Lecture-9 SIMS & NDT SIMS Non-Destructive Analysis (NDA) Basic Principles Instrumentation Mass Resolution Modes of Analysis Applications Non-Destructive Analysis (NDA) or Non-Destructive Testing (NDT)

Instrumentation SIMS CAMECA 6F Ion Sources Mass Analyzers Bombardment of a sample surface with a primary ion beam followed by mass spectrometry of the emitted secondary ions constitutes secondary ion mass spectrometry (SIMS). Ion Sources Ion sources with electron impact ionization - Duoplasmatron: Ar+, O2+, O- Ion sources with surface ionization - Cs+ ion sources Ion sources with field emission - Ga+ liquid metal ion sources Mass Analyzers Magnetic sector analyzer Quadrupole mass analyzer Time of flight analyzer Ion Detectors Faraday cup Dynode electron multiplier Vacuum < 10−6 torr Bombardment of a sample surface with a primary ion beam followed by mass spectrometry of the emitted secondary ions constitutes secondary ion mass spectrometry (SIMS). The first inklings of the SIMS process came when early mass spectroscopists noticed that ions from instrument construction materials were produced by ion sources. Later experiments extracted ions from the sources and accelerated them onto the sample, thereby producing the first SIMS primary ion beam. The first SIMS instrument was constructed under a NASA contract in the early 1960's to analyze moon rocks. When it performed better than expected, exact copies of the prototype were introduced into the market place. The use of SIMS for materials characterization has grown steadily during the intervening 30 years. SIMS requires a high vacuum with pressures below 10−4 Pa (roughly 10−6 mbar or torr). This is needed to ensure that secondary ions do not collide with background gases on their way to the detector (i.e. the mean free path of gas molecules within the detector must be large compared to the size of the instrument), and it also prevents surface contamination by adsorption of background gas particles during measurement. Ion detectors Mass Analyzers Ip Is Ion sources SIMS CAMECA 6F Mass analyzers http://www.youtube.com/watch?v=IO-KCjxznLs to~1:50

Cameca SIMS Accelerating voltage Secondary ions are extracted from the sample as they are produced. If large mass spectrometer components are held at ground potential, the sample must be held at high voltage, the accelerating potential. The secondary ions accelerate toward the ground plate of an electrostatic lens. This first lens is called the immersion or ion extraction lens. The second (transfer lens) focuses the ion beam onto the mass spectrometer entrance slits or aperture. This two lens system constitutes an ion microscope. The secondary ions could be projected onto an image detector for viewing the sample surface. Different transfer lenses produce different magnifications. Accelerating voltage Secondary ions have low kinetic energies from zero to a few hundred eV. L1, L2 and L3 - electromagnetic lens http://www.eaglabs.com/mc/sims-instrumentation.html

Energy Analyzer and Mass Spectrometer ESA bends lower energy ions more strongly than higher energy ions. The sputtering process produces a range of ion energies. An energy slit can be set to intercept the high energy ions. Sweeping the magnetic field in MA provides the separation of ions according to mass-to-charge ratios in time sequence. E Mass Analyzer (MA) Degree (r) of deflection of ions by the magnetic filed depends on m/q ratio. V - ion acceleration voltage Magnet Sector Electrostatic Sector r - radius of curvature of an ion Energy Focal plane http://www.youtube.com/watch?v=tOGM2gOHKPc&feature=relmfu ESA is to minimize fluctuation of kinetic energy of ions. At a specific electrical field E between the two cylinders of energy analyzer, all paraxial ions of particular energy will follow the central lines to be focused in a plane of the ESA slit. The spatial dispersion of ions according to the ion energies is obtained in the slit plane where ions with kinetic energy of interest are selected. When the fluctuation in kinetic energy of ions is substantially suppressed, the interference of ions is also reduced which provides higher mass resolution of mass spectrometers. The equation above shows the relationship between the magnetic field (B), the ion accelerating voltage (V), the mass-to-charge ratio (m/q), and the radius of ion curvature (r) in the magnetic field. In atomic units, m/q becomes m/z where z is the number of charges on the ion. The mass of ions separated on the slit can be calculated from equilibrium between the centrifugal and Lorentz forces as follows: mv2/R = qBv (for magnetic field perpendicularly oriented to the velocity vector of ions): where v=(2qU/m)1/2 and R – radius of central pass. https://www.youtube.com/watch?v=NuIH9-6Fm6U at~3:40-5:16 https://www.youtube.com/watch?v=EzvQzImBuq8 to~2:06 http://www.youtube.com/watch?v=lxAfw1rftIA at~1:00-4:12

