【正文】 a line drawn on the image with an indication of the length it represents. The procedure for determining the size of a scale bar or measuring features directly is the same. The easiest way of measuring the size of a feature under a microscope is to relate it to the size of the field of view. The simplest way of achieving this is to measure the size of the field of view at a low magnification, and then scale the size appropriately as the magnification is increased. The field of view can be measured approximately by looking at a ruler under the lowest magnification lens. Accuracy can be improved by using a graticule (Figure 15). A graticule is a slide with a very fine grating which, if metric, will usually measure 1mm across, and is divided into 100 segments, . each segment is 10 181。m at lower speed (typically with diamond particles 1 micron in diameter, and 100 rpm, to produce a smooth surface). A further step of polishing with 181。 smaller numbers mean coarser SiC particles. A typical starting paper would be 120 or 240 grit, followed by intermediate papers such as 320, 400, 600 or 800 grit. The final step is normally on 1200 grit paper, although 2500 and 4000 grit grades are available, and are used in some specialist polishing methods. Between each stage the specimen should be washed to prevent transport of coarse particles to a higher grade spoiling the grinding. An ultrasonic bath can also be used but is not necessary. When grinding manually, moderate pressure is normally sufficient。 for example, processes such as rolling and extrusion will tend to produce microstructures with elongated grains, as shown in Figure 3. Furthermore, when there is a microstructural change (such as during recrystallisation or a phase transformation), measurement of the extent of the transformation at different times can allow data on the rate to be gathered, which can be important when exploring the kiics of such processes. Quantification of Microstructure and Texture Introduction R Goodall, October 2022 4 Figure 3 – The microstructure of extruded aluminium, showing grains that are elongated in the direction of extrusion (the horizontal direction in the image). What can be Measured? As referred to above, a microstructure will consist of volume features, area features, line features and point features, which will have associated with them: Size Shape Volume Surface area Curvature Location All of these can be measured for the features on an image. An important point that will be returned to throughout the course is that fact that real microstructures will show statistical variations in these features. We therefore need to make a sufficiently large number of measurements, and need tools to allow us to quantify the measured parameters in a statistically meaningful way. Terminology Certain terminology is well established in the field of Quantitative Metallography (which is also sometimes called Stereology). P Number of point features / test points L Length of linear features / test line A Flat area of intercepted features / test area S Curved surface / interface area V Volume of 3D features / test volume N Number of features These symbols can be bined, . to give SV – Surface / interface per unit volume, VV – Volume of one phase in total volume (= volume fraction) or LA – Length of linear features per unit area. In this format, the quantity represented by the main text letter is divided by the quantity represented by the subscript letter. Further Reading for the Whole Course More detail on the topics covered in this course can be found in: ? Higginson and Sellars, Quantitative Metallography, Maney, 2022 ? Underwood, Quantitative Stereology, AddisonWesley, 1970 ? De Hoff and Rhines, Quantitative metallography, McGraw Hill 1968 ? Brandon and Kaplan, Microstructural Characterisation of Materials, Wiley, 2022 ? Randle and Engler, Introduction to Texture Analysis, CRC Press, 2022 Quantification of Microstructure and TextureSample Preparation Techniques for Optical Microscopy R Goodall, October 2022 5 Quantification of Microstructure and Texture 2. Sample Preparation Techniques for Optical Microscopy Most images we will look at of metallic materials are the result of optical microscopy of prepared samples, and metallography is simply the name given to the systematic method used to examine the structure of materials. This lecture covers the standard techniques used in the preparation of samples for optical microscopy. It should be noted that, although we will concentrate on metals here, these techniques work equally well for ceramics, polymers, semiconductors, etc. Sectioning The first step in the process of producing a specimen suitable for observation in the microscope is to obtain a suitably sized piece, which may need to be cut to the right size. When cutting a specimen from a larger piece of material, care must be taken to ensure that it is representative of the features found in the larger sample, or that it contains all the information required to investigate a feature of interest. For this reason, even when the artefact is sufficiently small to permit metallographic preparation, it may still be advantageous to section it so that potentially unrepresentative surface regions are not examined. Many cutting methods can be used to remove part of an artefact for metallographic preparation, but in certain circumstances the selection may be restricted due to the effect this may have on the microstructure. Abrasive cutting, for example using equipment such as that in Figure 1, may introduce a lot of damage and deformation into a specimen, and the high speed can cause heating of the sample which could alter the microstructure. For these reasons, low speed cutting processes are ofte