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1.
Jéhanno P. Kestler H. Venskutonis A. Böning M. Heilmaier M. Bewlay B. Jackson M. 《Metallurgical and Materials Transactions A》2005,36(3):515-523
A powder metallurgical (PM) processing route for the manufacturing of two different refractory metal silicide alloys comprising
inert gas atomization of presintered bars, hot isostatic pressing, and hot extrusion (reduction in cross section of 6:1) was
established. The mechanical properties between room temperature and 1200 °C of the PM-processed Mo-3Si-1B and Nb-24Ti-20Si-5Cr-3Hf-2Al
alloys (in wt pct) were assessed with tensile tests vs a state-of-the-art Ni-base single crystalline alloy (CMSX 4) and a directionally solidified (MASC) niobium-base silicide
alloy, respectively. The microstructural characterization of both the hot-isostatically pressed and extruded materials was
carried out applying scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) analysis.
The Mo-Si-B alloy is characterized by an intermetallic matrix surrounding globular Mo particles in the hot isostatic press
and a nearly continuous molybdenum solid solution matrix with dispersed intermetallic particles in the hot-extruded condition.
Hot extrusion results in a substantial reduction of the DBTT of about 200 °C and tensile strengths superior to CMSX 4 at temperatures
above 1000 °C. In the case of the Nb-base silicide alloy, a niobium solid solution surrounding intermetallic particles with
Nb5Si3-type structure characterizes the final alloy. In the intermediate temperature range of 500 °C to 816 °C, a strength level
equivalent to the directionally solidified MASC alloy was observed.
This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place
March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects
Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory
Metals Committee. 相似文献
2.
The structure and mechanical and service properties of Al-Li-Cu alloys are determined, and the results obtained are used to
find the effect of major and additional components on their properties and to design a high-strength heat-treatable cast alloy
with a low density. After quenching and maximum-strength aging, this alloy has the following level of mechanical properties
(casing in a metal mold): σu = 360–370 MPa and δ = 6.0–7.5%. 相似文献
3.
Hardening phase/intermetallic matrix pairs are chosen for composite materials (CMs) intended for long-term high-temperature
operation. These materials must have high and stable mechanical properties during a long time at high temperatures and loads.
The compatibility of the physicochemical and mechanical properties of CM components is estimated to choose hardening phase/intermetallic
matrix pairs in which the matrix is represented by an alloy based on NiAl or TiAl monoaluminide and the hardening phase is
a refractory thermodynamically stable oxide of a Group III transition metal M
2O3. The following two schemes are used to perform hardening of a CM with a matrix consisting of a TiAl or NiAl alloy by the
most thermodynamically stable interstitial phases, i.e., refractory oxides, at temperatures higher than the operating temperature
(T
op) of the IMM. The first scheme consists in creating Al2O3/TiAl CMs hardened by continuous single-crystal sapphire fibers using the impregnation of a bundle of single-crystal fibers
with a matrix melt followed by directional solidification. The TiAl-based matrix in these CMs serves as a binder connecting
oxide phase fibers and preventing them from fracture due to high adhesion forces between oxide fibers and the matrix and a
high fiber/matrix interface strength. In the second scheme, Y2O3/NiAl CMs are produced by powder metallurgy methods, which include severe deformation by extrusion accompanied by the formation
of deformation texture and subsequent recrystallization annealing. In these CMs, disperse refractory oxide particles stabilize
grain boundaries in a recrystallized matrix material and lead to the formation of directional structures with coarse elongated
grains and a low fraction of transverse boundaries. Al2O3/TiAl CMs containing 20–25 vol % hardening single-crystal sapphire Al2O3 fibers can operate at temperatures of 1000–1050°C (∼0.7T
m of matrix), which is 250–300°C higher than the maximum values of T
op of a TiAl-based matrix and 400-450°C higher than the maximum values of T
op of a Ti-based matrix. An Y2O3/NiAl composite with a directionally recrystallized structure of a NiAl-based matrix hardened by 2.5 vol % Y{ia2}O3 particles can be recommended for operation at temperatures of 1400–1500°C ((0.8–0.9)T
m of matrix), which are higher by 100–400°C than not only T
op but also T
m of Ni superalloys. 相似文献
4.
