Graduate Thesis Or Dissertation
 

Nickel nanoparticles-assisted diffusion brazing of stainless steel 316 for microfluidic applications

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  • Transient liquid-phase diffusion brazing is used in precision, hermetic joining applications as a replacement for diffusion bonding to reduce cycle times, reduce bonding pressure and improve yields. Studies showed that the interlayer used in diffusion brazing can be detrimental due to the use of melting point depressants (MPDs). The goal of this study was to investigate the role of nanoparticles and their size distribution in reducing bonding temperature of stainless steel surfaces for Microfluidic applications, as nanoparticles have inherently lower melting point and higher diffusivity than that of their bulk counterpart. The conventional interlayer has been replaced by a nickel nanoparticle (NiNP) film without any MPDs for diffusion brazing of stainless steel 316L laminae. Brazing was carried out in a uni-axial vacuum hot press at temperatures 750°C, 800°C, 900°C and 1000°C; at a bonding pressure of 10 MPa; at a heating rate of 10°C/min and dwell times of 1 and 2 hrs at each temperature. Comparison among the conventionally diffusion bonded, diffusion brazed and NiNP diffusion brazed samples is made with regard to microstructural evolution, diffusional profile and bond strength. Taken together, the results show that NiNP-assisted diffusion brazed samples have continuous bond line with low void fraction and high shear strength compared to conventionally diffusion bonded and brazed samples. Also, comparing within the NiNP diffusion brazed group, the samples brazed at 900°C have the best results. Effect of particle size on diffusion brazing of stainless steel 316 was also studied with the help of two different sets of nanoparticles (N1: average particle size of 46.7±6.2 nm and N2: average particle size 8.8±0.9 nm. Results showed that the sample brazed with 8.8 nm particles indicated better results with a more homogeneous bondline structure. The findings of this work have positive implications for the economics of NP-assisted diffusion brazing.
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file details Dissertation_Santosh_K_Tiwari.pdf 2017-10-20 Public Télécharger