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Fatigue Behavior of High Entropy Alloys
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
K. Liu, S.S. Nene, Shivakant Shukla, R.S. Mishra
Polycrystalline materials deform mainly with a dislocation motion along closed packed planes and directions through slip in uniaxial loading. However, the propensity of slip is controlled by material crystal structure [38,39]. Extensive study on deformation accommodation through slip under cyclic loading has led to claims that formation of fatigue intrusions and extrusions is the result of preferential slipping tendency of each grain under alternative tensile and compressive loading. However, the thinking has been that activation of additional deformation mechanisms such as mechanical twinning (TWIP effect) and strain induced martensitic transformation (TRIP effect) can effectively tune the fatigue properties. Stacking fault energy (SFE) is a key factor that governs the activation of these additional deformation modes in the material [40–42]. Engineering SFE of a polycrystalline material was considered to be difficult in conventional alloy design; however, the abundant chemical space available in HEAs/CCAs design has enabled very easy tuning of alloy SFE [18]. An interesting point to note in HEAs is the slope of the Stage III work hardening curve, which was rather steep and was due to reduction in dynamic recovery processes via TWIP or TWIP effects facilitated by low SFE [38,43].
Stress-Strain Behavior Investigation by Molecular Dynamic (MD) Simulation
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
Phenomena such as the formation of partial dislocation, the formation of twin boundaries, and the ability of dislocation to cross-slip are chiefly governed by stacking fault energy, thus influencing the yield behavior of the FCC metals [39]. In low-stacking-fault-energy material, slip occurs by nucleation and glide of the Shockley partial dislocations [40]. However, in case of high stacking fault energy values, which are attributed to smaller splitting distance between the partials, slip occurs via extended dislocations [40]. These extended dislocations propagate through the grains faster when compared with the partials; thus, the plastic deformation via slip occurs at lower strain values in high-stacking-fault-energy material as compared with low-stacking-fault-energy material.
Introduction to Cross Rolling of Biomedical Alloys
Published in Ashwani Kumar, Mangey Ram, Yogesh Kumar Singla, Advanced Materials for Biomechanical Applications, 2022
V. Murugabalaji, Matruprasad Rout
The microstructural investigations of the material are performed to understand the changes that could have occurred during the processing of the metal alloys. Usually, the microstructural characterisation studies are carried out using an optical microscope, a scanning electron microscope (SEM – analysing signals from electrons interacting with the atoms of the target specimen), a transmission electron microscope (TEM – analysing image from electrons transmitted through the target specimen) and X-ray diffraction (XRD – analysing the data from the diffraction of X-rays on the target specimen) to understand the underlying principles of mechanical deformation that could have occurred during the rolling process [17,18]. The evolution of the deformed microstructure is found to occur in three stages, viz. recovery, recrystallisation and grain growth [19]. Stacking fault energy (SFE) plays a vital role in the evolution of the deformed microstructure. The materials with low SFE show less tendency of recovery and recrystallisation is considered the major mechanism for microstructure evolution [20]. Dynamic recrystallisation (DRX) is the crucial phenomenon in enhancing the ductility of the specimen by the generation of strain-free grains during deformation. The DRX behaviour of the material significantly affects the microstructure and load requirement for processing the material [21]. The microstructure of the rolled specimen is generally viewed longitudinally to address the features of the deformation [22]. The characteristics of the microstructure evolved by the CR of the material are entirely different from those of the conventional rolling process, i.e. UR [23].
The Damage Mechanism of Alloy 690TT Caused by Fretting Wear in a Flowing Nitrogen Environment
Published in Tribology Transactions, 2021
Long Xin, Yongming Han, Yonghao Lu, Weidong Zhang, Tetsuo Shoji
The SPD process induced by fretting wear can refine the grain to a depth at the micrometer level beneath the wear surface. The structural evolution is affected by the stacking fault energy (SFE), hardness, and strength of the material (8–12). For instance, when the SFE of the material is different, recrystallization, grain refinement, and cold work-hardening compete with each other (12). If the friction and wear process parameters and the environment are different, different characteristics will be present in the wear-induced surface layer. Fretting wear–induced surface nanocrystalline layers are often called tribologically transformed structures (TTSs) (13, 14). On the one hand, due to the high hardness of the nanocrystalline layer, the wear resistance can be improved to some extent. On the other hand, due to its brittleness, cracking is easily initiated. Therefore, the surface nanocrystalline layer has been extensively researched.
Atomistic simulation of the stacking fault energy and grain shape on strain hardening behaviours of FCC nanocrystalline metals
Published in Philosophical Magazine, 2019
Lin Yuan, Peng Jing, Rajiv Shivpuri, Chuanlong Xu, Zhenhai Xu, Debin Shan, Bin Guo
The stacking fault energies for Al, Ni, Cu and Ag are 146,125,44.44,17.8 mJ/m2, becoming lower and lower. The slopes of layer-grained Ni, Ag and Cu are positive after yield and then change to negative with the progress of plastic deformation. The positive slope period corresponds to the second stage of single crystal strain hardening because dislocations interact with each other within grains, but the extent of dislocation interaction is not as severe as that in layer-grained Al. The ability of full dislocations to dissociate into partial dislocation in materials with high stacking fault energy is poor. Dislocation interaction takes place much easier than that in low stacking fault energy materials. As a result, the sessile dislocations formed by dislocation interaction will be higher in layer-grained Al than in layer-grained Ni,Cu,Ag, as shown in Figure 8. Sessile dislocation percentage is got by the total sessile dislocation length dividing total dislocation length in the model. At the negative slope period, grain interiors are full of stacking faults and dislocation configurations are destroyed gradually, which leads to the strain softening phenomenon. The first stage in layer-grained Ni, Cu, Ag is not obvious [36]. The decrease of stacking fault energy means more stacking faults in grain interior, affecting dislocation interaction and leading to distinct strain hardening indices.