【正文】 er the 3D structure. Figure 2 indicates why a certain amount of care must be taken when quantifying data obtained from such measurements. Quantification of Microstructure and Texture Introduction R Goodall, October 2022 3 Figure 2 – Schematic diagram indicating how the angle of a microstructure relative to a 2D section through a material can influence the apparent size of features. Why do Microstructural Features need to be Quantified? The spatial, size and geometrical distribution of microstructural features affect numerous mechanical and physical properties of the material, and can therefore be very important to quantify, both for research (to understand processingmicrostructureproperties links) and industry (quality control). The table below shows a short list of examples of such properties. Property Influenced by… Effect Yield Strength Grain Size Under the HallPetch relationship, a smaller grain size gives a higher yield strength as dislocations pile up at grain boundaries more rapidly. Volume Fraction If a reinforcement phase has been added (as in, for example a metal matrix posite) the amount present will affect the degree of reinforcement. The same is true in multiphase materials where one phase has a higher yield stress. Dislocation Density A material with a higher dislocation density (one that has been work hardened) will have a higher yield stress than a material with a relatively low dislocation density. Fracture Toughness Grain Size and Shape A microstructure with small interlocking grains will have a higher resistance to crack propagation than one with large grains, as the crack is forced to take a more tortuous path. Conductivity Volume Fraction Where phases of different thermal or electrical conductivity are present, their volume fractions will affect the conductivity of the material as a whole. Magic Properties Grain Orientation Steels for transformer cores are made with a very large (~cm) grain size and with a preferential orientation of {110}001 (Goss texture), which increases the magic flux density in the plane of the strip and reduces losses in service. Examination of the microstructure of an unknown material can also allow us to make deductions concerning its position and processing route。m at a relatively fast rotational speed (typically with diamond particles 6 microns in diameter which should remove the scratches produced from the finest grinding stage, and a speed of 300 rpm), and a finer polish 1181。m across. This allows much greater accuracy in measuring the field of view, and so greater accuracy in measuring features. Figure 15 Metric graticule in polarised light On some microscopes, a scale bar is superimposed on one of the eyepieces, which can be used to further improve the accuracy of measuring feature sizes. The scale bar can be calibrated by observing either a graticule or a ruler at a low magnification. For example, if 1 division is equivalent to 20 mm with a x5 magnification lens, each division is equivalent to 2 mm with a x50 magnification lens. By measuring a feature using the scale in the eyepiece, the actual size of the feature can be calculated by knowing the width of the divisions in the eyepiece. The scale bar on the eyepiece is particularly useful because it can be rotated and so both widths and lengths can be measured without rotating the specimen. Quantification of Microstructure and TextureSample Preparation Techniques for Optical Microscopy R Goodall, October 2022 13 Other Optical Microscopy Terms There are numerous details to advanced optical microscopy, which are beyond the scope of this course. The list below gives brief details of some of the other terms that may be encountered, and the reader is invited to consult the reading list for more detail。 heavy pressure is not required as it can cause further damage to the microstructure of the sample (rather than removing the damage induced by the sectioning process, as we are trying to do with this step), and also increases the risk of the specimen catching on the paper and being thrown off the wheel. The times required at each step can also be surprisingly short (often less than a minute). A useful way to tell is to rotate the specimen by 90176。C (SEM) Ascast aluminium alloy (cross polarised light optical microscopy, sample etched using Barker39。 Quantification of Microstructure and Texture Introduction R Goodall, October 2022 1 Quantification of Microstructure and Texture 1. Introduction What is a Microstructure? The microstructure of a metal or alloy is the arrangement of its structure on a very small scale。m 3D Atom Probe Microscopy Single atoms on the surface of a sharp needle specimen are ionised by field evaporation. These ions are projected toward a detector, and their position recorded. With time, a profile through the depth may also be built up. Only very small volumes possible More details may be found at: and Atomic 3D Quantification of Microstructure and Texture Introduction R Goodall, October 2022 2 Coarse pearlite in slow cooled Fe, C (wt%) (optical microscopy) Martensite laths in Fe, C (wt%) water quenched from 800176。 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。 a line drawn on the im