Mold–metal interface heat transfer coefficient values need to be determined precisely to accurately predict thermal histories
at different locations in automotive castings. Thermomechanical simulations were carried out for Al-Si alloy casting processes
using a commercial code. The cooling curve results were validated with experimental data from the literature for a cylindrical-shaped
casting. Our analysis indicates that the interface heat transfer coefficient (IHTC) initial value choice between chill–metal
and the sand mold–metal interfaces has a marked effect on the cooling curves. In addition, after choosing an IHTC initial
value, the solidification rates of the alloy near the chill–metal interfaces varied during subsequent cooling when the gap
began to form. However, the gap formation, which results in an IHTC change from the initial value, does not affect the cooling
curves within the vicinity of the sand–metal interface. Optimized initial IHTC values of 3000 and 7000 W m−2-K−1 were determined for a sand–metal interface and a chill (steel or copper)–metal interfaces, respectively. The initial IHTC
had a significant effect on the prediction of secondary dendrite arm spacing (SDAS) (varying between approximately 15 microns
and 70 microns) and ultimate tensile strength (UTS) (varying between approximately 250 MPa and 370 MPa) for initial IHTC values
that were less than the optimized value of 7000 W m−2 K−1 for the chill–metal interfaces. 相似文献
5.
V. G. Komkov V. V. Gostishchev E. Kh. Ri S. V. Dorofeev 《Russian Journal of Non-Ferrous Metals》2011,52(4):344-346
It is established experimentally that the influence that nanosecond electromagnetic pulses (NEMPs) have on the charge melt
during the carbothermic reduction of cassiterite in the Na2CO3-NaNO3 medium (1: 0.3) at t = 900–950°C accelerates the formation of the metal phase by a factor of ∼2 and affects its composition. As the duration of
irradiation increases to 30 min, the tin content in the crude alloy increases to ∼95%. The influence that the NEMP treatment
of the bronze melt has on its physicomechanical properties is revealed. It is shown that the influence of pulses for 10–15-min
increases the alloy density to 8.92 g/cm3, hardness by a factor of 1.24, and thermal conductivity by a factor of 2. 相似文献
6.
Aluminum matrix composites: Fabrication and properties 总被引:7,自引:0,他引:7
Aluminum alloy matrix composites containing 1 to 30 wt pct of fibrous and particulate nonmetals varying in size from 0.06
μm to 840 μm were fabricated. The composites were cast into cylindrical molds for friction and wear tests, hot extrusion and
tensile tests. The distribution of the nonmetals in the cast ingots was homogeneous. Friction and wear tests were done on
a pin (52100 bearing steel) and dish type machine without lubrication. It was found that composites containing ∼10 wt pct
or more of SiC, TiC, Si3N4, Al2O3, glass, solid waste slag, and silica sand wear less than the pure matrix alloy, but have slightly higher average coefficients
of friction. Wear in composites containing soft particles, especially MgO and boron nitride was higher than the pure matrix
alloy. The average coefficient of friction of all the composites was in the range of 0.35 to 0.58. Increasing the sliding
velocity reduced this range to ∼ 0.4 to 0.45. The longitudinal tensile properties of the extruded composites (with the exception
of loss of ductility in some cases) are comparable to that of the matrix alloys. Improvements in strength or ductility were
noted. For example, addition of 15 wt pct of 3 μm size Al2O3 particles raised the yield and ultimate strength of the Al-4 pct Cu-0.75 pct Mg alloy matrix from 227 to 302 MPa, and 356
to 403 MPa, respectively. The corresponding percent elongation decreased from 25.8 to 12.5. The fact that the various composites
can be readily cast and hot formed suggests a variety of engineering applications.
AKIRA SATO, formerly Visiting Scientist at Massachusetts Institute of Technology, Cambridge. 相似文献
7.
A metallographic study has been made of the denuded zones from diffusional flow in a hydrided alloy of magnesium with 6 wt
pct Zn and 0.5 wt pct Zr (ZK 60). At the deformation temperature of 450°C, with an initial grain size of 18 um, the alloy
was superplastic. Its maximum strain-rate sensitivity,m = (d log σ)/(d log ∈), was ⊥0.6 at fe –4 10~4 sec–1. A diffusional strain, ed = ΔLd/Ld, was calculated from measurements of zone thickness, ΔLd, and interzone distance,L
d.
