4/1/2011 1 GSM GSM Processing of Nanostructured Ceramics: Shaping, Sintering and Properties Mehdi Mazaheri Nov 2009 Introduction - Ceramics? low density, low sensitivity to corrosion, high rigidity and hardness even at high temperature Introduction (1)- Ceramics? Toughening Mechanism in Ceramics Crack deflection Peng et al., J. Am.Cerm.Soc., 1988 Introduction (1)- Ceramics? Toughening Mechanism in Ceramics (1) Crack deflection (2) Crack bridging (3) Fibers pullout (1) Crack blunting (2) Crack bridging
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Introduction (1)- Ceramics? · Introduction 2- Mechanical spectroscopy High temp. mechanical behavior Crystallization in glassy phase Onset of creep Mechanical spectroscopy * Forced
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4/1/2011
1
GSMGSM
Processing of Nanostructured Ceramics:
Shaping, Sintering and Properties
Mehdi Mazaheri
Nov 2009
Introduction - Ceramics?
low density, low sensitivity to corrosion, high rigidity and hardness even at high temperature
Introduction (1)- Ceramics?
Toughening Mechanism in Ceramics
Crack deflection Peng et al., J. Am.Cerm.Soc., 1988
Processing of 8YSZMicrostructure and Mechnical behaviour
CS LMS
HMS TSS
؟
Conclusion 1
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Spark Plasma Sintering
&
Thermo-Mechanical Properties
Spark plasma sintering P
Graphite dieGraphite die
SamplePulsed DC
The first SPS unit in Europe, Dr Sinter 2050, installed in 1998
P
SPS ≥ HP
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Pressure effectPressure effect
Sintering or packing?
⎟⎠⎞
⎜⎝⎛ +⎟⎟⎠
⎞⎜⎜⎝
⎛ Ω=
Δ−r
PkTG
Ddt
LLd sva
gbgb γφδ3
0
295)/(
For Coble creep based grain boundary sliding
in intermediated stage
⎠⎝
⎟⎠⎞
⎜⎝⎛ +⎟⎟⎠
⎞⎜⎜⎝
⎛ Ω=
Δ−r
PkTG
Ddt
LLd sva
gbgb γφδ 2
215)/(
30
in final stage
Dgb : GB diffusion coefficient, δgb : GB width, Ω : atomic volume, G : grain size, k : Boltzmann constant, T : the absolute temperature, γsv is the solid-vapour surface energy, r : pore size. pa : applied stress.
600
650
700
696ºC
500 nm
prior to
Strain rate: 10-5 s-1
MgO Superplasticity⎯ Grain boundary sliding
0.3 Tm vs 0.5Tm
0 5 10 15 20 25 30 35 400
50
100
150
200
250
300
350
400
450
500
550
796ºC
756ºC
Stre
ss (M
Pa)
Strain (%) 500 nm
after
Compressive deformation under constant cross-head speed
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0,006
0,008
0,010
P always on
100MPa 75MPa 50MPa25MPao)
/dt (
s-1)
Strain rate: >10-3 s-1
Grain sliding Diffusion
Densification rate
40 50 60 70 80 90 1000,000
0,002
0,004
25MPa
Relative Density
-d(Δ
L/L
o
0,010
⎟⎠⎞
⎜⎝⎛ +⎟⎟⎠
⎞⎜⎜⎝
⎛ Ω=
Δ−r
PkTG
Ddt
LLd sva
gbgb γφδ3
0
295)/(
in intermediated stage
⎟⎠⎞
⎜⎝⎛ +⎟⎟⎠
⎞⎜⎜⎝
⎛ Ω=
Δ−r
PkTG
Ddt
LLd sva
gbgb γφδ 2
215)/(
30
in final stage
Intermedialte stage, 32%≤ Vp ≤ 10%, no linear relationFinal stage, Vp ≤ 10%, no linear relation
40 50 60 70 80 90 1000,000
0,002
0,004
0,006
0,008
P always on
100MPa 75MPa 50MPa 25MPa
Relative Density
-d(Δ
L/L
o)/d
t (s-1
)
0.015
0.020P at Tf
100P 75P 50P 25P
dt (s
-1)
Densification rate:P at Tf
Strain rate: 10-2 s-1
40 50 60 70 80 90 100
0.000
0.005
0.010
Relative Density
-d(Δ
L/L
o)/d
90
95
100
Den
sity
[%]
92
96
100
900
1100
1300
1500
Den
sity
[%]
Grain Siz
Consolidating YAG under high pressure
80
85
1100 1200 1300 1400 1500 1600
100 MPa - 3 min100 MPa - 6 min 50 MPa - 3 min
Rel
ativ
e D
SPS Temperature [oC]
80
84
88
100
300
500
700
1200 1300 1400 1500 1600
Rel
ativ
e D ze [nm
]
SPS Temperature [oC]
34 nm nc-YAG@ 100 MPa / 3 min
Spherical powder, 34 nmJ. of Euro Ceram. Soc. (2007) , 27(11), 3331-3337
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Densification while retarding solution-reprecipitation
Bright-field TEM image, beta-powder, grain size: 76 nm, SPS 1500oC under 50 MPa for 3 min. Note the aggregate feature of the large grains.
Introduction (2)- Ceramics?Grain refining
High temperature mechanical properties
Increasing of fracture toughness
(G.B. sliding accommodated by diffusion or interface reaction mechanisms)
gat room temperature
Nano‐structured ceramics reinforced by nano‐particles or fibers
3 times higher fracture toughness (Zhang et al, Nature Materials, 2003)