New Journal of Glass and Ceramics, 2011, 1, 1-6
doi:10.4236/njgc.2011.11001 Published Online April 2011 (http://www.SciRP.org/journal/njgc)
1
The Effect of Using Nano ZrO2 on the Properties
of W-ZrC Composite Fabricated through Reaction
Sintering
Mostafa Roosta1, Hamidreza Baharvandi1, Hossein Abdizade2
1Malek Ashtar University of Technology, Tehran, Iran;
2School of Metallurgy and Materials Engineering, University of Tehran, Tehran, Iran.
Received January 10th, revised March 21st, 2011; accepted April 9th, 2011.
ABSTRACT
To fabricate W-ZrC composite through reaction sintering at first WC and ZrO2 powders with molar ratio of 3-1 are ball
milled, then the green body made from this mixture is sintered. Since reactivity is the main problem in sintering of mi-
cronized powders the starting ZrO2 powder is selected in nano size to see whether the reaction improves. The XRD pat-
tern indicates that W-ZrC composite has been formed, although some unreacted compounds still exist and some un-
wanted components have been created. In the case of using nano powders the amount of unreacted WC and ZrO2
phases and unwanted W2C phase reduces and the reaction progresses better. Additionally by using nano powders the
reaction progressed and the mechanical proprieties including density, hardness, Elastic modulus and Flexural strength
improved.
Keywords: W/ZrC Composite, Reaction Sintering, Tungsten Carbide, Nano Zirconium Oxide
1. Introduction
To improve low-temperature plasticity in tungsten and its
strength at high temperature, making composite is an
effective way. W-Cu and W-ZrC are the examples of
such composites. Strength at high temperature and ther-
mal shock resistance of those composites caused their
application at high temperature environments, such as the
nozzle throat of solid fuel rocket. In fact the ZrC has low
coefficient of thermal expansion, high elastic modulus,
good strength at high temperatures and low thermal con-
ductivity. Also it is compatible with tungsten because
they have a comparable melting point, similar coefficient
of linear expansion and both have relatively high thermal
conductivity. Furthermore W and ZrC exhibit little mu-
tual solid solubility at high temperature and do not react
to form other compounds. The density of zirconium car-
bide is almost one third of tungsten which results in a
lighter composite. Consequently W and ZrC make a
preferable composite [1-3].
Three way of production has been reported for fabrica-
tion of W/ZrC composites:
1) Displacive compensation of porosity (DCP): Porous
WC preforms are produced by gel casting, hot isostatic
pressing or other conventional ceramic processes and
then the porous preform will be exposed to molten Zr2Cu
at 1200 - 1300˚C and ambient pressure. The Zr2Cu liquid
rapidly infiltrate into the preform and undergoes a dis-
placement reaction with WC to yield dense ZrC/W com-
posite. Among the advantages of this process are less
required pressure and heat rather than hot press, possibil-
ity of making larger and more complex parts and lower
cost, but being a two-stage method, retention of cop-
per-rich phase which usually makes unwanted impurities
with a low melting temperature within the composite and
inability to control the exact size and porosity of the pre-
form and therefore production of the same part are the
disadvantages of this method [1-4].
2) Hot-press: This method is one of the most expen-
sive and perhaps the most common processes used for
making composites because of its simplicity. It is similar
to warm sintering unless the temperature and pressure are
applied simultaneously. Of all advantages that this method
contains, increasing the properties of row and sintered
material such as density, strength and fatigue properties
is the main one. Other advantages of this method are less
grain growth, less porosity, higher strength and improv-
ing the high temperature properties. However simple

The Effect of Using Nano ZrO on the Properties of W-ZrC Composite Fabricated through Reaction Sintering
2 2
shape of made parts which needs further machining de-
creases the speed of the production and increases the cost.
High pressure and high temperature required in this
method are the main disadvantage of hot pressing [5-12].
3) Reaction sintering: It is a new method for producing
W/ZrC composite in which metal powders are subjected
to high temperatures, typically in an inert atmosphere or
under vacuum. In this method ZrO2 and WC powders are
mixed in desired volume or mass fraction, at the presence
of a suitable binder. The mixed powders then form a
green body which at the next stage is heated at a tem-
perature sufficient for the binder to be volatilized, be-
tween 400 - 600˚C and then the temperature is elevated
up to 1850˚C to produce an oxide-reduced or partially-
sintered body. The temperature of the partially sintered
body is then raised to 2100˚C to complete the densifica-
tion [13].
