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Plasma spray of Functionally Graded Titanium-Hydroxyapatite on Titanium Substrate

Gholamzadeh, Mohammad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57723 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Sadrnezhad, Khatiboleslam
  7. Abstract:
  8. Hydroxyapatite (HA) is crucial in orthopedic and dental applications due to its similarity to hard tissues of body. Creating a coating with high adhesion, high corrosion resistance, and mechanical properties on orthopedic and dental implants can result in reducing the healing period, as well as increasing the durability of the implant. HA coating can cause the surface of the implant and bones to be strongly bonded together, letting the cells grow on it. Besides, titanium plasma sprayed (TPS) implants have been commercialized in the past decades due to their superior performance compared to uncoated implants in terms of bone-to-implant contact and bone retention. In this project, by using fixed plasma spray parameters, functional gradient coating of titanium/hydroxyapatite was deposited on the surface of the substrate. On the other hand, another sample, known as traditional ones, a monolayer coating of hydroxyapatite was deposited on the titanium substrate. For the functional gradient coating, the initial layer placed on the surface containing 100% porous titanium acts as a pre-layer. The next layers respectively contain 75%, 50%, 25% titanium and the last layer is 100% hydroxyapatite. In this research, X-ray diffraction analysis (XRD) was used to investigate the crystallinity and phase analysis of the coating, and it was observed that by performing heat treatment, the crystallinity of both types of mono-layer coating and the functional gradient increased by about 25%. SEM images were also used to check the morphology of the coating and EDAX analysis was used for elemental analysis and to check the gradient changes of elements in the coating. From its results, it was observed that functional gradient coating has reduced the porosity and cracks of the coating from about 16% to about 13.5% due to the reduction of residual stresses inside the coating layer. Due to the sintering phenomenon, heat treatment has reduced the amount of porosities by about 3%. The nanohardness test was also done to check the hardness and Young's modulus of the coating. The results indicated that producing functional gradient coating has increased the hardness of the samples. On the other hand, after heat treatment, the hardness of the coating has increased by about 5% for both types, and the Young's modulus has increased by 3% for single-layer hydroxyapatite coating and by 15% for functional gradient coating. The coating strength test was also done according to the ASTM D4541 standard, and the results showed that the strength of the functional gradient coating was 10 MPa higher than mono layer hydroxyapatite coating, and after heat treatment, the strength of the coating increased by about 15% for both types. Corrosion properties of coatings were determined through potentiodynamic test in body simulating solution (SBF). The results of the corrosion test showed that the the samples with functionally gradient coating and their subsequent heat treatment improved the corrosion resistance. After coating and heat treatment, the corrosion current density has decreased by 70% and the corrosion potential has increased by 47% compared to the substrate without titanium coating
  9. Keywords:
  10. Hydroxyapatite ; Bioceramic ; Plasma Spraying ; Dental Implant ; Ceramic Coating

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