Interface
microstructure of Ti3AlC2 and Al2O3
oxide scale
Z.
J. Lin, Z. M. Jin, Y. C. Zhou, M. S. Li and J. Y. Wang
Scripta Mater.
54(10)1815-1820(2006)
Absstract
The microstructural characteristics of the Ti3AlC2/Al2O3
interface have been investigated by means of
transmission electron microscopy (TEM). The orientation
relationships (ORs) between the Ti3AlC2 and the Al2O3
oxide scale are shown to be
(0001)Ti3AlC2‖(0001)Al2O3
and [11 20] Ti3AlC2‖[12 10] Al2O3
(OR-1)
(0001)Ti3AlC‖(0001)Al2O3
and [11 20 ]Ti3AlC2‖[1 100 ]Al2O3
(OR-2).
A high-resolution TEM image of the
interface is presented and two interfacial models are
proposed based on the observed orientation
relationships. |
Microstructural relationships between compounds in the Ti-Si-C
system
Z. J. Lin, M. J. Zhuo, Y. C. Zhou, M. S. Li, J. Y. Wang
Scripta
Mater., 55(5) 445-448 ,2006
Absstract
Microstructural relationships between Ti5Si3 and TiC,
and Ti3SiC2 and TiC are reported. Ti5Si3 and TiC were
determined to share a coherent interface following a new
set of orientation relationships, i.e., (11 2
4)Ti5Si3‖(1 1 0)TiC and [22 4 3]Ti5Si3‖[110]TiC.
Moreover, direct atomic resolution observation through
Z-contrast scanning transmission electron microscopy
showed that Ti3SiC2 nucleated within TiC. The close
microstructural relationships between compounds in the
Ti–Si–C system benefit the understanding of the reaction
mechanism for the synthesis of Ti3SiC2. |
Abnormal thermal
expansion and thermal stability of Ti3Al1-xSixC2 solid solutions
J. X. Chen, Y. C. Zhou and J. Zhang
Script. Mater.,
55(8): 675–678(2006)
Absstract
Ti3Al1-xSixC2 solid solutions exhibited abnormal high coefficients of thermal expansion at temperatures of >940
oC during heating, which was ascribed to the precipitation of Si as Ti5Si3. Ti5Si3 phase usually located at the grain boundaries of the solid solutions. |
Improving the Na2SO4-induced
corrosion resistance of Ti3AlC2 by
pre-oxidation in air
Z. J. Lin, Y. C. Zhou, M. S. Li, J. Y. Wang
Corro. Sci.
48(10): 3271–3280
(2006)
Absstract
Ti3AlC2 suffers severe Na2SO4-induced corrosion attacks at temperatures higher than 800 °C in air. A convenient and efficient pre-oxidation method is proposed to enhance the corrosion resistance of Ti3AlC2. The corrosion weight-changes of the pre-oxidized samples were decreased by about four orders of magnitude compared with those of the untreated specimens. The mechanism on improvement of corrosion resistance was investigated by means of thermogravimetric analysis, X-ray diffraction and scanning electron microscopy/energy-dispersive spectroscopy. A continuous and adherent -Al2O3 scale was prepared by high-temperature pre-oxidation treatment in air. The preformed dense Al2O3 scale has good compatibility with the Ti3AlC2 substrate, and consequently, can act as an efficient barrier against corrosion. Long-time corrosion tests demonstrate that the Al2O3 scale conserves after corrosion attack and is capable of long-term stability.
|
Influence of
pre-oxidation on the hot corrosion of Ti3SiC2
in the mixture of Na2SO4-NaCl melts
G. M. Liu, M. S. Li, Y. C. Zhou, Y. M. Zhang
Corro. Sci.
48(3) 650-661 (2005)
Absstract
Polycrystalline Ti3SiC2 suffered from serious hot corrosion attack in the mixture of 75wt.%Na2SO4 + 25wt.%NaCl melts at 850
oC. In order to improve the hot corrosion resistance of this material, pre-oxidation treatment was conducted at 1200
oC in air for 2 h. A duplex oxide scale with an outer layer of TiO2 and an inner layer of a mixture of TiO2 and SiO2 was formed during the pre-oxidation. Because the outer oxide layer of the pre-oxidation treated specimens could inhibit hot corrosion process, they exhibited good hot corrosion resistance in the mixture of 75wt.%Na2SO4 + 25wt.%NaCl melts at 850
oC for 50 h. However, during the hot corrosion the outer layer of TiO2 would degrade gradually. Once the outer layer damaged, the hot corrosion rate increased sharply, the corrosion behavior was similar to Ti3SiC2 corroded under the same conditions. The microstructure and phase compositions of the hot corrosion samples were investigated by SEM/EDS and XRD.
