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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
11.02.2005, Faculty of Metallurgy and Materials Science
Candidate:
mr. sc. Diana Ĉubela
Mentor:
prof. dr. Faik Uzunoviĉ

Thesis title:

A Contribution To The Research Of Technological Parameters Influence On The Proces Of Nitinol Fabrication And Plastic Deformation

Summary:
Titanium and Nickel alloy, with 48 - 55 at. % Ni (rest Ti), named Nitinol belongs to the group of the alloys that are called SHAPE MEMORY ALLOYS or MEMORY ALLOYS (SMA). These alloys have property of thermal and mechanical memory. There are numerous alloys that can remember their origin shape, but today, Nitinol and alloys based on Cu, like CuZnAl and CuAlNi, have the most spread commercial application.
From early application such as greenhouse window openers, trough to the plastic coated mobile phone antennas, current list of Nitinol applications has increase enormously, particularly throughout '90ies. Now NiTi shape memory alloys have been widely used in many areas such as engineering, electronic, safe technology, sensor tehnology, actuators, house devices, aerospace, airplane, automotive industry, toys, medical, etc.
Nitinol is alloy whose properties and application depend strongly on a fabrication processes and the problems that have not still been completely solved related to precise control of chemical composition, hot-working and cold-working conditions and shape memory - superelasticity treatments.
Nitinol was produced in semi-industrial conditions at the plant of Metallurgical Institute in Zenica. Testing results of the quality of the obtained alloy are related to technological parameters of the production and processing. The aim of this paper is to give an answer to the question which technological parameters are the most influential for the quality and is it possible and what kind of correction regarding literature instructions are needed for successful production of Nitinol at the Insitute.
The results of DSC analysis and tensile testing were confirmed that the alloy has shape memory and superelasticity properties, but temperature range this properties is under 0oC, and the their values are not on very good level. Mechanical properties for martensite and austenite condition of alloy are on the level of the values given in the literature for Nitinol. Microstructural examination on the REM confirmed that alloy matrix is intermetal compound NiTi, as well as a presence of TiC and brittle Ti2Ni phase. Their nonuniformed size as their hardness and brittleness had negative effects on the cold-working of the alloy.
It is possible to get Nitinol in semi-industrial conditions at the plant of the Institute, but particular attention has to be given to liquid phase of alloy aimed to shift the transformation temperature to higher values and to improve shape memory and superelasticity properties because of that the processing of the alloy would be more easier and the alloy would have wider application area.

Key words :
Nitinol, austenite-martensite transformation, shape memory, superelasticity, oneway memory effect, toway memory effect, chemical composition, hot and cold working, heat treatment, trainning, DSC analyse, tensile testing on low temperatures, electron microscopy


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