Grain, in materials

Structure defects decrease conductivity of the studied material, and then the intensity of the induced magnetic field is small and the signal received by the probe Hp is big (Fig.2). Low conductivity of austenite is a defects of the structure in case of residual austenite in the martensite structure, which with regard to the magnesite structure is as 1 5. Eddy currents produced in the studied area are subject to excitation in effect of small conductivity of austenite grains in the structure of the studied material. 

The main goal of ultrasonic grain noise suppression in material flaw detection is to improve the perceptual possibilities of the operator to observe defect echoes. The suppression is defined as perceptually ideal when a received signal (or image) which contains echoes buried in noise is filtered to yield nonzero values only at the positions of the defect echoes. 

Another example shows a 4 MHz longitudinal wave probe WSY70-4 normally used for testing of coarse grained austenitic material. In this application a high pulse amplitude is... 

Clays composed of mixtures of clay minerals having from 20—50% of unsorted fine-grain nonclay materials are most satisfactory. Large amounts of iron, alkaHes, and alkaline earths, either in the clay minerals or as other constituents, cause too much shrinkage and greatiy reduce the vitrification range thus, a clay with a substantial amount of calcareous material is not desirable. Face bricks, which are of superior quaHty, are made from similar materials but it is even more desirable to avoid these detrimental components (see Building materials, survey). 

The crystals, or grains, in a polycrystal fit together exactly but their crystal orientations differ (Fig. 10.4). Where they meet, at grain boundaries, the crystal structure is disturbed, but the atomic bonds across the boundary are numerous and strong enough that the boundaries do not usually weaken the material. 

Example Approximate calculation of the hardness of solids. This concept of shear yielding - where we ignore the details of the grains in our polycrystal and treat the material as a continuum - is useful in many respects. For example, we can use it to calculate the loads that would make our material yield for all sorts of quite complicated geometries. 

Explain what is meant by diffusion in materials. Account for the variation of diffusion rates with (a) temperature, (b) concentration gradient and (c) grain size. 

X-ray Diffraction (XRD) is a powerful technique used to uniquely identify the crystalline phases present in materials and to measure the structural properties (strain state, grain size, epitaxy, phase composition, preferred orientation, and defect structure) of these phases. XRD is also used to determine the thickness of thin films and multilayers, and atomic arrangements in amorphous materials (including polymers) and at inter ces. 

LEED beam is reduced to less than the sample grain size, individual grains in a polycrystal can be investigated. It is difficult to make low-energy electron beams this small, but in some materials large grain sizes can be achieved in polyctystals. 

In 1975 Wacker-Chemie introduced silicones under the name of m-polymers. These are also room temperature curing liquid polymers which give rubbery materials on cross-linking and are available both as one- and two-component systems. Their particular feature is that they contain dispersions of copolymers such as those of styrene and n-butyl acrylate in the shape of rods or rice grains in the fluid silicone polymer. A small amount of the organic copolymer is also grafted onto the silicone backbone. 

An EDX spectrum typical of thin-film analysis in TEM/(S)TEM is shown in Eig. 4.26. It was obtained from a polycrystalline TiC/Zr02 ceramic by use of an Si(Li) detector at 100 keV primary electron energy. Eor spectrum recording the electron probe of approximately 1 nm in diameter was focused on the triple junction between the grains in the STEM mode (Eig. 4.26a). Besides the elements expected for the material under investigation, viz. Ti and Zr, Si, Ee, and Co were also detected, hinting at the presence of a (Ee, Co) silicide as an impurity. Eor ceramic materials it is known that... 

Metallurgists originally, and now materials scientists (as well as solid-state chemists) have used erystallographic methods, certainly, for the determination of the structures of intermetallic compounds, but also for such subsidiary parepistemes as the study of the orientation relationships involved in phase transformations, and the study of preferred orientations, alias texture (statistically preferential alignment of the crystal axes of the individual grains in a polycrystalline assembly) however, those who pursue such concerns are not members of the aristocracy The study of texture both by X-ray diffraction and by computer simulation has become a huge sub-subsidiary field, very recently marked by the publication of a major book (Kocks el al. 1998). 

One of the most elegant experiments in materials science, directed towards a particularly detailed understanding of the energetics of grain boundaries, is expounded in Section 9.4. 

Palumbo, G. and Aust, K.T. (1992) Special properties of S grain boundaries, in Materials Interfaces Atomic-level Structure and Properties, eds. Wolf, D. and Yip, S. (Chapman Hall, London) p. 190. 

K. Higashi, "Deformation Mechanisms of Positive Exponent Superplasticity in Advanced Aluminum Alloys with Nano or Near-Nano Scale Grained Structures," in Materials Science Forum Vols. 170-172, pp. 131-140, T.G. Langdon ed., Trans Tech Publications, Switzerland, (1994). 

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