1.Hf3AlN: A Novel Layered
Ternary Ceramic with Excellent Damage Tolerance
Fangzhi Li, Bin Liu, Jingyang Wang, Yan-chun Zhou,
J. Am. Ceram. Soc.,
93  228 –234 (2010)
this work, bulk Hf3AlN ceramic was synthesized
by an in situ reaction/hot pressing method using Hf
and AlN as initial materials. The reaction path
during the synthesis process was investigated.
Hf3AlN was found to form via the reaction
of Hf and AlN above 1000oC. Furthermore,
physical and mechanical properties of Hf3AlN,
such as electrical conductivity, flexural strength,
and elastic moduli were also characterized. Similar
to typical layered ternary ceramics Ti3SiC2
and Ti3AlC2, Hf3AlN
possesses metallic conductivity and excellent damage
tolerance, which is also the first one of this type
that has ever been reported to crystallize in an orthorhombic
structure. It is believed that a typical layered crystal
structure and weak interlayer bondings contribute to
the damage tolerance of Hf3AlN. Moreover,
the stiffness of Hf3AlN can sustain a temperature
as high as 1450oC, being 250oC
higher than that of Ti3AlC2, which
renders it a promising high-temperature structural material.
and thermal properties of a Hf2[Al(Si)]4C5
ceramic prepared by in situ reaction/hot-pressing
L.F. He, H.Q. Nian, X.P. Lu, Y.W. Bao and Y.C. Zhou,
62 (2010) 427–430
ceramic has been fabricated by an in situ reaction/hot-pressing
using Hf, Al, Si and graphite as starting materials.
comparable mechanical properties to Zr2[Al(Si)]4C5,
and lower hardness and stiffness but higher strength
and toughness than HfC. The stiffness decreases slowly
with temperature and at 1600oC it remains
83% of that at ambient temperature. Compared to Zr2[Al(Si)]4C5
and HfC, however, Hf2[Al(Si)]4C5
exhibits a relatively higher coefficientof thermal expansion,
an intermediate specific heat capacity and a lower thermal
toughness determination of Ti3Si(Al)C2
and Al2O3 using a single gradient notched
beam (SGNB) method
Li, Chao Li, Jingjing Li, Yanchun Zhou, J.
Am. Ceram. Soc.,
 554–560 (2010)
oxidation behaviors of a Ti3AlC2/20(vol%)TiB2
composite, synthesized by means of in situ reactions
of Ti, Al, graphite, and B4C powder mixtures
under hot pressing, have been investigated at 1000–1400oC
in air. The Ti3AlC2/20TiB2
composite followed the logarithmic oxidation law, and
had a lower oxidation rate than the matrix Ti3AlC2.
During the oxidation
at 1000–1400oC, a continuous Al2O3
formed on the composite, meanwhile other different oxides
formed on the top surface of the Al2O3
layer, depending on the oxidation temperature: discontinuous
α-TiO2 at below 1200oC, mixture
of Al2TiO5 and TiO2
at 1300oC, and continuous Al2TiO5
at 1400oC. The selective oxidation of Al
occurred at the oxide/substrate interface through inward
diffusion of oxygen, and TiO2 overgrew the
Al2O3 layer to form coarse grains
through outward diffusion of titanium ions. When the
temperature was above 1280oC, Al2TiO5
appeared due to a eutectic reaction between TiO2
and Al2O3. The incorporation of
TiB2 promoted the generation of great numbers
voids at the Al2O3/substrate interface
and in the Al2O3 inner layer,
which is proposed as being the main reason for the Ti3AlC2/20TiB2
composite to follow a logarithmic oxidation law.
and Kinetics of the Hydrothermal Oxidation of Bulk Titanium
H. B. Zhang, Volker Presser,
Christoph Berthold, Klaus Georg Nickel, X Wang, Christoph Raisch
and Thomas Chasse, L. F. He and Y. C. Zhou, J.
Am. Ceram. Soc.,
 1148–1155 (2010)
Hydrothermal oxidation of bulk Ti3SiC2
in continuous water flow was studied at 500–700 oC
under a hydrostatic pressure of 35 MPa. The oxidation
was weak at 500–600 oC and accelerated at 700
oC due to the formation of cracks in oxides.