Basic Equations of Mass Spectrometry Ion’s kinetic E function of accelerating voltage (V) and charge (z). r Centrifugal force Applied magnetic field Lorentz force Balance as ion goes through flight tube r Combine equations to obtain: r Fundamental equation of mass spectrometry For every action there is an equal and opposite reaction. Centripetal force, an action, has the reaction of centrifugal force. The two forces are equal in magnitude and opposite in direction. Change ‘mass-to-charge’ (m/z) ratio by changing V or changing B. NOTE: if B, V, z constant, then: m/z = m/e for singly charged ions r - radius of circular ion path

MA ESA MA

Ion Detectors http://www.eaglabs.com/mc/sims-secondary-ion-detectors.html#next A Faraday cup measures the ion current hitting a metal cup, and is sometimes used for high current secondary ion signals. With an electron multiplier an impact of a single ion starts off an electron cascade, resulting in a pulse of 108 electrons which is recorded directly. Usually it is combined with a fluorescent screen, and signals are recorded either with a CCD-camera or with a fluorescence detector. Faraday Cup One of the greatest advantages of SIMS is its sensitivity (very low detection limit), which allows searching for traces of elements. Lowering the detectable limit can only be achieved by increasing the primary ion current density, increasing the analyzed area and ion yield using the yield enhancing primary ion species. Faraday cup - The detector slit limits the size of the secondary ion beam. The ion suppressor has a slightly more negative potential than the Faraday cage. The negative potential on the ion suppressor prevents escaping the secondary electrons induced upon the ion impact on the detector and thus enables to measure true ion signals. The deep Faraday cap with a small hole has a similar function – the suppression of the emission of secondary electrons. https://www.youtube.com/watch?v=f61eMq4Wg4w - animation Secondary electron Multiplier 20 dynodes Current gain 107 https://www.youtube.com/watch?v=NuIH9-6Fm6U at~5:18-6:50 and to~9:25

M/z

Time of Flight (TOF) SIMS - Reflectron http://www.youtube.com/watch?v=KAWu6SmvHjc TOF SIMS is based on the fact that ions with the same energy but different masses travel with different velocities. Basically, ions formed by a short ionization event are accelerated by an electrostatic field to a common energy and travel over a drift path to the detector. The lighter ones arrive before the heavier ones and a mass spectrum is recorded. Measuring the flight time for each ion allows the determination of its mass. http://www.iontof.com/technique-timeofflight-IONTOF-TOF-SIMS-TIME-OF-FLIGHT-SURFACE-ANALYSIS.htm http://serc.carleton.edu/research_education/geochemsheets/techniques/ToFSIMS.html (TOF) SIMS enables the analysis of an unlimited mass range with high sensitivity and quasi-simultaneous detection of all secondary ions collected by the mass spectrometer. Schematic of time of flight (TOF) spectrometer - reflectron

Time of Flight (TOF) Spectrometer TOF operates in a pulse mode. During a short pulse of E, ions are accelerated and acquire a constant kinetic energy: kinetic energy = mv2/2 but have different m/q and Vs. Thus they arrive to the detector in time sequence after travel the same distance. Time required to travel distance l from the ion origin to the detector is: The light ions with higher Vs arrive to the detector first. pulse width Schematic of TOF spectrometer with a spectrum In order to provide higher resolution the pulse should be as narrow as 1-10 ns. The pulse repetition frequency is usually in a kHz range.

