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Microstructure and Mechanical Properties of Two-step TLP Bonded 304 Stainless Steel with a Cobalt base Interlayer

Amini, Ali | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54376 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid; Ekrami, Aliakbar
  7. Abstract:
  8. Considering the wide applications of 304 stainless steel in various industries and the existing literature on transient liquid phase bonding of stainless steels with a variety of interlayers, the present work aimed to reduce the bonding time by using a two step bonding method. Faster bonding reduces both energy consumption during bonding and the base metal grain growth. It also leads to a lower reduction in the base metal and joint strength.Due to the melting point of the interlayer, different durations and a temperature of 1200°C were selected for the first step. This temperature was maintained for a specified period of time before it sharply dropped to and remained at 1180°C (the temperature of the second bonding step) until the bond formed. The second step was indeed also carried out using various durations. The optimal bonding conditions were determined by examining the microstructure of the bonds formed at different temperatures during different bonding times. In addition to the microstructure observations made with optical microscopy, a field emission scanning electron microscope was used to determine different phases at the bond area and in the diffusion-affected zone.Experimenting with various bonding times in both steps revealed the optimal time for the first and second steps to be 10 and 40 min, respectively.A number of mechanical tests including hardness and shear strength tests were then performed on the joints and the homogenization heat treatment of the specimens bonded under the optimal conditions were analyzed. An analysis of their shear strength and microstructure indicated that homogenization reduced their strength, rendering this heat treatment process unnecessary. Comparison of the optimal specimens in terms of shear strength with the base metal under the same bonding heat treatment conditions showed that the shear strength of the optimal specimen was 511.4 MPa, i.e., 81.6% of that of the base metal. Compared to the single step process, the bonding time was 37.5% shorter and there was less grain growth
  9. Keywords:
  10. Shear Strength ; Microstructure ; Transient Liquid Phase Boneling (TLPB) ; 304 Austenitic Stainless Steel ; Diffusion Affected Zone ; Mechanical Properties

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