charge Coupled Device". A CCD camera uses the same technology as the popular digital cameras used for everyday photography. They are used to transfer virtual image visible in the eye piece to computer. 12) Frame Grabber Card: A device that lets you capture individual frames out of a video camera or off a video tape.

4 OBJECTIVES: Objectives can be divided into four general groups namely, achromates, semiapochromates, apochromates and monochromates which are special class of objectives to be used with ultra violet light. The distinction between the first three classes is based on the design of objectives and the degree to which optical errors are corrected. OPTICAL ERRORS: Following two errors are observed in uncorrected objective. (1) Chromatic Aberration: This error is due to light. It is the failure of different wave lengths of electromagnetic radiation to come to the same focus after refraction. The index of refraction of a medium, such as optical glass, is greater for shorter wave lengths of visible radiation passing through it. When white light is passed through a simple positive lens from some source outside of its principal focus point, the light will be dispersed and series of color images of the source will be focused at different points along the principal axis of the lens. This type of error is known as longitudinal chromatic aberration. This gives rise to the formation of colored images of unequal sizes. If this type of error exists in objectives then the image will be surrounded by color halo and will lack in definition and clarity. (2) Spherical Aberration: This error is due to optical system. It is the loss of definition in the image arising from the surface geometry of a spherical lens or mirror. When the light of definite wavelength is passed through a simple positive lens from source outside of its principal focus point a series of images of the sources will be formed along the principal axis of lens. The light in passing through outermost margins of lens will be refracted to a greater degree and image formed thereby will be a point closer to the emergent side of lens than the same wavelength of light passing through the lens near the principal axis. But when white light, instead of monochromatic radiation, is passed this error becomes more complex and when combined with other aberrational errors the attending image will appear fuzzy and indistinct. TYPES OF OBJECTIVES: (1) Achromates: They are relatively free from aberrational and other optical errors and of relatively low cost. They are unable to render an image that posses true color. (2) Apochromates: They are finest objectives corrected for high degree of perfection and they have higher numerical aperture and higher magnification. (3) Semiapochromates: For aberrational errors, it is compromise between achromatic and apochromatic objectives. PROPERTIES OF OBJECTIVES: (1) Magnifying power: It is the ability of the objective to magnify the real object a definite number of times without the aid of the eyepiece. (2) Numerical Aperture (NA): It is light gathering ability of the objective. It is because of Numerical Aperture, which for any objective is a function of the design, that fine details in an object may, within limits, be completely and clearly resolved. Resolving power of objective is proportional to NA, wavelength of illumination, microscope adjustments etc. The amount of light received by objective is also influenced by index of refraction of objective and surface of object. In case of dry objectives the medium is air

5 and because of that NA is less for them. If we use wet objectives then in that case the medium used is Cedar Oil hence the NA will be more. NA = n (sin μ) Where μ is half angle of light aperture, n is index of refraction. n = 1 for Air, 1.5 for Cedar Oil (3) Resolving Power: It is described as ability of an objective to produce sharply defined separate images of closely spaced details in an object. It is also called fineness of detail. Fineness of Detail α NA & Fineness of Detail α 1 / λ Where λ is wavelength of light used. (4) Vertical Resolution: It is depth of focus or penetration. It is also called ability to produce sharply focused image when the surface of object is not truly plane. Vertical Resolution α 1 / NA & Vertical Resolution α 1 / Initial Magnification (5) Curvature of image field: It is a condition wherein sharpness of centrally focused image declines towards the outer edge of field of view. For the objectives of higher NA the effect of curvature is more but, by using specific type of eyepiece image can be reduced to flat field. EYEPIECES [OCULAR] : Eyepieces are used to enlarge the primary image formed by the objective and to render it visible as a virtual image, or to produce the primary image as real image, such as in photomicrography. TYPES OF EYEPIECES: (1) Negative types [hygenian]: They are the most representative and simples. When two non-achromatic, plano-convex lens elements are mounted in the eyepiece tube with convex sides of both elements towards the objective will form negative type of eyepiece. Their focus point will lie between two lenses hence we cannot use them as ordinary magnifiers. Image obtained in this case is not completely free from distortion due to lack of optical correction applied. They are used with low and intermediate powered achromates. (2) Positive Types [Ramsden]: When two plano-convex lens elements are mounted with convex side towards one another will form positive type of eyepiece. They are consisting of two or more lens elements. They combined together will behave as a positive lens. Focus point in this case lies in front of field lens hence they can be used as ordinary magnifiers. They have more chromatic aberration error than that of huygenian type but are better with respect to spherical errors. (3) Compensating Types: They are chromatically overcorrected and can be designed either as positive type or as negative type. They normally have higher magnification power. They are not suitable with achromatic objectives of lower power due to adverse chromatic effects. (4) Amplifying Types: They are used for photomicrography or for image projection over a short distance. They are consisting of a number of lens elements which as a group works as a true negative lens system. They are corrected for aberrational errors. They do not form secondary image but combining together with the objectives they form final image