SIMS can do trace element analysis WDS ~100ppm EDS ~1000ppm Detection limit is affected by

1 and 2 Static SIMS 3 Dynamic SIMS

Dynamic Secondary Ion Mass Spectrometry Dynamic SIMS involves the use of a much higher energy primary beam (larger amp beam current). It is used to generate sample depth profiles. The higher ion flux eats away at the surface of the sample, burying the beam steadily deeper into the sample and generating secondary ions that characterize the composition at varying depths. The beam typically consists of O2+ or Cs+ ions and has a diameter of less than 10 μm. The experiment time is typically less than a second. Ion yield changes with time as primary particles build up on the material effecting the ejection and path of secondary ions.

Dynamic SIMS – Depth Profiling Factors affecting depth resolution http://www.youtube.com/watch?v=-7gSbaslRCU&feature=related

Crater Effect (a) (b) (a) Ions sputtered from a selected central area (using a physical aperture or electronic gating) of the crater are passed into the mass spectrometer. (b) The beam is usually swept over a large area of the sample and signal detected from the central portion of the sweep. This avoids crater edge effects. The analyzed area is usually required to be at least a factor of 3  3 smaller than the scanned area.

Sample Rotation Effect

Gate Oxide Breakdown http://www.youtube.com/watch?v=IO-KCjxznLs&NR=1&feature=endscreen 2:08-2:40

Dynamic SIMS vs Static SIMS

http://www.youtube.com/watch?v=IO-KCjxznLs at~2:45-3:18

Mapping Chemical Elements Some instruments simultaneously produce high mass resolution and high lateral resolution. However, the SIMS analyst must trade high sensitivity for high lateral resolution because focusing the primary beam to smaller diameters also reduces beam intensity. High lateral resolution is required for mapping chemical elements. 197 AU 34 S The example (microbeam) images show a pyrite (FeS2) grain from a sample of gold ore with gold located in the rims of the pyrite grains. The image numerical scales and associated colors represent different ranges of secondary ion intensities per pixel.

Summary SIMS can be used to determine the composition of organic and inorganic solids at the outer 5 nm of a sample. To determine the composition of the sample at varying spatial and depth resolutions depending on the method used. This can generate spatial or depth profiles of elemental or molecular concentrations. These profiles can be used to generate element specific images of the sample that display the varying concentrations over the area of the sample. To detect impurities or trace elements, especially in semi-conductors and thin filaments. Secondary ion images have resolution on the order of 0.5 to 5 μm. Detection limits for trace elements range between 1012 to 1016 atoms/cc. Spatial resolution is determined by primary ion beam widths, which can be as small as 100 nm. SIMS is the most sensitive elemental and isotopic surface microanalysis technique (bulk concentrations of impurities of around 1 part-per-billion). However, very expensive. http://www.youtube.com/watch?v=QTjZutbLRu0 at~1:38-2:14 advantages and disadvantages of SIMS

Review Questions for SIMS What are matrix effects? What is the difference between ion yield and sputtering yield? When are oxygen and cesium ions used as primary ions? What is mass resolution? How can depth resolution be improved? Applications of SIMS Advantages and disadvantages of SIMS

Non-destructive Analysis (NDA) Non-destructive Testing (NDT) https://www.nde-ed.org/index_flash.php Introduction to NDT Overview of Six Most Common NDT Methods Selected Applications Nondestructive Testing The field of NDT is a very broad, interdisciplinary field that plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of less visible, but equally troubling events. Theses tests are performed in a manner that does not affect the future usefulness of the object or material. In other words, NDT allows parts and materials to be inspected and measured without damaging them. Because it allows inspection without interfering with a product's final use, NDT provides an excellent balance between quality control and cost-effectiveness. Generally speaking, NDT applies to industrial inspections. While technologies are used in NDT that are similar to those used in the medical industry, typically nonliving objects are the subjects of the inspections.  https://www.youtube.com/watch?v=tlE3eK0g6vU NDT very good

Definition of NDT The use of noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object. i.e. Inspect or measure without doing harm.

