Mechanical and Biodegradable Properties of Hydroxyapatite Coated Magnesium Deposited by Cold Spray

Md Razi, Hasniyati (2016) Mechanical and Biodegradable Properties of Hydroxyapatite Coated Magnesium Deposited by Cold Spray. PhD thesis, Universiti Sains Malaysia.

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    Proses semburan sejuk yang mudah dan telah diubahsuai digunakan untuk menyalut serbuk hidrosiapatit ke atas substrat magnesium tulen yang dipanaskan kepada 350°C atau 550°C dan dihaluskan permukaan samada 240 atau 2000 gred kekasaran dengan jarak ‘standoff’ 20 mm atau 40 mm. Prosedur ini diulang lima dan sepuluh kali. Satu reka bentuk faktorial pecahan (24-1) telah digunakan untuk menjelaskan faktor-faktor proses yang memberi kesan kepada ketebalan, kekuatan dan modulus elastik sampel. Analisis kaedah tindihan digunakan untuk menentukan nilai domain yang optimum. Kemudian, kaedah kecuraman digunakan untuk mengesah dan memindahkan nilai domain yang optimum. Sifat mekanik yang maksimum telah diperolehi pada jarak 30mm, gred kekasaran permukaan Ra=0.14 dan 460°C suhu pemanasan substrat yang menghasilkan salutan optimum dengan ketebalan 49.77μm, 462.61 MPa kekuatan dan 45.69 GPa modulus elastik. Lapisan hidroksiapatit tidak menunjukkan perubahan fasa pada suhu 550°C. Daya mikroskop atom menunjukkan topografi lapisan seragam dan mikroskop imbasan elektron menunjukkan ikatan yang baik antara lapisan bersalut dan substrat. Kajian biodegradasi menunjukkan bahawa lapisan apatit tulang yang terbentuk di atas permukaan lapisan selepas 24 jam boleh menggalakkan ikatan tulang dengan tisu hidup dan meningkatkan jangka hayat lapisan. Kajian kehilangan berat menunjukkan bioaktiviti bagi sampel bersalut lebih baik berbanding dengan sampel tidak bersalut. Ujian lekatan mendedahkan bahawa pengurangan kekuatan ikatan datang dari pembubaran lapisan kimia yang berterusan. Selepas 24 jam rendaman, kekuatan ikatan adalah 40 MPa. Ujian percepatan kakisan menunjukkan bahawa lapisan hidroksiapatit melindungi dan mencegah magnesium daripada kakisan dalam persekitaran mengakis. _________________________________________________________________________________________________________________________ A simple and modified cold spray process was developed in which hydroxyapatite powder was coated onto pure magnesium substrates preheated to 350°C or 550°C and ground to either 240 grit or 2000 grit surface roughness, with standoff distances of 20 mm or 40 mm. The procedure was repeated five and ten times. A fractional factorial design (24-1) was applied to elucidate the process factors that significantly affected the thickness, nanohardness and elastic modulus of the coating sample. The overlaid method analysis was employed to determine trade off optimal values from multiple responses. Then, steepest method was used to reconfirm and relocate the optimal domain. The maximum mechanical properties of the coating were determined at 30mm standoff distance, surface roughness Ra=0.14μ and 460°C substrate heating temperature which accommodate the optimum coating of 49.77μm thickness, 462.61 MPa nanohardness and 45.69 GPa elastic modulus. The hydroxyapatite coatings did not show any phase changes at 550°C. Atomic force microscopy revealed a uniform coating topography and scanning electron microscopy revealed good bonding between the coated layers and the substrates. The biodegradable study suggested that bone-like apatite layer formed on the surface of the coatings at 2 hours may promote bone bonding with living tissues and increase the longevity of coatings. The mass loss experiment concluded that coated sample shows a better bioactivity compared to uncoated sample. The adhesion test revealed that reduction of bond strength comes mostly from the continuation of chemical dissolution of coatings. After 24 hours of immersion, the bond strength was 40 MPa which satisfied the requirement for bioimplant application. The accelerated corrosion test concluded that the hydroxyapatite coating remarkably protects and prevent magnesium from corrosion in the corrosive environment.

    Item Type: Thesis (PhD)
    Additional Information: full text is available at
    Subjects: T Technology
    T Technology > TN Mining Engineering. Metallurgy > TN263-271 Mineral deposits. Metallic ore deposits. Prospecting
    Divisions: Kampus Kejuruteraan (Engineering Campus) > Pusat Pengajian Kejuruteraan Bahan & Sumber Mineral (School of Material & Mineral Resource Engineering) > Thesis
    Depositing User: Mr Mohd Jasnizam Mohd Salleh
    Date Deposited: 11 Jun 2018 11:17
    Last Modified: 11 Jun 2018 11:17

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