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Linear Viscoelasticity
Published in G. Thomas Mase, Ronald E. Smelser, Jenn Stroud Rossmann, Continuum Mechanics for Engineers, 2020
G. Thomas Mase, Ronald E. Smelser, Jenn Stroud Rossmann
Many materials behave elastically at room temperature and typical deformation conditions, but respond differently when exposed to extreme temperature or deformation rates. At a moderate temperature and loading, a polymer such as polymethylmethacrylate (PMMA), may be effectively modeled by a linear elastic constitutive equation. However, at a somewhat elevated temperature, the same material may have to be modeled as a viscous fluid. Steel, like other metals, becomes molten at high temperatures and can be poured into molds to form ingots. Additionally, at a high enough deformation rate, for example, at the 48 km/hr rate of a vehicle crash, or after significant thermal loading, steel will exhibit considerably altered stiffness properties. Many applications and examples of viscoelastic behavior may be found in Lakes (1999).
Microstructure and corrosion behaviour of AlCoFeNiTiZr high-entropy alloy films
Published in Surface Engineering, 2020
Hai-dou Wang, Jin-na Liu, Zhi-guo Xing, Guo-Zheng Ma, Xiu-fang Cui, Guo Jin, Bin-shi Xu
(Fe-Co-Ni)x (Al-Ti-Zr)100-x multi-component films were deposited on Si (100) substrate using RF magnetron sputtering system. Two equimolar targets (Φ=80 mm) of Fe-Co-Ni and Al-Ti-Zr were used. The two kinds of alloy targets were fabricated by conventional powder metallurgy technology [13–15]. Firstly, alloy ingots were prepared by vacuum melting furnace using the alloy powders which were prepared according to a certain element proportion. Secondly, smelted alloy ingots were refined and crushed ingots by a mechanical stamping method. Thirdly, alloy powder particle size was processed to 20-40 μm by mechanical ball grinding method. Lastly, the powders were sintered to block material. Then it would be processed into the shape of the target according to the size requirement. The mole ratio of each element in each alloy target was approximately 1:1:1. Before deposition, the Si substrates and the targets were cleaned by Ar plasma etching for 10 min at 400°C to remove the surface impurities and the oxides. The applied power was 300w and 30w for Fe-Co-Ni and Al-Ti-Zr alloy targets, respectively, for x = 25. The two targets co-sputtered during the preparation process. The working pressure was 0.1 Pa. Vacuum degree of the magnetron sputtering cavity bottom was 8×10−4 Pa. The gas flow rate was 80 sccm and the sputtering rate was 4 nm ms min−1. The working temperature of the sputtering cavity was 100°C. The film thickness was about 400 nm which was measured by a step thickness gauge. The total sputtering time and other sputtering parameters were shown in Table 1.