Mechanical behavior of Ti-Zr-Ni quasicrystals during nanoindentation

The parameters and mechanisms of deformation of a Ti_41.5Zr_41.5Ni₁₇ quasicrystal and a W + 12 at. % Ta single crystal under nanoindentation conditions were studied and compared. It was found that, initially, the deformation of the quasicrystal is elastoplastic; however, beginning from a certain critical load, the deformation acquires a steplike character with alternating segments of slow elastoplastic deformation and rapid plastic deformation. A qualitative model is proposed for the plastic deformation of quasicrystals during nanoindentation.     

Structure and Properties of Multi-Layer Films of High-Entropy Metals Deposited by the Ion-Plasma Method

Russian Physics Journal - The method for deposition of high entropy alloy (HEA) films is discussed. It consists in the film deposition on a substrate in vacuum from multi-component gas-metal plasma...     

The growth of single crystals of Ni-W alloy under conditions of high temperature gradient

The structure of single crystals of the NV-4 nickel alloy containing 32–36 wt % W is investigated. The temperature gradient at the crystallization front and the velocity of the crystallization front are the variable parameters of directional crystallization. The degrees of structural perfection of the single crystals grown under different conditions are compared. The crystallization parameters providing growth of single crystals that have high structural perfection and can be successfully used as seeds for the growth of single-crystal blades are determined. Typical defects formed upon directional crystallization of single crystals of the Ni-W (35 wt %) alloy are examined. The studied defects are classified, and the factors responsible for the disturbance of the single-crystal structure are analyzed.     

Self-organization processes in the cellular structure formation of Ni-W alloys

The self-organization processes, the growth steadiness, and the stability of the cellular structure morphology of Ni-W alloy single crystals with a tungsten concentration of 25–40% have been investigated. The temperature gradient in the crystallization front, the oriented crystallization rate, doping with aluminum, titanium, chromium, and molybdenum, and the tungsten concentration have been considered as nonequilibrium factors. The nonlinear dependence of the structure characteristics on the growth parameters, including the temperature gradient, the oriented crystallization rate, and the tungsten concentration, has been determined. Dendrite features of the cellular morphology of the crystallization front are the result of the self-organization processes and promote the steady growth of single crystals with a high degree of structural perfection. A mechanism of the morphological transition from hexagonal to square cells has been proposed.     

Structure and peculiarities of nanodeformation in Ti–Zr–Ni quasi-crystals

Ti–Zr–Ni samples with a substantial predominance of icosahedral quasicrystalline phase were produced by the melt-spinning technique. Their structure and mechanical properties were studied by X-ray diffraction and nanoindentation methods. The quasicrystalline phase was found to have a primitive lattice with the quasicrystallinity parameter a _q = 0.5200–0.5210?nm. Quasicrystalline deformation behaviour under nanoindentation versus phase composition and structure is discussed in comparison with single crystal W–12?wt%?Ta. The estimated elastic modulus E of the quasicrystalline phase shows no correlation with the element composition. The nanohardness was shown to increase with increasing quasicrystalline-phase perfection. Load–displacement curves of Ti–Zr–Ni quasicrystals (QCs) show stepwise character with alternation of elastic and plastic sections. Such non-uniform plastic flow in QCs might be caused by the localization of plastic deformation in shear bands. The non-uniformity of the plastic deformation increases with the increasing quasicrystalline phase perfection.     

Effects of inertia of dislocations on the probability of unpinning by ultrasound

The paper is concerned with theoretical models of dislocation segments fixed at their ends to local obstacles of either the same or two different types. The dislocation inertial properties are shown to influence substantially the probability of unpinning from the local obstacles as the crystal is subjected to ultrasonic oscillations. The unpinning probability in the presence of oscillations can be much higher than that with a constant load of the same magnitude. In the case of two types of obstacles, the weaker can play a “provocative” role facilitating unpinning of dislocations from the stronger obstacles. The considered effects constitute admittedly one of microscopic mechanisms of the plasticizing and “softening” action of ultrasound.