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Liquid Metal Engineering;
EXOMET and Metal-Matrix-
nanocomposites
W. D. Griffiths, N. Adkins and D. Shevchenko
School of Metallurgy and Materials, College of Engineering and Physical Sciences, University of Birmingham, Edgbaston, Birmingham, UK, B15 2TT.
The EXOMET project
1. Aimed for – a 50% increase in strength and ductility.
2. Creep-resistant Al alloys, up to around 300-350°C.
3. 26 institutions from 13 countries.
4. Runs 2012-2016.
The issues;
1. Nano-particle creation.
2. Prevention of nanoparticle agglomeration in the alloy.
3. Particle pushing / engulfment during solidification.
4. Casting to obtain desired mechanical properties.
5. Upscaling to industrial scales.
The EXOMET project
1. “Physical Processing of Molten Light Alloys under the Influence of External Fields”.
2. For grain refiners and nanocomposites.
3. 5-1 TiBor + grain refiners for Mg alloys.
4. Electromagnetic, ultrasonic and mechanical shearing.
The EXOMET project
1. “Physical Processing of Molten Light Alloys under the Influence of External Fields”.
2. For grain refiners and nanocomposites.
3. 5-1 TiBor + Mg grain refiners.
4. Electromagnetic, ultrasonic and mechanical shearing.
The EXOMET project
1. “Physical Processing of Molten Light Alloys under the Influence of External Fields”.
2. For grain refiners and nanocomposites.
3. Electromagnetic, ultrasonic and mechanical shearing.
1. Strengthening Mechanisms I
Load Transfer
∆σ���� � 0.5V σ��
Where Vp = volume fraction of particle = 1 or 2 vol.%
Δσload = 0.2 MPa
Strengthening Mechanisms II
Orowan
∆������� � �.�����
���
�
!�
ΔσOrowan = 2 MPa
Strengthening Mechanisms III
Hall-Petch
�"�##$%&'() � σ*+ ,-.$� !⁄
σ0 = 20 MPa
K = 0.04 MPa.m1/2
d = 50 μm
ΔσOrowan = 26 MPa
Strengthening Mechanisms IV
Coefficient of Thermal Expansion Mismatch
Δσ123� 3βG�b
12V ∆α∆T
1 <V bd
For SiC; dp = 50 nm and αSiC = 2.8x10-6 K-1ΔσCTE = 211 MPa
For SiC; dp = 50 nm and αAl = 22.2x10-6 K-1
Summary of the Strengthening
Mechanisms
∆� � ∆�>��� + ∆�"�##$%&'() + ∆�?@A! + ∆σBCDEFG
!
Δσload = 0.2 MPa
ΔσHall-Petch = 26 MPa
ΔσCTE = 211 MPa
ΔσOrowan = 2 MPa
2. Preform fabrication.
Water based slurry preparation (2 – 48 hours)
Mould heating for starch consolidation (2 -3 hours)
Preform firing to remove starch (4 – 20 hours)
The SiC preform.
Investigated the influence of
• Starch loading
• Slurry rolling time
• Starch consolidation timeOptimal composition:
30 g of SiC per 100 ml of water
43 g of starch per 100 gm of SiC
Maximum SiC loading 27 vol %
(39 wt% loading with AZ91)1.5 hours consolidation time 2 hours consolidation time
2 hours rolling time 48 hours rolling time
The Hot Isostatic Infiltration Technique
HIPing details;
Pressure – up to 200 MPa
Temperature – 700°C
Dwell time 10-30min
Full infiltration of SiC preform
Before After
The HIPped SiC preform
The wall thickness of top part of
the can was increased by 2 mm SiC preform infiltrated with AZ91
Masteralloy melting
ISM crucible
AZ31 solidified
in the crucible
Tensile results, AZ31 and AZ31 + 2vol.%SiC
0
50
100
150
200
250
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Tru
e S
tre
ss M
Pa
True Strain
AZ31AZ31 + SiC
AZ31 and AZ31+2vol.% SiC
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Mo
du
lus
of
Ela
stis
ity
( G
pa
)
1 2 3 4 5 6 7 8
1 – AZ31
2-8 – AZ31+SiC
0.0
5.0
10.0
15.0
20.0
25.0
30.0
AZ31
+
SiCMo
du
lus
of
Ela
stis
ity
(Gp
a)
AZ31 – 63 MPa
AZ31 +SiC – 78 Mpa
+ 24% PS0.2
AZ31
Element Weight% Atomic%
C K 2 4
O K 39 52
Mg K 1 1
Si K 54 42
Cu K 3 1
Totals 100
Element Weight% Atomic%
C K 9 17
O K 18 25
Mg K 1 1
Si K 69 56
Cu K 2 1
Totals 100Element Weight% Atomic%
O K 25 37
Si K 71 61
Cu K 4 1
Totals 100
EDS incertitude ± 1%
Particle sizes seems to be in
agreement with manufacturer
statement (40 nm).