6 . ILLUMINATION SYSTEMS: Bright field illumination: It is condition of lighting that renders a dark image on a bright, well-lit background field. Un-etched area becomes dark. This happens because the reflected light is recollected by the lenses while scattered light does not get recollected. The objective here first serves as condensing system to the incident light beam and then forms image. This is the conventional system by which micro-examinations are carried out. Dark field illumination: It is exactly the reverse condition to bright field illumination. Here bright image is rendered on dark background field. The objective here is used for forming image only. Here only scattered light is recollected, while reflected light rays are blocked. This produces very strong image contrast. Though this system is capable to reveal the details which are not possible by bright field system, it is very difficult for out photomicroscopy. PRACTICAL CONTENTS: 1) Study the operating principle of Metallurgical Microscope with the help of Ray Diagram. 2) Understand various optical errors. 3) Study various types of Objectives & Eyepieces. 4) Understand the illumination system and types. 5) Study the important specification and capabilities of Microscope & related computer aided system we have. 1) Explain the working principle of Metallurgical Microscope with the help of Ray Diagram. 2) Identify different important parts of Microscope and tabulate them mentioning their main functions. 3) Explain different errors related to the objectives. 4) Explain following properties of Objective briefly. (Mention mathematical relations existing between them, if any.) a) Magnifying Power b) Resolving Power c) Numerical Power d) Vertical Resolution 5) Explain various Objectives with their main feature. 6) Explain various Eyepieces with their main feature. 7) Differentiate between Dark field & Bright field illuminations. 8) List the important specifications of the Metallurgical Microscope you have studied and explain the usefulness of computer aided system we have. 1) Introduction to Physical Metallurgy By Sydney H. Avner 2) Principles of Metallographic Laboratory Practices By G.L.Kehl

7 Practical No. 03 Specimen Preparation for Micro examination To study procedure of specimen preparation for microscopic examination. A little can be learned regarding the structural characteristics of a metal by microscopic examination unless the surface that is to be examined is first prepared according to more or less rigid and precise procedures. With the use of modern metallurgical microscope and precision optical parts where the obtainable resolution may be as great as a fraction of the wavelength of the light used to illuminate the specimen, it is evident that perfect specimen preparation is of the greatest importance. Improper preparation is likely to remove all important inclusions, erode grain boundaries of temper hardened steel specimens, ultimately producing a structure, superficially at least, which upon micro-examination will appear entirely different from that which is truly representative and characteristic of metal. Obviously an examination of such a prepared specimen will lead only to erroneous interpretations and unreliable conclusions. PRACTICAL CONTENTS: 1) Determine the appropriate location and orientation of the specimen to be cut. 2) Mounting the specimen if required. 3) If the specimen to be observed is too uneven, or with burrs etc. achieve plane surface by either filling or grinding on coarse grade emery paper. 4) Take emery papers from coarse to finer abrasive grid (i.e 1/0, 2/0, 3/0 & 4/0). The emery is placed on any clean, hard, level surface. The specimen is rubbed back and forth across the entire length of paper under moderately applied pressure. While being ground, the specimen is held so that the new, finer scratches being introduced on the surface are approximately at right angles to the old scratches resulting from previous flattening operation. Switch over to next finer grade and repeat the same procedure. 5) Now for better surface finish go to the polishing wheel. The polishing wheel mounted cloth is rotated at appropriate speed and the specimen is moved continuously from the center to the periphery of the polishing wheel with moderate pressure. 6) Select suitable etchant for the specimen and carry out the etching. 7) Immediately after etching, wash the specimen under running water and dry it with alcohol. 8) Set the microscope with suitable selection of eye piece and objective for the desired magnification. 1) What is metallography? Briefly explain its importance in Metallurgy. 2) What is the basic difference between low grade no. emery paper and high grade no. emery paper in the intermediate polishing process. 3) What is an etchant? Why etching is required? List at least three name of etchant used for different material. 4) List the instruments and accessories you have used for preparing the sample along with their specification details.

