Metale z pamięcią kształtu i ich zastosowanie

Abstract

Shape memory alloys can be ascribed to a relatively new group of functional materials. Shape memory effect of these alloys is closely related to the reversible, thermoelastic martensitic transformation, which means structural changes, i.e. reconfiguration of thermally activated atoms or by applied external stress, or else by magnetic field. Shape memory is the material’s capacity to take on two different programmed shapes as a result of phase change taking place. Two different shapes are tightly connected with the structure change of these phases when warming up and cooling down. The book constitutes a synthesis of numerous publications, and presents an evolutionary process of knowledge development in this field of study. Hence, it provides a relatively big number of quoted sources illustrating a laborious way to understand complex processes and phenomena taking place in shape memory alloys, especially in those with a magnetic shape memory. The book is also above average thanks to exposing practical information. It concerns not only information on the technology of making alloys, but above all a description of procedures and optimal parameters of a thermo-mechanic processing to reach the most beneficial qualities of shape memory alloys. The first chapter of the book allows for obtaining knowledge within the scope of a martensitic transformation and martensite structure, understanding their nature, as well as the influence on the effects of shape memory accompanying a reversible martensitic change. The second chapter presents the phonomenon of shape memory, putting emphasis on oneand two-way shape memory and superelasticity connected with the transformation induced by external stress. This chapter also discusses the possibility of strain increase in the one-way shape memory effect, with the use of specially privileged crystallographic grain oriantation, i.e. the texture and anisotropy of the properties related to it. The next chapter deals with NiTi alloys and begins with the discussion of the phase equilibrium system and the processes of alloy production and modification, with particular emphasis on the processes of structure and microstructure shaping through dislocation reconfiguration in the process of recovery and their annihilation, grain size control by way of annealing temperature, or the use of the aging process for the precipitation of Ni4Ti3 particles which are coherent with the matrix in the alloys with increased nickel content, which give real possibilities of controlling the properties of alloys and implants. The chapter also presents the problem of bio-compatibility and resistence to pitting corrosion importat for medical implans. It also characterizes the layers passivated in an autoclave, which have a characteristic amorphous structure, have a high breakthrough potencial (1200 mV), are thin ( 4 nm) and do not show cracks as the result of strain accompanying the shape memory effec.The fourth chapter concerns alloys on the copper matrix characterised by a bigger complexity of structure and phase content, at the same time, creating big possibilities of controlling their qualities. The issue of high-temperature alloys characterised by Af > 120°C is presented in chapter five. The very alloys promise greater application on an industrial scale in constructions of operators regulating motor work in cars and planes. Chapter six covers ferromagnetic alloys in which the shape change is a result of imposing the field of pressures and a magnetic field on. The majority of alloys within this group bases on Heusler’s phases while a classic example are alloys close to Ni2MnGa. The last two chapters include the examples of using classical alloys in technology and medicine. When it comes to conventionalized applications in technology, the examples of separable pieces of hydraulic systems in planes, as well as robot holders, thermo-regulators, thermal engines and systems deadening vibrations were given. As regards the latest solutions, the applications of anti-seismic constructions of bridges, and the attempts to deaden the engines of gas turbines in planes were presented. Futhermore, chapter eight discusses all the staples used to join broken bones and a surgery backbone treatment. Yet another group of implants in question constitutes self-expanded stents and Amplatzer’s implant used to seal the loss of the interatrial and interventricular septum. The author’s intention, apart from explaining the nature of the phenomena of shape memory in metals, was to stimulate constructors’ imagination to use their unique properties, and encourage potential equipment producers to apply solutions based on these materials. The book may also be useful in doctoral programs and student education at faculties connected with engineering and materials science. Taking into account the complexity of the phenomena of shape memory, some fragments of the book were written taking into consideration the requirements of a didactic usefulness at the same time.