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Introduction to Metallic Glasses
Published in Sumit Sharma, Metallic Glass–Based Nanocomposites, 2019
As discussed above, splat quenching is a type of melt quenching. This is also known as melt spinning. In this technique, a thin layer of glass melt is spread over a cold substrate. The rate of cooling ranges from 105 K/s to 108 K/s. A very limited number of metallic glasses in a limited composition range can be synthesized using this method. For example, Fe-B-based amorphous alloys can be synthesized using this method but only in the composition range of 12–28 at% of boron (B). A composition having less than 12% of boron resulted in the formation of crystalline (body-centered cubic lattice [bcc]) solids alloys. To overcome these limitations, pulsed-laser facilities are used for rapid melting as well as rapid quenching. Application of laser pulses for extremely short intervals induces a very high cooling rate. For example, a nanosecond pulse laser induces a cooling rate of 1010 K/s whereas a picosecond pulse laser brings about a cooling rate of 1013 K/s. The achievement of ultrahigh cooling expertise opened a door for the formation of several types of glasses which were not possible otherwise. It was not possible to make such glassy Si with other methods. Similarly, as discussed above, glassy Fe-B alloys having less than 12% boron can also be prepared using pulse laser techniques, although a picosecond pulse laser poses several problems, which are discussed in the following paragraph.
Plasma Sprayed Ceramic Coatings
Published in Ken N. Strafford, Roger St. C. Smart, Ian Sare, Chinnia Subramanian, Surface Engineering, 2018
Each of the lamellae, of which the coating is made up, solidifies as a separate entity so that the internal structure of each may be considered separately. As pointed out previously, each particle cools at a rate comparable to rapid solidification processes, such as splat quenching and melt spinning, and they therefore have different structures than ceramics prepared by sintering. Crystallisation of a liquid occurs by nucleation and growth, but if the cooling rate is such that no nuclei are formed in the time interval between the melting point and the glass transition temperature, the liquid will harden to form an amorphous solid or glass. This is observed, for example, in some Al2O3-ZrO2 alloys [11].
Synthesis and characterization of multi‐component Nanocrystalline high entropy alloy
Published in Tanmoy Chakraborty, Prabhat Ranjan, Anand Pandey, Computational Chemistry Methodology in Structural Biology and Materials Sciences, 2017
Heena Khanchandani, Jaibeer Singh, Priyanka Sharma, Rupesh Kumar, Ornov Maulik, Nitish kumar, Vinod Kumar
High entropy alloys are microcrystalline and their properties can be significantly enhanced if they can be synthesized in nanocrystalline form [4–7]. Various processing routes such as casting, sputtering, splat quenching, mechanical alloying (MA), etc. have been used to synthesize high entropy alloys in recent studies [8] and among them, MA is a widely used solid state processing route for the synthesis of homogeneous nanomaterials [8–11]. It results in a decrease in tendency of ordering and leads to extended solid solubility. Therefore, the present study is taken up to investigate the synthesis and characterization of nanocrystalline hexanary (AlMgFeCuCrNi3.17) multi-component alloy using mechanical alloying.
Rapid Quenching of Molten Salts as an Approach for the Coordination Characterization of Corrosion Products
Published in Nuclear Science and Engineering, 2023
Juho Lehmusto, J. Matthew Kurley, Ercan Cakmak, James R. Keiser, Daniel Lindberg, Markus Engblom, Bruce A. Pint, Stephen S. Raiman
Based on the starting composition, the stoichiometric composition of the studied NaCl:MgCl2 mixture when molten was calculated to be NaMgCl3 (92%) and Na6MgCl8 (8%), giving a NaMgCl3-to-Na6MgCl8 ratio of 12.1. This ratio was 8.2 for splat quenching but dropped to 0.4 with the rapid-quenched samples, respectively (Fig. 3). All the ratios were calculated from the major peak areas of NaMgCl3 and Na6MgCl8. The low NaMgCl3-to-Na6MgCl8 ratio in the rapid-quenched sample indicated that much more Na6MgCl8 was present than was expected according to the stoichiometric calculations. The drastic difference between the ratios with different cooling rates suggests that the molten phase is different than predicted by equilibrium.
The influence of pyrolysing Al2O3 precursor on the high temperature properties of the YSZ-Al2O3 composite coating
Published in Surface Engineering, 2021
Saeid Taghi-Ramezani, Zia Valefi, Masud Mirjani, Reza Ghasemi
Figure 11 shows the XRD patterns of the YSZ-10 wt-%Al2O3 composite coatings applied with pyrolysed and un-pyrolysed Al2O3 powders. They demonstrate that the phase composition of both coatings is zirconia in two forms of non-transformable tetragonal phase (T′) with an amount of monoclinic phase and alumina in two forms of intermediate metastable γ-Al2O3, which could be regarded as the major phase and the smaller traces of α-Al2O3. The non-transformable tetragonal phase (T′) is typically the plasma sprayed zirconia, which is formed owing to the quenching of splats on the substrate. The cooling rate of the splats during the plasma spraying process was estimated to be 107°C s−1. During plasma spraying, there are some non-molten and partially molten particles forming the small amount of the monoclinic phase of zirconia [23,24]. The metastable γ-Al2O3 phase is a typical phase formed in the plasma sprayed alumina coating, as this process is associated with high temperature and rapid splat quenching. Small traces of the stable α-Al2O3 phase in the coating are owing to the non-molten and partially melted alumina particles [25].
Crystallographic characterization of steel microstructure using neutron diffraction
Published in Science and Technology of Advanced Materials, 2019
It has been confirmed in various kinds of C bearing steels after their work. For example, Sherby et al. have claimed that the crystal structure of a ferrous alloy with C content less than 0.6 mass% is bcc whereas that with higher than 0.6 mass% C is bct holding Equation (13) [97,98]. Their conclusion has been referred in a textbook [99]. Contrary to their conclusion, Cadeville et al. have shown the c/a of FeCx alloys (0.05) martensite prepared by splat quenching from liquid is bct [100]. In addition, the Rietveld analysis has been developed and recently applied to the determination of crystal structure of low or medium C martensite. As results, the understanding has been altered [101–103]; these reports claim that ‘the goodness to fit’ is better assuming bct rather than bcc structure in the Rietveld refinement for X-ray diffraction profile. Among them, Lu et al. have proposed the following relationship instead of Equation (13) for engineering low or medium C bearing steels [103].