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Si3N4-Al2O3-ZrO3 hot pressed composites
Materials
Chemistry, and Physics,
qqA12~3-“r02
A.
HOT
(1987) 205-729
PRESSED
P. VINCENZTNT
RELLOSI,
CNR,
18
Research
TRTEC,
205
COMPOSITES
and
G.N.
BABTNT
for
Ceramics
Institute
Technology,
Faenza
(Ttaly) Received
March
23,
1987,
accepted
May
13,
1987
ABSTRACT Development
of
microstructure, Vickers
room
temperature
MOR,
been
studied
83wt%Si
for
pressed
at
terious
presence
34.4MPa
Microcracking thermal
has
to
PI-phase
with
zirconia. Si3N4-A1
The 0
to
phases
the
substantial
in
of
the
of
a-j3
the
toughness
MOR
mismatch
microcrack
~370
for
a grain
is of
No
from
from MPa
to
between
model
conversion.
the
dele-
materials.
parameters
results
increase,
properly
ZrO2-induced
cell
hot
The
these
and
have
composites
temperatures.
avoided
because
materialto-
more
specific
is
hehaviour
toughness
A phenomenological
of and
reference
and
and
variation
progress
hardness
heen2azcrihed
than
times
observed
for
the in
Zr-O-N
heen
expansion
N -5wt%A1203-12wt%Zr02 vzr4ous
coefficients.
account
improvement
has
of
expansion
gested
for
thermal microhardness
sug-
the
detectable
the
presence
MPa
for
ZrO
boundary
of
a
composite ghase
effect,
grain
boundary
strengthening.
INTRODnCTION The phase
required
material and
an
size is
have amount
additive
to
limits
strength
nitride in
metastable,
of been
sinter
its
shown
related
difficult
0254-0584/87/$3.50
because
Tn
its
impurity
a fully
at
silicon to
to
metal
Si 7 N 4 to
performance
sintered
distribution.
and
high
nitride
improve
with
content,
of
the
high
dense
and
high
temperatures. and the
particle
Zr02-strengthened
rich
hot
Toughness
pressed
addition size
strength
silicon
of and
m-ZrO
2
[II
particle
N , retention of t-ZrO 3 4 2 mismatch, and the increa-
Si
thermal
0 Elsevier Sequoia/Printed
in The Netherlands
206
sed toughness has been
is mostly
shown
strengthening
associated
in binary
to lower
the hot pressing
reduction
of the amount
so 19,101.
tion
Also
to offer
cutting
Evolution
good high-temperature phase
performances made
have
formed
[Z-B]
during
inconsequent
hot
for the
phases,
properties,
was not detected
been
oxidation
but Al 0 did 2 3 as sintering aid has been
reported
from hot pressed
of microstructure,
temperature
Vickers
of zyttrite
(up to -
[2] or MgOtY 2 0 3 t3*41
proved
of such deleterious
it
and the forma[11,12].
in cast
iron machining
Si N -Al 0 -31'0 compo34 23 2
b 3 ) 141 .
sitions
room
such as MgO
temperature
the addition
tools
boundary
are readily
However
that microcrack
temperatures
grain
which
aids
of the easy-to-oxidize
Excellent using
to moderate
phases,
Use of sintering
pressing.
microcracking.
compositions,
of the catastrophic
of ZrN and or Zr-O-N
proven
Si3N4-ZrO2
is restricted
1073 K) because
with
flexural
microhardness
linear
strength
thermal
expansion
( (I), toughness
(HV) have been
studied,
( A),
(Krc) and
in comparison
with
a Si N -Al 0 reference material, for a Si3N4-A1203-Zr02 composite 34 25 hot pressed at 34.4 MPa for different times and temperatures.
EXPERIMENTAL Two batches and 95wtX
of composition:
Si3N4-SwtX
Si3N4-Swt%
Al 0 - 12wtX Zr02 2 3 by wet mixing commercial
Al 0 were prepared 2 3 and ZrO 2 powders (Table I) and homogeneizing
Si N Al 0 34' 23 plastic jar with
Table
83wt%
I. Main
alumina
balls
characteristics
in isobutyl
alcohol
of the starting
in
a
far 72 hours.
powders.
2 -1 : grain size surface area BET=lB,O m g pm: particle shape: irregular; from -_o,o~i to-4.0 a/pratio 13.4; chemical analysis: NI 38%, CW -1%: O-1.496, Fe-0.04%, Al-0.06%, Ca-0.03%.
Si N (SZ a$ck LC 10)
: Specific
Al 0 (A? c:a A-16)
: S.s.a.
BET
ZrO,,(Harshaw)
: S.s.a.
2 -1 ;mean grain BET 28 m g
2 -1 ; grain 17.7 m g
size from--.5
to-lpm
size --.4 urn.
207 Hot
pressing
was
performed
uniaxially,
in
induction
heated
-3 graphoil-lined Bulk
dies
MOR
microhardness,
pressed
and
plungers,
in
thermal
microstructure,
density,
rature
Bulk
graphite
and
toughness
torr
10
expansion were
and
vacuum. room
determined
tempe-
on
the
hoi
materials:
density
was
measured
by
geometrical
analyses
were
performed
was
investigated
and/or
liquid
displacement
techniques. + Microstructural
by
XRD
, SEM
++
+++ , WDS
and
++++ EDS
.
Thermal
expansion
1573
at
K,
sawed
a heating
from
the
Microhardness
has
pm)
surfaces
and
on-line
pression of
10
by
of
pressed been
and
g
on
toughness
K
was
a Vickers value
Three
point
30
cut
crosshead
Table
mm
up
samples
a
loading
load.
rate
Each
H
polished
to
diamond
(down
* equipped
microdurometer
measured
diamond
represents
room from speed
6 tests.
the
4x4~40
diamond
by
of
0.3
value
with
to
a detector 10
mm/set,
represents
0.1
set
the
im-
average
V
Hot
indentation
an
pyramidal the
average
IC
of
temperature
determinations.
utilizing
mm
on
SK/min,
measured
at
500
room
billets.
a Vickers
computer,
time
Fracture
Each
hot
rate
from
temperature
MOR
was
indenter
pressed
billets,
of
0.5
mm/min.
Each
microstructure
of
the
a load
of
10
5 determinations. ** measured on specimens
hot
conditions
at
test kg.
of
the
pressing
fracture
with
value and
26
mm
represents relevant
hot
pressed
materials
, Ni
filter,
F.R.G.
span
and
the
a
average
parameters are
3x3x
collected
of in
II.
+
Siemens
++
500,
CuK
Autoscan,
Etec
Corp.
+++
Autospec,
Etec
Corp.,
U.S.A.
++++
Edax
Philips,
NL.
0
Netzsch
* XI
Zwick 3212 microdurometer, Instrom,universal testing
PV
D
9100,
Geratebau
U.S.A.
- apparatus,
F.R.G.
F.R.G. machine,mod.l195,Canton,
MS,
U.S.A.
pressing
1853
1923
1923
1923
1973
1923
1923
1923
AZ2
AZ3
AZ4
AZ5
AZ6
Al
A2
A3
(K)
1813
T
Hot
AZ1
Sample
Table II. Composition, pressed from Si3N4-Swt%
pressing
60
30
30
(min)
220
120
60
120
220
120
t
conditions
A1203-12wt%
hot
0.87
0.60
0.31
0.94
0.92
0.74
0.72
0.32
0.13
conditions ZrO 2 and
and
some
a-Si
2 3
0
13.5
40.0
68.0
6.5
8.0
26.0
28.0
68.0
87.0
%
Al
N 34
systems.
microstructural
Residual
Si3N4-6wt%
Relative
99
98
95
98
97
97
97
95
93
%
of pressure
density
parameters (Applied
0.90
0.85
0.72
0.93
0.86
0.56
1.0
hot
(pm)
grain
MPa).
0.48
size
Mean
34.4
materials
209
RESULTS Microstructure Phase
composition a-si
Unconverted amounts
of
tative
N 3 4'
X-SiAlON
estimation
of
Table
III.
Approximate
tive
crystal
phase
Si3N4-Al
0
b5]
were
the
relative
XRD
Si2N20,
detected
by
amounts
m-Zr02 XRD. (Table
semiquantitative
content
in
the
hot
a-Si
N 3 4
P-SiAlON
III)
evaluation
pressed
Si2N20
and
A gross
Si
materials.
2 3
Sample
$'-SiAlON,
ZrO2Cm)
minor semiquantiwas
derived
of
the
N -A1203-ZrO 3 4
relaand
2
X-SiAlON
zr02w
AZ1
56
9
22
7
3
AZ2
41
20
22
7
3
AZ3
20
48
13
a
3
AZ4
17
51
13
a
3
AZ5
6
63
15
5
3
AZ6
5
69
16
3
2
63
28
Al A2
34
54
9
A3
from of
the each
racteristic
with
the
(height)
to
the
sum
reflections
Important
features
progress
(m+t)-ZrO
__
traces
40
_-
2
7
_-
2
82
intensity phase
9
of
content
in
ratio
of of
are:
the all i)
thea--_ the
of
a characteristic
intensities crystal
(heights)
of
the
cha-
phases.
a variations
of
conversion
and,
ii)
pressed
at
materials
reflection
hot
p'-SiAlON
spacings
a decreased higher
tempera-
2 tures
(1923-1973
K),
in
grain
zirconia
the
a-SiJN4--+P'-SiAlON The
which
boundary
(heights)
liquid
a partial
solubilization
of
phase.
transformation
a-Si3N4-p'-SiAlON
intensities
indicates
transformation of
characteristic
was XRD
assessed reflections:
from
the
210
I a
(210)
I
+
(102)
(1)
p'=
/
I
(210)
Residual samples
+ 1
a-Si
hot
(102)
N vs 3 4 --
pressed
hot
at
different
a
1
-
I
Residual
Although fine as N
the
MgO[20
, 211 stand
da =
where
k
of
I
I
250
200
150 (min.) pressing
time
for
the
S i3N4-Al
the On
is
the
a-phase this
co1 lected
data
Y203-
1 81
p7
for
a
appear
previous
order
1st
studies
, Ce02
order
cient
insuffi
[19]
similar
on
and
HPSN
kinetics,
to
precisely systems
sintered
desuch
Si-Al-O-
i.e.:
(2)
transformation in
the
rate
constant
and
a the
concentration
sample.
assumption,
transformation,
0 2 3
studied.
- ka
dt
for
2
reaction [16],
time
vs hot N zoipositions
a-Si
the
1,
temperatures.
100
Si3N4-A1203-ZrO
Fig.
ZrOz
hot pressing 1.
in
F
50
0
and
plotted
5wt%A1203
l! Fig.
is
b c
5wt%AI,03+12wt%
____
time
K
-1813
z
pressing
Ea= -450
apparent kJ/mol,
activation derived
energy from
the
for
the
Arrhenius
a-+ plot
p’ of
211
\ \\S1~N4+5wt%MgO \ kTmol-'
\<520 \
\
\
\
\
\
1F4/T Fig.
