Dynamic Scenarios of the Formation of Martensite with the {110} Habits in the Ni50Mn50 Alloy

Martensitic transformation B2–L10 in the ordered alloy Ni50Mn50, which occurs at comparatively high temperatures (980–920 K), is discussed with the use of dynamic concepts of the wave control of the threshold deformation. The proximity of the observed orientations of martensite-crystal habits (and of twin boundaries) to the planes of the {110} family makes it possible to use the longitudinal waves along the axes 〈001〉 (in the basis of the initial phase) as the driving factors. It is shown that at temperatures of the onset of the transformation there is a satisfactory correspondence between the calculated and experimental data on the tetragonality of martensite and on the volume effect. The opportunity of different dynamic scenarios of the formation of the final phase is noted, namely, of separate crystals; layered structures, in which the crystals of martensite with the identical orientation relationships alternate with the untransformed regions of austenite; and packets of pairwise-twinned crystals. Examples are given of morpho-types corresponding to these scenarios. © 2019, Pleiades Publishing, Ltd

Microstructure features of high-entropy equiatomic cast AlCrFeCoNiCu alloys

The structural and phase transformations that take place in the cast high-entropy equiatomic alloy AlCrFeCoNiCu after solidification, homogenizing heat treatment, and cooling have been studied. Analytical transmission microscopy, scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffraction analysis were used to conduct the studies. The elastic modulus, nano-, and microhardness have been measured. The alloy decomposition has been found to occur with the precipitation of no less than six nanoscale phases with different morphologies, structures (A2, B2, L12), and chemical compositions. All the nanophases are multicomponent solid solutions enriched with several elements, which indicates the pronounced elemental and phase nanomodulation over the alloy volume. © 2013 Pleiades Publishing, Ltd

Specific features of cast high-entropy AlCrFeCoNiCu alloys produced by ultrarapid quenching from the melt

Results of studying structural and phase transformations that occur in the cast high-entropy equiatomic AlCrFeCoNiCu alloy after ultrarapid quenching from the melt in an inert atmosphere (RQM) and various isothermal treatments are presented for the first time. The investigations have been performed using analytical, transmission and scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction structure and phase analyses, as well as measurements of the nanohardness, microhardness, and elastic moduli. It has been found that an ultrafine-grained structure is formed in this alloy during RQM. Already during quenching and, especially, during subsequent annealing, the alloy undergoes decomposition, which is accompanied by the precipitation in the bcc (B2) matrix of some nanosized phases, predominantly of equiaxed morphology, both atomically ordered (B2) and disordered (A2), with various chemical compositions. All nanophases are multicomponent solid solutions and are enriched in a few elements, which leads to a pronounced nanomodulation of the elemental and phase compositions over the alloy bulk, identified, in particular, from the presence of satellites in the vicinity of some reflections in selected-area electron diffraction patterns. © 2013 Pleiades Publishing, Ltd

Effect of heat treatment on structural and phase transformations in the Ti49.5Ni50.5 alloy amorphized by high-pressure torsion

Results are presented for a study of the structural and phase transformations that occur in the titanium-nickelide shape-memory alloy Ti 49.5Ni50.5 subjected to heat treatment after deformation-induced amorphization by megaplastic high-pressure torsion (HPT) using five or ten revolutions of Bridgman anvils. The investigations were performed using transmission and scanning electron microscopy, X-ray diffraction, and measurements of the temperature dependences of electrical resistivity and magnetic susceptibility. It has been established that the crystallization of the alloy already occurs upon low-temperature treatment, beginning with ∼500 K. The evolution of the structure and the stage character of the development of crystallization and recrystallization processes depending on temperature have been determined. It has been shown that the annealing of the amorphized alloy makes it possible to obtain highly homogeneous nanostructured, submicrocrystalline, or bimodal states in the B2 austenite. A complete diagram of thermoelastic martensitic transformations of the B2 austenite has been constructed in the region from a nanostructured to a conventional polycrystalline state (with a grain size of 20-50 μm). The effect of size on the stabilization of austenite has been revealed and its specific features have been studied for the B2 → R and B2(R) → B19′ martensitic transformations depending on the structural state of the alloy. © 2013 Pleiades Publishing, Ltd

The Effect of Heat Treatment on the Structure and Mechanical Properties of Nanocrystalline Cu–14Al–3Ni Alloy Subjected to High-Pressure Torsion

