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Friction Stir Welding Process
Published in Noor Zaman Khan, Arshad Noor Siddiquee, Zahid A. Khan, Friction Stir Welding, 2017
Noor Zaman Khan, Arshad Noor Siddiquee, Zahid A. Khan
The replacement of strained grains with new grains during straining above recrystallization temperature is termed as dynamic recrystallization. Continuous straining generates new dislocations within the recrystallized grains leading to the formation of subgrains, which in turn inhibit their future growth. Further straining results in fresh nucleation sites for recrystallization. Combination of nucleation and grain growth during continuous straining results in dynamic recrystallization. Dynamic recrystallization may be continuous or discontinuous. The steady state grain size (ds) obtained during dynamic recrystallization is expressed in terms of Z or σ (McQueen et al., 2011) in the following equations: ds−1=A+BlogZσs=C+Ddsp where A, B, C, D, and p are constants.
Microstructure and Mechanical Properties of Mg-Zn Based Alloys
Published in Leszek A. Dobrzański, George E. Totten, Menachem Bamberger, Magnesium and Its Alloys, 2020
Jae-Hyung Cho, Hyoung-Wook Kim, Suk-Bong Kang
The ZK40 and ZK60 alloys possessed better rollability. For this reason, different reductions in area (10% and 30%) were also carried out with the ZK40 and ZK60 sheets (initially 4 mm thick). In Figure 6.5, optical micrographs of as-rolled ZK40 alloys 1-mm thick subjected to reduction in area of 10%, 30%, or 50% were compared. The temperature of the warm rolling process was 523 K (250°C). With greater reduction in area, the volume fraction of dynamic recrystallization increased and overall grain size was further refined.
Joining of Dissimilar Materials Using Friction Welding
Published in Jaykumar J. Vora, Vishvesh J. Badheka, Advances in Welding Technologies for Process Development, 2019
In all systems, thermomechanical deformation or dynamic recrystallization is possible. During friction welding, the material near the interface undergoes frictional heating and plastic deformation. This favors dynamic recrystallization in low-strength materials. The width of this is more for low-strength materials (for Cu in Cu–Fe system). The extent of this will be different on two sides of the weldment. The magnitude depends on the thermophysical properties of the individual components.
Positron Annihilation Studies of Subsurface Zone Created during Friction in Pure Silver
Published in Tribology Transactions, 2019
Jerzy Dryzek, Krzysztof Siemek
Dynamic recrystallization is characterized by nucleation and growth of new defect-free grains that occur during deformation rather than after deformation and during separate heat treatment, as in static recrystallization. Usually it occurs during plastic deformation at high temperature. This process consists of the formation of new grains at the old grain boundaries. The nucleated new grains are free of defects, but the material continues to deform, causing an increase in dislocation density in the grain interior. This suppresses the grain growth or grains ceases to grow. Ultimately, dynamic recrystallization can result in very small grain size.
Dynamic multimode process monitoring using recursive GMM and KPCA in a hot rolling mill process
Published in Systems Science & Control Engineering, 2021
Gongzhuang Peng, Keke Huang, Hongwei Wang
Corresponding to the p-h curve is the spring equation for the rolling mill shown below. where is the thickness of the rolled piece, is the no-load roll gap, is the rolling force, is the pre-pressing force shown in Figure 6, is the stiffness coefficient of the rolling mill, and is the thickness change caused by the bending force, is the zero position of the roll gap, and is the oil film thickness compensation. is related to strain accumulation, dynamic recrystallization, static recrystallization, phase change and other factors. Existing rolling force models are derived from the concise deduction of relevant influencing factors under specific constraints, and the following expressions can be used. where is the bandwidth, is the horizontal projection length of the contact arc between the roll and the rolled piece, which is related to the radius of the roll. is the stress status modulus, which is determined by the shape parameter of the deformation zone. is the metal deformation resistance, which is related to the deformation temperature, deformation speed and degree of deformation. is the influence coefficient of the front and back tensile stress on the rolling force.
Microstructural features of dynamic recrystallization in alloy 625 friction surfacing coatings
Published in Materials and Manufacturing Processes, 2018
Stefanie Hanke, Ian Sena, Rodrigo S. Coelho, Jorge F. dos Santos
The distribution of grain boundary misorientation angles and the grain size in three different locations on the coating cross section – advancing and retreating side as shown in Fig. 5, as well as the middle of the same coating cross section – are presented in Fig. 6. In the middle of the cross section, the highest amount of both low-angle grain boundaries and twins (≈60° misorientation) exists. Annealing twins are related to fast high-angle grain boundary migration into highly deformed neighboring grains [18] during recrystallization. The grain size here is low (Ø 1.4 ± 1.1 µm) and its distribution is comparable to the advancing side (Ø 1.3 ± 0.9 µm), while on the retreating side a significantly larger fraction of grains with higher diameter prevails (Ø 3.8 ± 2 µm). On the retreating side, also the lowest number fraction of low-angle boundaries and twins exists, and the grain boundary misorientation angle of most grains is generally higher. These observations indicate a lower recrystallization and grain growth rate during processing on the retreating side, than on the advancing side and in the center. The same analysis has been carried out for the other rotational speeds, but the grain size was found to show less variation with process parameters, than between advancing and retreating sides within a single layer. It is interesting to note that the differences in torque measured for different rotational speeds, which may be explained by variations in process temperatures, do not seem to be related to different recrystallization grain sizes. Still, the measured torque is a macroscopic value, and more detailed investigations of the material flow, possibly using simulations, will be required to correlate the torque with the shear stress acting within the deforming material. Generally, the recrystallization grain size under steady-state dynamic recrystallization depends on the strain rate and the deformation temperature. Lower strain rates and higher temperatures result in larger grains, while the degree of strain has little effect on the grain size [19, 20]. At this point, it must be assumed that an increase in rotational speed leads to both higher temperatures and higher strain rates, therefore keeping the recrystallization grain size in a comparable range.