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

Microfluidic Technology

Micro Energy and Chemical Systems (MECS)Micro Total Analysis Systems (µTAS)

BIOMEDICAL

MEMS

CHEMICAL

BIOLOGICALCHEMICAL

ENERGY

Cell sorting

DNA Diagnostics

Inkjet Print Heads

Drug Delivery

MicroelectronicCooling Automotive Heat

Pumps

Portable Power Generation

Fuel ReformingPoint-of-use

Nanomaterial Synthesis

BiodieselSynthesis

Lab-on-a-chip

ProteomicsSingle Cell Analysis

Cytosensors

KidneyDialysis

BiopolymerSynthesis

Water Purification

Person Portable Cooling

Blood Processing

At-Home Sensors

>> 100 mL/minpL or nL

higherlower

25 µm < Channel Height < 250 µm

Fluid Volume

Application Temperature

Channel Dimensions < 100 µm

Analytical Microfluidics Arrayed Microfluidics

Emerging Industry

Fuel Processing

Chemical Processing

Heating & Cooling

Nanomaterial Synthesis

Separations

200 µm wide channels

“Number Up” Channels

channel header

channels

Single Lamina

• Channels – 200 µm wide; 100 µm deep

– 300 µm pitch

• Lamina (24” long x 12” wide)– ~1000 µchannels/lamina

– 300 µm thickness

Patterning: • photochemical machining

“Number Up” Laminae

• Device (12” stack)~ 1000 laminae= 1 x 106 reactor µchannels

• Laminae (24” long x 12” wide)– ~1000 µchannels/lamina

– 300 µm thickness Bonding: • diffusion bonding

Patterning: • photochemical machining

24”

12”

12”

12”

24”Cross-section of Microchannel Array

Outline

• Motivation and Objective

• Approach

• Results

• Summary

Diffusion Bonding: Concept Diffusion Bonding: Concept

a

b

c

d

e

a) 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

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 ▲

Analysis of Microchannel Samples

ObjectiveObjective• To Compare the diffusion bonded and

Nickel-Phosphorous (NiP) diffusion brazedsamples to obtain

– the characteristics of bonding – effect of NiP interlayer

• Bonding conditions

Sample Diffusion BondedDiffusion Brazed with

NiP

Patterning Laser micromachining Chemical etching

Laminae Thickness 0.028” 0.025”

BondingParameters

Temperature (oC) 1000 1000

Pressure (psi) 1000 1000

Ramp rate (oC/min) 20 15

Dwelling Time (hrs) 2 2

Diffusion Heating Cycle

0

200

400

600

800

1000

1200

0 100 200 300 400 500 600

time, min

tem

pe

ratu

re,

°C

diffusion boded

diffusion brazed

Scanning Electron Microscopy

200 µm 100 µm

SEM image of bond line for diffusion bonded sample

50 µm

SEM image of bond line for diffusion brazed sample

10 µm

10 µm

two phases present

intermetallic?

Defect QuantificationDefect Quantification

Diffusion Bonded SSDiffusion Bonded SS Diffusion Brazed SS – NiPDiffusion Brazed SS – NiP

µm, %

Wavelength Dispersive X-ray Spectroscopy Wavelength Dispersive X-ray Spectroscopy

-20

0

20

40

60

80

100

0 10 20 30 40 50 60 70

distance, µm

wei

gh

t %

ele

men

t

Ni_bonded Ni_brazedFe_bonded Fe_brazedP_bonded P_brazed

bo

nd li

ne

Elemental concentration across the bond line in diffusion bonded and diffusion brazed sample

Nanoscale Materials in Chemistry, Wiley, 2001Q Jiang, Materials chemistry and physics, 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

Role of NanoparticlesRole 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

3 3

1.s sv vdV g Dk

dt kTG t G

Ω: geometric correction factor

sv: interfacial energyDv: volume diffusion co-efficientG: grain sizeVs: fractional porosity

Outline

• Motivation and Objective

• Approach

• Results

• Summary

Objective and ProtocolObjectives

• 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

Deposition from NP suspension

Spin CoatingSpin Coating• Small capital cost

• Faster Process

• Low contamination

• Patterned surface

• Edge effect

• Wastage of material

Sample Coating material RPM Time

Stainless steel lamina NiNP added in Nicrobraz cement 1500 20 sec

+

_

Drip CoatingDrip Coating • Small capital cost

• Patterned surface

• Less wastage of material

• Non-uniformity of the coating

• Agglomeration

• Very crude method

+

_

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

Film Characterization

(a) Continuous and uniform film

(b) Nanoparticle film (50 to 100 nm dia.) implying that high diffusion rate still achievable at relatively lower temperatures

200 µm

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

a b

Experimental DesignIndependent variables Dependent variables

Bonding temperatureBonding pressure

Bonding timeSurface condition

Bonding environment

Void fraction

Warpage

sample temperature (°C) Pressure (psi) Time (min)

SS 1000 1000 120

SS-NiP 1000 1000 120

SS – NiNP interlayer 750 1000 60

SS – NiNP interlayer 750 1000 120

SS – NiNP interlayer 800 1000 60

SS – NiNP interlayer 800 1000 120

SS – NiNP interlayer 900 1000 60

SS – NiNP interlayer 900 1000 120

SS – NiNP interlayer 1000 1000 60

SS – NiNP interlayer 1000 1000 120

Outline

• Motivation and Objective

• Approach

• Results

• Summary

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

20 µm

a

10 µm

b

20 µm

c

Surface etched with “Aqua-Regia” (3HCl + HNO3)

Evidence of phase change!

Experimental Design

Process flow chart for bonding of Process flow chart for bonding of SS with NiNP interlayerSS with NiNP interlayer

CharacterizationCharacterizationSEM

MaterialsMaterials Nicrobraz cement with NiNP

Solution PreparationSolution Preparation 30 min ultrasonic stirring

30 min electromagnetic stirring

Spin CoatingSpin Coating1500 rpm, 20 sec

Diffusion BondingDiffusion Bonding 700°C - 900°C, 1000psi,

60 - 120 min

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°C900°C

1000°C

Bondline Characterization 50 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!

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

Acknowledgments

This research is sponsored by the National Science Foundation CTS.