Technology & Engineering
Microstructure of Metals
The microstructure of metals refers to the arrangement of grains and phases at a microscopic level within a metal. It includes the size, shape, and distribution of these grains, which greatly influence the mechanical and physical properties of the metal. Understanding and controlling the microstructure is crucial in engineering and manufacturing processes to achieve desired material properties.
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10 Key excerpts on "Microstructure of Metals"
eBook - ePubMaterials Selection for Design and Manufacturing
Theory and Practice
- Joseph Datsko(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
Chapter 4MICROCONSTITUENT DIAGRAMS AND MICROSTRUCTURES
INTRODUCTION
The preceding chapters on crystalline structures and material phases form a background to the concepts of microconstituent diagrams and microstructures presented in this chapter. The subject of microstructures is very important because it serves as a means to analyze and compare the mechanical properties of all materials. The common alternative, as is frequently done, is simply to list separately for each family of materials the common treatments and resulting properties. That approach yields tables listing the properties of the various steels, and other tables for the aluminum alloys, and still others for the titanium alloys, but it cannot reveal the fundamental ties among each family of materials. When the treatments and properties of each type of material are discussed separately, the differences among them are emphasized. When the treatments and properties of materials are studied on the basis of microstructure, however, the similarities among them are emphasized. One big advantage of this latter approach is that instead of being forced to select a material on the basis of its properties for a few standard treatments, one can specify a treatment that will give the material optimal properties for a given part and application.MICROSTRUCTURES
Microstructure is the geometric configuration or grain structure of a polished and etched plane surface of a material as seen through an optical microscope. The usual magnification is 50 × to 1500×. Thus microstructure is an intermediate-size structure between the macro (with no magnification) scale and the atomic scale. The individual grains that make up the microstructure are called microconstituents.Although the terms phase, microstructure, and microconstituents are similar and related, they do not all mean the same thing. The term phase is used to identify a portion of a material system on the basis of chemical composition. Microsconstituent is used to identify a portion of a material system on the basis of its visual appearance, after polishing and etching, under an optical microscope. Microstructure
eBook - PDF- K.-H. Zum Gahr(Author)
- 1987(Publication Date)
- North Holland(Publisher)
According to Hornbogen (ref.7,8) and Petzow (ref.7) the term microstructure of po 1 y c ry s t a 1 s e m bra ce s nu c 1ea r s t ru c tu re , atomic or molecular arrangement, crystal defects, crystal and 10 structural anisotropy and phase transformations. A real crystal can be distinguished from the ideal crystal by its defects. Crystal defects may be classified using their dimensions: 0 - dimensional or point defect: vacancy, interstitial or subst tutional solute atom. 1 - dimensional or line defect: dislocation. 2 - dimensional or area defect: grain or crystal boundary, tw boundary, stacking fault, antiphase boundary. 3 - dimensional or volume defect: hole and coherent, semicoherent or incoherent particle. Three- dimensional defects are obtained by joining together zero - dimensional defects. Crystal defects come into existence during crystallization from the liquid state, annealing and quen- ching, plastic deformation and/or irradiation. Figure 2-2 shows elements of the microstructure of crystalline inorganic mate- rials. It should be recognized that microstructures may vary extensively and depend on the properties of the materials. Figure 2-2. - Schematic representation of structural elements of inorganic solids. 1 1 The properties of materials are influenced by the crystal structure, size, shape and orientation, or the chemical composi- tion of the grains. They depend on the density of crystal defects such as vacancies or dislocations and on the type, volume, size, shape or orientation of second phases, e.g. precipitated parti- cles. Prediction of the properties of multiphase materials may be very complicated. Figure 2-3. - Light micrographs of microstructures of an Fe-36 at.% Ni-12 at.% A1 alloy. The microstructures presented in Fig.2-3 were produced by austenitizing at 130OoC and quenching in ice water, followed by aging in two steps at 500 and 80OoC.
