The Structure of Engineering Materials

This page contains experiments dealing with the structure of engineering materials and techniques for characterizing them.  There are three sets of experiments.  The first set focuses on microstructural characterization using optical microscopy. Students will learn about the optical microscope, digital imaging and quantitative metallography and will use this knowledge to fully characterize the microstructure of a prepared specimen.  The second set is devoted to the analysis of the structure of materials using x-ray diffraction. Students operate a modern diffractometer and use it to perform several types of analyses. The third part of the course offers hands-on demonstrations of non-destructive testing, x-ray radiography, molecular simulations and electron microscopy.

Optical micrograph (2x2 montage) of 1095 steel showing the characteristic pearlite structure with proeutectic cementite at the grain boundaries.

Two of the four optical microscopy stations available to students in this course.

1. Microstructure of Materials
This four-part experiment provides an introduction to the use of the reflected-light microscope, including digital imaging, image enhancement and analysis and the study of the microstructures of materials. Each student selects a material to study and performs a full qualitative and quantitative analysis of its microstructure. The four parts of this experiment are:

  1. Introduction to the Optical Microscope
    Understanding the basics of light optics, lenses, illumination systems and contrast methods are essential if one is to get the most out of their microscope. The students will study the microscope and determine its basic operating and performance characteristics.

    • Homework - get familiar with the optical microscope by answering basic questions about how it works and how the objective lens's numerical aperture effects the performance of the microscope.  Some of these questions can be answered only after you have spent a little time using the optical microscopes in our laboratories.

  2. Literature Review
    Students go to the library to learn as much as they can about the type of material they will be studying.  They must learn the basic terminology for the classes of alloys, the phases present, and the basic types of structures and morphologies.

  3. Qualitative Microstructural Analysis
    A qualitative examination of the microstructure will lead to a clear identification of every phase and feature present in the specimen.

    • Homework - get better acquainted with digital imaging as it applies to optical microscopy and learn to optimize your photo settings for any application.

  4. Quantitative Microstructural Analysis
    All major features of the microstructure are measured using standard stereological techniques. The emphasis is on using the correct method correctly, minimizing personal bias, and reporting the results in the correct manner.

    • Homework - get more familiar with the concept of grain size, including ASTM grain size, and measure grain size and volume fraction of phases from three artificial (idealized) microstructures.
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2. X-ray Diffraction
This part of the course consist of up to four experiments that  teach how x-ray diffraction can be used to analyze a number of crystallographic and microstructural characteristics of natural and engineering materials.

  1. The Scintag x-ray diffractometer used in this course.

    Introduction to X-Ray Diffraction
    This experiment provides an introduction to the use of an x-ray diffractometer in investigating the structure of materials. Students learn how to operate the diffractometer, how to design, set up and execute an experiment and how to process and interpret the results.

    • Homework - A few basic questions on the basics of x-ray diffraction plus to exercises that ask you to calculate sections of the diffraction pattern that will be collected during the experiment.
    • Procedure - Notes and the complete procedure for this experiment.

  2. The five-fingers region of the diffraction pattern for quartz, calculated in one of the homework exercises.
    Qualitative and Quantitative Phase Analysis
    Using the x-ray diffractometer the students determine the types and quantity of pure powders in a mixture. The powders are identified by comparing the results to the standard database of powder diffraction files. The quantities of powders present are determined by comparing the results to those from a set of standards which the students generate.

    • Homework - an exploration of the mass adsorption coefficient and its effect on diffraction intensity
    • Procedure - Notes and the complete procedure for this experiment

  3. Nanocrystalline aluminum oxide similar to that analyzed in the crystallite size experiments.
    Crystallite Size Analysis - 1
    The Scherrer and Warren-Averbach methods are used to determine the crystallite size of nanocrystalline powders such as 32 nm TiO2 and 24 nm Al2O3.  The results are compared to the manufacturer’s specifications (SSA method) and to images obtained from electron microscopes. This experiment is adapted from a paper by Krill et al.

    • Homework - explore the concept of crystallite size and size distributions, including a partial analysis of data from past experiments
    • Procedure - Notes and the complete procedure for this experiment.

  4. Profile fitting is used to accurately determine the intensity and width of the peak.  This technique can also work on partially overlapping peaks like those shown in this segment of the diffraction pattern of a TiO2 powder.
    Crystallite Size Analysis - 2
    Samples of nanocrystalline materials from Nanophase and Technanogy are analyzed in this experiment.  The Scherrer equation is the basis of this experiment. A LaB6 standard is used to determine the machine's peak broadening characteristics. Many peaks from the sample's pattern are used in the analysis to work out the strain component and eventually the crystallite size. This experiment is adapted from Suryanarayana and Norton's book.

    • Homework - explore the concept of crystallite size and microstrain and their measurement, including a run-through of the analysis of the type of data to be collected during the experiment.
    • Data - data for the homework assignment.
    • Data - data for the line-width standard.
    • Procedure - Notes and the complete procedure for this experiment.

  5. Residual Stress Measurements
    The x-ray diffractometer is used to determine how much the deformation of a piece of steel has distorted the crystalline lattice. This information is used to estimate the residual stress in the specimen.

    • Homework - explore the concept of residual stress and perform calculations that will help you understand the results from the experiment
    • Procedure - Notes and the complete procedure for this experiment

  6. Measuring Changes in Lattice Parameters and Density Due to Alloying
    The x-ray diffractometer is used to make careful measurements of the lattice parameters of Cu-Zn alloys in order to determine the zinc content. The procedure involves performing calculations, per Vegard's law, to predict the change in lattice parameters with zinc content, followed by a scan of a copper/brass sample where the copper is used as an internal standard.

    • Homework - Exercises and calculations related to Vegard's law and careful measurements of d-spacing
    • Procedure - the complete procedure for this experiment

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3. Other Topics
In addition to the above two parts of the course, one week is set aside for demonstrations of the following materials characterization techniques:

  1. Ultrasonic Inspection
    This is a demonstration of ultrasonic inspection techniques which utilizes a portable inspection unit to perform an inspection on a steel block. It also includes computer display of ultrasonic inspection data of a flaw in a composite structure.
  2. X-Ray Radiography
    This is simply a demonstration of x-ray radiographic techniques used in flaw detection. It includes locating and measuring the sizes of holes drilled in the back of a plate of steel, locating cracks in a part and identifying items trapped in a section of tubing. Student’s radiograph their own "specimens".
  3. Electron Microscopy
    The students get a tour of electron microscopes, transmission electron microscopes along with an introduction to analytical techniques such as EDS and EBSD.
  4. Acoustic Microscopy
    Demonstrations of imaging and scan modes used to image defects in microelectronic components and circuit boards.

An x-ray radiograph of a hard disk drive.

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The appendices page on this web site offers a number of documents that you will find useful during and after the laboratory session.  These include operating procedures for the equipment, tips and trick for digital imaging, and documents that will help you get the most out out your spreadsheet-based assignments and writing the laboratory reports. The documents you should look are:

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