Phase stability during martensitic transformation in ZrCu intermetallics: crystal and electronic structure aspects

This article is dedicated to the estimation of the relative stability for B2, B19` and Cm phase in ZrCu intermetallic compound through the ab-initio electronic structure calculations and subsequent crystal structure Rietveld refinement. The information about electronic and crystal structure of phases in ZrCu will allow selecting for this high temperature shape memory alloy such alloying elements that will significantly improve shape memory behavior through definite structural changes

Shape Memory Effect Driven by Diffusionless and Diffusional Transformations at Elevated Temperatures

Several alloy systems can be selected for high-temperature shape-memory alloys, defined as alloys with stable reverse martensitic-transformation temperatures above 100°C. However, due to the lack of minimum quality standards for stability, ductility, functional behaviour, and reliability, no successful applications have been realised so far. Nevertheless, research on high-temperature shape-memory alloys (HTSMA) is an important topic not only for scientific reasons but also due to the market pull. This paper reviews some novel HTSMA systems showing shape-memory effect at elevated temperatures driven by martensitic (diffusionless) and diffusional transformationsМожно привести достаточное количество систем сплавов, которые подпадают под определение высокотемпературных сплавов с эффектом памяти формы — сплавов, в которых стабильное обратное мартенситное превращение протекает при температурах выше 100°C. К сожалению, до сих пор не известно ни одного случая успешного применения высокотемпературных сплавов с эффектом памяти формы в силу отсутствия требований к их стабильности, пластичности, функциональному поведению и надежности. Тем не менее, исследования высокотемпературных сплавов с эффектом памяти формы являются важными не только с точки зрения фундаментальной науки, но и благодаря требованиям рынка. Настоящая работа посвящена рассмотрению некоторых новейших систем высокотемпературных сплавов с эффектом памяти формы, который определяется как мартенситным (бездиффузионным), так и диффузионными превращениямиМожна навести певну кількість систем сплавів, що можуть бути визначені, як високотемпературні сплави з ефектом пам’яті форми, що в свою чергу визначаються як сплави зі стабільними температурами зворотного мартенситного перетворення, вищими за 100°C. На жаль, невідомо жодного випадку успішного застосування високотемпературних сплавів з ефектом пам’яті форми, завдяки відсутності вимог щодо їх стабільності, пластичності, функціональної поведінки та надійності. Не зважаючи на це, дослідження високотемпературних сплавів з ефектом пам’яті форми є важливим не тільки з точки зору фундаментальної науки, але й завдяки вимогам ринку. Дана робота присвячена розглядові деяких новітніх систем високотемпературних сплавів з ефектом пам’яті форми, що зумовлений мартенситним (бездифузійним) та дифузійним перетворенням

Структура, фазовий склад і механічні властивості високоентропійних твердих розчинів на основі системи MnFeCoNiCu відносно колективної поведінки їхніх складових елементів

Structure and phase-composition changes of the cast multicomponent alloys based on MnFeCoNiCu are studied depending on variations in the enthalpy and entropy of mixing, the difference in atomic sizes, and the concentration of valence electrons, starting from the medium-entropy TiFeCoNi alloy and approaching the Cantor alloy. Changes in the crystal structure from h.c.p. to f.c.c. one as well as variations in the phase composition are revealed. As shown, the specified changes lead to significant strengthening with significant plasticity. Such plasticity is caused by the f.c.c.–h.c.p. martensitic transformation, which is combined with the plastic deformation of the distorted lattice, which, in its own turn, is characterized by significant strengthening.Досліджено зміни структури та фазового складу литих багатокомпонент-них стопів на основі MnFeCoNiCu в залежності від змін у ентальпії й ент-ропії змішання, ріжниці атомових розмірів і концентрації валентних електронів, починаючи від середньоентропійного стопу TiFeCoNi та на-ближуючись до стопу Кантора. Встановлено зміни у кристалічній струк-турі від ГЩП до ГЦК, а також варіяції фазового складу. Показано, що зазначені зміни приводять до значного зміцнення із істотною пластичніс-тю. Таку пластичність зумовлено ГЦК–ГЩП-мартенситним перетворен-ням, що поєднується з пластичною деформацією спотвореної ґратниці, яка характеризується значним зміцненням