What are Some Uses of NDT Methods? Flaw Detection and Evaluation Leak Detection Location Determination Dimensional Measurements Structure and Microstructure Characterization Estimation of Mechanical and Physical Properties Material Sorting and Chemical Composition Determination Fluorescent penetrant indication

Why Nondestructive? Test piece too precious to be destroyed Test piece to be reused after inspection Test piece is in service For quality control purpose Something you simply cannot do harm to, e.g. fetus in mother’s uterus Nuchal – the back of the neck

When are NDE Methods Used? There are NDE applications at almost any stage in the production or life cycle of a component. To assist in product development To screen or sort incoming materials To monitor, improve or control manufacturing processes To verify proper processing such as heat treating To verify proper assembly To inspect for in-service damage

Six Most Common NDT Methods Detection of surface flaws Visual Liquid Penetrant Magnetic Ultrasonic Eddy Current Radiography Detection of internal flaws

1. Visual Inspection Most basic and common inspection method. Portable video inspection unit with zoom allows inspection of large tanks and vessels, railroad tank cars, sewer lines. Most basic and common inspection method. Tools include fiberscopes, borescopes, magnifying glasses and mirrors. Robotic crawlers permit observation in hazardous or tight areas, such as air ducts, reactors, pipelines. Visual and Optical Testing (VT) Visual inspection involves using an inspector's eyes to look for defects. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. Visual examiners follow procedures that range from simple to very complex.

Liquid Penetrant Inspection https://www.youtube.com/watch?v=xEK-c1pkTUI to~2:26 Liquid Penetrant Inspection Low surface wetting A liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects. The excess liquid is removed from the surface of the part. A developer (powder) is applied to pull the trapped penetrant out the defect and spread it on the surface where it can be seen. High surface wetting Visual inspection is the final step in the process. The penetrant used is often loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity. With this testing method, the test object is coated with a solution that contains a visible or fluorescent dye. Excess solution is then removed from the surface of the object but is left in surface breaking defects. A developer is then applied to draw the penetrant out of the defects. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be readily seen. With visible dyes, a vivid color contrast between the penetrant and developer makes the bleedout easy to see. The red indications in the image represent a defect in this component. LPI offers flexibility in performing inspections because it can be applied in a large variety of applications ranging from automotive spark plugs to critical aircraft components. Penetrant material can be applied with a spray can or a cotton swab to inspect for flaws known to occur in a specific area or it can be applied by dipping or spraying to quickly inspect large areas. At right, visible dye penetrant being locally applied to a highly loaded connecting point to check for fatigue cracking. https://www.youtube.com/watch?v=tlE3eK0g6vU at~2:48-3:33 https://www.youtube.com/watch?v=bHTRmTQDZzg

Magnetic Particle Inspection (MPI) A NDT method used for defect detection. Fast and relatively easy to apply and part surface preparation is not as critical as for some other NDT methods. – MPI one of the most widely utilized nondestructive testing methods. MPI uses magnetic fields and small magnetic particles, such as iron filings to detect flaws in components. The only requirement from an inspectability standpoint is that the component being inspected must be made of a ferromagnetic material such as iron, nickel, cobalt, or some of their alloys. Ferromagnetic materials are materials that can be magnetized to a level that will allow the inspection to be effective. The method is used to inspect a variety of product forms such as castings, forgings, and weldments. Many different industries use MPI for determining a component's fitness-for-use. Some examples of industries that use magnetic particle inspection are the structural steel, automotive, petrochemical, power generation, and aerospace industries. Underwater inspection is another area where magnetic particle inspection may be used to test such things as offshore structures and underwater pipelines. Magnetic particle inspection is a nondestructive testing method used for defect detection. MPI is a fast and relatively easy to apply and part surface preparation is not as critical as it is for some other NDT methods. These characteristics make MPI one of the most widely utilized nondestructive testing methods. MPI uses magnetic fields and small magnetic particles, such as iron filings to detect flaws in components. The only requirement from an inspectability standpoint is that the component being inspected must be made of a ferromagnetic material such iron, nickel, cobalt, or some of their alloys. Ferromagnetic materials are materials that can be magnetized to a level that will allow the inspection to be affective. The method is used to inspect a variety of product forms such as castings, forgings, and weldments. Many different industries use magnetic particle inspection for determining a component's fitness-for-use. Some examples of industries that use magnetic particle inspection are the structural steel, automotive, petrochemical, power generation, and aerospace industries. Underwater inspection is another area where magnetic particle inspection may be used to test such things as offshore structures and underwater pipelines. https://www.youtube.com/watch?v=tlE3eK0g6vU at~1:10-2:48 MPI https://www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/cc_mpi_index.php