2.
sion
reaction.
Arrhenius
plot Data
of
for
(K-‘)
the
MgO-
rate and
constant
CeO 2
comparison.
Fig.
2,
compares
C-470
kJ/mol)
Si 3 N 4
(-480
with [19]
parameters
Previous
studies
sions
of
the of
Al
constant
0 is 2 3
P'-SiAlON near SiA'ON
Si
XRD
decrease phase
c-500
[17]
similar
and
at
of
N in
sites
by
(Fig.
the
hot
pressed
and
conver-
reported
CeO
b6,17,22]
stress
show
cell
3). Thus,
Al
and
which
and
for
-Si N 3 4 2 Y203-
temperature.
increase the
Al
amount
0 resp. a shift
results
parameters the
an to
materials,
reflections, of
also
kJ/mol'
proportional
our
for
a-p’
the
are
B'-SiAlON
[15,23-261
PLSiAlON
cupation
obtained
MgO-Si3N4
kJ/mol)
Lattice
results
for
-HPSN
with and
of
an
solid
cell
dimen-
fractional the
recorded
oc-
overall in
the
approximately
increasing
0 in
the
Although was
in
of
amount solution
liof
the
within
212
UNIT
CELL I 1
AA
DIMENSIONS
5Wt%
Al203
o l 5Wt%
Al203
‘-4s
--__
J
c (A, +12wt% ZrOz
2.96 2.94
I
---a
--so_ -_0
aA 7.66
,
-&OS_
2.92
0
2.90
)
7.64 7.62 7.60 (
I
3.
Fig.
Variation
function and
zro
p'content
Si
N
perztures
the
- Al
conversion,
the
cell
dimensions
( PI/( Cl++‘))
compositions 0 2 3
appear
[ZO] . On
lattice
lid
solution from
to
with
i.e.
the
range
.a
1I I
of
the
for
samples
of
hot
pressed
for
P'-SiAlON
as
Si
0 -
N -Al
dlf 3t
a
erezt3tem-
azd4times.
P'-SiAlON
ported
in
of
-I
I
0.6
0.4
the
the
- 0.3
to
with
increasing
basis
parameters in
decrease
of
of hot
the
progress
pressing
the
known
p'-SiAlON
pressed
time,
as
and
Al
has
mol%,
according
to
fracture
surfaces
re-
53between
been the
a-p'
III
the
0 2 3'
the
previously
relationships
materials
-0.1
of
alumina
in
evaluated
hot
soto
pressing
schedule.
Morphology -Polished, tion
and
etched
morphology
morphology
of
Fig.
clustering
of
ZrO
step, the
which dense
and of 4 on
2
occurred,
resulted
in
The
SEM
body.
shown 2' the sample
ZrO
grain
by
sizes
micrograph
the
AZ2,
possibly
were
polished
indicates
during from of
examined.
a polished
surface that
the
-0.2
DistribuSEM
noticeable
homogenization
urn to
-10
surface
pm of
in A3
213
Fig.
4.
showing
SEM
micrograph
clustering
SEM
Fig.
5.
Dark
areas
of
of
micrograph are
a polished
starting
associated
of
ZrO
surface
the
AZ2
sample
of
the
A3
sample.
2
a polished with
of
particles.
Si_N_O.
surface
214 (Fig.
Fi), shows
an homogeneous to silicon re path
very minor distribution
oxynitride.
is evident
from
amounts
of isolated
of darker
A mixed
areas
residual
which
might
pores
correspond
intergranularltransgranular
SEM micrographs
of fracture
and
fractu-
surfaces
for
both
Si N -A1203-ZrO 2 (Figs. 6a, c) and Si3N4-Al 2 0 3 (Figs. 7a, b). 3 4 Similar to other HPSN [19, 27-321 a preferred orientation was
detected, peaks,
On the basis
the growing
of the intensities
$-SiAlON
grains
show
of X-ray a trend
diffraction
to align
their
a)
of fracture surfaces Fig. 6. SEM micrographs pressed at: a) AZ3, 1923 K, 60 min.: b) AZ5, AZ6, 1973 K, 120 min.
of AZ materials, hot 1923 K, 220 min.: c)
b)
a) Fig.
7. SEM micrograph
basal
of fracture
and b) A3 sample
60 min),
plane
aligning
(002) parallel
effect
surface
of Al sample
a)
(1923 K,
(1923 K, 220 min).
with
increases
the hot pressing
at increased
direction.
hot pressing
This
time.
Properties Thermal Repeated ple.
expansion thermal
Dilatometric
expansion
curves
Al 0 -ZrO materials 2 3 2 Fig. 9 shows thermal
runs were
of the first
(AZ3 and AZ5!
three
runs
are reported
on each AZ samfor some SiSN4in Figs.
8a, h.
for Si N -Al 0 samples (Al 34 23 which begins and A3). The martensitic t-+m transformation of ZrO 2 at temperatures as high as 1328 K is incomplete, the finer ZrO 2 symmetry down to room tempeparticles remaining in the tetragonal rature. relevant
Microcracking thermal
and ZrO 2 grains, the thermal The
curves
in the bulk
expansion originates
expansion
linear
expansion
performed
mismatch
of the AZ samples, between
the irreversible
the nitride
matrix
elongation
shown
by
curves.
thermal
expansion
coefficients
samples
for different
materials
and temperature
heating,
i.e. before ----
sformation,
due to the
and after
are collected
the beginning
in Table
IV.
f h 1 of AZ and A intervals
of the m--+t
on tran-
216
DILATOMETRIC
m
TESTS
It I I
1
I
,’
/ /
1
,
I
. //’
1 /
I/(
,/
/I
/’
,
/ /(/
’
, .
0 ~~
/
,
H
l’
/ I’
’ 6’
I’
a
,,e
/’
_--A/
/’
w ‘)r
500
1000 T
_--
500
1500
(Kb
1000
T(K)
1500
*
Fig. 8. Thermal expansion curves for AZ materials hysteresis loop and irreversible elongation. zro III'indicate order of the repeated tests. a) AZ3, b) AZ5, 1973 K, 220 min.
showing m-tSuffix I, II and 1973K, 60 min.;
217
500
1500
Id00
T(K) Fig.
9.
Al:
1923
Table
Thermal K,
IV.
expansion
60
Average
Sample
curves 1923
linear
K,
for 220
thermal
Si3N4-A1
0
2 3
A materials
hot
pressed
at:
min.
expansion
coefficients
materials,
within
( A)
selected
for tem-
ranges.
Thermal exp.
test
IO AZ1
A3:
2 and
Si3N4-A1203-ZrO perature
min;
A(293-91;
K)
h(293-111;
x10
X10
K)
3.09
3.14
4.!io
110
3.19
3.17
4.65
1110
3.16
3.27
4.75
3.35
3.38
4.40
AZ3
IO IO
3.43
3.48
4.!io
AZ5
110
3.29
3.32
1110
3.23
3.32
4.75 5.25
10
3.69
3.86
5.15
110
3.82 3.52
3.96 3.71
4.50 5.55
AZ6
1110
A(zgz-993
K)
A(293-1173
K)
A(293-1473
Al
IO
3.00
3.18
3.39
A3
10
2.89
3.06
3.30
K)
218 Microhardness values for both A and AZ samples (Table V) locat e at the V upper limit among other hot pressed Si N -based materials [33,34] 3 4 and exceed those for both single crystal (H = 19.6 GPa) and poV5OO lycrystalline Si3N4 p5,361 . No appreciable effect on microhardThe H
ness
results
Table xural
from
the presence
of ZrO
2'
V. Fracture toughness (K ), microhardness strength (CJ) of Si3N4- A?;03 and Si3N4-Al
Sample
H
K Ic (MPa1'2)
(H 0
2 3
) and fleXl?&rials.
U(MPa)
(CPa) V500
(' 30%) AZ1 AZ2 AZ3 AZ4 AZ5 AZ6
4.0 5.7 6.3 5.6 5.7 5.8
23.5 29.8 24.5 20.9 20.5 19.1
f f 4 f f 4
1.4 1.6 2.5 1.5 1.4 1.7
360 f: 33 n.d. n.d. 599 A 30 630 * 25 n.d.
Al A2 A3
6.0 6.0 4.9
29.5 f 23.6 * 21.2 f
3.5 2.5 2.2
314 * 20 n.d. 36% * 54
Fracture
toughness
and strength
Fracture
toughness
(KIcf has been
level
accuracy,
malized
from
the Evans
for hot pressed
K&H
alI2
where
H is the hardness
median
= 0.203
crack
length.
for SiAlON-based [1,39,40 ]-
(c/a
ZrO2
Si3N4
and Charles
(Table
V), at a 30%
L371 relationship
nor-
[38] :
-3/2 (3) a the impression
Measured
materials seems
obtained
radius
and C the radial/
K
values agree with Ic and silicon nitride-based
practically
not to affect
those
reported
composites
fracture
toughness
of our materials. MOR has been in Table -dense similar
determined
V, which
ZrO
2
show
containing
to those
on selected
a relevant material
previously
samples;
aincrease (AZ4 and AZ9)
reported
data
are reported
in the nearly-fullywhose
for SOwt%SiAlON
strengths
are
- SOwt%ZrO
2
Cutting
tool
Cutting
performance -
tools
were
tested
in
were
obtained
prepared
from
grey
cast
iron
(Az2,
AZ4,
A3)
Al,
A3,
Azl,
machining as
AZ2
and
AZ4
samples results
[z3 ( 141 . Excellent
reported
in
l1
Fig.
10,
which
show?
+IORKlNG CONDITIONS
,:utting speed
45Om mm-'
depth of cut
1.5m-n
feed rate
0.35mm rev-l
1.0 BREAKAGE
FREIXIENCE
high(100%) :A1
very
hlgh(507.1: S,AZl,AZ2. tow (50%) : YS very LOW (5%)
K,G,AZ4,A3
J
0.0 0
Fig.
10.
rials
in
ratory
pieces
Flank the
wear
vs --
number
machining
(S;
flank
number
of
wear
K;
Q)
vs. ---
laboratory
the
and
; YS:
number
some
pieces
iron,
Si
worked
for
compared
N -7wt%Y
cu?t!ng
of
pressed
worked
cast
Si3N4zbased
hot
Y,03-14wt%Si02)
of
grey
Si3N4-lOwt%CeO
(Ce:
commercial
other
200
100 Worked
the
: a,
AZ
and
to
other
A mate-
03-14wt%SiOz)
laboand
tools.
pieces
in
comparison
(Ce:
Si3N4-lOwt%CeO
; YS:
commercial
Si3N4-based
2 cutting
with
Si3N4-7wt% tools
(s,K,Q).