This was a reasonably constant fraction of the total strain,e, up to the limiting strain of ⊥220 pct. Over a strain-rate range of 3.3 x 10–3 sec–1 to 3.3 x 10⊥5 sec–1,e
d
/e increased from about 0.05 to 0.30. 相似文献
8.
Creep strengthening in a discontinuous SiC-Al composite 总被引:2,自引:0,他引:2
Kyung-Tae Park Farghalli A. Mohamed 《Metallurgical and Materials Transactions A》1995,26(12):3119-3129
High-temperature strengthening mechanisms in discontinuous metal matrix composites were examined by performing a close comparison
between the creep behavior of 30 vol pct SiC-6061 Al and that of its matrix alloy, 6061 Al. Both materials were prepared by
powder metallurgy techniques. The experimental data show that the creep behavior of the composite is similar to that of the
alloy in regard to the high apparent stress exponent and its variation with the applied stress and the strong temperature
dependence of creep rate. By contrast, the data reveal that there are two main differences in creep behavior between the composite
and the alloy: the creep rates of the composite are more than one order of magnitude slower than those of the alloy, and the
activation energy for creep in the composite is higher than that in the alloy. Analysis of the experimental data indicates
that these similarities and differences in creep behavior can be explained in terms of two independent strengthening processes
that are related to (a) the existence of a temperature-dependent threshold stress for creep, τ0, in both materials and (b) the occurrence of temperature dependent load transfer from the creeping matrix (6061 Al) to the
reinforcement (SiC). This finding is illustrated by two results. First, the high apparent activation energies for creep in
the composite are corrected to a value near the true activation energy for creep in the unreinforced alloy (160 kJ/mole) by
considering the temperature dependence of the shear modulus, the threshold stress, and the load transfer. Second, the normalized
creep data of the composite fall very close to those of the alloy when the contribution of load transfer to composite strengthening
is incorporated in a creep power law in which the applied stress is replaced by the effective stress, the stress exponent,n, equals 5, and the true activation energy for creep in the composite,Q
c
, is equal to that in the alloy.
formerly Research Associate, Materials Section, Department of Mechanical and Aerospace Engineering, University of California
This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the
1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint
TMS-SMD/ASM-MSD Composite Materials Committee. 相似文献
9.
Li Yuchun Zhou Tao Li Zhiyo Tian Zhongliang Qin Qinwei 《Powder Metallurgy and Metal Ceramics》2007,46(3-4):145-152
In aluminum electrolysis industry, traditional carbon electrodes have many disadvantages under molten-salt corrosive conditions
(970°C), such as large quantities of CO2 production and quick consumption of carbon. The best way is cermet, which is a kind of graded composite material and consists
of spinel NiFe2O4 as a ceramic phase and Ni-Fe-X alloy as a metal phase. The fabrication of NiFe2O4 powder is studied by chemical co-precipitation method with different co-precipitation chemicals (NH3· H2O, NaOH); differential thermal analysis and thermal gravity (TG) test have also been carried out to evaluate the performance
of fabricated powder. The fabrication of Ni-Fe-X alloy is studied with three different kinds of powder compositions (NiFeAlCuZn,
NiFeAlCuSn, and NiFe), different forming methods and sinter conditions are also compared and discussed in detail. DTA, XRD,
density, hardness and anti-oxidation tests are carried out to test the performance of fabricated materials. Finally, fabrication
technical condition of cermet is studied and determined according to graded composite slurry casting method, which combines
the ceramic phase and metal phase with good performance. The fabrication technique presented in this study is valuable for
making new anti-corrosion electrode material used in aluminum electrolysis.
Published in Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 52–61, 2007. 相似文献
10.
A new process for the preparation and casting of metal-particulate non-metal composites is described. Particulate composites
of ceramic oxides and carbides and an Al-5 pet Si-2 pct Fe matrix were successfully prepared. From 10 to 30 wt pct of A12O3, SiC, and up to 21 wt pct glass particles, ranging in size from 14 to 340 ώ were uniformly distributed in the liquid matrix
of a 0.4 to 0.45 fraction solid slurry of the alloy. Initially, the non-wetted ceramic particles are mechanically entrapped,
dispersed and prevented from settling, floating, or agglomerating by the fact that the alloy is already partially solid. With
increasing mixing times, after addition, interaction between the ceramic particles and the liquid matrix promotes bonding.
