Warunki powstawania struktury martenzytycznej w stopach Ni-Mn-Ga wykazujących magnetyczną pamięć kształtu

Rafał Wróblewski

Abstract

The dissertation comprises results of the experiments carried out on the NiMnGa magnetic shape memory alloys (MSMA). Several alloys, with variable chemical composition, having generic formula Ni50Mn25+xGa25-x (x = 0 ÷ 5) were prepared. Some of the alloys contained terbium addition up to 2 at. %. Polycrystalline ingots were examined to determine effect of chemical composition on the structure and transition temperatures. The composition can be expressed by the valence electron concentration, e/a. It turned out that for the e/a < 7,65 the structural transition temperatures increase and for the e/a > 7,65 decrease together with the Curie temperature. It is also shown the terbium addition improves the mechanical properties by decreasing the mean grain size. During the study, the alloy for practical application at room temperature, having mean composition 50 % at. Ni, 30% Mn at., 20% at Ga, was obtained. Subsequently bulk polycrystalline, particulate and singlecrystalline, non-stoichiometric NiMnGa alloys were examined in order to determine the heat treatment effect and the form of the alloy on the structure and properties of NiMnGa MSMAs. At ca. 1030 K these alloys undergo order – disorder transformation, L21 - B2. It is shown that annealing above this temperature has an effect on the structure ordering, thus affecting the type of the martensite which is formed in the alloy. In bulk (polycrystalline and singlecrystalline) NiMnGa alloys, during slow cooling from above the order – disorder transformation the 7M martensite forms. Moreover, thanks to the internal stresses measurements, it is shown that the type of the martensite formed in the alloy depends on the form of that alloy.
Diploma typeDoctor of Philosophy
Author Rafał Wróblewski (FMSE / DCFM)
Rafał Wróblewski,,
- Division of Construction and Functional Materials
Title in PolishWarunki powstawania struktury martenzytycznej w stopach Ni-Mn-Ga wykazujących magnetyczną pamięć kształtu
Languagepl polski
Certifying UnitFaculty of Materials Science and Engineering (FMSE)
Disciplinematerial sciences and engineering / (technology domain) / (technological sciences)
Defense Date22-10-2010
Supervisor Marcin Leonowicz (FMSE / DCFM)
Marcin Leonowicz,,
- Division of Construction and Functional Materials

Internal reviewers Jerzy Szawłowski (FMSE / DSE)
Jerzy Szawłowski,,
- Division of Surface Engineering
External reviewers Bogusław Major
Bogusław Major,,
-
Pages95
Keywords in Englishxxx
Abstract in EnglishThe dissertation comprises results of the experiments carried out on the NiMnGa magnetic shape memory alloys (MSMA). Several alloys, with variable chemical composition, having generic formula Ni50Mn25+xGa25-x (x = 0 ÷ 5) were prepared. Some of the alloys contained terbium addition up to 2 at. %. Polycrystalline ingots were examined to determine effect of chemical composition on the structure and transition temperatures. The composition can be expressed by the valence electron concentration, e/a. It turned out that for the e/a < 7,65 the structural transition temperatures increase and for the e/a > 7,65 decrease together with the Curie temperature. It is also shown the terbium addition improves the mechanical properties by decreasing the mean grain size. During the study, the alloy for practical application at room temperature, having mean composition 50 % at. Ni, 30% Mn at., 20% at Ga, was obtained. Subsequently bulk polycrystalline, particulate and singlecrystalline, non-stoichiometric NiMnGa alloys were examined in order to determine the heat treatment effect and the form of the alloy on the structure and properties of NiMnGa MSMAs. At ca. 1030 K these alloys undergo order – disorder transformation, L21 - B2. It is shown that annealing above this temperature has an effect on the structure ordering, thus affecting the type of the martensite which is formed in the alloy. In bulk (polycrystalline and singlecrystalline) NiMnGa alloys, during slow cooling from above the order – disorder transformation the 7M martensite forms. Moreover, thanks to the internal stresses measurements, it is shown that the type of the martensite formed in the alloy depends on the form of that alloy.
Thesis file
Wroblewski.pdf 19.85 MB
Citation count*5 (2020-09-18)

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