|
Effect of Si Content on
the Oxidation Resistance of Ti3Al1−xSixC2 (x≤0.25) Solid Solutions
at 1000–1400◦C
in Air
J. X. Chen and Y. C. Zhou
Oxid. Metals.,
65(1/2)123-135(2006)
Absstract
The oxidation behavior of Ti3Al1−xSixC2 (x≤0.25) solid
solutions was investigated in flowing air at 1000–1400
◦C for up to 20 h. Similar to Ti3AlC2, Ti3Al1−xSixC2 (x≤0.15) solid solutions display excellent oxidation
resistance at all temperatures because of the formation
of the continuous α-Al2O3 protective layers. However,
Al2(SiO4)O formed during oxidation of Ti3Al1−xSixC2 (x
=0.2 and 0.25) solid solutions at and above 1100◦C,
which is believed to be responsible for the
deterioration of oxidation resistance of
Ti3Al0.75Si0.25C2 at 1300◦C. Additionally, Ti5Si3 was
also found in the oxidized samples. This implies that
Ti5Si3 precipitated from Ti3Al1−xSixC2 solid solutions
during oxidation. But it has been proven that Ti5Si3 has
little effect on the oxidation resistance of the
material, which is attributed to an interstitial carbon
effect. |
Effect of Na2SO4 and
water vapor on the corrosion of Ti3SiC2
G. M. Liu, M. S. Li and Y. C. Zhou
Oxid. Metals
66(1-2):115-125(2006)
Absstract
The corrosion behavior of polycrystalline Ti3SiC2 was
studied in the presence of Na2SO4 deposit and water
vapor at 900 C and 1000 oC. The mass gain per unit area
of the samples superficially coated with Na2SO4 exposed
to water vapor was slightly lower than that of the
samples corroded without water vapor. The microstructure
and composition of the scales were investigated by SEM/EDS
and XRD. Pores were observed in the corroded sample
surfaces. The main corrosion phases on the sample
surface were identified by XRD as TiO2, Na2Si2O5 and
Na2TiO3. After Ti3SiC2 corroded in the presence of the
Na2SO4 deposit and water vapor, the scale had a
three-layer microstructure, which was different from the
duplex corrosion scale formed on Ti3SiC2 beneath the
Na2SO4 film without water vapor. Because water vapor
penetrated the corrosion layer and then reacted with
SiO2 to form volatile Si(OH)4, an intermediate porous
and TiO2-enriched layer formed in the corrosion layer. |
Intermediate
phases in Ti3SiC2 and Ti3Si(Al)C2
solid solutions synthesis from elemental powders
H. B
Zhang, Y. C. Zhou and Y. W. Bao
J. Europ. Ceram. Soc.
26(12)2373-2380(2006)
Absstract
In this paper, we investigated the reaction path to synthesize Ti3SiC2 by the in situ hot pressing/solid–liquid reaction method. The effect of different content of Al addition on this process was also examined. Ti3SiC2 mainly formed from the reaction between Ti5Si3Cx, TiCx, TiSi2 and graphite at 1400–1500
oC. As an inescapable impurity in Ti3SiC2, TiCx was removed by addition of small amounts of Al. This was owing to the fact that the addition of a minor quantity of Al increased the amount of “effective TiCx” and relatively decreased that of “invalid TiCx”. Further increasing Al content, however, resulted in the presence of TiCx again in the final product. This was due to the fact when significant amounts of Al was added, the stoichiometric ratio of silicon and graphite has been deviated from that for Ti3SiC2. More Si and less graphite were needed to prepare a monolithic Ti3Si(Al)C2 solid solution with high Al content.
|
Hot corrosion and
protection of Ti2AlC against Na2SO4 salt in air
Z. J. Lin, Y. C. Zhou, M. S. Li, J. Y.
Wang
J.
