Effect of Ni3Ti formation on the oxidation kinetics of NiTi shape memory alloys

Nawawi, Nazihah (2014) Effect of Ni3Ti formation on the oxidation kinetics of NiTi shape memory alloys. Masters thesis, Universiti Sains Malaysia.

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    Abstract

    Nikel – Titanium (NiTi) aloi ingatan bentuk telah mendapat populariti yang tinggi dalam implan dan peralatan perubatan sejak beberapa dekad yang lalu disebabkan oleh keserasian biologi aloi ini. Keserasian biologi ini dicapai dengan pembentukan lapisan nipis titanium dioxida (TiO2) di permukaan hasil daripada proses pengoksidaan terkawal. Lapisan ini berkesan menghalang pelepasan nikel ke dalam tubuh manusia. Tindak balas pengoksidaan TiO2 ini adalah kompleks dan kadar tindakbalas adalah sangat tinggi terutama pada suhu tinggi. Ia melibatkan pembentukan Ni3Ti dan larutan pepejal Nin(Ti) apabila tempoh pengoksidaan dipanjangkan. Kajian ini mengukur kadar pembentukan ketebalan Ni3Ti untuk mengkaji hubungan pembentukan TiO2 terhadap variasi suhu dan masa. Sampel aloi diletakkan pada suhu 700 - 900°C pada jangka masa yang berbeza (10 – 200 minit) di dalam persekitaran udara. Didapati bahawa pertumbuhan lapisan Ni3Ti pada 900°C adalah parabola dan mencapai ketepuan kira-kira 4 μm selepas 60 minit. Pada 700°C, lapisan mencapai ketepuan pada ketebalan kira-kira 1 μm selepas 60 minit. Pada keadaan yang melampau (pada suhu 900°C selama 200 minit) pertumbuhan ketebalan kekal stabil pada ~ 3.5 - 4.0 μm walaupun selepas pengoksidaan dipanjangkan tempohnya. Keputusan Analisis Termogravimetri (TGA) yang dijalankan pada kondisi eksperimen yang sama telah menunjukkan bahawa tingkah laku pertumbuhan TiO2 adalah faktor penentu pertumbuhan lapisan Ni3Ti dan lapisan TiO2 juga memperlihatkan pertumbuhan parabola. Nickel - Titanium (NiTi) shape memory alloys have gained its popularity in many medical implants and their apparatus for the past few decades owing to their excellent biocompatibility. This attribute is achieved by the formation of thin layer of titanium dioxide (TiO2) at the surface from a controlled oxidation process. This layer effectively hinders nickel release into the human body. Oxidation reaction of TiO2 is complex and the reaction rate is very high especially at elevated temperature. It involves the formation of Ni3Ti and solid solution Nin(Ti) as the oxidation prolongs. This work quantifies the rate of Ni3Ti formation thickness for establishing a relation in controlling the thickness growth of TiO2 with respect to temperature and time variations. The alloy was subjected to heat treatment at 700 – 900°C for various times (10 – 200 minutes) in air environment. It was found that the growth of Ni3Ti layer at 900oC is parabolic and reached saturation at thickness of about 4 m after 60 minutes. While at 700°C, the layer reached saturation at thickness of about 1 μm after 60 minutes. At the extreme condition (900°C for 200 minutes) the thickness growth remained stable at ~ 3.5 – 4.0 μm although after excessive oxidation treatment. Thermogravimetric Analysis (TGA) results that were ran under same oxidation conditions (700 - 900°C in air at same treatment time) has shown that the TiO2 growth behaviour is the determining factor for the Ni3Ti layer and it exhibited parabolic behaviour.

    Item Type: Thesis (Masters)
    Subjects: T Technology > TJ Mechanical engineering and machinery
    T Technology > TJ Mechanical engineering and machinery > TJ181-210 Mechanical movements
    Divisions: Kampus Kejuruteraan (Engineering Campus) > Pusat Pengajian Kejuruteraan Mekanikal (School of Mechanical Engineering) > Thesis
    Depositing User: Mr Badli Syahar Bakhtier
    Date Deposited: 12 Apr 2017 09:48
    Last Modified: 19 Jun 2017 16:11
    URI: http://eprints.usm.my/id/eprint/33023

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