DISCUSSION Development
of
microstructure
Densification,
hot
pressed
phenomena tions the
or liquid
diffusing
and where
by
the phase,
species
a-P’
transformation
sintered
silicon
nitride
processes
are
transport
capability
according and
some
to
and
either
the
processing
are
grain
liquid-phase
governed of
the
inherent
growth
by
interface
for
aided reac-
diffusing
species
chemical
reactions,
parameters
such
as
both
in
atmosphe-
220
re,
applied
above
processes
silicon also
stress
has been
nitride
should
of liquid
and temperature. reported
materials.
follow
Detailed
[16,17, 26,42-443
The densification
the same pattern,
is formed
information
at high
for several
mechanisms
provided
temperature
on the
of SiAlON
a sufficient
where
dissolution
amount of
Q-
Si N and its reprecipitation as PI-phase [20] is realized, this 3 4 process offering the main contribution to densification and to the overall
development
Densification
of microstructure.
in our materials
tes at T > 1723 K at a value retical
density
and with
the material
during
grain
version,
growth)
material
transport
which
of available
densificatjon,
thus
most
complete than
fraction
in a few minu-
the expected
in the microstructure ( a-+$
of hot pressing
without
such lead
further
as surface
to structural
vacuum
may play
spaces
a role
rel.iable for covalent
bonded
diffusion
condensiother
and evapo-
modifications
without
with
an increase
in the evolution
compounds
of
remarkable
, evaporation/condensation
[20,21,45,46]
theo-
a-Si3N4conver-
of
to solution/diffusion/reprecipitation
redistribution
structure
stage
take place
processes
ration/condensation,
a small
lower
modifications
the final
In addition
fication.
a little
only
p' . So the gross
ted to
is nearly
in
of the microappearing
the
[Zl] .
The reaction:
Si3N4
(s)--+
which
takes
K, would sfer
JSi(g) place
provide
through
+ 2N2
with
(g)
a vapour
a mechanism
the gas
phase
the developing
p' . This
contact
and reduces
points
diffusion. vely
the interfering cation
of liquid
favours
filling
the stress
atm at 1963 by ion tran-
a-Si 3N 4 grains
gradients
further
-3
of the regions
in compositions
phase,
10
conversion
the residual
evaporation/condensation,
is reached.
of about
for the a--+p from
As a consequence,
low amount
pressure
sintering before
at crystal
for grain
containing
to
boundary
a relati-
is stopped complete
by
densifi-
221 when
Nevertheless, tical
as
P'-SiAlON,
cient
amount
lower
densification
lions
and
Higher
of
liquid
at
ascribed
ii)
and,
the
and
of
The
rates
to:
the
the
the
the
amount
of
aconverted
for
30
metal
beneath
hours,
the
impurities
scale.
In
perties minium sing
in
the the
Figure
higher
A1203/Si
in
the
liquid
phase,
which
surface
of
that
being
phase
in
the
N ratio 3 4 especially
increases
boundary
the
amount
characteri-
observed
SiAlON
depleted
in
zone
influence
region
lower may
is
by
XRD
the
hulk
nearer the
amount
of
play
at
to
of
diffc-
oxidized
on
also
a criti-
variation
samples
higher
the
phase
Remarkable
been
being
obvious
conversion
1 shows
grain
has
near-surface
the
phase.
the
phase,
liquid
for
this
refractory/viscosity
top'
the
boundary
a-_,p
the
to
0 , 2 3
Si3N4-Al
1)
the
boundary
aluminium
renc-
2
and
p content
and
addition
of
the
(Fig.
of
temperature,
a+p
which
chemical
of
lransformation.
of
K
ZrO
insuffi-
to
amount
of
aspect
depths
to
throrc_
[zo].
observed
composition
cal
rent
of
grain
temperature,
place
been
because
composition
liquid
actual
have
the an
although
take
a larger
processing
at
associated,
compared
i)
approaches
compositions,
formed
rearrangement
dissolution
higher
pressed
is
are
materials
some
modifies
stics
rates
composition
hot
phase
materials,
containing
2
SiAlON
our
reaction
Zr02-containing
ZrO
for
structural
a-p
possibly
the
at
1773
than
in
the
oxide
transport
ihc
pro-
disposable
a role
in
alu-
depres-
rate.
ZrO
increases
the
phase-conversion
rate
2 whereas
the
largely in
the
at
the
unaffected
stages
is
solubilized
findings
change
in
of
phase
del
from
early
These
the
lla),
grains
and
3).
the
of
in
in
growth
a-3 the
on
fresh
by cell
p’ grain
of
P'takes
p' nuclei
evaluating
boundary
At
the
places from
the
the
Al
it
most
the
with
of
the
continuous
the
progress
phenomenological
beginning on
content 0 2 3 appears that
the
of
p'-phase to
is
phase.
explanation the
PI-phase
the
parameters,
according h.
of
transformation
a reliable
lla,
of
parameters
Also,
parameters
Figs.
cell
actual
the
offer
cell
the
transformation
proposed
(Fig.
of
(Fig.
$-phase
alumina
the
variation
of
preexisting
AI-O-N-S1
the
mo-
process p-Si
liquid.
N 3 4 In this
lJlnuclei dA++
a Si4+ N3-
Fig.
11.
Phenomenological
reaction a)
in
hot
initial,
b)
model
pressed final
Si
for
a solid
solution
quasi-equilibrium
high
in
conditions
liquid.
outer
the
to
pained
by
Some
inner
and
Al
region
of
a counterdiffusion
equilibrium.
With
and
nitrogen
continuously
and
the
of
liquid
grain
The
alumina.
tion
of
this
constituent.
now
the
p'-nuclei, species phase
and
termining
the
the
is
0 materials; 2 3
formed
growing
diffusion
is
progress
of
the
supplied phase
by
to
a-Si
the
composition
preexisting
p grains
Balance
of
with
state
activities
aluminium
and
of
vacant
diffusion
composition
of
sites. are
the
which
the
of
thermochemi-
Transport
therefore
silicon
is
both
composi-
poorer
atomic the
in
source,
a depletion
the
nitrogen
the accom-
3 N 4 grain
from
oxygen
a counterdiffusion the
N grain 3 4
suffers
P'on
sur-
from
a-+p'reaction,
growing
of
the
assure
for
the
meet
required p-Si
preexisting 4+ 3and N Si
to
p'and
established
accommodate
the
2-
o 2-
each
boundary
exolution
solid
and
are
together to
conversion
Si3N4-Al
conditions
fresh
requires
0
of
cal
are
Al
between
3+ rounding
a-+p~SiAlON 2 and
stage. 3+
stage
the
N -Al203-ZrO 3 4
in
species core and
the
of
the
silicon
liquid
important
in
de-
$-phase.
Properties The
thermal
expectedly
lower
expansion than
coefficients for
Si3N4-A1203-Zr02
for
Si
N -Al
0
c~m~osi~e~.
materials The
higher
are
223
A value
for
cts
higher
the
Al
bl
at
3 4
AZ6
of
reported
N
x
content
coefficient
Si
(3.00
for
4
is
-6
in
P'-SiAlON
K-J)
ttIan
p' of being
p'-SiAlON
comparable
series
10
in
latter,
lower
than
(z=3)
an
12.
(2.89 the
that
hvalue
A plot
Fig.
A3
the
temperature.
reported
for
of
This
x
of the
-6K-1
thermal for
shows
10
A
expansion
a-Si3N4.
2.?
x
10-6K-1
within
an
refle-
1
AZl-
the
increase
for
of
the
Si3Nq-A12%-Zr02
Fig.
12.
Average
function
of
thermal
expansion
of
what
would
on
thermal
crystal the
thermal
with
be
P'-SiAlON
and
of
the
it
should
be
taken
unt
and
crease
glass
is
evolution
A
(293-1173
expected
to
a -Si
different
the
the
for
of
hardly
continuous that
the
the
additive
constituting
boundary can
KJ,
as
phase
to
the
ZrO
change
in
of
no in
most
Forp',
both
both
of
its hot
the
Si-Al-0-N-(Zr,
complexity
pressing
and
its
conditions.
2
of
thermal
performed.
a redistribution
@-phase
based
contribution
a-P'conversion, the
rule
a,p'and
the
be
inverse
amothe
large
de-
converted
N 3 4'
expansion
for
a simole
grain
during
be
i.e. ---
calculation
considering
thermal
the
of
material
place
unpredictable under
glassy
account
but
should
hand,
the
into
compared
other
applying
A precise
composite
0 takes 2 3 A
materials, In
of
composition,
in
by
coefficients
alone.
expansion
Al
coefficient
-Lncreasing$/atp'content,
predicted
expansion
species
overall
expansion
flj(atP')
impurity) continuous
224 Processing rosity,
grain
hardness.
and microstructural
techniques
composition
size and phase
the most
Fnr our materials,
ratio are the j3/l/atp'
and grain
such
are all affecting
relevant
Figure
size.
parameters
variance
13 is a plot
as po-
micro-
parameters of HV
“S
500 --
I
,
,
0
1
,
1
.
I
25 residual
.
I
I
.
*
I
I
I
75 50 cc-phase (“/d)
8
and Si 3N 4-Al 0 Fig. 13. Vickers microhardness of Si N -Al 0 -ZrO 2 3 2 a-gi3N hot pressed materials as a function zf4 3 4'
30-
2
a
2
25-
0 0
>” I
20-
1
1
0.4
,
I
0.8 0.6 mean grain size
I
1.0 (Brn)
Fig. 14. Vickers microhardness of Si N -Al 0 -ZrO a 4 2 3 2.and hot pressed material as a function c mean grain size.
Si3N4-A1203
225 a-si
residual data
by
N 3 4'
Parr
and
The
behaviour
Mastin
the
basal
p -Si3N4
single
crystal
14
a plot
and
[47]
a-Si
reported
is
fairly
good
Chakraborty
N planes 3 4 under
in
to
be
identical
and
about
agreement
Mukerij
28%
[3S]
harder
microhardness
with
, who
than
test
condi-
tions.
Figure bodies. size
The
shows
is
linearly
parameters in
in
determining
sed.