Efforts to mix the non-wetted particles into the liquid alloy above its liquidus temperature were unsuccessful. The composite
can then be cast either when the metal alloy is partially solid or after reheating to above the liquidus temperature of the
alloy. End-chilled plates and cylindrical slugs of the composites were sand cast from above the liquidus temperature of the
alloy. The cylindrical slugs were again reheated and used as starting material for die casting. Some of the reheated composites
possessed “thixotropy.” Distribution of the ceramic particles in the alloy matrix was uniform in all the castings except for
some settling of the coarse, 340ώ in size, particles in the end-chilled cast plates. 相似文献
11.
P. Y. Deshmukh D. R. Peshwe J. Bhatt S. U. Pathak 《Transactions of the Indian Institute of Metals》2011,64(6):575-581
This paper discusses the effect of the dispersion of amorphous nano size (35–55 nm) SiO2 particles in Al–Mg (5%) alloy. Amorphous SiO2 (>95% SiO2) extracted from rice husk was added to the Al–Mg (5%) alloy in the proportion of 5 wt% of the Al–Mg alloy. The work aims
to study the evolution of different phases like MgAl2O4, Mg2Si, and MgO in Al–Mg–SiO2 composite using amorphous nano SiO2. Experimental results of the synthesized composite show presence of MgAl2O4 (Spinel structure) and other phases like MgO and Mg2Si which impart hardness of 126.82 HV10g to the composite. The Al–Mg (5%) SiO2 composite microstructure appeared as a typical lamellar structure. The XRD and energy dispersive spectroscopy analysis display
the presence of Mg2Si formed along the grain boundary. 相似文献
12.
H.-J. Jun K.S. Lee J. Eckert Y.W. Chang 《Metallurgical and Materials Transactions A》2008,39(8):1831-1837
The deformation behavior of a monolithic Zr55Cu30Al10Ni5 (at. pct) bulk metallic glass (BMG) fabricated by suction casting has been investigated at elevated temperatures in this
study. A series of compression tests has been performed in the supercooled liquid temperature region. In the homogeneous flow
regime, this alloy exhibited a transition from the Newtonian to non-Newtonian flow depending upon both the strain rate and
the temperature. These two flow modes were then described by applying the Newtonian viscous flow theory and the transition
state theory, respectively. On the basis of a dynamic materials model (DMM), a processing map could successfully be constructed
to estimate the feasible forming conditions for this BMG alloy. Imaginary laboratory-scale extrusion tests were also performed
to determine solid-to-solid formability, and the results from both the finite element method (FEM)-based simulation and processing
map were then compared and discussed.
This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February
25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of
Materials Committee. 相似文献
13.
V. N. Anikin I. V. Blinkov A. O. Volkhonskii N. A. Sobolev S. G. Tsareva R. V. Kratokhvil A. E. Frolov 《Russian Journal of Non-Ferrous Metals》2009,50(4):424-431
Structure and phase formation during the deposition of coatings of the Ti-Al-Ni system (Al ≈ 3.5 at %) by the ion-plasma method
are investigated. The controlled process parameter was the bias potential (U
b) applied to the substrate made of the VK6 hard alloy. At U
b = 120 V (samples of group 1), titanium nitride close to the stoichiometric composition and solid solution of Al in α-Ti are
formed, while at U
b = 120 V (group 2), nonstoichiometric titanium nitride and complex nitride (Ti, Al)N are formed. The hardness and elasticity
modulus for coatings of group 1 were equal to 23.8 GPa and 462 GPa, and for group 2 they were 30.8 GPa and 565 GPa, respectively.
The latter are characterized by a level of adhesion strength of 53–55 N as opposed to 39–40 N for coatings of group 1. Qualification
tests for the durability of the cutting tool with developed coatings are performed. For example, upon turning steel 45, it
increases by a factor of 6.3 and for gray cast iron it increases by a factor of 5; during end milling cut of the EI 698-VD
alloy it increases by a factor of 2.5. 相似文献
14.