Magnetic Particle Inspection https://www.youtube.com/watch?v=qpgcD5k1494 to~3:03 Magnetic Particle Inspection The part is magnetized. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions. Flux leakage If iron particles are sprinkled on a cracked magnet, the particles will be attracted to and cluster not only at the poles at the ends of the magnet but also at the poles at the edges of the crack. This cluster of particles is much easier to see than the actual crack and this is the basis for magnetic particle inspection. Cracks just below the surface can also be revealed. Relative direction between the magnetic field and the defect line is important. The magnetic particles form a ridge many times wider than the crack itself, thus making the otherwise invisible crack visible. https://www.youtube.com/watch?v=dQoB7jpxSe8 MPI testing procedure

Magnetic particles Pulverized iron oxide (Fe3O4) or carbonyl iron powder can be used Colored or even fluorescent magnetic powder can be used to increase visibility Powder can either be used dry or suspended in liquid

Examples of visible dry magnetic particle indications Indication of a crack in a saw blade Indication of cracks in a weldment One of the advantages that a magnetic particle inspection has over some of the other nondestructive evaluation methods is that flaw indications generally resemble the actual flaw. This is not the case with NDT methods such as ultrasonic and eddy current inspection, where an electronic signal must be interpreted. When magnetic particle inspection is used, cracks on the surface of the part appear as sharp lines that follow the path of the crack. Flaws that exist below the surface of the part are less defined and more difficult to detect. Below are some examples of magnetic particle indications produced using dry particles. Before and after inspection pictures of cracks emanating from a hole Indication of cracks running between attachment holes in a hinge

Examples of Fluorescent Wet Magnetic Particle Indications Magnetic particle wet fluorescent indication of a cracks in a drive shaft Magnetic particle wet fluorescent indication of a crack in a bearing The indications produced using the wet magnetic particles are more sharp than dry particle indications formed on similar defects. When fluorescent particles are used, the visibility of the indications is greatly improved because the eye is drawn to the "glowing" regions in the dark setting. Below are a few examples of fluorescent wet magnetic particle indications. Magnetic particle wet fluorescent indication of a cracks at a fastener hole

Advantages of MPI One of the most dependable and sensitive methods for surface defects fast, simple and inexpensive direct, visible indication on surface unaffected by possible deposits, e.g. oil, grease or other metals chips, in the cracks can be used on painted objects results readily documented with photo or tape impression

Limitations of MPI Only good for ferromagnetic materials sub-surface defects will not always be indicated relative direction between the magnetic field and the defect line is important objects must be demagnetized before and after the examination the current magnetization may cause burn scars on the item examined

Ultrasonic Inspection (Pulse-Echo) https://www.youtube.com/watch?v=gqJN8tyosDw to~0:42 Ultrasonic Inspection (Pulse-Echo) In ultrasonic testing, high-frequency sound waves are transmitted into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo, whereby sound is introduced into a test object and reflections (echoes) from internal imperfections or the part's geometrical surfaces are returned to a receiver.   The time interval between the transmission and reception of pulses give clues to the internal structure of the material. Below is an example of shear wave weld inspection. Notice the indication extending to the upper limits of the screen. This indication is produced by sound reflected from a defect within the weld. https://www.youtube.com/watch?v=tlE3eK0g6vU at~6:45-8:00 or to 11:35

