Introduction
Over the centuries, various kinds of metals have played a significant role in building constructions. With the immediate development of science and technology, there have also appeared different techniques of smelting, alloys, and forging. Science also managed to provide a deeper understanding of the metals microstructure and the effects of processing techniques on the material behavior.
Engineers have been working on the properties of different metals leading to the creation of new composites and alloys. In that regard, the research on shape memory alloys constitute the centre of discussions among the engineers and scientists over three decades, as they are still examining their unique characteristics, behavior and common types (Lagoudas 1). The main objective of this particular research is to study the main types of shape memory alloys (SMAs), their transition temperature, unique features, their production, and application.
Main Discussion
Brief History of Shape Memory Materials
The first mentioning of shape memory materials was with the discovery of martensite in 1890, which was the first step for phenomenal discovery of the shape memory effect (Ladouglas 4). This property is explained by such process as martensic phase transformation, which means that a molecular structure changes upon heating (Bhattacharya 4). This conversion is revealed through alloy deformation at a low temperature and its recovery to original form when heating the material to a specific temperature. The phenomenon was found by Chang and Read (Otsuka and Wayman 2).
The marensic transformation phase gave answers to the origin of the microstructure observed in the shaper memory materials. To study them, it is necessary to consider the deformation processes in single crystals occurred in the austenite state and to describe different states of the materials during those deformations. Relying on the facts and formulas, the results of transformation processes depend on the energy density that influence on lattice distortion (Bhattacharya 46). The martensic phase transformation is a solid-to-solid stage without diffusion of atoms despite the temperature variation.
The above processes began to be widely studied by different scientists. The next breakthrough took place with the discovery of nickel-titanium alloys during the investigation of material designed for heat shielding (Lagoudlas 4). It has been established that the material has an extreme shape recovery property and, later, this phenomenon was named as shape memory effect. Other elements like copper and iron appeared later and caused considerable decline in transformation temperatures.
Since the appearance of ‘smart’ materials, numerous commercial implementations have been introduced in electronic, medicine, and other fields. Nowadays there exist different types of shape memory alloys where copper-aluminum-nickel alloy, and nickel-titanium (NiTi). However, there exist other types of ‘smart’ materials including iron and gold composites.
Pseudo-Elasticity and Other Properties of Shape-Memory Materials
Pseudo elastic behavior is connected with stress-induced deformation leading to tension generation while loading and posterior reformation during a high-temperature phase. As a whole, the process itself consists in large deformation at high temperature and shape recovery when the pressure is eliminated (Ladouglas13). If looking this process in detail, it consists of several complicated process starting from austenite phase triggering the martensic transformation. The stressed induced deformation is succeeded by the development of inelastic strains proceeding to the stress level where the loading path encounters the end-phase transformation (Lagoudlas 13). Upon the transformation completion, one can observe that there is an evident increase of slope between the strains. Revert process begins with the unloading the path returning to the austenite stage and the recovery of shape.
It is also worth saying that the consequences of transformation can expose the shapes memory effect, which is disclosed super-elastic behavior and rubber-like behavior, different stages of yielding and diverse phase diagram (Hane and Shield 3901). However, the study of different shape memory materials has proved that a certain phase choice is valid for specific types of crystal polymers.
There are researchers dedicating their studies to different kind of behavior of the shape-memory alloys with the enclosure of such variable as electric current density and steady initial temperature of thermoelectric SMA. The results of the research on solution behavior and transient heat transfer have shown that the problem of constant temperature decreasing with electric current density of magnitude that cooling cannot last incessantly since it is another unique property of shape memory alloys (Ding and Lagoudlas 50). The researchers, thus, have managed to obtain the fixed the lowest temperature bound.
Manufacture of Shape Memory Alloys
With regard to the application of smart and functional materials, these alloys are produced and required in different forms. Therefore, there are different methods are applied for processing and production of shape-memory alloys. Apart from this, the manufacturer generates different forms and shape-memory characteristics and properties (Srivatsan 43). Hence, some of the methods apply a combination of Ni and Ti produce the alloys, others use the powder of these chemical powders for further synthesis. In whole, the production process may imply casting methods, thin film and metal foam methods and powder metallurgy processes (Srivatsan).
The alternative ways for ingot metallurgy have been chosen to solve the problems during such processes as melting and machining. Alloy process techniques, hence, involve vacuum induction melting, which is used from SMA production in large quantities for commercial application. Electron beam re-melting, that is used to manufacture super ingots, which is provides the advantage of carbon elimination from the alloy, as the melting is carried out in a copper crucible (Strivatsan 45). Other production methods involve solid-state metallurgy methods, foam, and film manufacturing.
Practical Application of Smart Materials
The modern application and development of ‘smart’ materials is reduced to the use of the super-elastic effect of shape memory ingots. Hence, the medical application of the metals also relies on its pseudo-elastic properties; this field takes advantage of such qualities as corrosion and biocompatibility of nitinol (Pons 101). Those ingot metals are applied in producing glasses with frames made of shape memory alloys. Such glasses can undergo significant transformations and suffer a minimum of losses. Shape memory alloys are also applied in the field of nuclear technology. They are used for protecting people working in a radiation environment (Rosinski 826).
Drawing a conclusion, shape memory alloys can be considered as one of the most important discoveries in the field of technology and science. Their unique properties of elasticity and shape recovery have greatly contributed to the improvement of various fields of social and economic life. The studies of microstructure have also revealed other issues that should researched in the future, as some of the properties are still concealed. In addition, shape memory materials are rather fascinating, as they have a potential for further application.
Works Cited
Bhattacharya, Kaushik. Microstructure of martensite: why it forms and how it gives rise to the shape memory effect. UK: Oxford University Press, 2003.
Ding, Zhondhai, and Lagoudas, Dimitris C. Solution behavior of the transient transfer problem in thermoelectric shape memory alloy actuators. SIAM Journal on Applied Mathematics. 57.1 (1997): 34-52.
Hane, Kevin F., and Shield, Thomas W. Microstructure in a Copper-Aluminum-Nickel Shape-Memory Alloy. The Royal Society. 455.1991 (1999): 3901-3915.
Ladouglas, Dimitris C. Shape memory alloys: modeling and engineering applications. US: Springer, 2008.
Otsuka, Kazuhiro, and Wayman, Marvin. Shape memory materials. UK: Cambridge University Press, 1999.
Pons, Jose. Emerging actuator technologies: a micromechatronic approach. US: John Wiley and Sons, 2005.
Rosinski, Stan. Effects of radiation on materials: 20th international symposium. NJ: ASTM International. 2001.
Strivatsan, T. S. Processing and Fabrication of advanced materials, XVII, volume 1.New Delhi: I. K. International Pvt Ltd, 2009.