8 1) Introduction to Physical Metallurgy By Sydney H. Avner 2) Principles of Metallographic Laboratory Practices By G.L.Kehi 3) Material Science By O.P.Khanna 4) Material Science and Engineering By William D. Calliater, Jr.

9 Practical No. 04 Micro-Examination of Standard Specimen To understand procedure and relevance of Micro-Examination. Microexamination is study of internal structure of a material i.e. microstructure, which can be carried out by light microscopy or electron microscopy. An observation of microstructure in a microscope will show size and shape of grains and the size, shape and distribution of various phases and inclusions and segregations. These structural characteristics have great effect on mechanical properties of a material. The microstructure will reveal the mechanical and thermal treatment of the material and it may be possible to predict the expected behavior under a given set of conditions. PRACTICAL CONTENTS: 1) Select the etchant required as per the specimen. 2) Carry out etching 3) Immediately after etching, wash the specimen under running water and dry it with alcohol. 4) Set the microscope with suitable selection of eye piece and objective for the desired magnification. 5) Sketch the microstructure observed. 1) Record the microstructure observed in microscope with the aid of schematic diagram. 2) Explain the impact of microstructure on various properties of materials 1) Introduction to Physical Metallurgy By Sydney H. Avner 2) Principles of Metallographic Laboratory Practices By G.L.Kehl 3) Material Science By O.P.Khanna

10 Practical No. 05 Demonstration of heat treatment of steel To study of Fe C system, demonstrate different heat treatment processes, show the effect of different quenching media (Oil, water and Brine) on the hardness of steel According to the functional requirements of the component, different engineering components need different hardness for their long service life. Different quenching media generate different final microstructures (like coarse pearlite, fine pearlite, bainite, martensite etc.) and thus give different hardness values. So the type of quenching media and the cooling rate both decide the final microstructure. To derive the suitable hardness, material technologists must know the effect of the quenching

11 medium and cooling rate, on the hardness of steel. Knowledge of generating different hardness is of great help in industries for the manufacture of components like gears, cams, shafts, axles, pins etc. to increase their service life. THEORY: Quenching, which means drastic(rapid) cooling, always gives high hardness in ferrous systems (metal involving iron) because of mechanism of allotropic transformation suppression. Mechanism of heat removal during quenching is grouped into three stages: 1) Vapour Blanket Stage: Here the quenching medium (Oil, Water or Brine) vaporizes at the metal surface due to the high temperature and a thin film of vapour called vapour blanket, surrounds the hot metal. Presence of vapour retards the heat transfer process and hence the rate of cooling is relatively low. 2) Vapour Transport Cooling Rate: Here metal has cooled a temperature where vapour blanket is no longer stable. Because of absence of vapour between metal and liquid, heat transfer rate increases and cooling rate is maximum. 3) Liquid Cooling Stage: Here the metal reaches the temperature of boiling point of quenching medium. Heat given by the hot metal is utilized in boiling the liquid. In this stage, cooling rate is lowest. To avoid cracks, distortion and warpage, quenching medium should show high initial cooling rate to avoid transformation in the nose region of the TTT curve, followed by slow cooling rate through out the low temperature range. Rise in temperature of quenching medium due to immersion of the component, should be controlled by selecting the proper volume of quenching medium along with necessary cooling arrangement so that heat transfer rate gets maintained the level desired. PRACTICAL CONTENTS: 1) Measure the initial hardness of the given specimen on Rockwell Hardness Tester. 2) Load these specimens in the furnace and heat them to the hardening temperature for 20 to 30 minute. 3) Quench these specimens in oil, water and brine respectively. 4) Measure the hardness of each of them after cooling. 1) Draw the Fe Fe3C diagram with all major transformations. 2) What is soaking time? State its importance. 3) Enlist various heat treatment processes. 4) What is the necessity of studying the effect of quenching media?

