Effect of deviations of composition from the quasi-binary section TiNi-TiCu on structural and phase transformations in rapidly quenched alloys

Methods of X-ray diffraction, transmission and scanning electron microscopy, and selected-area electron diffraction (SAED) have been used to study the phase and elemental composition and structure of alloys close to the stoichiometric Ti50Ni25Cu25 alloy. Based on the method of rapid quenching of the melt (free-jet melt spinning), alloys of the quasi-binary TiNi-TiCu section have been prepared, which in the initial as-cast state exhibited the thermoelastic martensitic transformations B 2 < B 19 and related shape-memory effects. The chemical composition of the Ti50 + x Ni25Cu25 - x alloys was varied by changing titanium and copper concentrations within x ≤ ±1 at % (from Ti49Ni25Cu26 to Ti51Ni 25Cu24). It has been established that quenching at a cooling rate equal to 106 K/s leads to the amorphization of all the alloys under consideration. Heating to 723 K and higher leads to the devitrification of the alloy with the formation of a nanocrystalline or submicrocrystalline structure of the B2 austenite. The mechanical properties of these alloys have been measured in the initial amorphous state and in the polycrystalline martensitic state. It has been shown that, depending on the extent of the deviations of the alloy composition from the stoichiometry, which cause the decomposition of the alloys in the process of nanocrystallization, regular changes are observed in their mechanical properties and in the shape-memory effects. The kinetics of the processes of the devitrification of the alloys, as well of the forward and reverse martensitic transformations, have been studied, their characteristic temperatures have been determined, and a diagram of the dependence of the characteristic temperatures on the chemical composition of the alloys has been constructed. © 2013 Pleiades Publishing, Ltd

Design and development of Ti-Ni, Ni-Mn-Ga and Cu-Al-Ni-based alloys with high and low temperature shape memory effects

In recent years, multicomponent alloys with shape memory effects (SMEs), based on the ordered intermetallic compounds B2-TiNi, L21-Ni2MnGa, B2- and D03-Cu-Me (Me = Al, Ni, Zn), which represent a special important class of intelligent materials, have been of great interest. However, only a small number of known alloys with SMEs were found to have thermoelastic martensitic transformations (TMTs) at high temperatures. It is also found that most of the materials with TMTs and related SMEs do not have the necessary ductility and this is currently one of the main restrictions of their wide practical application. The aim of the present work is to design and develop multicomponent alloys with TMTs together with ways to improve their strength and ductile properties, using doping and advanced methods of thermal and thermomechanical treatments. The structure, phase composition, and TMTs were investigated by transmission- and scanning electron microscopy, as well as by neutron-, electron- and X-ray diffraction. Temperature measurements of the electrical resistance, magnetic susceptibility, as well as tests of the tensile mechanical properties and special characteristics of SMEs were also used. Temperature-concentration dependences for TMTs in the binary and ternary alloys of a number of quasi-binary systems were determined and discussed. It is shown that the ductility and strength of alloys required for the realization of SMEs can be achieved through optimal alloying, which excludes decomposition in the temperature range of SMEs' usage, as well as via various treatments that ensure the formation of their fine- (FG) and ultra-fine-grained (UFG) structure. © 2019 by the authors.Funding: This work was performed within the framework of state task “Structure”, grant no. AAAA-A18-118020190116-6 and the cooperative laboratory of the Ural Federal University n.a. the First President of Russia B.N. Yeltsin and the Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences

Crystal Structure of Martensite and Orientation Relationships During Thermoelastic Martensitic Transformations in Ni-Mn-Based Alloys

Orientation relationships (OR’s) for the B2↔L10 thermoelastic martensitic transformations (TMT’s) in Ni50Mn50 alloy were determined by transmission and scanning electron microscopy methods, which differ from the Bain OR’s previously accepted for them. Electron microscopic studies have shown that L10 martensite has a hierarchic morphology of packets of thin plates of pairwise twinned crystals with flat boundaries of habit close to {110

Microstructure and Thermoelastic Martensitic Transformations in Ni-Mn-Al Based Alloys

The physical properties and structure, thermoelastic martensitic transformations (TMT’s) of Ni50Mn50

Comparative Electron-Microscopic Study of Shape Memory Alloys of Systems Cu-Ni-Al and Ni-Mn-Al

The microstructure of Cu-Ni-Al and Ni-Mn-Al alloys in a wide range of chemical compositions has been studied by transmission and scanning electron microscopy methods, diffraction of electrons and X-rays. The phase composition of all the investigated alloys and the mechanism of the fracture under deformation have been determined.     Keywords: thermoelastic martensitic transformation, brittleness, fractography, longperiod lattice, electron-microscopic studies

Research and development of fine and lengthy nanostructured high-strength materials based on ternary alloy Ti50Ni25Cu25 with shape memory effect for intelligent sensors and nanoactuators

Основной целью работы является получение и комплексное систематическое исследование тонко- и длинномерных наноструктурных высокопрочных материалов на основе сплавов системы Ti50Ni25Cu25 с эффектами памяти формы. Данные материалы будут получены с использованием методов быстрой закалки расплава спиннингованием. В настоящем проекте решены следующие задачи: - изготовлены ленты тройных сплавов состава вблизи стехиометрического Ti50Ni25Cu25, используя метод быстрой закалки расплава спиннингованием; - изучены микроструктуры и фазовый состав сплавов в исходном состоянии и после термообработки с помощью методов рентгеноструктурного анализа и электронной микроскопии; - измерены критические температуры начала и конца прямого и обратного мартенситного превращения, построены его диаграммы в зависимости от среднего размера нанозерен; определены температурные, деформационные и силовые характеристики эффектов памяти формы полученных сплавов и выяснена природы их зависимостей от химического состава (отклонения от стехиометрии Ti50Ni25Cu25) и структурного состояния; - измерены механические свойства сплавов на растяжение в состоянии после закалки и после термической обработки.Main main purpose of the work is obtaining and complex systematic research of thin and length nanostructural high-strength materials on the basis of Ti50Ni25Cu25 alloys with shape memory effects. These materials will be obtained by the superrapid quenching technique using the method of melt spinning. In the present work the following tasks are solved: - the melt-spun ribbons of ternary alloys with chemical composition near stoichiometric composition Ti50Ni25Cu25 were produced by the superrapid quenching technique using the method of melt spinning of molten alloy onto a cold substrate; - microstructures and phase composition of the alloys in an initial state and after heat treatment were studied using the methods of X-ray diffraction and electron microscopy; - critical temperatures of the forward and reverse martensitic transformations have been determined, the diagrams of the dependence of the critical temperatures on the average size of nanograins have been constructed; temperature, deformation and force characteristics of the shape memory effects of the alloys have been determined and the nature of their dependences on the chemical composition (a deviation from stoichiometric composition Ti50Ni25Cu25) and the structural state was found out; - mechanical properties of alloys in the initial state and after heat treatment have been measured.Программа развития УрФУ на 2013 год (п.1.2.2.3

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

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