Europ. Ceram. Soc.,
26 (6): 3871–3879(2006)
Absstract
The hot corrosion behavior of Na2SO4-coated Ti2AlC was investigated by means of thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy. This carbide displays good hot corrosion resistance below the melting point of Na2SO4 while the corrosion attacks become virulent when the salt is molten. A protectively continuous Al2O3 layer forms and imparts good corrosion resistance, and consequently, the corrosion kinetics is generally parabolic at 850
oC. However, porous oxide scales fail to protect the Ti2AlC substrate at 900 and 1000
oC. The segregation of sulfur at the corrosion scale/substrate interface accelerates the corrosion of Ti2AlC. Furthermore, a convenient and efficient pre-oxidation method is proposed to improve the high-temperature hot corrosion resistance of Ti2AlC. An Al2O3 scale formed during pre-oxidation treatment can remarkably restrain the infiltration of the molten salt into the substrate and prevent the substrate from severe corrosion attacks.
|
Pressure-induced
polymorphism in Al3BC3: A first-principles study
J. Y. Wang, Y. C. Zhou, Z. J. Lin, T. Liao
J. Solid State
Chem., 179 (2006) 2739–2743
Absstract
Al3BC3, an isostructural phase to Mg3BN3, experienced no
pressure-induced phase transformation that occurred in
the latter material (J. Solid State Chem. 154 (2000)
254–256). The discrepancy is not clear yet. Using the
first-principles density functional calculations, we
predict that Al3BC3 undergoes a hexagonal-to-tetragonal
structural transformation at 24 GPa. The predicted phase
equilibrium pressure is much higher than the previously
reported pressure range, i.e., 2.5–5.3 GPa, conducted on
phase stability of Al3BC3. A homogeneous orthorhombic
shear strain transformation path is proposed for the
phase transformation. The transformation enthalpy
barrier is estimated to yield a low value, i.e., 0.129 eV/atom, which ensures that the transformation can
readily take place at the predicted pressure. |
Influence of
sol-gel derived Al2O3 film on the oxidation
behavior of a Ti3Al based alloy
M. Zhu,
M. S. Li, Y. L. Li and Y. C. Zhou
Mater. Sci. & Eng. A
415(1-2)
177-183(2006)
Absstract
Al2O3 thin films were deposited on a Ti3Al based alloy
(Ti–24Al–14Nb–3V–0.5Mo–0.3Si) by sol–gel processing.
Isothermal oxidation at temperatures of 900–1000 ◦C and
cyclic oxidation at 800–900 ◦C were performed to test
their effect on the oxidation behavior of the alloy.
Results of the oxidation tests show that the oxidation
parabolic rate constants of the alloy were reduced due
to the applied thin film. This beneficial effect
became weaker after longer oxidation time at 1000 ◦C.
TiO2 and Al2O3 were the main phases formed on the alloy.
The thin film could promote the growth of Al2O3, causing
an increase of the Al2O3 content in the composite
oxides, sequentially decreased the oxidation rate. Nb/Al
enriched as a layer in the alloy adjacent to the
oxide/alloy interface in both the coated and uncoated
alloy. The coated thin film decreased the thickness of
the Nb/Al enrichment layer by reducing the scale growth
rate. |
Tribological
behavior of Ti2SnC particulate reinforced copper matrix
composites
J. Y. Wu,
Y. C. Zhou, and J. Y. Wang
Mater. Sci. Eng. A
422(2006)266-271
Absstract
The layered ternary carbide Ti2SnC has outstanding mechanical and electrical properties. Therefore, the Cu matrix composite reinforced by Ti2SnC expects combined merits of both materials. In this article, we synthesized the copper matrix composites reinforced by Ti2SnC ceramic particles using hot-pressing method. The tribological behaviors of pure copper and composites reinforced with Ti2SnC were studied on a blockon-ring tester. The blocks were slid against 52100 steel rings under dry ambient conditions. It showed that the friction coefficient and wear rate of Cu matrix composites decreased significantly by incorporation of Ti2SnC particles. The wear rate of pure copper was about eight times that of the Cu–10 vol.% Ti2SnC composite under a sliding velocity of 1 and a normal load of 30 N. The satisfied low friction coefficient and wear resistance prove that Ti2SnC is a promising reinforcement material for Cu matrix composite. In addition, the effects of sliding velocity and normal load on wear behavior were investigated for pure copper and Cu–Ti2SnC composites. |
In situ reaction synthesis
and characterization of Ti3Si(Al)C2/SiC
composites
D. T. Wan, Y. C. Zhou, Y. W. Bao, C. K.
Yan
Ceram. Inter.,
32(8) :883–890 (2006)
Absstract
The reaction route, microstructure, and properties of Ti3Si(Al)C2/SiC composites with 5–30 vol.% SiC content prepared by in situ hot pressing/solid–liquid reaction synthesis process are investigated. In contrast to monolithic Ti3Si(Al)C2, the SiC particle-reinforced composites exhibit higher elastic modulus, Vickers hardness, fracture toughness, improved wear, and oxidation resistance, but have a slight loss in flexural strength. The improvement in the properties is mainly ascribed to the contribution of SiC particles, and the strength degradation is due to the residual tensile stresses in the matrix. |
Failure mode dependence of
strengthening effects in Ti3AlC2/10 vol.%Al2O3 composite
J. X. Chen, M. Y. Liu, Y. W. Bao and Y.
C. Zhou
Inter. J. Mater. Res.