The kinetics obeyed a linear time-law. Due to the high
solubility of silica in hydrothermal water, the
resulting oxide layers only consisted of titanium oxides
and carbon. Besides general oxidation, two special modes
are very likely present in current experiments: (1)
preferential hydrothermal oxidation of lattice planes
perpendicular to the c-axis inducing cleavage of grains
and (2) uneven hydrothermal oxidation related to the
occurrence of TiC and SiC impurity inclusions.
Nonetheless the resistance against hydrothermal
oxidation is remarkably high up to 700 oC.
Structure and Theoretical Elastic Property of a New Ternary
Nian, L. F. He, F. Z. Li, J. Y. Wang and Y.C. Zhou, J.
Am. Ceram. Soc.,
 1164–1168 (2010)
HfAl4C4, a new ternary aluminum
carbide, was discovered and its crystal structure was
determined by a combination of X-ray diffraction,
transmission electron microscopy, and first principles
calculations. The crystal structure is trigonal
belonging to the P 3m1 space group. The refined lattice
constants are a=0.3308 nm, c=2.190 nm. First-principles
method was used to calculate the theoretical
second-order elastic constants, bulk modulus, shear
modulus, and the Young’s modulus of HfAl4C4.
It shows that HfAl4C4 has
relatively high elastic stiffness.
strengthening of Ti3SiC2 through magnetron
sputtering Cu and subsequent annealing
H. P. Guo J. Zhang, F. Z. Li,
Y. Liu J. J. Yin, Y.C. Zhou, J.
Europ. Ceram. Soc.,
sputtering deposition Cu and subsequent annealing in
the temperature range of 900–1100 ◦C
for 30–60 min were conducted with the motivation to
modify the surface hardness of Ti3SiC2.
Owing to the formation of TiC following the reaction
Ti3SiC2 + 3Cu→3TiC0.67
+Cu3Si, the surface hardness was enhanced
from 5.08 GPa to a maximum 9.65 GPa. In addition, the
surface hardness was dependent on the relative amount
of TiC, which was related to Cu film thickness, heat
treatment temperatures and durations of annealing. Furthermore,
after annealing at 1000 ◦C for 30 min
the Cu-coated Ti3SiC2 has lower
wear rate and lower COF at the running-in stage compared
with Ti3SiC2 substrate. The reaction
was triggered by the inward diffusion of Cu along the
grain boundaries and defects of Ti3SiC2.
At low temperature and short annealing time, i.e. 900
or 1000 ◦C for 30 min, Cu diffused
inward Ti3SiC2 and accumulated
at the trigonal junctions first. At higher temperature
of 1100 ◦C or prolonging the annealing
time to 60 min, considerable amount of Cu diffused to
Ti3SiC2 and filled up the grain
boundaries leaving a mesh structure.
thermal, and oxidation properties of a Zr2[Al(Si)]4C5–SiC
composite prepared by in situ reaction/hot-pressing
L. F. He, F. Z. Li, X. P. Lu,
Y. W. Bao , Y. C. Zhou, J.
Europ. Ceram. Soc.,
mechanical and thermal properties, as well as oxidation
behavior, of in situ hot-pressed Zr2[Al(Si)]4C5–30
vol.% SiC composite have been characterized. The microstructure
is composed of elongated Zr2[Al(Si)]4C5
grains and embedded SiC particles. The composite shows
superior hardness (Vickers hardness of 16.4 GPa), stiffness
(Young’s modulus of 386 GPa), strength (bending strength
of 353MPa), and toughness (fracture toughness of 6.62MPam1/2)
compared to a monolithic Zr2[Al(Si)]4C5
ceramic. Stiffness is maintained up to 1600 ◦C
(323 GPa) due to clean grain boundaries with no glassy
phase. The composite also exhibits higher specific heat
capacity and thermal conductivity as well as better
oxidation resistance compared to Zr2[Al(Si)]4C5.
Machinable and Electrically Conductive Ti2AlC and
X. H. Wang, Y. C. Zhou, J.
Mater, Sci. Technol.,
and Ti3AlC2 are the most light-weight and oxidation
resistant layered ternary carbides belonging to
the MAX phases. This review highlights recent achievements
on the processing, microstructure, physical,
mechanical and chemical properties of these two machinable
and electrically conductive carbides. Ti2AlC
and Ti3AlC2 display superior properties
such as fracture toughness, electrical and thermal conductivities,
and oxidation resistance over their binary counterpart.
This paper provides a comprehensive overview of the
processing-microstructure-property correlations of these
two carbides. Potential fields of applications for Ti2AlC
and Ti3AlC2 are surveyed. In addition,
we point out methods for further improving their properties
some specific applications through appropriate structural
design and modification.
