engleski

Correlation of microstructure and functional properties of shape memory alloys

Shape memory alloys (SMAs) belong to a group of new functional metallic materials. They are used in different fields: medicine, electrical and electronic industry, machine industry etc. Shape memory effect is a remembrance of previously deformed shape of the material, and in physical sence is a consequence of martensitic transformation in structure of a homogenouous substance. Necessary condition for obtaining the shape memory is the presence of the reversible phase transformation of austenite (high- temperature phase) in martensite. This transformation is obtained by mechanical (deformation) or thermal methods (heating and cooling). Noumerous alloys show shape memory effect. In this paper, an overview of the most important three groups of alloys: Ni-Ti alloy (nitinol), Cu-alloy (Cu-Zn-Al, Cu- Al-Ni, etc.) and iron based alloys (Fe-Pt, Fe- Mn-Si, etc.) will be presented. Besides nitinol, copper-based alloys (CuZnAl, CuAlNi) have the highest application, which are much cheaper and relatively easy to produce, and they are used as sensor, actuator, etc. Also, production methods of these alloys such as "melt-spinner" technique (rapid solidification), production of alloys by conventional and continuous casting, etc. will be presented. Besides the development trend and characterization of these alloys, a part of our own research obtained on nitinol and copper based alloys, particularly from the standpoint of their production (casting), heat treatment, microstructure and functional properties (hardness, corrosion resistance, etc.) will be presented in this work.

shape memory alloys ; martensite ; functional properties ; microstructure

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