As
within
thermal
cycling.
ing
from
eking
ZrO the
hot
bly
associated
a sufficiently
larger
than
for
low
phase
rupture
of
are
chining ge,
etc).
phase. our
by
hot
Coe
pressed
fracture key
damage, Among
of
criteria impact other
in
grain
et
al.
has AZ
dense
bodies.AZl
to
between
a microcraloading.
observed.
can
hot be
pres-
presuma-
which
is of
exhibits hot
of
both
hardness
temamount
grain
hardness
inverse and
a
a ve-
pressing
amount
the
to
cool-
a substantial
favour with
complies [48]
of
de-
speci-
formation
low
scarce
seems
asses-
during
phase
the
them
is
materials
AZS)
et -
sub,jected
that
been
promotes
relatively
be
subsequent
which
formation
which
or
the
Coe
of
pressed
occur
and
promote
materials
hot
boundary
with
The
hardly
also
(AZ4,
associated to
a behaviour
Hardness, tures
strength
in
suggested
temperature
each
ceramic
for
by
population
fresh
effect
grain
independent
of
can
during
strength
amount
being
temperature,
generated
flexural
the
in
pressed
increasing
influence
might
toughening
texture
boundary
brittleness, ships
easily
insufficient
boundary
room
A composition,
flexural
grain
to
high
interconnected
perature, of
in
not
composite
2
that
hot
results
a microcrack
micr,ocracking
evident
with
separate
suspected
be
previous ratio
8a,b,
the
with
characteristics
pressing
improvement
at
the
N -A1203-ZrO 3 4
is
would
with
ci/(Cl+#)
Figs.
induced
no
sed
ry
Si
It
2
Nevertheless,
more
from the
pattern
The
materials
concluded
some
the
and
in
size
microhardness
agreement
microhardness
veloped
mens
good
size our
VA grain
decreasing
a fairly
[48] . Grain
al,
H v500
of
and
relationmodulus
of
Si3N4+lwt%MgO.
toughness, for
strength
materials
damage,
wear
specifications,
and
microstructural
resistance resistance, the
overall
to
damage
thermal
fea(i.e.
shock
performance
madamaof
226 Si3N4-based
cutting
i)
(with
hardness
tools
optimal
ii) the degree
GPa);
to type
mance
in grey cast
tions
appears
boundary
and the excellent
of
secondary
on
[13,14]
in the range
between
cutting
:
20-25
the work
tools,
phases.
pie-
is specifical-
The good
perfor-
of some of the A and AZ oomposi-
to the low amount compromise
stability
found
interaction
iron machining
the good
phase,
to depend
being
in Si3N4-based
and amount
related
reported
H V5GOvalue
of chemical
ce and the tool which, ly related
has been
of a reactive
between
in oxidizing
hardness
glassy
grain
and toughness,
environment
[49] .
CONCLUSIONS
Hot pressed characterized. re occur
Si N -Al 0 -ZrO 2 composites have been prepared and 34 23 Densification and development of the microstructu-
through
liquid
additive-densified reached.
phase
nitrides.
This may
sintering Complete
be as an effect
mechanisms
common
densification
to most
has not been
of evaporation/condensation
pro-
cesses. A phenomenological nuous
variation
occurs
during
No evident
interpretation
of the cell parameters
improvement
crease
temperature
in the room
interconnected
from
compared
an higher with
Because
of reactive ce
content
material
good
grain
strength
P)-SiAlON,
which
in liquid
phase
at high
of Zr-O-N
composites 0 -2rG 2 2 3 iron machining.
Si3N4-Al
and excellent
phase,
phases
proved
resul-
ZrO
.
2 and toughness, low amount
oxidation
in the hot pressed
excellent
with
body
but without
of hardness
in-
temperature,
of strength , the relatively
boundary
from
associated
in the dense
composition
combination
results
and the relevant
has been
developed
of similar
value
due to the absence
cast
for the conti-
toughness
in the matrix,
texture
of the suitable
the reasonably
of the
of the fracture
dispersed
ting
given
hot pressing.
the Zr02 particles
the more
has been
cutting
tools
resistanbodies, in grey
ACKNOWI,~DGEMKNTS We wish samples
to thank
Mr. D. Dalle
and for his helpful
Fabbriche
technical
for fabrication
activity.
of the
227 REFERENCES N.
Claussen
J. Am. Ceram.
A. Bellosi,
P. Vincenzini,
Rahini,
G.N.
R. Visani, -ZrO
and J. Jahn,
composites,
2
Faenza, G.N.
in P. Vincenzini
(rd.),
in Science
A. Bellosi
Babini,
Effect
Dufour
(eds.),
bility
of materials
P. Vincenzini, (1986)
Report
G.N.
of the secondary
hot pressed
Babini
No 831209,
F.F.
Lange,
7
J.D.
Desmaison,
J. Am. Ceram. M. Billy
Sot.,
of zirconium
nitride
Plenum
Press,
J. Weiss, (1979)
New York,
L.J.
Si3N4-MgG-Y2G3-
Science
Publishers
Ceramics
Int.,
B.V.,
12
CNR-Irtec,
Internal
68.
Smeltzer,
Vannenberg in oxygen,
1977,
Gauckler
63 (1980)
in f. Wood,
(eds.1,
Oxidation
0. 1,indq beha-
in Reactivit ,y of Solids,
p. 107.
and T.Y.
Tien,
J. Am. Ceram. ___...
Sac., --
62
632,
Bahini,
Report
A.
Bellosi
No 84/232,
10 G.N. Bahini, Report
and P. Vincenzini,
CNR-Irtec,
Internal
and P. Vincenzini,
CNR-Irtec,
Internal
1984.
A. Bellosi
No 84/243.
11 S. Dutta
and B.J.
Sanders
13 G.N. Babini,
Babini,
Special
Ceram.
Adv.
Sot.,
67 (1984)
Ceram.
Mat.,
89.
2 (l986)
R. Chiara
and M. Bruno,
Adv.
R. Chiara
and M. Bruno,
Proceedings
166.
Ceram.
146.
A. Bellosi,
8, London,
R.J. wimmer,
Sot.,
J. Am.
Miekowski,
A. Bellosi,
Ceramics
Land,
Buzek,
and D.M.
2 (1987)
Ceram.
Elsevier
W.W.
and
viour
15 P.L.
the system
sta-
1983.
and N.C.
14 G.N.
from
and L.C.
on the thermal
phase
and P. Vincenzini,
C. Helgesson
Mat.,
behaviour
in P. Barret
and G.N. Babini,
vist,
12 W.A.
and
of Si N 3 4 12, Ceramurgica s.r.l.,
and P. Vincenzini,
A. Hellosi
6
G.N.
Fabbriche
133.
ii A. Bellosi,
9
Oxidation
94,
1984, p. 471.
in Reactivity of Solids, 2' Amsterdam 1985, p. 827.
8
61 (1978)
D. Dallc
of Ceramics
-zro
4
Sot.,
61 (2978)
R.W. 56.
18-20
December
Burns,
of
1985.
and N.S.
Choudhury,
J. Am.
228 16 L.J. Bowen, ter.
R.J.
13 (1978)
Sci.,
17 L.J. Rowen, 61 (1978) la G.N.
T.G.
Carruthers
and R-J.
Brook,
J. Ma-
341.
Carruthers
T.G.
and R.J.
Brook,
J. Am. Ceram.
Sot.,
335. A. Bellosi
Babini,
11 (1984) -
and P. Vincenzini,
Mater.
Chem.
Phys.,
365.
19 G.N. Babini, (1980)
Weston,
A. Bellosi,
and P. Vincenzini,
Ceramics
Int.,
6
91.
20 M. Kuwabara,
M. Benn
and F.L.
Riley,
J. Mater.
Sci.,
15 (1980)
1047. 21 M.N.
Rahaman,
(1981)
Special
on Trent,
24 Y. Oyama
Brook,
J. Mater.
in D. Taylor
1981,
Sci.,
16
Kai Shi,
26 R.J.
Lumby,
J. Mater.
Sci.,
B, North
Ceramic
82 (1974)
Research
(eds.),
Association,
3Sl.
Yogyo-Kyo
Kai Shi, 80 (1972)
11 (1976)
1135.
and A.J.
6, British
Ceramics
and P. Popper
p. 119.
and 0. Kamigaito,
Jack,
1975,
Jack
7, The British
Yogyo-Kyo
25 K.H.
Taylor,
Ceramic
in P. Popper
Research
Ass.,
327.
(ed.) Spe_
Stoke-on-Trent,
p. 283.
27 Kossowsky, 28 F.F.
and H.K.
Ceramics
23 Y. Oyama,
cial
and R.J.
660.
22 S. Hampshire
stoke
Riley
F.L.
J. Matei,. Sci.,
Lange,
29 K. Nuttall
J. Am. Ceram. and D.P.
30 J.E. Weston, (1978)
P.L.
32 A. Bellosi,
Thompson,
Pratt
J. Mater., CNR-Irtec,
33 G.N. Babini,
A. Bellosi
(eds.),
The Institute 34 A, Bellosi, (1987)
Sot.,
1603.
56 (1973)
J. Mater.
and B.C.H.
518.
Sci..
Steele,
9 (1974)
J. Mater.
850.
Sci.,
13
2137.
31 J.E. Weston,
Taylor
8 (1973)
Special
Sci.,
15 (1980)
Internal
Report
N. ?9/117,
and C. Galassi, Ceramics
of Ceramics, G.N. Babini
1568.
in S.P. Howlett
8, British
Stoke-on-Trent,
and C. Galassi,
1979.
Ceramic 1986,
J. Mater.
and D.
Proceedings,
p. 65. Sci.,
22
1687.
35 D. Chakraborty 36 C, Greskovich
and 3. Mukerji, and H.C.
Yeh,
J.
3. Mater. Hater.
Sci.
Sci.,
15 (1980)
Lett.,
3051.
2 (1983)
657.
229
Evans
and
Niihara,
A.
37
A.G.
38
K. C
39
E.A.
Charles,
Nakahira
J.
and
Am.
Ceram.
T.
Hirai,
in
G.S.
Sot.,
Comm.
59
Am.
(1976)
Ceram.
371.
Sac.,
13-14(1984).
S.T.
Buljan
Metal
and
Ceramic
V.K.
Sarin,
Composites,
Elsevier
Upadhyaya Sci.
(ed.1,
Pub.
B.V.,
Sintered Amsterdam,
1984. 40
Seshadri,
S.G. (1983)
41
Advances The 42
G.N.
M.
Rtihle,
Ceramics
in
A.
King,
Heuer
Science
3.
Ceramic
Babini,
G.N.
L.
Ceram.
Eng.
Proc.,
4
Society,
and
L.W.
and
Technology
Columbus
OH,
Hobbs of
1981,
(eds.),
Zirconia, p.
A.
Bellosi
and
P.
Vincenzini,
Annali
A.
Bellosi
and
P.
Vincenzini,
Ceramics
A.
Bellosi
and
P.
Vincenzini,
Mater.
137.
di
Chimica
507.
(1980) 44
in
Babini,
(1980) 43
and
American
G.N.
and
853.
Claussen
N.
Srinivasan
M.
Int.,
3
91. Babini,
11 -
(1984)
45
P.
Drew
46
G.
Greskovich
and
Parr
G.F.
Chem.
Phys.,
365. and
M.H.
Mater.
LeWiS,J.
S.
Sci.,
Prochazka,
J.
9
Am.
(1974)
Ceram.
261. Sot.,
60
(1977)
471. 47
N.L.
Haywood, 48
London,
R.F.
Coe,
cial
Ceramics
on-Trent, 49
and
A.
Rellosi,
cation.
R.J.
Mastin, 1960,
Lumby 5,
1972, G.N.
p. and
British p.
in
P.
Popper
ted.),
Special
Ceramics,
102. M.F.
Pawson,
Ceramic
in
Research
P.
Popper
Association,
(ed.),
Spe-
Stoke-
361.
Babini
and
P.
