China 
Africa 
Explore chapters and articles related to this topic
Industrial Applications of Microstructural Characterization — Current and Potential Future Issues and Applications
Published in Jeffrey P. Simmons, Lawrence F. Drummy, Charles A. Bouman, Marc De Graef, Statistical Methods for Materials Science, 2019
David Furrer, Ryan Noraas, David B. Brough
In addition to the lack of grain size distribution information, average grain definitions alone also do not provide information about grain size orientation distribution. Many materials can recrystallize to fine uniform grain sizes, but neighboring grains or clusters of grains can exhibit very low angles of crystallographic misorientation. These regions of near-common crystallographic orientation can effectively act as a single, larger grain assemblage. This has been seen in nickel-base superalloys [11] and titanium alloys [874]. When nickel-base superalloys are statically recrystallized in special cases, sub-grains within the prior larger grains can result with the sub-grains having very low angle boundaries. This condition has been previously termed “ghost grains” where many of the properties such as ultrasonic inspectability (or attenuation) and tensile strength are controlled by the larger prior grain structure. In titanium materials, local colonies of aligned alpha grains or often termed micro-texture regions (MTRs) can result and can cause a similar impact to material and component properties [1152]. It can be seen from these examples that average grain size of single or multi-phase materials cannot completely describe capability and equivalency of these materials and associated components.
Mechanical Behavior of Materials
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
Mechanical properties of metals depend on the type of grain boundary that exists between grains. Grain boundaries are categorized based on the misorientation of two grains. Misorientation means variation in crystallographic orientation between two neighboring grains of a polycrystalline metal. Grain boundary geometry is described through a grain misorientation process. The misorientation is also defined as the difference between misorientation angle and misorientation axis of two lattices. Grain boundaries consist of both tilt and twist boundaries. A tilt boundary is the one in which one crystal has been twisted about an axis that lies in the boundary plane, relative to the other crystal. A twist boundary is the one in which one crystal has been twisted about an axis perpendicular to the boundary plane, with respect to the other crystal. Grain boundaries are of two types, based on the misorientation of grains. They are low-angle GBs and high-angle GBs. If the misorientation between grains is less than 15°, then it is known as sub-GBs or low-angle GBs. If the misorientation between the grains is greater than 15°, then it is known as high-angle GBs. Misorientation is calculated from the product of one orientation and the inverse of the other. The grain orientation is defined by an orientation matrix (g). The misorientation between two neighboring grains (grain 1 and grain 2) is given as follows: () M=g1−1g2
Engineering Mechanics and Mechanical Behavior of Materials
Published in Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu, Interdisciplinary Engineering Sciences, 2020
Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu
In polycrystalline materials, the grains with atoms having identical orientation on chemically etched surfaces, can be viewed under an optical microscope (chemical reagent etches grain boundary and grain differently). The difference in crystal orientation between two neighboring grains is determined by the angle of misorientation. Based on the angle of misorientation, the low- and high-angle grain boundaries can be defined and the transition from one to another typically takes place at 5–10°.
Microstructure and mechanical property of high power laser powder bed fusion AlSi10Mg alloy before and after T6 heat treatment
Published in Virtual and Physical Prototyping, 2022
Mengna Liu, Kaiwen Wei, Runsen Zhou, Xiaoze Yue, Xiaoyan Zeng
Grain boundary misorientation is also an important crystallographic feature. Generally, the grain boundary angles can be divided into high-angle grain boundaries (HAGBs) which are higher than 15° and low-angle grain boundaries (LAGBs) which are lower than 15° (Mehta et al. 2021). The results of the HAGBs and LAGBs distribution of the as-printed and T6 sample are shown in Figure 11. It is found that both the grain boundaries of the two kinds of samples are dominated by HAGBs. To be specific, the HAGBs and LAGBs number fraction of the as-printed sample is 67.3% and 32.7%, respectively. After T6 heat treatment, the HAGBs number fraction increases to 77.1% and the LAGBs number fraction decreases accordingly to 22.9%. It is worth noting that the proportion of the equiaxed grains with no LAGBs increases after T6 treatment, as marked by the yellow dotted line in Figure 11(b).
Strengthening effect of grain and twin boundaries in zirconium bi-crystal micropillars
Published in Philosophical Magazine Letters, 2021
Jaiveer Singh, Shanta Chakrabarty, Prita Pant
Recently, the role of both grain and twin boundaries has been investigated by compression of bi-crystal micropillars [23–28]. Ng and Ngan [24] studied the behaviour of polycrystalline Al micropillars and showed that a grain boundary inside a bi-crystal micropillar can trap dislocations inside the sample which can lead to significant enhancements in strength and strain-hardening rate [24,28]. Kheradmand et al. [23] have studied the interaction of dislocations with grain boundaries in bi-crystalline high-purity Ni micropillars. A clear change in the mechanical behaviour of bi-crystalline micropillars was seen when the crystal size was below 1 μm. This was attributed to dislocation:grain-boundary interactions becoming more dominant in smaller pillars than dislocation:dislocation interactions. Owing to dislocation accumulation near grain boundaries, an increase in the misorientation was also observed. Contradictory results were reported by Kunz et al. [26] who found that Al bi-crystal pillars showed a lower rate of work hardening than single-crystal pillars on account of the absence of defects or dislocation pile-ups near the boundary regions. Li et al. [25] showed that neither grain boundaries nor twin boundaries in bi-crystals resulted in a significant increase in the strength of samples [25,27].
Topological model of type II deformation twinning in NiTi martensite
Published in Philosophical Magazine, 2019
R. C. Pond, J. P. Hirth, K. M. Knowles
The formation of type II twins is also illustrated in Figure 2. Here, the disconnections described above are again generated on the glide plane, but accumulate in a different manner, forming a tilt wall perpendicular to . After partitioning of the strains and rotational distortions of the defects between the adjacent crystals, a symmetrical tilt boundary is formed on the plane. The misorientation can be described by, for example, the axis/angle pair, , or . In this way, the interface formed corresponds to the type II conjugate twin on the invariant plane. However, while the overall deformation is equal to a simple shear of magnitude on , the mechanism of formation involves both shear on and accommodational relaxation. Hence, it does not correspond directly with the classical model.