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Ceramic Armour
Published in Paul J. Hazell, Armour, 2023
Higher densities and small grain sizes can be achieved by hot pressing. This is achieved when, simultaneously, pressure and temperature are applied to the powder. The application of pressure increases the contact stresses between particles and rearranges them to optimize their packing arrangement. This leads to a reduced densification time and can lead to a reduction in the temperature required to sinter— thereby reducing the amount by which the grains grow. This will lead to a final product with an increased final strength compared to a ceramic that was densified using pressureless sintering. Hot pressing can provide a near-theoretical density material with a very fine grain structure and therefore optimized strength, and therefore most suitable for armour applications. The same types of fine-grained powders suitable for pressureless sintering are usually suitable for hot-pressing applications. In most cases, a grain growth inhibitor will be added to inhibit grain growth to achieve a maximum density with minimum grain size.
Recrystallization and Grain Growth
Published in Zainul Huda, Metallurgy for Physicists and Engineers, 2020
Grain growth is the third stage of annealing; it refers to the increase in the average grain size of the metal when the metal is heated beyond the completion of recrystallization (see Figure 14.1). The control of grain growth is great technological importance because many material properties strongly depend on the grain size and its distribution (Huda et al., 2014; Huda and Ralph, 1990).
Metal Forming I—Deformation and Annealing
Published in Zainul Huda, Manufacturing, 2018
Grain growth is the third stage of annealing; it refers to the increase in the average grain size of the metal when the metal is heated beyond the completion of recrystallization (see Figure 5.4). The control of grain growth is of great technological importance because many material properties strongly depend on the grain size and its distribution (Huda and Ralph, 1990; Huda et al., 2014).
Dynamic grain models via fast heuristics for diagram representations
Published in Philosophical Magazine, 2023
Andreas Alpers, Maximilian Fiedler, Peter Gritzmann, Fabian Klemm
Grain growth is an important field of study in materials science as the resulting grain structures strongly influence the mechanical and physical properties of metals, ceramics, and other polycrystalline materials [1, 2]. Although, starting with works of Smith, von Neumann, and Mullins in the 1950s [3–5], a number of different models have been introduced over the years, understanding and controlling grain growth remains challenging, both in theory and practice. For instance, the recent empirical study [6] demonstrates that neither the classical Hillert model [7] nor the MacPherson–Srolovitz model [8] capture anisotropic grain growth adequately. Even more drastically, [9] concludes that ‘a new model for grain boundary migration is needed to predict microstructure evolution’; see also [10–13].
Microstructural studies and parametric optimization of dissimilar friction stir welds
Published in Welding International, 2023
Yash Dugar, Nishant Singh, Ajit Kumar, Gowtham Vinayagamurthy, S. P. Shanmuganatan, Madhusudan Manjunath
The tool pin plunges and traverse across the joint, forming a weld nugget. High temperature and intense plastic deformation in the weld pose a recrystallized microstructure with very fine grains. The microstructures and qualities of the nugget are connected to the extent of plastic deformation of the material [20]. Recrystallization is a process in which grains of a crystal structure come in a new structure or new crystal shape. Precisely, recrystallization is most notably related to recovery and grain growth. The speed and pin geometry of the tool decides the fragmentation. The frictional heat facilitated recrystallization and tool stirring fragmented the new crystal formed. The parent metal grains are elongated as the sheet has been solution treated and precipitation hardened. The treated sheet is further rolled to desired temper in cold rolling process.
Effect of friction stir welding parameters on corrosion behaviour of aluminium alloys: an overview
Published in Corrosion Engineering, Science and Technology, 2022
Firdausi H. Zamrudi, Asep R. Setiawan
Plastic deformation and temperature increase can simultaneously result in dynamic recrystallisation phenomena in the SZ. If this occurs, the recrystallised grains might experience grain growth so that the grain size increases. The increased rotational tool speed increases the workpiece's HI and temperature. At higher temperatures, the effects of the grain growth phenomenon will be more visible, leading to a larger grain size. However, dynamic recrystallisation occurs only in the SZ area. In the TMAZ region, plastic deformation's magnitude and temperature are insufficient to initiate recrystallisation. While in the HAZ area, grains do not undergo plastic deformation, and the increase in temperature in this area is relatively small, so no grain growth phenomenon is detected. These changes in grain size in the weld area will further affect the corrosion resistance of the FSWed metal. The welding speed increase during FSW tends to decrease the grain size in the stir zone of the FSWed sample [34]. The increase in the welding speed will lead to a decrease in HI in the weld area. As a result, the peak temperature in the weld centre will be lower, resulting in smaller grain size in the stir zone. Table 3 shows the grain size variation in the SZ, TMAZ, WZ and PM areas.