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Processing Challenges and Properties of Lightweight High Entropy Alloys
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
Khin Sandar Tun, Manoj Gupta, T.S. Srivatsan
Another important factor that does exert an influence on the formation of solid solution will be the atomic size mismatch effect. Since the elemental atoms in the high entropy alloy randomly occupy the lattice sites based on a statistical average probability of occupancy, the large atomic size difference does cause significant lattice distortion in the alloy that tends to reduce the overall stability of the solid solution [27]. The atomic size mismatch that affects lattice distortion can be expressed using the following relationship [27,35]: δ=100∑i=1nci(1−rir¯)2
Solid Solutions
Published in Bankim Chandra Ray, Rajesh Kumar Prusty, Deepak Nayak, Phase Transformations and Heat Treatments of Steels, 2020
Bankim Chandra Ray, Rajesh Kumar Prusty, Deepak Nayak
An interstitial solid solution is said to be formed only when the solute atoms occupy the interstitial free space among the atoms of the solvent crystal lattice. Usually, elements with very small atomic size (less than 1 Å) are suitable for having an interstitial solid solution, which can fit into the available interstitial sites in the solvent phase. Hydrogen, carbon, boron, and nitrogen are among the solutes that can be accommodated at such interstitial sites. However, hydrogen (atomic size ~0.46 Å) is the only element that has a size usually lower than that of the interstitial site. Other elements, being relatively larger than the interstitial sites, cause a volume expansion of the lattice. Therefore, only a limited number of metals (such as Fe, Ni, and Ti) do have significant solubility for these elements. Steel is a classic example of interstitial solid solution/alloy, where the carbon atoms do occupy the interstitial sites of iron lattice.
Creep and Fatigue Behavior of Materials
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
Strengthening of metals is more favored by adding solute atoms to the matrix of the solvent, and this alloying process is used to enhance the strength of pure metals. This process generally occurs in solid solutions, which are of two types: substitutional solid solution and interstitial solid solution. In case of substitutional solid solution, the solute atom has almost the same size as that of the solvent atom, and it occupies the lattice position, whereas in interstitial solid solution, the solute atom sits in the interstitial site due to its comparatively smaller size than the solvent atom. The lattice distortions induced by the solute atoms restrict the dislocation motion, and this leads to an increase in the yield strength of the metal. Strain field around solute atoms impede the interactions with the dislocation and as well their motion, which enhances the strength of metals. Substitutional solute atoms produce spherical distortion, whereas interstitial solute atoms produce non-spherical distortion (maximum strength obtained by non-spherical distortion). The factors that affect the solid solution strengthening are solute atoms’ size, solute atoms’ concentration, stress field symmetry of solute, and solute atoms’ shear modulus.
Improvement of the Thermal Stability of Zircon by Formation of the Solid Solution of Cr in Zircon
Published in Journal of Asian Ceramic Societies, 2020
Hudsa Majidian, Leila Nikzad, Mohammad Farvizi
The study of the elemental substitution in zircon revealed that cations can be substituted at the Zr or Si sites [33]. Therefore, some degree of solid solution can be expected between zircon and the additives. Temperature is the most influencing factor in the formation of a solid solution. The formation of the solid solution is faster at higher temperatures [28,34]. Figure 3 shows the shift of the zircon peaks at different temperatures. Zircon peak was shifted to higher angles by the addition of 1 and 2 wt.% chromia at all temperatures. This can be interpreted by the different ionic radius of Cr3+ and Zr4+ [35]. The shift of zircon peak is attributed to the deformation of the crystal lattice caused by the solid solution formation of chromia in the zircon lattice which causes internal stress [36,37]. Zircon peak of ZC1 and ZC2 samples is both on the right side of the ZC0 sample, whereas, ZC4 sample is on the left side of them. In fact, there is a little shift of zircon peaks to lower angles at 4 wt.% of chromia. As can be seen later (Figure 6), at 4 wt.% of chromia, a secondary phase is formed at grain boundaries. These secondary phases contain Cr, Zr, O, and Si elements. Therefore, for the formation of this phase, Zr atoms need to migrate out from the zircon structure to react with Cr. Therefore, the zircon lattice internal stress can be compensated by the exit of Zr ion. This leads to some changes in lattice parameters resulting in the shift back of the zircon XRD peak.
Development of dense Sr-substituted CaAl12O19 (CA6) ceramics synthesized by sol-gel combustion method
Published in Journal of Asian Ceramic Societies, 2021
Sk S. Hossain, Preeti Jani, P. K. Roy, Japes Bera
Figure 4 (a) and Figure 4 (b) illustrate the values of BD and AP of samples sintered at 1500, 1550, and 1600°C, respectively. It is observed that the AP of sintered samples is reduced significantly with increasing temperature. The BD of x = 0 composition is improved from 2.73 to 3.14 g/cm3 with increasing sintering temperature from 1500 to 1600°C. It is ascribed due to the larger atomic diffusion in-between CA6 particles with the increase in temperature. The BD value (3.14 g/cm3) of 1600°C sintered CA6 ceramic is expressively good compared to the previous reports (<3 g/cm3) [1,2]. It may be due to the SGC synthesis process of CA6 powder, which produced homogenous fine particles. The fine particles are helping for good packing and atomic diffusion due to high surface energy. Meanwhile, the BD of sintered samples is also progressively increased with Sr2+ substitution up to x = 0.2 composition, and then it is slightly reduced for x = 0.3 composition. The ratio of BD to the theoretical density is depicted in Figure 4(c), which also expresses the same indication as Figure 4(a). The 1600°C sintered specimen with x = 0.2 composition shows highest BD (3.39 g/cm3) and lowest AP (4.92%). Sr2+ is replacing Ca2+ to form solid solutions in the system. The key factors for solid solution formation include valence states and ionic radius. The difference between Ca2+ and Sr2+ ionic radii is less than 15%, which favors the formation of a substitutional solid solution. The peak shifting in Figure 2 and increase in cell volume (Table 1) also supports the data. Around 90% theoretical density is achieved in x = 0.2 composition at 1600°C. The enhanced densification in CA6 with Sr2+ incorporation may be due to the formation of defects in the spinel blocks [2] and more easier diffusion of ions owing to the defects. In x = 0.3 composition, the decrease in density may be due to the increase of Sr2+, as SA6 has a higher liquidus temperature compared to CA6. CA6 – SA6 forms a complete solid solution; however, the liquidus increases with the increase in SA6 [21]; thereby, the densification will progressively be difficult due to the increase in SA6.