Ultrasonic Inspection (Pulse-Echo) High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound. Principle of ultrasonic testing LEFT: A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo. RIGHT: A defect creates a third indication and simultaneously reduces the amplitude of the back wall indication. The depth of the defect is determined by the ratio D/Ep Ultrasonic Probe f Pulse-echo ultrasonic measurements can determine the location of a discontinuity in a part or structure by accurately measuring the time required for a short ultrasonic pulse generated by a transducer to travel through a thickness of material, reflect from the back or the surface of a discontinuity, and be returned to the transducer. In most applications, this time interval is a few microseconds or less. d = vt/2 or v = 2d/t where d is the distance from the surface to the discontinuity in the test piece, v is the velocity of sound waves in the material, and t is the measured round-trip transit time. Ultrasonic probe is made of piezoelectric transducers. Oscilloscope, or flaw detector screen https://www.youtube.com/watch?v=UM6XKvXWVFA at~1:18-3:08 http://www.doitpoms.ac.uk/tlplib/piezoelectrics/applications.php

How It Works? At a construction site, a technician tests a pipeline weld for defects using an ultrasonic instrument. The scanner, which consists of a frame with magnetic wheels, holds the probe in contact with the pipe by a spring. The wet area is the ultrasonic couplant (medium, such as water and oil) that allows the sound to pass into the pipe wall. Spline cracking Non-destructive testing of a swing shaft showing spline cracking. Backwall Spline – any of a series of projections on a shaft that fit into slots on a corresponding shaft, enabling both to rotate together. Lower end Upper end https://www.youtube.com/watch?v=UM6XKvXWVFA at~3:08-4:10

Images obtained by C-Scan High resolution scan can produce very detailed images. Both images were produced using a pulse-echo techniques with the transducer scanned over the head side in an immersion scanning system. For the C-scan image on the left, the gate was setup to capture the amplitude of the sound reflecting from the front surface of the quarter. Light areas in the image indicate area that reflected a greater amount of energy back to the transducer. In the C-scan image on the right, the gate was moved to record the intensity of the sound reflecting from the back surface of the coin. The details on the back surface are clearly visible but front surface features are also still visible since the sound energy is affected by these features as it travels through the front surface of the coin. Gray scale image produced using the sound reflected from the front surface of the coin Gray scale image produced using the sound reflected from the back surface of the coin (inspected from “heads” side)

Applications of Ultrasonic Inspection Ultrasonic inspection is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is used in many industries including steel and aluminium construction, metallurgy, manufacturing, aerospace, automotive and other transportation sectors. Limitations of Ultrasonic Inspection 1. Manual operation requires careful attention by experienced technicians. 2. Extensive technical knowledge is required for the development of inspection procedures. 3. Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect. 4. Surface must be prepared by cleaning and removing loose scale, paint, etc. 5. Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected unless a non-contact technique is used.  6. Inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors. The transducers alert to both normal structure of some materials, tolerable anomalies of other specimens (both termed “noise”) and to faults therein severe enough to compromise specimen integrity. These signals must be distinguished by a skilled technician, possibly requiring follow up with other nondestructive testing methods. Non-contact techniques include Laser and Electro Magnetic Acoustic Transducers (EMAT).

Eddy Current Testing (ECT) Electrical currents are generated in a conductive material by an induced alternating magnetic field. The electrical currents are called eddy currents because they flow in circles at and just below the surface of the material. Interruptions in the flow of eddy currents, caused by imperfections, dimensional changes, or changes in the material's conductive and permeability properties, can be detected with the proper equipment. Eddy current testing can be used on all electrically conducting materials with a reasonably smooth surface. The test equipment consists of a generator (AC power supply), a test coil and recording equipment, e.g. a galvanometer or an oscilloscope Used for crack detection, material thickness measurement (corrosion detection), sorting materials, coating thickness measurement, metal detection, etc. https://www.youtube.com/watch?v=tlE3eK0g6vU at~11:36-12:38

