Introduction to the world of metallography
You may have never heard about this “metallography” thing, but if you have ever used telephones or had a plane trip, you have definitely benefited from its existence. This kind of “study” describes the atomic and chemical structure of all types of metallic alloys using microscopy as a tool.
Think first, the metallography as we know it nowadays owes much to the contribution of 19th century scientist Henry Clifton Sorby. His pioneering work in modern iron and steel production in Sheffield, UK, highlighted this intimate relationship between microstructure of metals and the macroscopic properties of things built with them. Metallography was first invented in 1949, from its humble beginnings the Atomic energy commission (AEC) Metallography Group grew, and in 1954 the AEC instructed it to organize more formally with officers, directors, and committees. The basic organizational structure that has developed is essentially the same as the current IMS structure. The IMS structure is nothing more than the Incident Management System: basic structure at its most basic, it consists of an incident commander, who also assumes responsibility for operations, planning and logistics.
But let’s get back to the topic, what is metallography and what is it used for. You can ask yourself why we need metallography in our life. I’m here to let you know that. Basically, as you already know, it is the study of materials microstructure. It helps determine if the materials have been processed correctly and if it is therefore a critical step for determining product reliability and for determining why the materials have failed. With others first and more understandable it helps companies decide which materials are stable enough to build bridges, cars or motorcycles.
Hence, the other question is for what purpose is this study used? By examining and quantifying the microstructure of a material, its performance can be better understood. Thus, metallography is used at almost every stage of a part's life: from initial material development to inspection, manufacturing, inspection of manufacturing processes, and even, if necessary, defect analysis.
The significance of this study is high, it can ensure that the right metal is used for important things like cars, airplanes and electronics. It is also crucial in facilitating the development of new materials. Thousands of standardized alloys are available today and even more are under development as demand for lighter and stronger metals continues. As you can see, the science behind metallography is indeed significant and important, not only to know which metal can be used for creating specific components. Ceramic and polymeric materials may also be prepared using metallographic techniques. It is an extremely important field, as we use countless metals and alloys in everyday life, and in many cases, it is “vital” to know their crystal structure, phases, inclusions, and grain distribution. They determine their properties and the usability of the tools and parts made from them. Metallographic methods can also detect material defects such as cracks, inclusions, enrichments, inhomogeneities, corrosion, etc. Also, ceramics, polymers, composites, and other materials can also be examined by metallographic methods.
But how can you prepare metallographic samples? I’ll tell you, the surface of the metallographic sample is prepared by various methods of grinding, polishing and etching. After preparation, it is often analyzed by optical examination or electron microscopy. Only by using metallographic techniques can the person skilled in the art identify the alloys and predict the properties of the material. Mechanical preparation is the most common preparation method. Successfully, finer abrasive grains are used to remove material from the sample surface until the desired surface quality is achieved. There are many different machines for this grinding and polishing that are able to meet different quality, capacity and reproducibility requirements. The systematic method of preparation is the simplest way to achieve real structure. Therefore, the rules suitable for most materials should be followed when preparing the sample.
In the following rows it lets you know what is the methodology behind the metallography. The surface of the metallographic sample is prepared by various methods of grinding, polishing and etching. After preparation, it is often analyzed by optical or electron microscopy. Only using metallographic techniques can the person skilled in the art identify the alloys and predict the properties of the material. The steps include cutting, assembly, sanding, fine sanding, polishing, etching, and microscopic examination, respectively. Samples should be kept clean, and the preparation procedure carefully followed to reveal accurate microstructures.
There is an interesting part in the steps, which I would like to describe better, which is the microscopic examination. Many different microscopic techniques are used in metallographic analysis. The prepared samples should be examined with the naked eye after etching to detect visible areas that have reacted abnormally to the etching as a guide for performing the microscopic examination. Light optical microscopy (LOM) examination should always be performed before any electron metallographic (EM) technique, as these are more time consuming, and instruments required for this are much more expensive. In addition, certain characteristics are best observed using LOM, such as the natural color of the component is seen in LOM but not in EM systems. In addition, the image contrast of the microstructures at relatively low magnification, e.g. The LOM scan is fast and can cover a large area. Thus, the analysis can determine whether more expensive, time-consuming testing techniques are needed using electronic microscopy, and where the work should be concentrated.
In the last paragraph, I will talk about what quantitative metallography is, so it involves measuring the components of the microstructure to provide more reliable data for material engineering and quality control purposes. Typical microstructural measurements include the length, width, and area of the characteristics, or the relative amount of a structure or phase.
We thank Sándor Dezső for research and compilation.