- Zaki Ahmad(Author)
- 2011(Publication Date)
- IntechOpen(Publisher)
Another important field of material characterization is the description of microstructure heterogeneities. Such heterogeneities are often related to risks of premature damage nucleation and preferential defects (void, cracks, corrosion, etc.) occurrence and propagation. One of the most important elements of the microstructure of metallic materials is the set of second phase particles. Particle size and shape distributions and the type of spatial dispersion (homogeneous, long-range or short range ordered, clustered, etc.) are often the major attributes of a particular microstructure (Humphreys & Hatherly, 2004; Polmear, 2006). Thin foils made from aluminium-manganese based alloys, such as AA3003, are the material most frequently used as fins in automotive heat exchangers (Hirsch, 2006). This application imposes very strict requirements on properties and related foil microstructures. The development of an appropriate production technology is contingent on the perfect knowledge of the impact of processing parameters on microstructure transformation, including the changes of the set of particles (Hirsch, 2006; Slámová et al., 2006). In statistical setting, we deal with microstructures containing random objects in a space or plane, which may be second phase particles, pores, grains and their sections or projections. The question frequently asked is whether two microstructures come from a material with the same geometrical characteristics of microstructure. This statement forms a null hypothesis H 0 and the aim is to develop a statistical two-sample test of H 0 against an alternative hypothesis that the geometrical characteristics are different. In the literature, parametric models of microstructures as random sets are mostly used (Derr & Ji, 2000; Ohser & Mücklich, 2000) and the authors recommend Monte Carlo testing which is based on the possibility of simulating a random set under the null hypothesis.
- James C. M. Li(Author)
- 2011(Publication Date)
- Jenny Stanford Publishing(Publisher)
In particular the differences are related to the density of dislocations in the refined grains, the distribution function of the grain boundary structure/properties, and the grain geometry. Some of the most characteristic microstructures obtained by HE processing are illustrated in Fig. 5.1. Figure 5.1 Microstructures of HE materials deformed to a total true strain of ~4: (a) aluminum, (b) the 2017 aluminum alloy, (c) copper, (d) titanium, (e) austenitic stainless steel, and (f) Eurofer 97 steel. 9 In the case of pure aluminum (Fig. 5.1a), equiaxed grains, almost free of dislocations, are observed, whereas in pure copper (Fig. 5.1c) a dislocation cell Microstructural Features of Nanocrystalline Metals 136 The Effect of Microstructural Features on the Mechanical Properties of Nanocrystalline Metals structure is present after the same true strain. Grain refinement is much more ef ficient in the case of aluminum alloys (Fig. 5.1b) and titanium (Fig. 5.1d). However, in both cases the grains show a significant dislocation density. Hydrostatically extruded stainless steel (Fig. 5.1e) exhibits a very different microstructure, which possesses a high fraction of twin boundaries. 5.2.2 Grain Size As the primary objective of SPD processing is to reduce the grain size, its quantitative evaluation is of major importance. In order to quantify grain size, various parameters can be used, including the equivalent diameter, d 2 , defined as the diameter of a circle with the same surface area, or the mean intercept length, l . The equivalent diameter, d 2 , is measured for the population of individual grains/subgrains revealed in transmission electron microscopy (TEM) observations. The grain size is then quantified by its average value, E( d 2 ). The mean intercept length is determined for the entire population with no individual grains being measured.
- D. Scott MacKenzie, George E. Totten(Authors)
- 2005(Publication Date)
- CRC Press(Publisher)
The other nitrides are often visible in the light microscope, although submicroscopic size nitrides can also be present. Sigma and chi can be produced in certain stainless steels after high-temperature exposure. 3.5 SUMMARY The microstructure of ferrous alloys is very complicated and this review has only touched the surface of knowledge about steel microstructures. It is a basic tenet of physical metallurgy that composition and processing establishes the microstructure and that microstructure influences most properties and service behavior. To maintain control of the quality of steel products and to diagnose problems in processing, testing, or service, the microstructure must be identified and, in some cases, quantified. This can only be accomplished when the metallographer can properly distinguish the phases or constituents present. This depends upon proper specimen preparation and etching. The following micrographs illustrate nearly all of the commonly encountered phases and constituents in iron-based alloys while showing advantages and disadvantages of different etching techniques. FIGURE 3.1 Well-formed flakes of graphite in gray cast iron. As-polished; original at 200 . 162 Analytical Characterization of Aluminum, Steel, and Superalloys FIGURE 3.3 Primary, second-ary and tertiary alpha dendrite arms in gray cast iron. As polished; original at 500 . Undesirable flake shape. FIGURE 3.2 Primary alpha dendrite in hypoeutectic gray iron with well-formed graphite flakes. As polished; original at 100 . FIGURE 3.4 Example of undercooled graphite in gray cast iron (Fe–3.58% C–1.65% Si–0.51% Mn–0.014% S–0.15% P–0.22% Ti) in the as-polished (left) and etched (right, with 2% nital) conditions. The magnification bars are both 50 m m long. Microstructure of Ferrous Alloys 163 FIGURE 3.5 Primary alpha den-drites in hypoeutectic gray iron. The specimen was etched with 2% nital and the magnification bar is 100 m m long.