G. S. Vinod kumar M. Chakraborty F. Garcia-Moreno J. Banhart 《Metallurgical and Materials Transactions A》2011,42(9):2898-2908
A novel foamable aluminum alloy has been developed. It contains sub-micron-sized MgAl2O4 (spinel) particles that are generated in situ by a reaction of SiO2 with a molten Al-Mg alloy. The study involves an optimization of parameters such as Mg concentration, SiO2 particles size, and reaction time and shows that a composite containing MgAl2O4 particles as chief reinforcement in the matrix leads to effective foaming. Composites containing large sized transition phases
and particle agglomerates in the matrix yield poor foam structure. The best foamable composite obtained contained 3.4 vol.
pct of ultrafine (80 nm to 1 μm) MgAl2O4 particles uniformly distributed in an Al-Si alloy matrix. The corresponding metal foam contained 75 pct porosity and exhibited
a uniform distribution of cells. 相似文献
15.
L. V. Artyukh O. A. Belous A. A. Bondar M. P. Burka T. Ya Velikanova N. I. Tsyganenko 《Powder Metallurgy and Metal Ceramics》1997,36(1-2):15-23
We have investigated alloys in the Cr-Mo-Ti-C, Cr-Re-Ti-C, and Cr-Mo-Re-Ti-C systems in the eutectic <Cr>+<TiC> crystallization
region. We found a four component quasibinary eutectic <Cr, Mo>+<TiC> with 4–8 at. % molybdenum content with melting point
1630°C. Additions of 3–11 at. % Mo or 5–20 at. % Re to the base eutectic alloy Cr79Ti12C9 doubles the Vickers hardness at 1000°C (to approximately 2000 MPa), and simultaneous introduction of molybdenum and rhenium
(the alloy Cr51Mo8Re20Ti12C9) raises the hardness to 3000–3500 MPa.
Ukrainian Materials Science Institute, National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos.
1–2, pp. 15–23, January–February, 1997. 相似文献
16.
Aging of composite materials (CMs) based on an aluminum D16 alloy and reinforced by Al3Ti intermetallic inclusions (0–10 vol %) having formed upon an in situ reaction and by SiC particles (0–30 vol %) ≤3 or 28
μm in size is studied. Oxide ceramic nanoparticles (0.1 wt %) are used to modify the structure of the CMs. The structures
of the CMs before and after aging are analyzed by optical microscopy and scanning electron microscopy on a microscope equipped
with an X-ray energy dispersive spectrometer. The hardness of the CMs is measured. The overall hardening of aged CMs is shown
to result from a competition between the hardening effects induced by the formation of Guinier-Preston zones and the precipitation
of the high-temperature θ and S phases. These effects are controlled by the dislocation density in the matrix. 相似文献
17.
S. Saroja M. Vijayalakshmi Baldev Raj 《Transactions of the Indian Institute of Metals》2008,61(5):389-398
An alloy of Titanium with 5% Tantalum and 1.8% Niobium has been developed which possesses high corrosion resistance in highly
oxidising environments. The microstructural basis that enabled design of optimum thermo-mechanical treatments has been established
for this alloy. The classification of the alloy, transformation temperatures and different types of phase transformations
were evaluated for the first time by experimental methods like metallography and calorimetry and empirical methods. Systematic
microstructural modifications were introduced by thermo-mechanical treatments to improve corrosion resistance and mechanical
properties. The Ti-5Ta-1.8Nb alloy exhibited interesting texturing behaviour. Deformation and transformation textures exhibited
during unidirectional cold rolling and subsequent β→α+β transformation were studied using XRD and Electron Back Scatter Diffraction
techniques. The cross section of a wire drawn specimen exhibited (1 0–1 0)α texture while a cold rolled specimen showed (0 0 0 2)α deformation texture along the length — width direction. The transformation texture by itself was found to be dependent on
the type of deformation texture, (1 1 −2 0)α in cold rolled and (1 1 −2 2)α texture in the case of wire drawn alloy. A new method has been proposed to determine theoretical misorientation angle and
axis between variants of hcp a product transforming from a parent bcc crystal, obeying Burgers Orientation Relationship. The
role of variant selection mechanisms in the final texture of the alloy has been demonstrated by comparison of texture maps
obtained by X-ray Diffraction with those computed. 相似文献
18.
The behavior of a Ni-Cr-Co base alloy with significant additions of Mo, Ti and Al (Nimonic 105) under hot working conditions
was studied using hot compression tests in the temperature range of 1223 to 1523 K and strain rates between 0.38 and 64.3
s-1.