(8)1115-1118(2006)
Absstract
The high-temperature mechanical properties of both Ti3AlC2 and Ti3AlC2/10 vol. %Al2O3 composites, including compressive strength, bending strength, and fracture behavior, were investigated. The strengthening effect caused by Al2O3 strongly depended on the mode of failure: significant enhancement in strength was only observed under the brittle mode of failure; whereas under the ductile mode of failure the strengthening effect was impaired due to Ti3AlC2 matrix softening and stress relaxation. |
In-situ
processing and high-temperature properties of Ti3Si(Al)C2/SiC
composites
Y. C.
Zhou, D T Wan, Y. W. Bao and J. Y. Wang
Inter. J. Appl. Ceram. Tech.
3(1)47-54 (2006)
Absstract
Ti3SiC2 has many salient properties including low
density, high strength and modulus, damage tolerance at
room temperature, good machinablity, and being resistant
to thermal shock and oxidation below 1100 oC. However,
the low hardness and poor oxidation resistance above
11001C limit the application of this material. The poor
oxidation resistance at temperatures above 1100 oC was
because of the absence of protective layer in the scale
and the presence of TiC impurity phase. TiC impurity
could be eliminated by adding a small amount of Al to
form Ti3Si(Al)C2 solid solutions. Although the
high-temperature oxidation resistance was significantly
improved for the Ti3Si(Al)C2 solid solutions, the
strength at high temperatures was lost. One important
way to enhance the high-temperature strength is to
incorporate hard ceramic particles like SiC. In this
article, we describe the in situ synthesis and
simultaneous densification of Ti3Si(Al)C2/SiC composites
using Ti, Si, Al, and graphite powders as the initial
materials. The effect of SiC content on high-temperature
mechanical properties and oxidation resistance were
investigated. The mechanisms for the improved
high-temperature properties are discussed. |
Damage
tolerance of nanolayer-grained ceramic:a
quantitative estimation
Y. W. Bao,
C. F,. Hu and Y. C. Zhou
Mater. Sci. & Tech.
22(2)227-230(2006)
Absstract
In order to meet increasing requirement for the
evaluation and design of damage tolerance of brittle
materials, a simple expression was proposed to estimate
the damage tolerance quantitatively using basic material
parameters, based on the features of damage tolerance
and fracture mechanics. The calculated results from this
equation indicated that the damage tolerance of
nanolayer grained ceramics was over 10 times higher than
that of some brittle ceramics, while glass has the
lowest damage tolerance. Therefore, the damage tolerance
of various ceramics can be estimated directly using
their basic properties data without the necessity of
additional tests. SEM examination and finite
element simulation showed that the high damage tolerance
of the layer grained ceramics was attributed to
delamination in grains, interlocking microstructures and
crack deflection. |
In-situ Synthesis of Ti3AlC2/TiC-Al2O3
Composite from TiO2-Al-C System
J. X. Chen, J. L. Li and Y. C. Zhou
J.
Mater. Sci. Technol.,22(4)455-458(2006)
Absstract
Ti3AlC2/TiC-Al2O3 composite was synthesized by a
combustion reaction in TiO2-Al-C system. The effect of
the compositions in raw materials on the products was
investigated. Ti3AlC2/TiC-Al2O3 composite was obtained
at the molar ratio of TiO2:Al:C=3.0:5.0~5.1:1.8~2.0. The
reaction path for the 3TiO2-5Al-2C system was proposed.
Al3Ti, Ti2O3, TiO, and
δ-Al2O3 are found to be
transitional phases. Finally, Ti3AlC2/TiC-Al2O3
composite forms at ~900 oC of furnace temperature. The
measured Vickers hardness, fracture toughness, and
flexural strength of the nearly dense sample from
3TiO2-5Al-2C are 13.3±1.1 GPa, 5.8±0.3 MPa·m1/2, and
466±39 MPa, respectively. |
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