12 5) What should be the nature of quenching media to avoid cracks, distortion or warpage of component being hardened? 1) Introduction to physical metallurgy: Sydney H. Avner 2) Physical Metallurgy principles: Reed Hill 3) Materials science and engineering : William D. Callister, Jr.

13 Practical No. 06 Study of powder metallurgy To understand various processes of powder metallurgy Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape or form (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). The powder metallurgy process generally consists of four basic steps: (1) powder manufacture, (2) powder blending,(3) compacting, (4) sintering. Compacting is generally performed at room temperature, and the elevated-temperature process of sintering is usually conducted at atmospheric pressure. Optional secondary processing often follows to obtain special properties or enhanced precision.[1] Two main techniques used to form and consolidate the powder are sintering and metal injection molding. Recent developments have made it possible to use rapid manufacturing techniques which use the metal powder for the products. Because with this technique the powder is melted and not sintered, better mechanical strength can be accomplished. PRACTICAL CONTENTS: 1) Introduction to Poeder Metallurgy By A. K. Sinha 2) Principles of Metallographic Laboratory Practices By G.L.Kehl 3) Material Science By O.P.Khanna

14 Practical No. 07 Ultrasonic Test To understand principle, procedure and capabilities of ultrasonic test. The basic principle of the method is detecting the change in attenuation of sound energy (ultrasonic) the change being caused by a flaw or the material. In this test ultrasonic sound waves (above the audible range) capable of penetrating and medium of appreciable thickness at speeds of several thousand meter/sec, are used. The frequency may range from 1 to 15 MHz. There will be changes in probing medium when there is a flaw which will be detected and indicated by the equipment the ultrasonic flaw detector. The pulse-echo technique is widely preferred. This employs a single probe (transducer) as transmitter and receiver of ultrasonic waves. The ultrasonic waves with high frequency are generated by piezoelectric effect. When these high frequency waves, enter the material being tested, part of it is reflected and converted back to an electrical impulse. This electrical impulse is amplified and rendered visible as an indicator or pip on the screen of the oscilloscope. When the sound wave reaches the other side of the other side of the material, it is reflected back and shows as another pip on the screen further to the right of the first pip (pulse). If there is a flaw between the front and back surfaces of the material (i.e the thickness), it will show as a third pip (pulse) on the screen between the two indications or pulses. Since the indications on the oscilloscope screen measure the elapsed time between reflection of the pulse from the front and back surfaces, the distance between indications is a measure of thickness of the material. The location of a defect can therefore be accurately determined from the location on the screen. Angle probes may be used to detect flaws which are not oriented perpendicular to the direction of propagation of sound waves. PRACTICAL CONTENTS: 1) With the help of the manual of the equipment, get acquainted with the operating details of ultrasonic flaw detector. 2) Calibrate the instrument using I.I.W.-V1 Block. 3) Scan the given samples and report the indications in following manner. Sr. No CRT Reading Length of defect from probing surface (mm) 4) Sketch the samples you have scanned illustrating the flaws in it.

15 1) Briefly explain the principle of Ultrasonic Testing. State various methods of conducting UT and sketch the operating principle of the method you have used in lab. 2) Evaluate UT with other with respect to other NDT methods you know. 3) Illustrate internal construction of following probes and mention the selection criteria for each of them. a) Normal Probe b) Dual Crystal Probe c) Angle Probe 4) Explain briefly following terminology in context of UT. a) Attenuation b) Dead Zone c) Near Zone d) Couplants e) Acoustic impedance f) Sensitivity 1) Introduction to physical metallurgy: Sydney H. Avner 2) Instrument manual available in Lab 3) Material Science And Engineering : William D. Callister 4) Practical Non-Destructive Testing : Raj Baldev, Jayakumar T & Thavasimuthu M.

