Powder Production through Atomization & Chemical
Reactions
N. Ashgriz
Centre for Advanced Coating Technologies
Department of Mechanical & Industrial Engineering
University of Toronto
NSERC
CRSNG
Outline

Overview of the previous work
 MMC

Present research
 nanomaterial
 Spray
(Aerosol) method
 Colliding drops
Metal Matrix Composite Powder
Ceramic Particles
(high strength,
stiffness & thermal stability)
Metal Matrix
(high toughness,
strength, machinability)
MMC Properties Compared to Matrix Material:






Up to a 20% Improvement in Yield Strength
Lower Coefficient of Thermal Expansion
Higher Modulus of Elasticity (50%)
More Wear Resistant
Low Fracture Toughness
Poor Fatigue Properties
Powder Production Methods

Atomization (Over 60% by weight of all powders
produced in North America. )




Mechanical crushing
Chemical reduction
Vapor condensation
Electrolytic method
World wide Atomization capacity is 106 metric tons/year.
Annual market size of metal powder is $3 billion and corresponding
P/M size is $6 billion.
MMC




Matrix: Al, Ti, Ni, Steel
Particles: SiC, TiC, Al2O3, SiN4, Si
Difficult to incorporate due to non-wetting
(>90o) behavior
Undesirable interfacial reaction at high T
(brittle interfacial phase)
Methods of MMC Production
1. Atomization of Premixed MMC



SiC particles mixed into molten
aluminum alloy;
Without stirring SiC particles settle (Al =
2400 kg/m3 and SiC = 3200 kg/m3);
Brittle interfacial reactions occur due to
long resident times
Rotating Disk Atomization


Highest atomization
energy efficiency.
Better control of the
breakup process.
Vz(r,z)
V(r,z)
Vr(r,z)


Sever stresses due to
high RPM.
Thermal shock due to
sudden impingement of
the melt.
(r)
R
Controlling Parameters




RPM
Feed Rate
Disk Design
Liquid Metal Properties
Atomization Modes



Direct Drop Mode;
Ligament Mode;
Sheet Formation Mode.
Ligament Formation
Qd l  0.096 Re
R
Re 

2
0.95
We
1.15
R 
We 

3
2
Centrifugal Atomization With
Particle Injection
Disk
•Minimized interfacial interaction;
•Limited reinforcement segregation;
•Rapidly solidified microstructure.
Experimental Apparatus
Tank
X-Y
Controls
Motor for
Raising Rod
Crucible and Furnace
Connection
for Argon
SS
Plate
Gasket
Bolt
Crucible
6061 Aluminum alloy chosen as matrix
Bottom
of Rod
Air Motor And Disk




Disk preheated to 750 oC with
4000 Watt light
A pneumatic die grinder was
used to rotate the 3 inch
diameter disk.
Disk speed:24,000 RPM.
Disk is centered with X-Y table
during experiment.
Heating Light
Disk
Nozzle
Air
Motor
Rotating Disk Atomization in He




N=45000RPM
m=0.2kg/s
Cupper alloy: Cu-1%
Cr - 0.6%Zr
Titanium Alloy: Ti15%Mo -2.7%Nb –
3%Al - 0.2%Si
ASTM 112 - 95 Grain Size
25.4 m
Magnification 1000X
Microstructure of particle in 150-106 m size range. The ASTM grain size
of this microstructure is approximately 10
SiC Volume Fraction
in Composite Powder
SiC
Particle
Average:
SiC 18% Vol.
Void 1.2% Vol.
Void
Aluminum
Particle
SiC Volume Fraction
in Composite Powder
Significant
Particle
Penetration.
SiC Particle
Magnification 1000X
25.4 m
Microstructure of particle in 150-125 m size range. The
ASTM grain size is 11.9. The area of SiC particles is 11.1%.
The area fraction of the void is 0.3%.
SiC Volume Fraction
in Composite Powder
25.4 m
Magnification 1000X
Microstructure of particle in 90-106 m size range. The
ASTM grain size is 10.6. The area of SiC particles is 13.3%.
The area fraction of the void is 0.6%.
Conclusions



A new method of MMC powder production is
developed;
SiCp are successfully injected into the Al
matrix. (18% vol SiC)
MMC particles are not spherical;
 Mainly,
ligaments, teardrops & tad poles.
 Oxidation believed to be the main cause.
THANK YOU