TEM BF image
Particles were found within the
Al-Si matrix.
TEM observation of a Mg-SiC nano-
composite
By KeeHyun Kim
SiC
SiC
SiC
SiC
SiC
SiC
SiC
SiC
SiC
Other images(the scale marker bar is 200 nm)
SiC
SiC
SiC
SiC
SiC
SiC
SiC
SiC
SiC SiC
SiC SiC
SiC
SiC
SiC
SiC
Polycrystalline SiC
Tilting
SiC particles are crystalline and
polycrystals, confirmed by
diffraction patterns
Magnified images
SiC
SiC
SiC
SiC
Matrix
Matrix
Matrix
Matrix
Oxidation of the matrix - MgO
Some particles are pure Si not SiC !!!
Silicon particles
Please see and compare with SiC point analysis
Summary of work to date.
• SiC, Al2O3, AlN, Al(OH)3 nanopowders investigated as candidate materials for preforms.
• SiC and Al2O3 materials were selected. (AlN reacts with water).
• Slurry composition has been optimised.
• SiC and Al2O3 preforms have been infiltrated with AZ91
• Tensile testing of AZ31+2vol.% SiC was undertaken and showed significant performance improvement, (Young’s Modulus and PS0.2).
3. Electromagnetic Stirring and
Cavitation in an Induction Furnace
Designed by Pericleous and Valdez at Greenwich University, and built by ALD.
Electromagnetic Stirring and Ultrasonic Cavitation
(K. A. Pericleous, Greenwich University)
4. Positron Emission and Annihilation
PEPT uses a radioactive isotope which decays by releasing a positron (β+); the positrons collide with local electrons to produce two back-to-back γ-rays.
Positron Emission Tomography
• Positron Imaging uses a particular type of radioactive isotope, (specifically, 18F), that decays by releasing a positron (β+).
• The positron collides with a local electron giving off 2 γ-rays emitted back-to-back.
• Detection of the γ-rays allows the original location of the particle, along a line, to be found.
• Detection of multiple pairs allows the particle location to be to be found by triangulation.
In this example a rat has been
dosed with a radioactive glucose
compound, (containing C-11),
that accumulates in the kidneys
and the pituitary gland, which
allows their function to be
studied.
Positron Emitting (β+) Isotopes
Nuclide
•Half-Life
82Rb 78 s
15O 122 s
13N 10 min.
11C 20.3 min.
68Ga 68 min.
18F 110 min.
45Ti 3.1 h.
62Zn / 62Cu 9.2 h.
66Ga 9.7 h.
64Cu 12.7 h.
140Nd / 140Pr 3.4 days.
124I 4.2 days.
82Sr / 82Rb 25 days
68Ge / 68Ga 271 days
22Na 2.6 years.
Labelling Methods
1. Bombardment of an oxide particle by 3He. Oxygen in the outer
layers is converted to 18F. Detectable particles are typically sub-
mm, 600-400 μm.
2. Bombardment of water by 3He produces water containing 18F.
This is adsorbed onto the particle surface, (either alumina or an
ion-exchange resin). Smaller, <100 μm, or more active, particles
can be made.
Effect of casting temperature
Casting Temperatures (a) 85℃℃℃℃, (b) 110℃℃℃℃, (c) 87℃℃℃℃ and (d) 87℃℃℃℃
a) b) c) d)
The sand casting.
Results of Al plate castings.
Two particle tracks for alumina particles entrained in Al alloy sand-cast plate castings.
(a) size = 355 to 425 µm. (b). size = 425 to 710 µm
Initial Particle Location
b) a)
View of particle simulation after 3
seconds of simulated time.(~1000 particles.s-1)
Flow Direction
Flow Velocity – Higher velocities displayed darker
Particle locations
Flow Direction
Modelled inclusion trapping in liquid
Al in a sloping launder.
The PEPT Experiment
600 µm particle track
Summary
Previous attempts at metal-matrix failed due to
processing problems.
Current attempts at making nanocomposites are
to deploy a wider range of novel processing
techniques and have a greater chance of success.
Future Work
1. The manufacture of Al-MMnC’s.
2. The introduction of Mg-MMnC’s into Al alloys.
3. The use of electromagnetically-generated cavitation to disperse MMnC’s.
4. The use of electromagnetic stirring to disperse the MMnC’s.
5. The use of PEPT to study particle behaviour during electromagnetic stirring.
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