The microstructure of the Nimonic 105 is complex and the matrix contains second phases in the form of Ni3 (Ti, Al) dispersion (γ′), various Cr and Ti carbides and titanium cyanonitrides inclusions.
However, the results show that above the dissolution temperature of the γ′ phase, the alloy behaves like a single phase nickel-base
solid solution from the point view of steady state flow stress-temperature-strain rate relationships, and the activation energies
for hot working and static recrystallization.
Under deformation conditions where the γ′ phase is present, as in the case of creep, the activation energy is almost doubled.
The hot working temperature range giving sound product is 1280 to 1450 K (170 K) at a strain rate of 0.4 s-1 and decreases to 1400 to 1480 K (80 K) at a strain rate of 65 s-1. At temperatures above the higher limit the alloy suffers intercrystalline cracks due to hot shortness and at temperatures
below the lower limit the alloy suffers transcrystalline cracks due to excessive strain hardening. 相似文献
19.
G. Frommeyer W. Kowalski R. Rablbauer 《Metallurgical and Materials Transactions A》2006,37(12):3511-3517
A rapidly solidified and thermomechanically processed fine-grained eutectic NiAl−Cr alloy of the composition Ni33Al33Cr34 (at, pct) exhibits structural superplasticity in the temperature regime from 900°C to 1000°C at strain rates ranging from
10−5 to 10−3 s−1. The material consists of a B2-ordered intermetallic NiAl(Cr) solid solution matrix containing a fine dispersion of bcc chromium.
A high strain-rate-sensitivity exponent of m=0.55 was achieved in strain-rate-change tests at strain rates of about 10−4 s−1. Maximum uniform elongations up to 350 pct engineering strain were recorded in superplastic strain to failure tests. Activation
energy analysis of superplastic flow was performed in order to establish the diffusion-controlled dislocation accommodation
process of grain boundary sliding. An activation energy of Q
c=288±15 kJ/mole was determined. This value is comparable with the activation energy of 290 kJ/mole for lattice diffusion of
nickel and for 63Ni tracer selfdiffusion in B2-ordered NiAl. The principal deformation mechanism of superplastic flow in this material is grain-boundary
sliding accommodated by dislocation climb controlled by lattice diffusion, which is typical for class II solid-solution alloys.
Failure in superplastically strained tensile samples of the fine-grained eutectic alloy occurred by cavitation formations
along NiAl‖‖Cr interfaces. 相似文献
20.
Y. Wu S. K. Hwang J. W. Morris Jr. 《Metallurgical and Materials Transactions A》2003,34(10):2077-2087
The Y modification of a two-phase (γ+α
2) TiAl-(Mn,Mo,C) alloy was studied with an aim to improve, mainly, the oxidation resistance and the mechanical properties
in a high-temperature air environment. The experimental alloy was prepared by the elemental powder metallurgy (EPM) method.
The addition of up to 0.6 at. pct Y resulted in a significant improvement in tensile properties and compressive yield strength
and an anomalous yielding phenomenon withal. Two structural characteristics were identified: first, microstructural refinement
in terms of the grain size as well as the interlamellar spacing, and second, precipitation of fine oxides that might scavenge
harmful oxygen. Deformation was found to be mainly provided by 1/2<110] ordinary dislocations and a much lesser amount of
<011] superdislocations as compared to what has been reported in other (γ+α
2) TiAl alloys. The oxidation resistance of the experimental alloy was evaluated by air-exposure tests at 800 °C, from which
the oxidation kinetics and the morphological and phase characteristics of the oxide scales were analyzed. With a Y addition,
the constituents of the oxide scale changed from those of the Y-free alloy. In the case of the Y-free alloy, the oxide scale
which formed upon extended air exposure (350 hours) at 800 °C consisted of a mixture of TiO2 and α-Al2O3. In the case of the alloy modified with Y (0.6 at. pct), however, the oxide scale formed in an identical environment was
considerably different: it consisted of a complex mixture of TiO2, α-Al2O3, Y2O3, and Al5Y3O12. The formation of the multiphase (Y,Al)O-rich oxide scale impedes the oxygen transport and the thermal-expansion stress in
the Al2O3 layer. It is also suggested that a Y addition reduces the oxygen solubility and concentration of oxygen vacancices in the
TiO2 layer.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献