Vincenzini,
submitted
for
publi-
Chemistry, and Physics,
qqA12~3-“r02
A.
HOT
(1987) 205-729
PRESSED
P. VINCENZTNT
RELLOSI,
CNR,
18
Research
TRTEC,
205
COMPOSITES
and
G.N.
BABTNT
for
Ceramics
Institute
Technology,
Faenza
(Ttaly) Received
March
23,
1987,
accepted
May
13,
1987
ABSTRACT Development
of
microstructure, Vickers
room
temperature
MOR,
been
studied
83wt%Si
for
pressed
at
terious
presence
34.4MPa
Microcracking thermal
has
to
PI-phase
with
zirconia. Si3N4-A1
The 0
to
phases
the
substantial
in
of
the
of
a-j3
the
toughness
MOR
mismatch
microcrack
~370
for
a grain
is of
No
from
from MPa
to
between
model
conversion.
the
dele-
materials.
parameters
results
increase,
properly
ZrO2-induced
cell
hot
The
these
and
have
composites
temperatures.
avoided
because
materialto-
more
specific
is
hehaviour
toughness
A phenomenological
of and
reference
and
and
variation
progress
hardness
heen2azcrihed
than
times
observed
for
the in
Zr-O-N
heen
expansion
N -5wt%A1203-12wt%Zr02 vzr4ous
coefficients.
account
improvement
has
of
expansion
gested
for
thermal microhardness
sug-
the
detectable
the
presence
MPa
for
ZrO
boundary
of
a
composite ghase
effect,
grain
boundary
strengthening.
INTRODnCTION The phase
required
material and
an
size is
have amount
additive
to
limits
strength
nitride in
metastable,
of been
sinter
its
shown
related
difficult
0254-0584/87/$3.50
because
Tn
its
impurity
a fully
at
silicon to
to
metal
Si 7 N 4 to
performance
sintered
distribution.
and
high
nitride
improve
with
content,
of
the
high
dense
and
high
temperatures. and the
particle
Zr02-strengthened
rich
hot
Toughness
pressed
addition size
strength
silicon
of and
m-ZrO
2
[II
particle
N , retention of t-ZrO 3 4 2 mismatch, and the increa-
Si
thermal
0 Elsevier Sequoia/Printed
in The Netherlands
206
sed toughness has been
is mostly
shown
strengthening
associated
in binary
to lower
the hot pressing
reduction
of the amount
so 19,101.
tion
Also
to offer
cutting
Evolution
good high-temperature phase
performances made
have
formed
[Z-B]
during
inconsequent
hot
for the
phases,
properties,
was not detected
been
oxidation
but Al 0 did 2 3 as sintering aid has been
reported
from hot pressed
of microstructure,
temperature
Vickers
of zyttrite
(up to -
[2] or MgOtY 2 0 3 t3*41
proved
of such deleterious
it
and the forma[11,12].
in cast
iron machining
Si N -Al 0 -31'0 compo34 23 2
b 3 ) 141 .
sitions
room
such as MgO
temperature
the addition
tools
boundary
are readily
However
that microcrack
temperatures
grain
which
aids
of the easy-to-oxidize
Excellent using
to moderate
phases,
Use of sintering
pressing.
microcracking.
compositions,
of the catastrophic
of ZrN and or Zr-O-N
proven
Si3N4-ZrO2
is restricted
1073 K) because
with
flexural
microhardness
linear
strength
thermal
expansion
( (I), toughness
(HV) have been
studied,
( A),
(Krc) and
in comparison
with
a Si N -Al 0 reference material, for a Si3N4-A1203-Zr02 composite 34 25 hot pressed at 34.4 MPa for different times and temperatures.
EXPERIMENTAL Two batches and 95wtX
of composition:
Si3N4-SwtX
Si3N4-Swt%
Al 0 - 12wtX Zr02 2 3 by wet mixing commercial
Al 0 were prepared 2 3 and ZrO 2 powders (Table I) and homogeneizing
Si N Al 0 34' 23 plastic jar with
Table
83wt%
I. Main
alumina
balls
characteristics
in isobutyl
alcohol
of the starting
in
a
far 72 hours.
powders.
2 -1 : grain size surface area BET=lB,O m g pm: particle shape: irregular; from -_o,o~i to-4.0 a/pratio 13.4; chemical analysis: NI 38%, CW -1%: O-1.496, Fe-0.04%, Al-0.06%, Ca-0.03%.
Si N (SZ a$ck LC 10)
: Specific
Al 0 (A? c:a A-16)
: S.s.a.
BET
ZrO,,(Harshaw)
: S.s.a.
2 -1 ;mean grain BET 28 m g
2 -1 ; grain 17.7 m g
size from--.5
to-lpm
size --.4 urn.
207 Hot
pressing
was
performed
uniaxially,
in
induction
heated
-3 graphoil-lined Bulk
dies
MOR
microhardness,
pressed
and
plungers,
in
thermal
microstructure,
density,
rature
Bulk
graphite
and
toughness
torr
10
expansion were
and
vacuum. room
determined
tempe-
on
the
hoi
materials:
density
was
measured
by
geometrical
analyses
were
performed
was
investigated
and/or
liquid
displacement
techniques. + Microstructural
by
XRD
, SEM
++
+++ , WDS
and
++++ EDS
.
Thermal
expansion
1573
at
K,
sawed
a heating
from
the
Microhardness
has
pm)
surfaces
and
on-line
pression of
10
by
of
pressed been
and
g
on
toughness
K
was
a Vickers value
Three
point
30
cut
crosshead
Table
mm
up
samples
a
loading
load.
rate
Each
H
polished
to
diamond
(down
* equipped
microdurometer
measured
diamond
represents
room from speed
6 tests.
the
4x4~40
diamond
by
of
0.3
value
with
to
a detector 10
mm/set,
represents
0.1
set
the
im-
average
V
Hot
indentation
an
pyramidal the
average
IC
of
temperature
determinations.
utilizing
mm
on
SK/min,
measured
at
500
room
billets.
a Vickers
computer,
time
Fracture
Each
hot
rate
from
temperature
MOR
was
indenter
pressed
billets,
of
0.5
mm/min.
Each
microstructure
of
the
a load
of
10
5 determinations. ** measured on specimens
hot
conditions
at
test kg.
of
the
pressing
fracture
with
value and
26
mm
represents relevant
hot
pressed
materials
, Ni
filter,
F.R.G.
span
and
the
a
average
parameters are
3x3x
collected
of in
II.
+
Siemens
++
500,
CuK
Autoscan,
Etec
Corp.
+++
Autospec,
Etec
Corp.,
U.S.A.
++++
Edax
Philips,
NL.
0
Netzsch
* XI
Zwick 3212 microdurometer, Instrom,universal testing
PV
D
9100,
Geratebau
U.S.A.
- apparatus,
F.R.G.
F.R.G. machine,mod.l195,Canton,
MS,
U.S.A.
pressing
1853
1923
1923
1923
1973
1923
1923
1923
AZ2
AZ3
AZ4
AZ5
AZ6
Al
A2
A3
(K)
1813
T
Hot
AZ1
Sample
Table II. Composition, pressed from Si3N4-Swt%
pressing
60
30
30
(min)
220
120
60
120
220
120
t
conditions
A1203-12wt%
hot
0.87
0.60
0.31
0.94
0.92
0.74
0.72
0.32
0.13
conditions ZrO 2 and
and
some
a-Si
2 3
0
13.5
40.0
68.0
6.5
8.0
26.0
28.0
68.0
87.0
%
Al
N 34
systems.
microstructural
Residual
Si3N4-6wt%
Relative
99
98
95
98
97
97
97
95
93
%
of pressure
density
parameters (Applied
0.90
0.85
0.72
0.93
0.86
0.56
1.0
hot
(pm)
grain
MPa).
0.48
size
Mean
34.4
materials
209
RESULTS Microstructure Phase
composition a-si
Unconverted amounts
of
tative
N 3 4'
X-SiAlON
estimation
of
Table
III.
Approximate
tive
crystal
phase
Si3N4-Al
0
b5]
were
the
relative
XRD
Si2N20,
detected
by
amounts
m-Zr02 XRD. (Table
semiquantitative
content
in
the
hot
a-Si
N 3 4
P-SiAlON
III)
evaluation
pressed
Si2N20
and
A gross
Si
materials.
2 3
Sample
$'-SiAlON,
ZrO2Cm)
minor semiquantiwas
derived
of
the
N -A1203-ZrO 3 4
relaand
2
X-SiAlON
zr02w
AZ1
56
9
22
7
3
AZ2
41
20
22
7
3
AZ3
20
48
13
a
3
AZ4
17
51
13
a
3
AZ5
6
63
15
5
3
AZ6
5
69
16
3
2
63
28
Al A2
34
54
9
A3
from of
the each
racteristic
with
the
(height)
to
the
sum
reflections
Important
features
progress
(m+t)-ZrO
__
traces
40
_-
2
7
_-
2
82
intensity phase
9
of
content
in
ratio
of of
are:
the all i)
thea--_ the
of
a characteristic
intensities crystal
(heights)
of
the
cha-
phases.
a variations
of
conversion
and,
ii)
pressed
at
materials
reflection
hot
p'-SiAlON
spacings
a decreased higher
tempera-
2 tures
(1923-1973
K),
in
grain
zirconia
the
a-SiJN4--+P'-SiAlON The
which
boundary
(heights)
liquid
a partial
solubilization
of
phase.
transformation
a-Si3N4-p'-SiAlON
intensities
indicates
transformation of
characteristic
was XRD
assessed reflections:
from
the
210
I a
(210)
I
+
(102)
(1)
p'=
/
I
(210)
Residual samples
+ 1
a-Si
hot
(102)
N vs 3 4 --
pressed
hot
at
different
a
1
-
I
Residual
Although fine as N
the
MgO[20
, 211 stand
da =
where
k
of
I
I
250
200
150 (min.) pressing
time
for
the
S i3N4-Al
the On
is
the
a-phase this
co1 lected
data
Y203-
1 81
p7
for
a
appear
previous
order
1st
studies
, Ce02
order
cient
insuffi
[19]
similar
on
and
HPSN
kinetics,
to
precisely systems
sintered
desuch
Si-Al-O-
i.e.:
(2)
transformation in
the
rate
constant
and
a the
concentration
sample.
assumption,
transformation,
0 2 3
studied.
- ka
dt
for
2
reaction [16],
time
vs hot N zoipositions
a-Si
the
1,
temperatures.
100
Si3N4-A1203-ZrO
Fig.
ZrOz
hot pressing 1.
in
F
50
0
and
plotted
5wt%A1203
l! Fig.
is
b c
5wt%AI,03+12wt%
____
time
K
-1813
z
pressing
Ea= -450
apparent kJ/mol,
activation derived
energy from
the
for
the
Arrhenius
a-+ plot
p’ of
211
\ \\S1~N4+5wt%MgO \ kTmol-'
\<520 \
\
\
\
\
\
1F4/T Fig.