A New Method to Improve the High-Temperature Mechanical
Properties of Ti3SiC2 by Substituting
Ti with Zr, Hf, or Nb
D. T. Wan, L. F. He, L. L.
Zheng, J. Zhang, Y. W. Bao, Y. C. Zhou, J.
Am, Ceram. Sci., 93(6):
shows a unique combination of the properties of both
metals and ceramics. However, its stiffness and strength
lose rapidly above 1050 oC, which is the
main obstacle for the high-temperature application of
this material. To improve the high-temperature mechanical
properties of Ti3SiC2, Zr, Hf,
or Nb were used as dopants in Ti3(SiAl)C2.
At room temperature, the Zr-, Hf-, or Nb-doped Ti3(SiAl)C2
ceramics have comparable stiffness, hardness, strength,
and fracture toughness with those of Ti3(SiAl)C2.
At high temperatures, however, a significant improvement
in stiffness and strength has been achieved for (Ti1-
(T=Zr, Hf, or Nb). (Ti1-xTx)3(SiAl)C2
can retain high degrees of stiffness and strength up
to 1200 oC,
which is 150 oC higher than those for Ti3(SiAl)C2.
Variation of microstructure and composition of the Cr2AlC
coating prepared by sputtering at 370 and 500 °C
J.J. Li, L.F. Hu, F.Z. Li, M.S.
Li, Y.C. Zhou, Surface
& Coatings Technology
Cr2AlC coating was deposited at 370 and
500 °C by D.C. magnetron sputtering from an
Cr2AlC target. The phase composition and
preferential orientation of the coating were
investigated using XRD, and the microstructure of
the coating was characterized by TEM. Results
indicated that Cr2AlC coating
with a strong (110) preferential orientation could
be obtained. The coating microstructure was clearly
affected by the deposition temperature. At 370 °C,
the deposited coating possessed a triple-layered
structure with an α-(Cr, Al)2O3
inner layer, an amorphous intermediate layer and a
crystalline Cr2AlC outer layer.
However, the coating deposited at 500 °C had a
single-layered structure consisting of crystalline
Cr2AlC layer. The growth mechanism
of the Cr2AlC coating at different
deposition temperatures is discussed.
Electrophoretic Deposition of Ti3Si(Al)C2
from Aqueous Suspension
Liang, Z. Q. Sun, J. X. Chen, X.
Liu, Y. C. Zhou, J.
Am, Ceram. Sci., 93
 1916–1921 (2010)
Ti3Si(Al)C2 films were
electrophoretically deposited at 3 V on
indium-tin-oxide (ITO) conductive glass from Ti3Si(Al)C2
aqueous suspension with 1 vol% solid loading at pH 9
in the absence of any dispersant. The surface
morphology, cross section microstructure, and
preferred orientation of the films were investigated
by scanning electron microscopy and X-ray
diffraction. The as-deposited Ti3Si(Al)C2
films exhibited (00l) preferred orientation and the
thickness can be controlled by the
deposition–drying–deposition method. These results
demonstrate that electrophoretic deposition is a
simple and feasible method to prepare MAX-phases
green films at room temperature.
Theoretical elastic stiffness, structural stability and
thermal conductivity of La2T2O7
(T = Ge, Ti, Sn, Zr, Hf) pyrochlore
B. Liu, J.Y. Wang, F.Z. Li, Y. C. Zhou, Acta
In order to achieve better understanding of the
structural/property relationships of La2T2O7
(T = Ge, Ti, Sn, Zr, Hf) pyrochlore,
first-principles calculations were conducted to
investigate the bonding characteristics, elastic
stiffness, structural stability and minimum thermal
conductivity. The results show that the relatively
weak La–O bonds play a predominant role in
determining the structural stability, mechanical and
thermal properties of these compounds. In addition,
the elastic and thermal properties are influenced
when the T atom changes from Ge to Hf. When the
bonding strength is enhanced by applying hydrostatic
pressure, apart from c11, c12,
and B, which normally increase at high pressures, it
is found that the shear elastic moduli, c44
and G, which relate to the shear deformation
resistance, abnormally remain almost constant. The
underlying mechanism may help to explain the damage
tolerance of pyrochlore compounds. After
comprehensive consideration of the elastic
anisotropy, a modified David Clarke-type equation is
used to calculate the minimum thermal conductivity
of the studied pyrochlore materials, which display
an extraordinary low thermal conductivity.