Attention should be paid to the characteristics of materials in microscopic research
(1) Multi-scale of material microstructure: Olympus microscope atomic and molecular level, crystal defect level such as dislocation, grain microstructure level, mesostructure level, macrostructure level, etc.;
(2) Inhomogeneity of material microstructure: the actual microstructure often has inhomogeneity in geometry, inhomogeneity in chemical composition, and inhomogeneity in microscopic properties (such as microhardness, local electrochemical potential) sex, etc.;
(3) The directionality of the microstructure of the material: including the anisotropy of the grain shape, the directionality of the low-magnification structure, the crystallographic orientation, the directionality of the macroscopic properties of the material, etc., which should be analyzed and analyzed separately. representation;
(4) The variability of the microstructure of materials: changes in chemical composition, external factors and time changes that cause phase transitions and microstructure evolution may lead to changes in the microstructure of materials. In addition to quantitative analysis, attention should be paid to whether it is necessary to study the solid state phase transition process, microstructure evolution kinetics and evolution mechanism;
(5) The possible fractal characteristics of the material microstructure and the resolution-dependent characteristics that may exist in specific metallographic observations: it may cause the quantitative analysis results of the microstructure to strongly depend on the image resolution. More attention should be paid to this when conducting quantitative analysis of tissue morphology and storing and processing microstructure digital image files;
(6) Limitations of non-quantitative research on the microstructure of materials: Although the qualitative research on the microstructure can meet the needs of materials engineering, the analysis and research of materials science always needs to quantify the geometry of the microstructure. Determination and error analysis of the obtained quantitative analysis results (random error, systematic error, gross error);
(7) Limitations of material microstructure cross-section or projection observation, etc. Observations of deep erosion of the three-dimensional structure of cast iron flake graphite and pearlite have shown that such limitations can easily lead to misinterpretation of cross-sectional or projected images.
It should be noted that different stereological principles and relations must be used for cross-sectional images (such as optical metallography and SEM images) and projection images (such as TEM images), and the stereological analysis of projection images is much more difficult[ 2].
For the limitations of (6) and (7), deep etching, grain or second phase separation, radiography, stereo vision, confocal microscopy, atomic force microscopy, field ion microscopy, micro-CT and related technologies , Reconstruction of three-dimensional tissue structure from a series of cross-sectional images and other methods have been used for direct imaging and experimental observation of three-dimensional microstructure of materials. But most of them are only suitable for very special cases, or the workload is huge, or they can only image and observe the surface of the sample. Among them, the industrial micro-CT technology is very effective for the non-destructive testing of large-sized defects with obvious density differences inside the material, and may become a new research and development direction, but the resolution for the observation of the microstructure of materials remains to be seen. Increased (currently its highest resolution is on the micron level). When it is possible to experimentally obtain a series of cross-sectional metallographic images, 3D reconstruction and computer simulation techniques are very helpful for 3D direct observation. Also, direct observation does not always mean direct measurement. It is worth noting that: in the case where the three-dimensional visualization of material organization cannot be realized or its quantitative characterization data cannot be obtained even though it has been visualized, stereological analysis can obtain unbiased quantitative measurement of three-dimensional tissue structure at a small cost. Therefore, it has become an indispensable tool for quantitative analysis and characterization of microstructure that is worthy of promotion.
The continuous emergence and improvement of new methods for acquiring, storing and transmitting images of the microstructure of materials, as well as better image processing and analysis methods, the continuous development and popularization of stereology principles and experimental techniques, and the rapid development of computer hardware and software capabilities Both provide a rare opportunity for the development and application of material microstructure morphology from qualitative characterization to quantitative characterization, from two-dimensional observation to three-dimensional geometric shape information testing. The high degree of automation of experimental methods and the easy acquisition of a large amount of microstructure quantitative data have also led to more possibilities for the misuse or unnecessary use of some advanced image analysis experimental methods, which cannot but be highly valued.