eBook - PDFAluminium Alloys
Recent Trends in Processing, Characterization, Mechanical behavior and Applications
- Subbarayan Sivasankaran(Author)
- 2017(Publication Date)
- IntechOpen(Publisher)
Chapter 8 Effect of the Processing Conditions on the Microstructural Features and Mechanical Behavior of Aluminum Alloys Tomasz Tański and Przemysław Snopiński Additional information is available at the end of the chapter http://dx.doi.org/10.5772/intechopen.70682 Abstract Aluminum and aluminum alloys are widely used for aircraft structures, where they are subjected to demanding conditions and where is an increased demand for weight reduction and fuel savings. Aluminum comprises 8% of the earth ’ s crust and is, there-fore, the most abundant structural metal. Its production since 1965 has surpassed that of copper and now comes next to iron. This increased use of aluminum alloys leads to a need for deeper understanding of their mechanical properties and the impacts of processing parameters. The mechanical properties can determine by controlling the microstructures of the alloys. For example, precipitation hardening is the main strength-ening mechanism improving the tensile and yield strength. Solute atoms, precipitates and dispersoids influences to the yield strength, since they act as distributed pinning points for mobile dislocations, thus increasing the shear stress required to move the dislocations. Another approach is the manipulation of a grain size that can be performed by alloying or plastic deformation processes. Therefore, the precise understanding of each mechanism that can influence the properties of aluminum and its alloys is very important. The aim of this chapter is to shed light on the influence of the processing history on the microstructure and mechanical properties. Keywords: aluminum, heat treatment, structure, properties, severe plastic deformation 1. Aluminum — introduction Aluminum is the third most abundant element in the earth ’ s crust and the most abundant metallic element. For the last five decades, it has been second only to iron in an industrial use.
eBook - PDF- Zoia Duriagina(Author)
- 2019(Publication Date)
- IntechOpen(Publisher)
Microstructure-Tailored Stainless Steels with High Mechanical Performance at Elevated… http://dx.doi.org/10.5772/intechopen.80468 125 subgrains (see Figure 10d and e ) inhibiting dislocation movement. These phenomena are typical in materials with low stacking fault energies such as austenitic stainless steels. In the third region threshold value of the material is reached after 400 MPa stress and the materials fails in a dual ductile-brittle mode. Figure 10f and g ) shows striations, cup and cone dimples and brittle cleavages confirming a dual failure mode. 3.3. Mechanical performance and microstructural studies of SLM stainless steels at high temperatures (>800°C) The microstructure of a polycrystalline material is a key parameter in determining a wide range of its properties including mechanical strength, toughness, electrical conductivity and magnetic susceptibility [43, 44]. One important aspect of microstructure is the size of the grains and its influence on the properties. Thus, to design the grain size and restrict grain growth, microstructural engineering has become of fundamental importance [45]. High temperature applications are critically influenced by grain growth, precipitation and phase changes. Biggest issue which is very common and probable in materials exposed at high temperatures is the abnormal grain growth, where one or more grains will grow abnormally in the micro-structure. The presence of abnormally large grains is detrimental to the mechanical properties of polycrystalline structures [46]. Mechanical properties of SLM 316L at 1100 and 1200°C is listed in Table 5 and compared to conventional 316L materials at the same temperature [47]. The Superior, 10 times higher, mechanical strength of 300 and 150 MPa of 316L SLM (for tem-peratures 1100 and 1200°C respectively) compared to 35–40 and 20 MPa, points out that the rapid grain growth and loss of strength has been avoided.