In this study, the W-ZrC composite is fabricated by
reaction sintering of WC and ZrO2 Powders that are se-
lected in micron and nano size to see the differences be-
tween the resultant composites. One objective of the
present study is to investigate the changes after using the
nano particles instead of micron particles. Therefore in
order to compare the composites at first a sample refer-
ence is made from micron powders, then it will be com-
pared with a composite that has been made by using nano
powders. For this the volume fraction of different phases
which has been formed in both composites is approxi-
mately estimated by the ratio of the integrated area of the
peaks and the total XRD patterns [14] to see the effi-
ciency of process. The densities of best obtained samples
are determined using Archimedes method, according to
ASTM B311 standard method. The hardness is evaluated
in accordance with ASTM E10. Moreover the bending
strength of the composite has been measured by bending
test according to ASTM C1161 and the modulus of elas-
ticity is measured as well, by ASTM C1419 test standard
method. Also by secondary electron microscopy (SEM)
and back scattered electron (BSE) the morphology of
samples are studied.
2. Experimental
Commercial tungsten carbide powder (d50 = 2 µm, purity
= 99.5%) and zirconium oxide (in two sizes d50 = 75 nm
and d50 = 1 µm, purity = 99.6%) are used as raw materi-
als. Figure 1 shows the morphology and particle size of
these starting powders.
To fabricate W/ZrC composite through reaction sin-
tering method, at first ZrO2 and WC powder were mixed
at presence of a binder so that a precursor was formed.
To produce a workpiece weighing 150 g, WC and ZrO2
powders are mixed according to Table 1 with optimum
molar ratio of 3 - 1 [13] between WC and ZrO2, although
10 nm
(a)
10 µm
(b)
5 µm
(c)
Figure 1. The morphology of a) Nano ZrO2, b) Micron ZrO2
and c) WC powders.
Table 1. The amount of WC and ZrO2 for production of a
150 g workpiece.
Code of
Sample WC to ZrO2 molar ratioParticle Size
WC + ZrO2
(g)
WC
(g)
ZrO2
(g)
3W1Z-M 3:1 Micron 150 124 26
3W1Z-N 3:1 Nano 150 124 26

The Effect of Using Nano ZrO on the Properties of W-ZrC Composite Fabricated through Reaction Sintering3
2
regarding the desired proportion of W to ZrC in compos-
ite this ratio may be different. After 6 hours mixing in
alcohol media, the resulting mixture is dried 12 hours in
an oven. Finally this mixture is gelcasted to make a pre-
form from WC and ZrO2 powder [15-18]. The gelcasting
was done according to the steps showing in Figure 2, in
which sodium alginate (C6H7NaO6), sodium hexameta-
phosphate ((NaPO3)6), phosphate calcium (Ca3(PO4)2)
and ammonium citrate ((NH4)3C6H5O7) were used as
monomers and after adding each of them mixing contin-
ues for 10 minutes. Then the mixture of WC and ZrO2
were added slowly and finally hexane acid (C6H10O4)
was added as initiator, that at this stage the workpiece
must be casted quickly before hardening. The mold used
here is made of rubber which compared with other mate-
rials and offered the best results.
The workpiece remains 24 hours at room temperature,
heated 6 hours in an oven at 50 - 60˚C to burn polymeric
additives and then for calcination, it is pulled out from
the mold and heated in a vacuum furnace at 600 - 700˚C.
The last step is sintering that usually is done at about
1500˚C. Figure 3 shows the sintering process for gel
casting. The gel casted body is sintered in a vacuum fur-
nace at 2100˚C [13], according to the cycle showing in
Figure 4.
In order to detect the type of synthesized phases and
components XRD analysis with the Cu Kα radiation (λ =
1.54 Å) was carried out and the integrated area of the
Applying polymeric materials (Cross linker and Monomer)
Mixing raw materials (WC and ZrO
2
) to create a homogeneous slurry
Sintering by heating in vacuum at 1500˚C
Drying at temperature of 60˚C to burn additives
Drying at ambient temperature for 24 hours
Pulling out the piece from mould
Casting in a die and beginning of gelation
Adding catalyst and initiator
Figure 3. The sintering process of gel casting.
Figure 4. The sintering process of reaction sintering.
eaks were calculated to obtain the volume fraction of
rC composite x-ray dif-
pattern of 3W1Z-M sample,
sh
p
the phases in the composite. Additionally the micro-
structure of the samples was studied using scanning elec-
tron microscope. To see the differences between phases
in the composites, the back scattered electron (BSE) im-
ages were studied as well as secondary electron (SE)
images.
3. Results and Discussion
To control the formation of W-Z
fraction of the powders before reaction and after making
the composites were analyzed to see whether the reaction
is complete or not. Figure 5 shows the XRD pattern of
composite made from micron powders (3W1Z-M) and
Figure 6 shows the XRD pattern of composite made
from nano powders (3W1Z-N) in which 1) is WC pow-
der, 2) ZrO2 powder, 3) The mixture of WC and ZrO2
and 4) W-ZrC composite.
Figure 5 is the XRD
owing the peaks belong to ZrC and W phases that con-
firms the formation of W/ZrC composite was successful.
