PhD Thesis_RuiMSMartins.pdf - RUN UNL

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In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization Chapter 5 Conclusions and Future Works Chapter 5 – Conclusion and Future Works 201
In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization 5. CONCLUSIONS AND FUTURE WORKS 5.1. CONCLUSIONS The technological importance of films has led to an unabated interest in the detailed characterization of their structure, morphology and their interfaces. A better understanding of the underlying growth mechanisms and their microstructural development requires sophisticated in-situ techniques. XRD is such a well-established and powerful technique as demonstrated in this thesis work for the study of Ni-Ti SMA films. Numerous examples of investigations on Ni-Ti films can be found in the literature but it has been also reported that the deposition of Ni-Ti films with definite stoichiometry and high purity remains a challenge, and important issues like formation of film texture and its control are still unresolved. The first experiments performed worldwide concerning in-situ X-ray investigations of the microstructural development during Ni-Ti film growth have been presented. The magnetron-sputtering chamber installed at ROBL proves to be a very efficient instrument to follow in situ, the evolution of the structure of the Ni-Ti growing film. The experimental procedure adopted leads to a controlled manipulation of the composition and preferential orientation of the film. It has been found that the type of substrate plays an important role for the preferential orientation of sputtered Ni-Ti films: - an amorphous SiO 2 buffer layer induces the development of the (100) orientation of the B2 phase during deposition on heated substrates (≈ 470ºC); - a TiN buffer layer allows a control of the crystallographic orientations of Ni-Ti films and acts as an efficient diffusion barrier. Ni-Ti films mainly containing grains with (100), or (110), or (211) planes of the B2 phase parallel to the film surface could be produced using TiN buffer layers. The preferential orientation of the sputtered Ni-Ti films is also influenced by the application of a substrate bias voltage. In this work, it has been revealed that the control of the energy of the bombarding ions could be used as a tool for the manipulation of the transformation temperatures. Furthermore, films exhibiting SME above RT have been produced. The present thesis work as well allowed the identification of different phenomena on the growth of graded Ni-Ti films leading to the optimisation of the deposition parameters for Chapter 5 – Conclusion and Future Works 202
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RUI MIGUEL DOS SANTOS MARTINS IN-SI
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ACKNOWLEDGEMENTS The research work
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At CENIMAT, Luís Pereira also carr
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SUMÁRIO O fabrico de películas fi
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LIST OF SYMBOLS AND ABREVIATIONS α
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TABLE OF CONTENTS Introduction ....
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LIST OF FIGURES Fig. 1.1: Power/wei
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Fig. 2.3: Calculated integrated pho
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Fig. 3.25: Pole figures of Ni-Ti B2
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Fig. 3.66: SAED pattern obtained on
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LIST OF TABLES Tab. 1.1: Factors af
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In-situ XRD studies during growth o
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