2.
sion
reaction.
Arrhenius
plot Data
of
for
(K-‘)
the
MgO-
rate and
constant
CeO 2
comparison.
Fig.
2,
compares
C-470
kJ/mol)
Si 3 N 4
(-480
with [19]
parameters
Previous
studies
sions
of
the of
Al
constant
0 is 2 3
P'-SiAlON near SiA'ON
Si
XRD
decrease phase
c-500
[17]
similar
and
at
of
N in
sites
by
(Fig.
the
hot
pressed
and
conver-
reported
CeO
b6,17,22]
stress
show
cell
3). Thus,
Al
and
which
and
for
-Si N 3 4 2 Y203-
temperature.
increase the
Al
amount
0 resp. a shift
results
parameters the
an to
materials,
reflections, of
also
kJ/mol'
proportional
our
for
a-p’
the
are
B'-SiAlON
[15,23-261
PLSiAlON
cupation
obtained
MgO-Si3N4
kJ/mol)
Lattice
results
for
-HPSN
with and
of
an
solid
cell
dimen-
fractional the
recorded
oc-
overall in
the
approximately
increasing
0 in
the
Although was
in
of
amount solution
liof
the
within
212
UNIT
CELL I 1
AA
DIMENSIONS
5Wt%
Al203
o l 5Wt%
Al203
‘-4s
--__
J
c (A, +12wt% ZrOz
2.96 2.94
I
---a
--so_ -_0
aA 7.66
,
-&OS_
2.92
0
2.90
)
7.64 7.62 7.60 (
I
3.
Fig.
Variation
function and
zro
p'content
Si
N
perztures
the
- Al
conversion,
the
cell
dimensions
( PI/( Cl++‘))
compositions 0 2 3
appear
[ZO] . On
lattice
lid
solution from
to
with
i.e.
the
range
.a
1I I
of
the
for
samples
of
hot
pressed
for
P'-SiAlON
as
Si
0 -
N -Al
dlf 3t
a
erezt3tem-
azd4times.
P'-SiAlON
ported
in
of
-I
I
0.6
0.4
the
the
- 0.3
to
with
increasing
basis
parameters in
decrease
of
of hot
the
progress
pressing
the
known
p'-SiAlON
pressed
time,
as
and
Al
has
mol%,
according
to
fracture
surfaces
re-
53between
been the
a-p'
III
the
0 2 3'
the
previously
relationships
materials
-0.1
of
alumina
in
evaluated
hot
soto
pressing
schedule.
Morphology -Polished, tion
and
etched
morphology
morphology
of
Fig.
clustering
of
ZrO
step, the
which dense
and of 4 on
2
occurred,
resulted
in
The
SEM
body.
shown 2' the sample
ZrO
grain
by
sizes
micrograph
the
AZ2,
possibly
were
polished
indicates
during from of
examined.
a polished
surface that
the
-0.2
DistribuSEM
noticeable
homogenization
urn to
-10
surface
pm of
in A3
213
Fig.
4.
showing
SEM
micrograph
clustering
SEM
Fig.
5.
Dark
areas
of
of
micrograph are
a polished
starting
associated
of
ZrO
surface
the
AZ2
sample
of
the
A3
sample.
2
a polished with
of
particles.
Si_N_O.
surface
214 (Fig.
Fi), shows
an homogeneous to silicon re path
very minor distribution
oxynitride.
is evident
from
amounts
of isolated
of darker
A mixed
areas
residual
which
might
pores
correspond
intergranularltransgranular
SEM micrographs
of fracture
and
fractu-
surfaces
for
both
Si N -A1203-ZrO 2 (Figs. 6a, c) and Si3N4-Al 2 0 3 (Figs. 7a, b). 3 4 Similar to other HPSN [19, 27-321 a preferred orientation was
detected, peaks,
On the basis
the growing
of the intensities
$-SiAlON
grains
show
of X-ray a trend
diffraction
to align
their
a)
of fracture surfaces Fig. 6. SEM micrographs pressed at: a) AZ3, 1923 K, 60 min.: b) AZ5, AZ6, 1973 K, 120 min.
of AZ materials, hot 1923 K, 220 min.: c)
b)
a) Fig.
7. SEM micrograph
basal
of fracture
and b) A3 sample
60 min),
plane
aligning
(002) parallel
effect
surface
of Al sample
a)
(1923 K,
(1923 K, 220 min).
with
increases
the hot pressing
at increased
direction.
hot pressing
This
time.
Properties Thermal Repeated ple.
expansion thermal
Dilatometric
expansion
curves
Al 0 -ZrO materials 2 3 2 Fig. 9 shows thermal
runs were
of the first
(AZ3 and AZ5!
three
runs
are reported
on each AZ samfor some SiSN4in Figs.
8a, h.
for Si N -Al 0 samples (Al 34 23 which begins and A3). The martensitic t-+m transformation of ZrO 2 at temperatures as high as 1328 K is incomplete, the finer ZrO 2 symmetry down to room tempeparticles remaining in the tetragonal rature. relevant
Microcracking thermal
and ZrO 2 grains, the thermal The
curves
in the bulk
expansion originates
expansion
linear
expansion
performed
mismatch
of the AZ samples, between
the irreversible
the nitride
matrix
elongation
shown
by
curves.
thermal
expansion
coefficients
samples
for different
materials
and temperature
heating,
i.e. before ----
sformation,
due to the
and after
are collected
the beginning
in Table
IV.
f h 1 of AZ and A intervals
of the m--+t
on tran-
216
DILATOMETRIC
m
TESTS
It I I
1
I
,’
/ /
1
,
I
. //’
1 /
I/(
,/
/I
/’
,
/ /(/
’
, .
0 ~~
/
,
H
l’
/ I’
’ 6’
I’
a
,,e
/’
_--A/
/’
w ‘)r
500
1000 T
_--
500
1500
(Kb
1000
T(K)
1500
*
Fig. 8. Thermal expansion curves for AZ materials hysteresis loop and irreversible elongation. zro III'indicate order of the repeated tests. a) AZ3, b) AZ5, 1973 K, 220 min.
showing m-tSuffix I, II and 1973K, 60 min.;
217
500
1500
Id00
T(K) Fig.
9.
Al:
1923
Table
Thermal K,
IV.
expansion
60
Average
Sample
curves 1923
linear
K,
for 220
thermal
Si3N4-A1
0
2 3
A materials
hot
pressed
at:
min.
expansion
coefficients
materials,
within
( A)
selected
for tem-
ranges.
Thermal exp.
test
IO AZ1
A3:
2 and
Si3N4-A1203-ZrO perature
min;
A(293-91;
K)
h(293-111;
x10
X10
K)
3.09
3.14
4.!io
110
3.19
3.17
4.65
1110
3.16
3.27
4.75
3.35
3.38
4.40
AZ3
IO IO
3.43
3.48
4.!io
AZ5
110
3.29
3.32
1110
3.23
3.32
4.75 5.25
10
3.69
3.86
5.15
110
3.82 3.52
3.96 3.71
4.50 5.55
AZ6
1110
A(zgz-993
K)
A(293-1173
K)
A(293-1473
Al
IO
3.00
3.18
3.39
A3
10
2.89
3.06
3.30
K)
218 Microhardness values for both A and AZ samples (Table V) locat e at the V upper limit among other hot pressed Si N -based materials [33,34] 3 4 and exceed those for both single crystal (H = 19.6 GPa) and poV5OO lycrystalline Si3N4 p5,361 . No appreciable effect on microhardThe H
ness
results
Table xural
from
the presence
of ZrO
2'
V. Fracture toughness (K ), microhardness strength (CJ) of Si3N4- A?;03 and Si3N4-Al
Sample
H
K Ic (MPa1'2)
(H 0
2 3
) and fleXl?&rials.
U(MPa)
(CPa) V500
(' 30%) AZ1 AZ2 AZ3 AZ4 AZ5 AZ6
4.0 5.7 6.3 5.6 5.7 5.8
23.5 29.8 24.5 20.9 20.5 19.1
f f 4 f f 4
1.4 1.6 2.5 1.5 1.4 1.7
360 f: 33 n.d. n.d. 599 A 30 630 * 25 n.d.
Al A2 A3
6.0 6.0 4.9
29.5 f 23.6 * 21.2 f
3.5 2.5 2.2
314 * 20 n.d. 36% * 54
Fracture
toughness
and strength
Fracture
toughness
(KIcf has been
level
accuracy,
malized
from
the Evans
for hot pressed
K&H
alI2
where
H is the hardness
median
= 0.203
crack
length.
for SiAlON-based [1,39,40 ]-
(c/a
ZrO2
Si3N4
and Charles
(Table
V), at a 30%
L371 relationship
nor-
[38] :
-3/2 (3) a the impression
Measured
materials seems
obtained
radius
and C the radial/
K
values agree with Ic and silicon nitride-based
practically
not to affect
those
reported
composites
fracture
toughness
of our materials. MOR has been in Table -dense similar
determined
V, which
ZrO
2
show
containing
to those
on selected
a relevant material
previously
samples;
aincrease (AZ4 and AZ9)
reported
data
are reported
in the nearly-fullywhose
for SOwt%SiAlON
strengths
are
- SOwt%ZrO
2
Cutting
tool
Cutting
performance -
tools
were
tested
in
were
obtained
prepared
from
grey
cast
iron
(Az2,
AZ4,
A3)
Al,
A3,
Azl,
machining as
AZ2
and
AZ4
samples results
[z3 ( 141 . Excellent
reported
in
l1
Fig.
10,
which
show?
+IORKlNG CONDITIONS
,:utting speed
45Om mm-'
depth of cut
1.5m-n
feed rate
0.35mm rev-l
1.0 BREAKAGE
FREIXIENCE
high(100%) :A1
very
hlgh(507.1: S,AZl,AZ2. tow (50%) : YS very LOW (5%)
K,G,AZ4,A3
J
0.0 0
Fig.
10.
rials
in
ratory
pieces
Flank the
wear
vs --
number
machining
(S;
flank
number
of
wear
K;
Q)
vs. ---
laboratory
the
and
; YS:
number
some
pieces
iron,
Si
worked
for
compared
N -7wt%Y
cu?t!ng
of
pressed
worked
cast
Si3N4zbased
hot
Y,03-14wt%Si02)
of
grey
Si3N4-lOwt%CeO
(Ce:
commercial
other
200
100 Worked
the
: a,
AZ
and
to
other
A mate-
03-14wt%SiOz)
laboand
tools.
pieces
in
comparison
(Ce:
Si3N4-lOwt%CeO
; YS:
commercial
Si3N4-based
2 cutting
with
Si3N4-7wt% tools
(s,K,Q).