Peculiarities of the martensitic transformation in ZrCu intermetallic compound - potential high temperature SMA

Interaction of two martensitic phases during martensitic transformation (MT) in ZrCu intermetallic compound was studied by means of in situ high-temperature X-ray diffraction studies, internal friction and calorimetric measurements. Some regularities of the mutual formation and disappearance of two martensites on thermal cycling through the temperature interval of the MT were established. The mechanism of the MT in ZrCu intermetallic compounds is discussed

Irreversible Processes During Martensitic Transformation in Zr-Based Shape Memory Alloys

The purpose of this paper is to explain the thermodynamical and shape memory behaviour in comparison with structural parameters for Zr-based intermetallics - a new class of potential shape memory alloys (SMA) for high-temperature applications [1]. Electrical resistivity, structural, shape memory and calorimetric measurements were carried out for the Zr2CuNi - Zr2CuCo quasibinary cross-section. It was shown that the martensitic transformation (MT) of the high -temperature B2 phase resulted in the simultaneous formation of the two martensitic phases belonging to the P21/m (B19' type) and Cm space groups in the case of Zr2CuNi similar to ZrCu [2]. Co for Ni substitution causes the changes in the martensite volume fractions up to formation of only B19' type martensite in Zr2CuCo compound without significant changes in lattice parameters for both martensites. Such substitution also decreases generally the transformation heats and energy dissipated during the full cycle of MT. The non-thermoelastic behaviour that was observed in [l] for Zr2CuNi changes to a thermoelastic one in the case of MT in Zr2CuCo. Shape memory effect (SME) is nearly complete for alloys with high Ni content (not less than 85% of shape recovery ratio (Ksme)). It becomes complete at Co additions. The effect of the interaction between two martensites on the non-thermoelastic MT behaviour and SME in Zr-based intermetallics is discussed in the present paper

Alloying of ZrCu-based high temperature shape memory alloys

A systematic study was carried out by means of paramagnetic susceptibility measurements, X-ray diffractometry, and X-ray photoelectron spectroscopy (XPS) in order to determine crystal and electronic structure changes along with alloying additions. The experimental MT temperatures were compared with those calculated for ZrCu-based alloys with the help of Shabalovskaya semi-empirical approach [1]. The results of such a comparison will be discussed

B2 Intermetallic Compounds of Zr. New Class of the Shape Memory Alloys

It is known that the B2 equiatomic intermetallic compounds of Zr (ZrCo-based [1], ZrCu [2], ZrRh [3]) undergo a martensitic transformation (MT) with wide temperature hysteresis. It was found that the MT is accompanied by the perfect shape memory effect (SME) for ZrCu [2] and ZrRh [3]. In this report we represent the results of structural analysis, electrical resistivity, calorimetric and SME measurements for ZrCu- and ZrCo-based compounds. Interrelation between structural, thermodynamical parameters of MT and SME in this alloys will be described. The shape memory aspects of this potential alloys for the application at high temperatures will be discussed

Martensitic transformation in Fe-Mn-(Si, Ge, Sn) alloys

Effect of Ge and Sn on the martensitic transformation and shape memory effect in Fe-Mn(22-26at.%)-Si alloys is investigated by the substitution of Si by Ge or Sn from 1.5% to 6at. %. It was found that addition of Ge causes the transformation to perform in several steps. Substitution of Sn makes this effect more superior. Resistometry, calorimetric and dilatometer measurements reveal that one of the transformation stages is close to second order. It is characterized by small values of the thermal hysteresis and heat effect. Shape memory effect measurements have shown that only one of the transformations has a distinct shear nature. At the same time the relief typical for martensitic transformation was observed by optical microscopy. The nature of both stages of transformation is discussed