- David Brandon, Wayne D. Kaplan, David Brandon(Authors)
- 2008(Publication Date)
- Wiley(Publisher)
That is, the property is not single-valued, but is best described by a probability function. We know that not all men are 180 cm tall, nor do they all weigh 70 kg. Rather, there are empirical functions describing the probability that an individual taken from any well-defined population will have a height or weight that falls within a set interval. Clearly, if an engineering property is stochastic in nature, then it is likely that the material parameters which determine that property will also be stochastic, so that we need to determine the statistical distribution of the parameters used to define these material properties. The second support pier needed to build our bridge is on the microstructural side of the chasm. It is constructed from our understanding and knowledge of the mechanisms of image formation and the origins of image contrast, in combination with a quantitative analysis of the spatial relationship between microstructural image observations and the bulk structure of the material. This geometry-based, quantitative analysis of microstructure is termed stereology , the science of spatial relationships, and is an important component of this book (see Chapter 9). For the time being, we will only consider the significance of some terms which are used to define a few common microstructural parameters. 1.1.3.1 Grain Size. Most engineering materials, especially structural materials, are polycrystalline, that is, they consist of a three-dimensional assembly of individual grains, each of which is a single crystal whose crystal lattice orientation in space differs from that of its neighbours. The size and shape of these individual grains are as varied as the grains of sand on the seashore. If we imagine the polycrystalline aggregate separated out into these individual grains, we might legitimately choose to define the grain size as the average separation of two parallel tangent planes that touch the surfaces of any randomly oriented grain.
- Masato Murakami(Author)
- 1993(Publication Date)
- World Scientific(Publisher)
68 CHAPTER 5 MICROSTRUCTURE 1. Introduction Microstructural characterization is very important in order to understand materials' properties. Many misleading conclusions have been drawn about the nature of oxide superconductors, due to a lack of microstructural understanding. Oxide superconductors are very complicated systems, and they consist of many elements and have complex structures. Therefore, most samples (even so-called single crystals) contain various second phases and defects such as stacking faults, dislocations, oxygen deficient regions, cracks. These defect structures are strongly dependent on processing conditions, and are very important for flux pinning enhancement. Furthermore, phase diagrams are not fully understood in these systems, which makes it difficult to choose suitable conditions for sample preparation. It is also important to note that oxygen concentration also affects superconducting properties. It is thus very important to characterize microstructure of the samples as carefully as possible, to study the relationship between their microstructure and properties. In this chapter, we first show results of macroscopic structural observations of melt processed samples and then present detailed microscopic structural characterization of MPMG processed YBaCuO samples by transmission electron microscopy. 2. Microstructure of melt processed samples 2.1. Microstructure of solidified samples Fig. 1 shows microstructure of a YBa2Cu30 x sample slowly cooled from 1200°C, observed by computer aided microanalysis (CMA, see chapter 2). Existing phases can be identified by their colors: light blue = YBa2Cu307; dark blue = Y2BaCuC>5; yellow = GS Fig. 1. Micro structure of an YBaCuO sample slowly cooled from 1200°C, observed by computer aided electron probe microanalysis. Existing phases can be identified by their color: light blue = YBa2Cu3C>7; dark blue = Y2BaCuOs; yellow = BaCu02; and red = CuO.
- Dino Fiorani, Giorgio Sberveglieri(Authors)
- 1994(Publication Date)
- World Scientific(Publisher)
Thus, nanocrystalline metals as a new class of materials are interest ing from several points of view. From a fundamental scientific perspective, it becomes now possible to study systema tically the structu ral, thennodynamic and mechanical properties of grain boundaries which have not been accessible to such an extend in the past. For technological applications these processes offer synthesis routes for extremely fine-scaled metals and composites which might find applications as ductile refractory materials, materials for effective hydrogen storage, preparation of otherwise immiscible alloys, sensors, penneable membranes etc . However, these materials in most cases are only usefull if the nanostructure is stable up to elevated tem pe ratures. 2. Experimental With both methods (i) and (ii), a decrease of the grain size to nanometer scales can be achieved leading to a drastic increase of the number of grain boundaries with typical densities of > 1 ()8 interfaces per m. Since the long and short range order typical for a crystalline or glassy state of matter is lacking in the grain boundaries if averaged over the sample volume drastic changes of the physical properties of nanocrystalline materials are ex pe cted if compared with conventional polycrystals [1]. For 'pure ' metals in the fonn of fme powder particles and compacted pellets with a grain size typically about 10 nm, the following pro pe rties have been found to be characteristic for the nanocrystalline state in comparison with the single crystal or conventional polycrystal: -reduction of density to -0.9 [8], -stored energy of up to 40% of the heat of fusion [9], -increase of the specific heat at constant pressure of the grain boundary component up to 50% [10],
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