DISCUSSION Development
of
microstructure
Densification,
hot
pressed
phenomena tions the
or liquid
diffusing
and where
by
the phase,
species
a-P’
transformation
sintered
silicon
nitride
processes
are
transport
capability
according and
some
to
and
either
the
processing
are
grain
liquid-phase
governed of
the
inherent
growth
by
interface
for
aided reac-
diffusing
species
chemical
reactions,
parameters
such
as
both
in
atmosphe-
220
re,
applied
above
processes
silicon also
stress
has been
nitride
should
of liquid
and temperature. reported
materials.
follow
Detailed
[16,17, 26,42-443
The densification
the same pattern,
is formed
information
at high
for several
mechanisms
provided
temperature
on the
of SiAlON
a sufficient
where
dissolution
amount of
Q-
Si N and its reprecipitation as PI-phase [20] is realized, this 3 4 process offering the main contribution to densification and to the overall
development
Densification
of microstructure.
in our materials
tes at T > 1723 K at a value retical
density
and with
the material
during
grain
version,
growth)
material
transport
which
of available
densificatjon,
thus
most
complete than
fraction
in a few minu-
the expected
in the microstructure ( a-+$
of hot pressing
without
such lead
further
as surface
to structural
vacuum
may play
spaces
a role
rel.iable for covalent
bonded
diffusion
condensiother
and evapo-
modifications
without
with
an increase
in the evolution
compounds
of
remarkable
, evaporation/condensation
[20,21,45,46]
theo-
a-Si3N4conver-
of
to solution/diffusion/reprecipitation
redistribution
structure
stage
take place
processes
ration/condensation,
a small
lower
modifications
the final
In addition
fication.
a little
only
p' . So the gross
ted to
is nearly
in
of the microappearing
the
[Zl] .
The reaction:
Si3N4
(s)--+
which
takes
K, would sfer
JSi(g) place
provide
through
+ 2N2
with
(g)
a vapour
a mechanism
the gas
phase
the developing
p' . This
contact
and reduces
points
diffusion. vely
the interfering cation
of liquid
favours
filling
the stress
atm at 1963 by ion tran-
a-Si 3N 4 grains
gradients
further
-3
of the regions
in compositions
phase,
10
conversion
the residual
evaporation/condensation,
is reached.
of about
for the a--+p from
As a consequence,
low amount
pressure
sintering before
at crystal
for grain
containing
to
boundary
a relati-
is stopped complete
by
densifi-
221 when
Nevertheless, tical
as
P'-SiAlON,
cient
amount
lower
densification
lions
and
Higher
of
liquid
at
ascribed
ii)
and,
the
and
of
The
rates
to:
the
the
the
the
amount
of
aconverted
for
30
metal
beneath
hours,
the
impurities
scale.
In
perties minium sing
in
the the
Figure
higher
A1203/Si
in
the
liquid
phase,
which
surface
of
that
being
phase
in
the
N ratio 3 4 especially
increases
boundary
the
amount
characteri-
observed
SiAlON
depleted
in
zone
influence
region
lower may
is
by
XRD
the
hulk
nearer the
amount
of
play
at
to
of
diffc-
oxidized
on
also
a criti-
variation
samples
higher
the
phase
Remarkable
been
being
obvious
conversion
1 shows
grain
has
near-surface
the
phase.
the
phase,
liquid
for
this
refractory/viscosity
top'
the
boundary
a-_,p
the
to
0 , 2 3
Si3N4-Al
1)
the
boundary
aluminium
renc-
2
and
p content
and
addition
of
the
(Fig.
of
temperature,
a+p
which
chemical
of
lransformation.
of
K
ZrO
insuffi-
to
amount
of
aspect
depths
to
throrc_
[zo].
observed
composition
cal
rent
of
grain
temperature,
place
been
because
composition
liquid
actual
have
the an
although
take
a larger
processing
at
associated,
compared
i)
approaches
compositions,
formed
rearrangement
dissolution
higher
pressed
is
are
materials
some
modifies
stics
rates
composition
hot
phase
materials,
containing
2
SiAlON
our
reaction
Zr02-containing
ZrO
for
structural
a-p
possibly
the
at
1773
than
in
the
oxide
transport
ihc
pro-
disposable
a role
in
alu-
depres-
rate.
ZrO
increases
the
phase-conversion
rate
2 whereas
the
largely in
the
at
the
unaffected
stages
is
solubilized
findings
change
in
of
phase
del
from
early
These
the
lla),
grains
and
3).
the
of
in
in
growth
a-3 the
on
fresh
by cell
p’ grain
of
P'takes
p' nuclei
evaluating
boundary
At
the
places from
the
the
Al
it
most
the
with
of
the
continuous
the
progress
phenomenological
beginning on
content 0 2 3 appears that
the
of
p'-phase to
is
phase.
explanation the
PI-phase
the
parameters,
according h.
of
transformation
a reliable
lla,
of
parameters
Also,
parameters
Figs.
cell
actual
the
offer
cell
the
transformation
proposed
(Fig.
of
(Fig.
$-phase
alumina
the
variation
of
preexisting
AI-O-N-S1
the
mo-
process p-Si
liquid.
N 3 4 In this
lJlnuclei dA++
a Si4+ N3-
Fig.
11.
Phenomenological
reaction a)
in
hot
initial,
b)
model
pressed final
Si
for
a solid
solution
quasi-equilibrium
high
in
conditions
liquid.
outer
the
to
pained
by
Some
inner
and
Al
region
of
a counterdiffusion
equilibrium.
With
and
nitrogen
continuously
and
the
of
liquid
grain
The
alumina.
tion
of
this
constituent.
now
the
p'-nuclei, species phase
and
termining
the
the
is
0 materials; 2 3
formed
growing
diffusion
is
progress
of
the
supplied phase
by
to
a-Si
the
composition
preexisting
p grains
Balance
of
with
state
activities
aluminium
and
of
vacant
diffusion
composition
of
sites. are
the
which
the
of
thermochemi-
Transport
therefore
silicon
is
both
composi-
poorer
atomic the
in
source,
a depletion
the
nitrogen
the accom-
3 N 4 grain
from
oxygen
a counterdiffusion the
N grain 3 4
suffers
P'on
sur-
from
a-+p'reaction,
growing
of
the
assure
for
the
meet
required p-Si
preexisting 4+ 3and N Si
to
p'and
established
accommodate
the
2-
o 2-
each
boundary
exolution
solid
and
are
together to
conversion
Si3N4-Al
conditions
fresh
requires
0
of
cal
are
Al
between
3+ rounding
a-+p~SiAlON 2 and
stage. 3+
stage
the
N -Al203-ZrO 3 4
in
species core and
the
of
the
silicon
liquid
important
in
de-
$-phase.
Properties The
thermal
expectedly
lower
expansion than
coefficients for
Si3N4-A1203-Zr02
for
Si
N -Al
0
c~m~osi~e~.
materials The
higher
are
223
A value
for
cts
higher
the
Al
bl
at
3 4
AZ6
of
reported
N
x
content
coefficient
Si
(3.00
for
4
is
-6
in
P'-SiAlON
K-J)
ttIan
p' of being
p'-SiAlON
comparable
series
10
in
latter,
lower
than
(z=3)
an
12.
(2.89 the
that
hvalue
A plot
Fig.
A3
the
temperature.
reported
for
of
This
x
of the
-6K-1
thermal for
shows
10
A
expansion
a-Si3N4.
2.?
x
10-6K-1
within
an
refle-
1
AZl-
the
increase
for
of
the
Si3Nq-A12%-Zr02
Fig.
12.
Average
function
of
thermal
expansion
of
what
would
on
thermal
crystal the
thermal
with
be
P'-SiAlON
and
of
the
it
should
be
taken
unt
and
crease
glass
is
evolution
A
(293-1173
expected
to
a -Si
different
the
the
for
of
hardly
continuous that
the
the
additive
constituting
boundary can
KJ,
as
phase
to
the
ZrO
change
in
of
no in
most
Forp',
both
both
of
its hot
the
Si-Al-0-N-(Zr,
complexity
pressing
and
its
conditions.
2
of
thermal
performed.
a redistribution
@-phase
based
contribution
a-P'conversion, the
rule
a,p'and
the
be
inverse
amothe
large
de-
converted
N 3 4'
expansion
for
a simole
grain
during
be
i.e. ---
calculation
considering
thermal
the
of
material
place
unpredictable under
glassy
account
but
should
hand,
the
into
compared
other
applying
A precise
composite
0 takes 2 3 A
materials, In
of
composition,
in
by
coefficients
alone.
expansion
Al
coefficient
-Lncreasing$/atp'content,
predicted
expansion
species
overall
expansion
flj(atP')
impurity) continuous
224 Processing rosity,
grain
hardness.
and microstructural
techniques
composition
size and phase
the most
Fnr our materials,
ratio are the j3/l/atp'
and grain
such
are all affecting
relevant
Figure
size.
parameters
variance
13 is a plot
as po-
micro-
parameters of HV
“S
500 --
I
,
,
0
1
,
1
.
I
25 residual
.
I
I
.
*
I
I
I
75 50 cc-phase (“/d)
8
and Si 3N 4-Al 0 Fig. 13. Vickers microhardness of Si N -Al 0 -ZrO 2 3 2 a-gi3N hot pressed materials as a function zf4 3 4'
30-
2
a
2
25-
0 0
>” I
20-
1
1
0.4
,
I
0.8 0.6 mean grain size
I
1.0 (Brn)
Fig. 14. Vickers microhardness of Si N -Al 0 -ZrO a 4 2 3 2.and hot pressed material as a function c mean grain size.
Si3N4-A1203
225 a-si
residual data
by
N 3 4'
Parr
and
The
behaviour
Mastin
the
basal
p -Si3N4
single
crystal
14
a plot
and
[47]
a-Si
reported
is
fairly
good
Chakraborty
N planes 3 4 under
in
to
be
identical
and
about
agreement
Mukerij
28%
[3S]
harder
microhardness
with
, who
than
test
condi-
tions.
Figure bodies. size
The
shows
is
linearly
parameters in
in
determining
sed.