16 Practical No. 08 Magnetic Particle Test To understand principle. procedure & capabilities of Magnetic Particle Test. The magnetic particle test is one of the most powerful surface and/or subsurface crack detection method/s for Ferromagnetic Materials. The principle of the operation is that, when a component under test is magnetized, discontinuities which lie in a direction generally transverse to the direction of magnetic field will cause a leakage field to be formed. If leakage field is strong enough, its presence and therefore the discontinuity is detected by use of finely divided ferromagnetic particles applied over the surface. Some of the ferromagnetic particles are influence by leakage field and form an outline of the discontinuity called as an indication. The indication may give about size, shape and location of the flaw. PRACTICAL CONTENTS: 1) Determine the setting up procedure, parameters. 2) Clean the specimen thoroughly. Degreasing may be carried out by spirit or trichloroethylene bath. 3) Setup the equipment for the nature of the defect to be detected (cracks, surface, subsurface, porosity etc.). Based on it select the electrical current source. 4) Apply magnetic particles. 5) Perform the test in different orientations of magnetic field application and record the nature and extent of indication with and without fluorescent powder. 6) Demagnetize the work piece and check for results. 1) Briefly explain the principle and procedure of MPT with neat sketches. 2) Comment on applications, advantages and limitations of MPT. 1) Introduction to physical metallurgy: Sydney H. Avner 2) Instrument manual available in Lab

17 Practical No. 09 Dye Penetrant Test To understand principle, procedure & capabilities of Liquid / Dye Penetrant Test Dye penetrant test is essentially useful in detecting minute discontinuities such as cracks, shrinkages and porosity that are open to the surface. Parts to be tested are treated with a penetrant. Penetrant is usually light, oil-like liquids which is applied by dipping, spraying or brushing or in some other convenient manner. The liquid penetrant is drawn into cracks and other discontinuities by strong capillary action. After the penetrant ahs had time to seep in, the portion remaining on the surface is removed by wiping or washing. This leaves the penetrant in all surface-connected discontinuities. The pest part is now treated with a dry powder or a suspension of powder in a liquid. This powder or developer acts like a sponge drawing the penetrant from the defect and enlarging the size of the area of penetrant indication. PRACTICAL CONTENTS: 1) Prepare the surface to be investigated and make it free from dirt and grease. 2) Apply cleaner, allow some time so that surface gets dried. 3) Spray dye penetrant on the surface and allow some time (usually 3 to 5 min. varies from 2 min to few days) 4) Wipe out excess penetrant. (This may be carried out by a light spray of cleaner and wiping it out) 5) Apply developer and observer indications. 6) If needed the developer once again. 7) Observe the defect 1) What types of properties of the dye are required to perform the LPT accurately? 2) Why the developer is used in LPT? 3) List the limitation & capabilities of LPT. 4) Mention the IS No. for DPT. 5) Draw the neat sketch of sample & indications 1) Introduction to physical metallurgy: Sydney H. Avner 2) Practical Non Destructive Testing: Raj Baldev, Jayakumar T., Thavasimuthu M. 3) rad_index.htm

18 Practical No. 10 Study of Eddy current test & Radiography test To understand principle, procedure & capabilities of Eddy current test & Radiography test Eddy-current testing uses electromagnetic induction to detect flaws in conductive materials. There are several limitations, among them: only conductive materials can be tested, the surface of the material must be accessible, the finish of the material may cause bad readings, the depth of penetration into the material is limited by the materials' conductivity, and flaws that lie parallel to the probe may be undetectable. Eddy current inspection is one of several NDT methods that use the principal of electromagnetism as the basis for conducting examinations. Several other methods such as Remote Field Testing (RFT), Flux Leakage and Barkhausen Noise also use this principle. Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from eddies that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right. In a standard eddy current testing a circular coil carrying current is placed in proximity to the test specimen (which must be electrically conductive).the alternating current in the coil generates changing magnetic field which interacts with test specimen and generates eddy current.variations in the phase and magnitude of these eddy currents can be monitored using a second 'receiver' coil, or by measuring changes to the current flowing in the primary 'excitation' coil. Variations in the electrical conductivity or magnetic permeability of the test object, or the presence of any flaws, will cause a change in eddy current and a corresponding change in the phase and amplitude of the measured current. This is the basis of standard (flat coil) eddy current inspection, the most widely used eddy current technique. However, eddy-current testing can detect very small cracks in or near the surface of the material, the surfaces need minimal preparation, and physically complex geometries can be investigated. It is also useful for making electrical conductivity and coating thickness measurements Radiation Safety Ionizing radiation is an extremely important NDT tool but it can pose a hazard to human health. For this reason, special precautions must be observed when using and working around ionizing radiation. The possession of radioactive materials and use of radiation producing devices in the United States is governed by strict regulatory controls. The primary regulatory authority for most types and uses of radioactive materials is the federal Nuclear Regulatory Commission (NRC). However, more than half of the states in the US have entered into

