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Joining of Yttria Stabilized Zirconia to Stainless Steel 420 by Nickel & Silver Nano Paste

Gorji, Amir Hossein | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45730 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Simchi, Abdolreza; Kokabi, Amir Hossein
  7. Abstract:
  8. Joining of yttria-stabilized zirconia (YSZ) to stainless steel (SS) is considered for various applications such as solid oxide fuel cells, thermal barrier coatings, and medical implants. In the present work, a series of brazing pastes utilizing silver and nickel nanoparticles (~80 nm) mixed with carboxymethyl cellulose as the organic phase were developed to join 5YSZ to 420 SS. The effects of processing parameters such as time and temperature of brazing and the composition of the paste on the microstructure of the joint and its mechanical strength were studied. The mechanism of interface formation was elaborated by scanning electron microscopy (SEM) and electron probe micro analyzer (EPMA). The mechanical strength of the joints was evaluated by shear test. It was found that better joints could be obtained by increasing the concentration of the nanoparticles in the paste. Particularly, the concentration of silver nanoparticles is important to cause denser interface due to higher sintering activity of silver nanoparticles compared to Nickel. However, excess amount of the solids in the paste could lead to particles aggregation and bonding heterogeneity. Increasing of the brazing time and temperature eases diffusion of elements and thus improve the joint strength. Optimization of the processing parameters by L16 Taguchi method was performed to attain the most suitable joining procedure. It was found that a paste with 72% solid loading yields maximum shear strength of 23±1 MPa when brazing was performed at 330 ◦C for 120 min. Further work should be performed to optimize sintering process of the paste to attain full densification upon brazing
  9. Keywords:
  10. Nanoparticles ; Nickel ; Silver ; Yttria-Stabilized Zirconia (YSZ) ; Stainless Steel ; Sintering ; Metal-Ceramic Joint ; Nanopaste

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