As
within
thermal
cycling.
ing
from
eking
ZrO the
hot
bly
associated
a sufficiently
larger
than
for
low
phase
rupture
of
are
chining ge,
etc).
phase. our
by
hot
Coe
pressed
fracture key
damage, Among
of
criteria impact other
in
grain
et
al.
has AZ
dense
bodies.AZl
to
between
a microcraloading.
observed.
can
hot be
pres-
presuma-
which
is of
exhibits hot
of
both
hardness
temamount
grain
hardness
inverse and
a
a ve-
pressing
amount
the
to
cool-
a substantial
favour with
complies [48]
of
de-
speci-
formation
low
scarce
seems
asses-
during
phase
the
them
is
materials
AZS)
et -
sub,jected
that
been
promotes
relatively
be
subsequent
which
formation
which
or
the
Coe
of
pressed
occur
and
promote
materials
hot
boundary
with
The
hardly
also
(AZ4,
associated to
a behaviour
Hardness, tures
strength
in
suggested
temperature
each
ceramic
for
by
population
fresh
effect
grain
independent
of
can
during
strength
amount
being
temperature,
generated
flexural
the
in
pressed
increasing
influence
might
toughening
texture
boundary
brittleness, ships
easily
insufficient
boundary
room
A composition,
flexural
grain
to
high
interconnected
perature, of
in
not
composite
2
that
hot
results
a microcrack
micr,ocracking
evident
with
separate
suspected
be
previous ratio
8a,b,
the
with
characteristics
pressing
improvement
at
the
N -A1203-ZrO 3 4
is
would
with
ci/(Cl+#)
Figs.
induced
no
sed
ry
Si
It
2
Nevertheless,
more
from the
pattern
The
materials
concluded
some
the
and
in
size
microhardness
agreement
microhardness
veloped
mens
good
size our
VA grain
decreasing
a fairly
[48] . Grain
al,
H v500
of
and
relationmodulus
of
Si3N4+lwt%MgO.
toughness, for
strength
materials
damage,
wear
specifications,
and
microstructural
resistance resistance, the
overall
to
damage
thermal
fea(i.e.
shock
performance
madamaof
226 Si3N4-based
cutting
i)
(with
hardness
tools
optimal
ii) the degree
GPa);
to type
mance
in grey cast
tions
appears
boundary
and the excellent
of
secondary
on
[13,14]
in the range
between
cutting
:
20-25
the work
tools,
phases.
pie-
is specifical-
The good
perfor-
of some of the A and AZ oomposi-
to the low amount compromise
stability
found
interaction
iron machining
the good
phase,
to depend
being
in Si3N4-based
and amount
related
reported
H V5GOvalue
of chemical
ce and the tool which, ly related
has been
of a reactive
between
in oxidizing
hardness
glassy
grain
and toughness,
environment
[49] .
CONCLUSIONS
Hot pressed characterized. re occur
Si N -Al 0 -ZrO 2 composites have been prepared and 34 23 Densification and development of the microstructu-
through
liquid
additive-densified reached.
phase
nitrides.
This may
sintering Complete
be as an effect
mechanisms
common
densification
to most
has not been
of evaporation/condensation
pro-
cesses. A phenomenological nuous
variation
occurs
during
No evident
interpretation
of the cell parameters
improvement
crease
temperature
in the room
interconnected
from
compared
an higher with
Because
of reactive ce
content
material
good
grain
strength
P)-SiAlON,
which
in liquid
phase
at high
of Zr-O-N
composites 0 -2rG 2 2 3 iron machining.
Si3N4-Al
and excellent
phase,
phases
proved
resul-
ZrO
.
2 and toughness, low amount
oxidation
in the hot pressed
excellent
with
body
but without
of hardness
in-
temperature,
of strength , the relatively
boundary
from
associated
in the dense
composition
combination
results
and the relevant
has been
developed
of similar
value
due to the absence
cast
for the conti-
toughness
in the matrix,
texture
of the suitable
the reasonably
of the
of the fracture
dispersed
ting
given
hot pressing.
the Zr02 particles
the more
has been
cutting
tools
resistanbodies, in grey
ACKNOWI,~DGEMKNTS We wish samples
to thank
Mr. D. Dalle
and for his helpful
Fabbriche
technical
for fabrication
activity.
of the
227 REFERENCES N.
Claussen
J. Am. Ceram.
A. Bellosi,
P. Vincenzini,
Rahini,
G.N.
R. Visani, -ZrO
and J. Jahn,
composites,
2
Faenza, G.N.
in P. Vincenzini
(rd.),
in Science
A. Bellosi
Babini,
Effect
Dufour
(eds.),
bility
of materials
P. Vincenzini, (1986)
Report
G.N.
of the secondary
hot pressed
Babini
No 831209,
F.F.
Lange,
7
J.D.
Desmaison,
J. Am. Ceram. M. Billy
Sot.,
of zirconium
nitride
Plenum
Press,
J. Weiss, (1979)
New York,
L.J.
Si3N4-MgG-Y2G3-
Science
Publishers
Ceramics
Int.,
B.V.,
12
CNR-Irtec,
Internal
68.
Smeltzer,
Vannenberg in oxygen,
1977,
Gauckler
63 (1980)
in f. Wood,
(eds.1,
Oxidation
0. 1,indq beha-
in Reactivit ,y of Solids,
p. 107.
and T.Y.
Tien,
J. Am. Ceram. ___...
Sac., --
62
632,
Bahini,
Report
A.
Bellosi
No 84/232,
10 G.N. Bahini, Report
and P. Vincenzini,
CNR-Irtec,
Internal
and P. Vincenzini,
CNR-Irtec,
Internal
1984.
A. Bellosi
No 84/243.
11 S. Dutta
and B.J.
Sanders
13 G.N. Babini,
Babini,
Special
Ceram.
Adv.
Sot.,
67 (1984)
Ceram.
Mat.,
89.
2 (l986)
R. Chiara
and M. Bruno,
Adv.
R. Chiara
and M. Bruno,
Proceedings
166.
Ceram.
146.
A. Bellosi,
8, London,
R.J. wimmer,
Sot.,
J. Am.
Miekowski,
A. Bellosi,
Ceramics
Land,
Buzek,
and D.M.
2 (1987)
Ceram.
Elsevier
W.W.
and
viour
15 P.L.
the system
sta-
1983.
and N.C.
14 G.N.
from
and L.C.
on the thermal
phase
and P. Vincenzini,
C. Helgesson
Mat.,
behaviour
in P. Barret
and G.N. Babini,
vist,
12 W.A.
and
of Si N 3 4 12, Ceramurgica s.r.l.,
and P. Vincenzini,
A. Hellosi
6
G.N.
Fabbriche
133.
ii A. Bellosi,
9
Oxidation
94,
1984, p. 471.
in Reactivity of Solids, 2' Amsterdam 1985, p. 827.
8
61 (1978)
D. Dallc
of Ceramics
-zro
4
Sot.,
61 (2978)
R.W. 56.
18-20
December
Burns,
of
1985.
and N.S.
Choudhury,
J. Am.
228 16 L.J. Bowen, ter.
R.J.
13 (1978)
Sci.,
17 L.J. Rowen, 61 (1978) la G.N.
T.G.
Carruthers
and R-J.
Brook,
J. Ma-
341.
Carruthers
T.G.
and R.J.
Brook,
J. Am. Ceram.
Sot.,
335. A. Bellosi
Babini,
11 (1984) -
and P. Vincenzini,
Mater.
Chem.
Phys.,
365.
19 G.N. Babini, (1980)
Weston,
A. Bellosi,
and P. Vincenzini,
Ceramics
Int.,
6
91.
20 M. Kuwabara,
M. Benn
and F.L.
Riley,
J. Mater.
Sci.,
15 (1980)
1047. 21 M.N.
Rahaman,
(1981)
Special
on Trent,
24 Y. Oyama
Brook,
J. Mater.
in D. Taylor
1981,
Sci.,
16
Kai Shi,
26 R.J.
Lumby,
J. Mater.
Sci.,
B, North
Ceramic
82 (1974)
Research
(eds.),
Association,
3Sl.
Yogyo-Kyo
Kai Shi, 80 (1972)
11 (1976)
1135.
and A.J.
6, British
Ceramics
and P. Popper
p. 119.
and 0. Kamigaito,
Jack,
1975,
Jack
7, The British
Yogyo-Kyo
25 K.H.
Taylor,
Ceramic
in P. Popper
Research
Ass.,
327.
(ed.) Spe_
Stoke-on-Trent,
p. 283.
27 Kossowsky, 28 F.F.
and H.K.
Ceramics
23 Y. Oyama,
cial
and R.J.
660.
22 S. Hampshire
stoke
Riley
F.L.
J. Matei,. Sci.,
Lange,
29 K. Nuttall
J. Am. Ceram. and D.P.
30 J.E. Weston, (1978)
P.L.
32 A. Bellosi,
Thompson,
Pratt
J. Mater., CNR-Irtec,
33 G.N. Babini,
A. Bellosi
(eds.),
The Institute 34 A, Bellosi, (1987)
Sot.,
1603.
56 (1973)
J. Mater.
and B.C.H.
518.
Sci..
Steele,
9 (1974)
J. Mater.
850.
Sci.,
13
2137.
31 J.E. Weston,
Taylor
8 (1973)
Special
Sci.,
15 (1980)
Internal
Report
N. ?9/117,
and C. Galassi, Ceramics
of Ceramics, G.N. Babini
1568.
in S.P. Howlett
8, British
Stoke-on-Trent,
and C. Galassi,
1979.
Ceramic 1986,
J. Mater.
and D.
Proceedings,
p. 65. Sci.,
22
1687.
35 D. Chakraborty 36 C, Greskovich
and 3. Mukerji, and H.C.
Yeh,
J.
3. Mater. Hater.
Sci.
Sci.,
15 (1980)
Lett.,
3051.
2 (1983)
657.
229
Evans
and
Niihara,
A.
37
A.G.
38
K. C
39
E.A.
Charles,
Nakahira
J.
and
Am.
Ceram.
T.
Hirai,
in
G.S.
Sot.,
Comm.
59
Am.
(1976)
Ceram.
371.
Sac.,
13-14(1984).
S.T.
Buljan
Metal
and
Ceramic
V.K.
Sarin,
Composites,
Elsevier
Upadhyaya Sci.
(ed.1,
Pub.
B.V.,
Sintered Amsterdam,
1984. 40
Seshadri,
S.G. (1983)
41
Advances The 42
G.N.
M.
Rtihle,
Ceramics
in
A.
King,
Heuer
Science
3.
Ceramic
Babini,
G.N.
L.
Ceram.
Eng.
Proc.,
4
Society,
and
L.W.
and
Technology
Columbus
OH,
Hobbs of
1981,
(eds.),
Zirconia, p.
A.
Bellosi
and
P.
Vincenzini,
Annali
A.
Bellosi
and
P.
Vincenzini,
Ceramics
A.
Bellosi
and
P.
Vincenzini,
Mater.
137.
di
Chimica
507.
(1980) 44
in
Babini,
(1980) 43
and
American
G.N.
and
853.
Claussen
N.
Srinivasan
M.
Int.,
3
91. Babini,
11 -
(1984)
45
P.
Drew
46
G.
Greskovich
and
Parr
G.F.
Chem.
Phys.,
365. and
M.H.
Mater.
LeWiS,J.
S.
Sci.,
Prochazka,
J.
9
Am.
(1974)
Ceram.
261. Sot.,
60
(1977)
471. 47
N.L.
Haywood, 48
London,
R.F.
Coe,
cial
Ceramics
on-Trent, 49
and
A.
Rellosi,
cation.
R.J.
Mastin, 1960,
Lumby 5,
1972, G.N.
p. and
British p.
in
P.
Popper
ted.),
Special
Ceramics,
102. M.F.
Pawson,
Ceramic
in
Research
P.
Popper
Association,
(ed.),
Spe-
Stoke-
361.
Babini
and
P.
Vincenzini,
submitted
for
publi-