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Strengthening Mechanisms in Metals
Published in Zainul Huda, Metallurgy for Physicists and Engineers, 2020
Grain-boundary strengthening refers to the strengthening of a polycrystalline material owing to the presence of grain boundaries in its microstructure. We learned in Chapter 2 that solidification of a polycrystalline material results in a grained microstructure with grain boundaries (see Figure 2.13). Strictly speaking, a grain boundary is an array of dislocations (Huda, 1993). When a solid is under a shear stress, dislocations tend to move through the lattice (see section 9.1). However, a dislocation approaching a grain boundary will not be able to easily cross it into the adjacent grain (see Figure 9.3). In order for the dislocation to easily cross the grain boundary, greater stress is needed to be applied. This mechanism is called grain-boundary strengthening.
Automotive Architecture
Published in Patrick Hossay, Automotive Innovation, 2019
Perhaps one of the most interesting characteristics of new steel innovations is the capacity to define ultra-fine grain structuring and reinforcement at the nanometer scale, causing variants of third-generation materials to be named nanostructured steels. With grains in the 10–100 nm range, they are defined by assemblies of crystals which can at times have only a few dozen atoms each, orders of magnitude smaller than conventional steel. With careful control of crystal development and grain growth, defects including the grain boundaries that degrade conventional steel’s strength can be controlled or excluded. The fine grain structure also impeded the motion of dislocations, an effect that defines grain boundary strengthening (Image 7.9). The smaller the grain, the stronger and tougher the material becomes (called the Hall–Petch relationship in material science). In this case, the results are metals with extraordinary properties, well outside the performance boundaries of even the most impressive existing AHSS. Future third-generation AHSS can offer nearly twice the strength of many second-generation steels and about eight times the strength of mild steel.9
Wear properties of Fe-16Mn-10Al-5Ni-0.86C lightweight steel manufactured by laser powder bed fusion
Published in Powder Metallurgy, 2023
Tae-Hoon Kang, Amol B. Kale, Han-Soo Kim, Kee-Ahn Lee
EPMA mapping in Figure 3 indicates the element distribution. The LPBF LWS has an uneven distribution of Fe, Mn, Al, Ni and C elements, whereas the conventional LWS reveals the elements evenly distributed in the matrix, which is more similar to the EBSD phase map. Therefore, based on aforementioned results, both LPBF-built and conventional LWSs show differences in size and fraction of B2-IMC due to differences in manufacturing process, and a phenomenon that looks different from other surfactants. The inhomogeneous distribution of Fe, Mn, Al, Ni and C elements in the LPBF LWS is due to the complex thermal history and rapid solidification rate during the LPBF process. The EPMA mapping results show that these elements are not uniformly distributed throughout the microstructure and can concentrate in certain areas. The uneven distribution of these elements can have a significant impact on the microstructure and properties of the material. Such as the concentration of Al and Ni at the grain boundaries can promote grain boundary strengthening, resulting in improved mechanical properties. On the other hand, the concentration of C in the interdendritic regions can lead to the formation of carbides, which can reduce ductility and toughness.
Formation of functionally graded hybrid composite materials with Al2O3 and RHA reinforcements using friction stir process
Published in Australian Journal of Mechanical Engineering, 2022
Chandra Vikram Singh, Praveen Pachauri, Shashi Prakash Dwivedi, Satpal Sharma, R. M. Singari
Optimum combination of friction stir process parameters (tool shape of triangular, tool rotational speed of 560 rpm and tilt angle of 0 degree) enhanced the Grain-boundary strengthening of composite material. Grain-boundary strengthening is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries are insurmountable borders for dislocations and that the number of dislocations within a grain has an effect on how stress builds up in the adjacent grain, which will eventually activate dislocation sources and thus enabling deformation in the neighbouring grain, too. So, by changing grain size one can influence the number of dislocations piled up at the grain boundary and yield strength of composite (Ritukesh et al. 2019; Wang et al. 2019; Dinaharan et al. 2019).
Grain boundary strengthening of carbon-doped TiZrN coatings by laser carburization
Published in Journal of Asian Ceramic Societies, 2021
Taewoo Kim, ByungHyun Lee, Seonghoon Kim, Eunpyo Hong, Ilguk Jo, Heesoo Lee
The improved mechanical properties of the carbon-doped TiZrN coating can be explained by the intergranular structure, as shown schematically in Figure 5b. Previous results indicated that grain boundary strengthening occurred due to the formation of a-C through the short-circuit diffusion of carbon. Thus, grain boundary strengthening is the main strengthening mechanism rather than solid solution strengthening.