Application of nickel nanoparticles in diffusion bonding of stainless steel surfaces презентация

Tiwari and Brian K. Paul
School of Mechanical, Industrial and Manufacturing Engineering
Oregon State University

100 µm deep
300 µm pitch
Lamina (24” long x 12” wide)
~1000 µchannels/lamina
300 µm thickness

Patterning:
photochemical machining

µchannels

Laminae (24” long x 12” wide)
~1000 µchannels/lamina
300 µm thickness

Bonding:
diffusion bonding

Patterning:
photochemical machining

reduced voids

c) Final yielding and creep (some voids left)


d) Continued vacancy diffusion, leaving few small voids

e) Bonding is complete

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 ▲

diffusion brazed
samples to obtain
the characteristics of bonding
effect of NiP interlayer

Bonding conditions

image of bond line for diffusion brazed sample

two phases present

intermetallic?

v. 83, 2003, pp. 225-227

Au

Ag

“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

Effect of NP Size on Properties

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
γsv: interfacial energy
Dv: volume diffusion co-efficient
G: grain size
Vs: fractional porosity

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

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

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

implying that high diffusion rate still achievable at relatively lower temperatures

SEM images of the (a) coated and (b) dried (200°C, 30 min) nickel nanoparticles film on SS substrate

a

b

of phase change!

interlayer

makes little difference
Major advantage going from 750 and 800 C

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!

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