Application of Nickel Nanoparticles in Diffusion Bonding of Stainless Steel Surfaces

1. Application of Nickel Nanoparticles in Diffusion Bonding of Stainless Steel Surfaces Santosh Tiwari and Brian K. Paul School of Mechanical, Industrial and Manufacturing Engineering Oregon State University

2. Microfluidic Technology Micro Total Analysis Systems (µTAS) Micro Energy and Chemical Systems (MECS) MEMS ENERGY CHEMICAL Inkjet Print Heads Microelectronic Cooling Lab-on-a-chip Drug Delivery Automotive Heat Pumps Person Portable Cooling DNA Diagnostics Portable Power Generation Cell sorting Biodiesel Synthesis Single Cell Analysis Water Purification Fuel Reforming Proteomics Point-of-use Nanomaterial Synthesis Kidney Dialysis Biopolymer Synthesis At-Home Sensors Cytosensors CHEMICAL Blood Processing BIOLOGICAL BIOMEDICAL Channel Dimensions < 100 µm 25 µm < Channel Height < 250 µm pL or nL Fluid Volume >> 100 mL/min Application Temperature lower higher Arrayed Microfluidics Analytical Microfluidics

3. Emerging Industry Fuel Processing Chemical Processing Nanomaterial Synthesis Heating & Cooling Separations

4. “Number Up” Channels 200 µm wide channels • Patterning: • photochemical machining channel header • Channels • 200 µm wide; 100 µm deep • 300 µm pitch • Lamina (24” long x 12” wide) • ~1000 µchannels/lamina • 300 µm thickness channels Single Lamina

5. “Number Up” Laminae Laminae (24” long x 12” wide) ~1000 µchannels/lamina 300 µm thickness • Patterning: • photochemical machining 12” 24” 24” Cross-section of Microchannel Array 12” 12” • Device (12” stack) • ~ 1000 laminae • = 1 x 106 reactor µchannels • Bonding: • diffusion bonding

6. Outline • Motivation and Objective • Approach • Results • Summary

7. Diffusion Bonding: Concept a b c d e • Initial 'point' contact • b) Yielding and creep leading to reduced voids • c) Final yielding and creep (some voids left) • d) Continued vacancy diffusion, leaving few small voids • e) Bonding is complete

8. Diffusion Brazing of SS 316L Filler materials such as Ni, Cu, Au etc. Nickel Almost 100 % solid solubility in Fe Good corrosion and wear resistance Compatible with stainless steel Temperature depressant materials (TDMs) like Si, B, P etc. added to reduce the melting temperature Transient liquid phase bonding Adverse effect of TDMs Formation of secondary phases Bond strength and ductility ▼ Additional heat treatment cycle ~ up to 24 hrs Time and Cost ▲

9. Analysis of Microchannel Samples Objective To Compare the diffusion bonded and Nickel-Phosphorous (NiP) diffusion brazed samples to obtain the characteristics of bonding effect of NiP interlayer Bonding conditions

10. Scanning Electron Microscopy 100 µm 200 µm 10 µm 50 µm 10 µm SEM image of bond line for diffusion bonded sample • two phases present • intermetallic? SEM image of bond line for diffusion brazed sample

11. Defect Quantification Diffusion Brazed SS – NiP Diffusion Bonded SS µm, %

12. Wavelength Dispersive X-ray Spectroscopy bond line Elemental concentration across the bond line in diffusion bonded and diffusion brazed sample

13. Effect of NP Size on Properties Ag Au “As the size decreases beyond a critical value, due to the surface –to-volume ratio, the melting temperature decreases and becomes size dependent” Nano Al : 2nm (200oC) and 9nm (660oC) Generally, critical value is ~10nm Nanoscale Materials in Chemistry, Wiley, 2001 Q Jiang, Materials chemistry and physics, v. 83, 2003, pp. 225-227

14. Role of Nanoparticles Nano-sized particles exhibit lower melting temperature than the bulk material lower activation energy required to liberate atoms from the surface tremendously high surface area causing higher diffusion rate The densification rate during sintering Ω: geometric correction factor sv: interfacial energy Dv: volume diffusion co-efficient G: grain size Vs: fractional porosity

15. Outline Motivation and Objective Approach Results Summary

16. Objective and Protocol Objectives to compare NiNP-brazed samples with diffusion bonded and NiP diffusion brazed samples to investigate the microstructural evolution and bond strength of the stainless steel shims bonded using a Ni NP interlayer Sample Preparation Materials Stainless steel 316L shims of 1.0 mm thickness (1”x1”) Suspension: Nicrobraz binder mixed with Ni nanoparticles Processing Laser machining and deburring Coating of NiNPs: ~5 µm thick Drying: 200°C for 30 min Diffusion bonding

17. Deposition from NP suspension Spin Coating Small capital cost Faster Process Low contamination Patterned surface Edge effect Wastage of material + + _ _ Drip Coating • Small capital cost • Patterned surface • Less wastage of material • Non-uniformity of the coating • Agglomeration • Very crude method

18. Nicrobraz Binder A commercially available water based binder (Wall Colmonoy Corporation) Low viscosity: better for deposition Readily wets the surface of clean metal substrates Excellent adherence and a relatively short drying time Low content of binder material to minimize outgassing during the bonding cycle All binding material volatilizes by 540°C leaving behind the compact layer of particles No residue remains on the parts after brazing, when using nickel-based filler metals Ideally suited for application of nickel-based brazing filler metals

19. Film Characterization 200 µm b a SEM images of the (a) coated and (b) dried (200°C, 30 min) nickel nanoparticles film on SS substrate • Continuous and uniform film • Nanoparticle film (50 to 100 nm dia.) implying that high diffusion rate still achievable at relatively lower temperatures

20. Experimental Design

21. Outline Motivation and Objective Approach Results Summary

22. Bonded and Brazed Samples (a) diffusion bonded SS at 1000°C, 2 hrs (b) NiP diffusion brazed at 1000°C, 2 hrs and (c) NiNP diffusion brazed SS at 1000°C, 2 hrs b a 20 µm 10 µm c 20 µm Surface etched with “Aqua-Regia” (3HCl + HNO3) Evidence of phase change!

23. Experimental Design Materials Nicrobraz cement with NiNP Solution Preparation 30 min ultrasonic stirring 30 min electromagnetic stirring Spin Coating 1500 rpm, 20 sec Diffusion Bonding 700°C - 900°C, 1000psi, 60 - 120 min Characterization SEM Process flow chart for bonding of SS with NiNP interlayer

24. Void Fractions Key findings 2X time makes no statistical difference Temperature above 800 C makes little difference Major advantage going from 750 and 800 C 750°C 800°C 900°C 1000°C

25. Bondline Characterization50 nm Ni on SS 1000X – X-section of nano Ni bonded SS; 750 C, minutes 500X – X-section of nano Ni bonded SS; 800 C, minutes Evidence of phase change between 750 and 800 C!

26. Summary A 50 nm+ dia. nickel nanoparticle (NiNP) interlayer has been shown to: lower the bonding temperature for diffusion brazing eliminate the use of melting temperature depressants NiNP-brazing yielded low void fractions no deleterious secondary phases expected require less time at lower temperature than conventional diffusion techniques 50 nm+ dia. NiNPs appear to have gone through phase change between 750 and 800 C Currently evaluating shear strength of joints

27. Acknowledgments This research is sponsored by the National Science Foundation CTS.