In spite of that some WC and ZrO2 phases are observed
which illustrates that reaction between these two phases
Figure 2. The steps in gel casting of WC/ZrO2.

The Effect of Using Nano ZrO on the Properties of W-ZrC Composite Fabricated through Reaction Sintering
4 2
6 is the XRD pattern of 3W1Z-N sample. In
th
to form W/ZrC composite was not complete. Also the
W2C phase that was formed during mixing, still exist in
the composite. According to the integrated area of the
peaks related to these phase and the total XRD patterns,
the volume fraction of them is calculated and listed in
Table 2.
Figure
F by Sicros the hologhe
sa
se in back scattered elec-
tro
alues for mechanical properties of the
bo
is pattern ZrC and W phases are visible that point out
the formation of W/ZrC composite through reaction sin-
tering. On the other hand some ZrO2 phase is observed
but there is no WC any more. The W2C phase still exists
in the composite. According to the integrated area of
peaks in the XRD patterns, the volume fractions of these
phases are shown in Table 3.
Figure 5. XRD pattern of composite fabricated by reaction
sintering of micron WC/ZrO2.
Figure 6. XRD pattern of composite fabricated by reaction
sintering of nano WC/ZrO2.
Table 2. The volume fraction of different phases in the
3W1Z-M Sample.
Phase W ZrC ZrO 2 WC W2C
Vol% 40.1 19.7 10.2 9.1 20.9
Table 3. The volume fraction of different phases in the
3W1Z-N sample.
Phase W ZrC ZrO 2 W2C
Vol% 45.1 24.7 10.9 19.3
inallyEM mgraphmorpy of t
mples is studied. Figure 7 shows the BSE micrograph
of W-ZrC composite and Figure 8 shows the BSE mi-
crograph in 3W1Z-N sample.
As it is clear the bright pha
n images related to heavier elements. On the other
hand in the images, the composite is made of a dark
phase and a bright phase which represent zirconium car-
bide and tungsten respectively. To prove this EDX-line
scan of both phases were studied. Figure 9 shows the
EDX-line scan of bright phase and dark phase in W/ZrC
composite. Accordingly in 3W1Z-N sample the amount
of W is more, that shows the reaction in nano powder
improved better.
The average v
th nano and micron samples, including density, hard-
ness, Elastic modulus and Flexural strength, are listed in
Figure 7. The BSE micrograph of W/ZrC composite pre-
pared by reaction sintering in 3W1Z-M sample.
Figure 8. The BSE micrograph of W/ZrC composite pre-
pared by reaction sintering in 3W1Z-N sample.

The Effect of Using Nano ZrO on the Properties of W-ZrC Composite Fabricated through Reaction Sintering5
2
asibility of fabricating W/ZrC com-
Table 4 Comparing to prior ZrC-W composites [2] these
values for mechanical properties are acceptable. Anyway
the variances might be because the reaction between
ZrO2 and WC did not go to completion and because of
the effect that the un-reacted components have on the
properties of the composite.
4. Conclusions
In this study the fe
posite through reaction sintering was studied and the
differences of composite made from nano and micron
ZrO2 were investigated. The W/ZrC composite was pro-
duced by mixing WC and ZrO2 powders, gel casting the
mixture to produce a green body and then sintering at
2100˚C. The XRD patterns and SEM images indicate that
W/ZrC composite has been fabricated successfully by
this method, although some extra compounds have been
formed. Moreover the XRD pattern of nano sample
(a)
(b)
Figure 9. EDX-line scan of (a) Dark phase and (b) Bright
phase in 3W1Z-N sample.
ties and standard deviation
r made W/ZrC composites.
(g/cm ) (GPa)
astic modulus
(GPa)
Flexural strength
(MPa)
Table 4. The mechanical proper
fo
Sample Density
3Hardness El
3W1Z-M 12.1 4.3 339 431
showed th rean was m successfu pro-
ceeded more effectively, with rega45%WrC
acomd to ~4-20%ZrC in micron
useful discussion
and M. Hajizamani for pro-
, Y. Zhou and G. Song, “Compressive
Deformation Behavior of a 30 vol.%ZrCp/W Composite
at Temperaturterials Science and
Engineering A, , pp. 382-389.
at thectioore
rd to ~
l and
-25%Z
in nano smple pare0%W
sample. Additionally the amount of unreacted ZrO2 de-
creases and there remains no WC in nano sample. The
amount of unwanted W2C phase decreases as well. Even
when some weak points, like the inefficiency of process
and presence of ZrO2 phase, were taken to consideration,
the produced composites showed good mechanical prop-
erties, comparable to the composites fabricated through
hot-press and other conventional methods. Anyway the
composite produced by nano powders possess better
properties rather than the micron one.
5. Acknowledgements
The authors would like to express their gratitude to Dr. Y.
d Vahidshad in writing the article an
and suggestion in this study
viding language help.
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