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.