Abstract: The effect of heat treatment on the microstructure, phase composition, mechanical properties, and microhardness of the shape-memory Сu–14 wt % Al–3 wt % Ni alloy prepared in the nanocrystalline state, which results from the severe plastic high-pressure torsion (HPT), is studied. Electron microscopy and X-ray diffraction analysis are used in combination with electrical resistivity measurements in order to obtain data on the peculiarities of thermoelastic martensitic transformations and decomposition in the HPT-processed alloy subjected to thermal actions. © 2021, The Author(s).The study was performed in terms of state assignment no. АААА-А18-118020190116-6 (Struktura) of the joint laboratory of the Institute of Metal Physics, Ural Branch, Russian Academy of Sciences and Ural Federal University

Formation of nanocrystalline structure in the amorphous Ti50Ni25Cu25 alloy upon severe thermomechanical treatment and the size effect of the thermoelastic martensitic B2 a dagger" B19 transformation

The results of the comparative analysis of the Ti 50Ni 25Cu 25-alloy structures produced in the initial amorphous state by rapid quenching from the melt (RQM), after severe plastic deformation by torsion under high pressure (HPT), and postdeformation heat treatment (PHT) are presented. The study was carried out using neutron and X-ray diffraction, transmission and scanning electron microscopy, and measurements of electrical properties. The initially amorphous alloy has been established to nanocrystallize after torsion under a pressure of 7 GPa to 0.5 revolutions of the anvil. Then, after 1, 5, 10, and 15 rev, the alloy again undergoes the strain-induced amorphization even with the retention, even after 5-15 rev, of a large number of highly dispersed nanocrystals less than 3-4 nm in size with a distorted B2 lattice in the amorphous matrix. Their crucial role as nuclei of crystallization provides the total low-temperature nanocrystallization during subsequent annealing starting from 250-300°C. It is shown that PHT of the alloy amorphized by HPT makes it possible to produce extremely uniform nanocrystalline (NC), submicrocrystalline (SMC), or bimodal (NC + SMC) austenitic B2-type structures in it. A complete diagram of thermoelastic martensitic transformations in the region of B2-austenite states, from nanostructured state to conventional polycrystalline one, has been constructed. The size effect on the stabilization of martensitic transformation in nanocrystalline B2 alloy has been established. © Pleiades Publishing, Ltd., 2012

Features of phase composition and structure of high-entroic multicomponent steel FeWMoCrVSiMnC

The results of studying the phase composition, structure, and hardness of a synthesized multi-component Fe–W–Mo–Cr–V–Si–Mn–C steel are presented. Investigations were performed via using methods of the analytical transmission and scanning structural and orientation electron microscopy,optical metallography, X-ray energy-dispersion spectroscopy, X-ray phase and structure analysis,measurements of Rockwell hardness. It has been established that the steel has a high hardness (62 HRC) and is in an ultrafine-grained composite-wise martensite–multi-carbide state. In this case, all different type of carbides are uniformly distributed over the volume of the steel and are of either nano- or submicro-crystalline size in dependence of the type of the carbide phase. The state of the steel, synthesized via laser remelting, from the viewpoint of the character of the spatial distribution of the chemical and phase constituents, has turned out to be very much resembling that one which is typical of some high-entropy alloys already studied.Представлены результаты изучения фазового состава, структуры и твердости в высокоэнтропийной многокомпонентной стали FeWMoCrVSiMnC после синтеза и последующей термообработки. Исследования проведены методами аналитической просвечивающей и растровой структурной и ориентационной электронной микроскопии, оптической металлографии, рентгеновской энергодисперсионной спектроскопии, рентгенофазового и структурного анализа, измерений твердости по Роквеллу. Установлено, что сталь имеет высокую твердость (62 HRC) и находится в ультрамелкозернистом композитном мартенситно-мультикарбидном состоянии. При этом все карбиды однородно распределены по объему стали и имеют нано- и субмикроразмерные масштабы в зависимости от типа карбида

Phase and structural transformations in the Ti49.5Ni50.5 alloy with a shape-memory effect during torsion under high pressure

Results of investigations of structural and phase transformations that occur in the titanium-nick-Elide-based alloy Ti 49.5Ni 50.5 with a shape memory effect during severe plastic deformation by torsion under high pressure (HPT) are reported. The studies were performed using transmission and scanning electron microscopy, neutron and X-ray diffraction, and measurements of temperature dependences of electrical resistivity. The martensitic B2 → B19' transformation was found to be induced in the alloy when applying a high pressure. After unloading, the martensitic B19' phase is retained in the alloy. The fine structure of the B19' martensite and its evolution into nanocrystalline and, subsequently, amorphous state during HPT with 1/4, 1/2, 1, 5, and 10 rev have been studied. It was shown that, after HPT, all nanosized crystallites whose sizes are less than 30-50 nm have a B2-type structure and, therefore, the reverse martensitic B19' → B2 trans-formation is realized in the alloy at room temperature after unloading. © Pleiades Publishing, Ltd., 2012