Eddy Current Instruments Voltmeter Coil's magnetic field Coil Eddy current's magnetic field Eddy currents The most basic eddy current testing instrument consists of an alternating current source, a coil of wire connected to this source, and a voltmeter to measure the voltage change across the coil. An ammeter could also be used to measure the current change in the circuit instead of using the voltmeter. While it might actually be possible to detect some types of defects with this type of an equipment, most eddy current instruments are a bit more sophisticated. In the following pages, a few of the more important aspects of eddy current instrumentation will be discussed. Solenoid - A current-carrying coil of wire that acts like a magnet when a current passes through it. Conductive material https://www.youtube.com/watch?v=zJ23gmS3KHY to~1:24 what is Eddy current

Applications of ECT Crack Detection Material Thickness Measurements https://www.youtube.com/watch?v=9A5fQtOwnzw Applications of ECT Crack Detection Material Thickness Measurements Coating Thickness Measurements Conductivity Measurements for Material Identification Heat Damage Detection Case Depth Determination Heat Treatment Monitoring Here a small surface probe is scanned over the part surface in an attempt to detect a crack.

Advantages of ECT Sensitive to small cracks and other defects Detects surface and near surface defects Inspection gives immediate results Equipment is very portable Method can be used for much more than flaw detection Minimum part preparation is required Test probe does not need to contact the part Inspects complex shapes and sizes of conductive materials

Limitations of ECT Only conductive materials can be inspected Surface must be accessible to the probe Skill and training required is more extensive than other techniques Surface finish and roughness may interfere Reference standards needed for setup Depth of penetration is limited Flaws such as delaminations that lie parallel to the probe coil winding and probe scan direction are undetectable

Radiography Radiography involves the use of penetrating gamma- or X-radiation to examine material's and product's defects and internal features. An X-ray machine or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other media. The resulting shadowgraph shows the internal features and soundness of the part. Material thickness and density changes are indicated as lighter or darker areas on the film. High Electrical Potential Electrons - + X-ray Generator or Radioactive Source Creates Radiation Exposure Recording Device Radiation Penetrate the Sample https://www.youtube.com/watch?v=VscasN8jgfo Introduction to radiography

Film Radiography The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation. The film darkness (density) will vary with the amount of radiation reaching the film through the test object. Defects, such as voids, cracks, inclusions, etc., can be detected. X-ray film The most common detector used in industrial radiography is film. The high sensitivity to ionizing radiation provides excellent detail and sensitivity to density changes when producing images of industrial materials. = less exposure Top view of developed film = more exposure https://www.youtube.com/watch?v=tlE3eK0g6vU at~3:35-6:45

Applications of Radiography Can be used in any situation when one wishes to view the interior of an object To check for internal faults and construction defects, e.g. faulty welding To ‘see’ through what is inside an object To perform measurements of size, e.g. thickness measurements of pipes Limitations of Radiography There is an upper limit of thickness through which the radiation can penetrate, e.g. -ray from Co-60 can penetrate up to 150mm of steel The operator must have access to both sides of an object Highly skilled operator is required because of the potential health hazard of the energetic radiations Relative expensive equipment

Radiographic Images

Examples of radiograph                                                                                              Burn through (icicles) results when too much heat causes excessive weld metal to penetrate the weld zone. Lumps of metal sag through the weld creating a thick globular condition on the back of the weld. On a radiograph, burn through appears as dark spots surrounded by light globular areas.

For More Information on NDT The Collaboration for NDT Education www.ndt-ed.org The American Society for Nondestructive Testing www.asnt.org

Review Questions for NDT Applications of NDT What are six most common NDT methods? Can liquid penetrant inspection be used to detect internal flaws? Why? Why relative direction between the magnetic field and the defect line is important in magnetic particle inspection? Why are couplants needed for ultrasonic inspection (UI)? Limitations of UI? Advantages and disadvantages of eddy current testing. What is rediography? Limitations of radiography.