19 "agreement" with the NRC to assume regulatory control of radioactive material use within their borders. As part of the agreement process, the states must adopt and enforce regulations comparable to those found in Title 10 of the Code of Federal Regulations. Regulations for control of radioactive material used in Iowa are found in Chapter 136C of the Iowa Code. For most situations, the types and maximum quantities of radioactive materials possessed, the manner in which they may be used, and the individuals authorized to use radioactive materials are stipulated in the form of a "specific" license from the appropriate regulatory authority. In Iowa, this authority is the Iowa Department of Public Health. However, for certain institutions which routinely use large quantities of numerous types of radioactive materials, the exact quantities of materials and details of use may not be specified in the license. Instead, the license grants the institution the authority and responsibility for setting the specific requirements for radioactive material use within its facilities. These licensees are termed "broadscope" and require a Radiation Safety Committee and usually a full-time Radiation Safety Officer. PRACTICAL CONTENTS: 1) Prepare the surface to be investigated and make it free from dirt and grease. 2) Observe the defect 1) Explain principle of Eddy current test. 2) Explain principle of Radiography test. 3) Enlist merits & demerits of Eddy current test & Radiography test. 4) What precaution one has to take before doing radiography test? why? 1) Introduction to physical metallurgy: Sydney H. Avner 2) Practical Non Destructive Testing: Raj Baldev, Jayakumar T., Thavasimuthu M. 3) rad_index.htm

20 Practical No. 11 Jominy Hardenability Test To understand the concept of hardenability and its relevance to heat treatment procedure to be adopted in practice. Hardenability is the property that determines the depth and distribution of hardness induced by quenching in a ferrous alloy. The Jominy test, together with the appropriate data, is ideally suited for predicting the hardness at a particular location within a section of any given size regardless of the steel from which the section is made. It establishes a correlation between the cooling rate and corresponding distance from the quenched end for each of the test bars. This relationship is the fundamental one and remains substantially unaltered so long as the Jominy procedure is strictly adhered to. It is possible through this correlation to predict hardness within any given shaped object once the cooling rate is known at the location of interest. Such cooling rates within the objects may be determined experimentally or may be obtained by reference to appropriate published data if the size shape and heat treatment of the object correspond to the condition under which data were obtained. PRACTICAL CONTENTS: 1) Understand the theory and relevance of hardenability. 2) Heat the specimen to the austenitizing temperature and soak it at this temperature for 30 minutes. 3) After soaking a test specimen is removed rapidly and placed on a quenching fixture. 4) The water tap shall be opened as soon as the test piece is fixed in position and the time of spraying shall be at least 10 minutes. After this time, the cooling of the test specimen is removed rapidly and placed on a quenching fixture. 5) Two flats for measuring the hardness shall be ground on the surface 1800 apart and parallel to the axis of the test piece, along its entire length. They should be 0.4 to 0.5 mm deep shall be ground with an abundant supply of coolant so as to prevent any heating likely to modify the microstructure of the quenched test piece. 6) Rockwell hardness measurements are made at an interval of 1.5 mm along the longitudinal center line of the flat surface. 7) Record the observations as under Specimen Material: Hardness before test: Temperature & Socking Time: Sr. No Distance from the quenched end (mm) Hardness (HRC)

21 8) Plot the graph of Distance v/s Hardness 1) Draw the neat diagram of standard specimen and practical set up. 2) What is hardenability? What are the factors on which hardenability depends? 3) What kind of transformation is desirable to have a greater hardenability? 4) Differentiate between hardness and hardenability. 5) What is the grain structure of martensite? 6) How is hardenability curve useful? 7) Why it is necessary to cool the test specimen of Jominy hardenability test while grinding two flat surfaces for measurement purpose? 1) Introduction to physical metallurgy: Sydney H. Avner 2) Physical Metallurgy Principles: Reed Hill 3) Material Science And Engineering : William D. Callister