共查询到20条相似文献,搜索用时 31 毫秒
1.
John C. Woo S. K. Varma R. N. Mahapatra 《Metallurgical and Materials Transactions A》2003,34(10):2263-2271
Quaternary additions of 2 at. pct of Ta or Zr were made to the ternary Ti-44Al-xNb (X=9 and 11) alloys to study the oxidation behavior at 900 °C, 950 °C, and 1000 °C for a period of 1 week. The Ta addition improves
the oxidation resistance, while it is degraded by Zr compared to the ternary alloys. Identification of the oxides formed in
the scale has been characterized by energy-dispersive atomic X-ray (EDAX) in a scanning electron microscope (SEM). The transmission
electron microscope (TEM) analysis of the microstructures developed during oxidation has been compared with Ti-44Al-xNb alloys in order to determine the influence of quaternary additions of Ta and Zr on the phase transformations taking place
during the extended period of heating. The formation of spotty α
2 in the isolated γ grains appears to be associated with the inferior oxidation resistance of xNb2Zr alloys.
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
2.
Interstitial additions and precipitation hardening in fully lamellar gamma TiAl have been investigated in recent years, with
a prime objective of improving the high-temperature creep resistance. As a result of this alloy development effort, the alloy
system K5 (Ti46Al-2Cr-3Nb-0.2W) was found to show remarkably improved creep resistance when reinforced with C or C+Si additions
and then aged appropriately. Precipitation strengthening is the proposed mechanism accounting for the observed creep strengthening
of K5SC alloys, with emphasis being paid on the effect of B2 particles, ζ-type silicides, and H-type carbide precipitates delineating γ/γ interfaces. In this study, the creep-deformed microstructures of fully lamellar K5 (S-C)-type alloys in aged and unaged conditions
were characterized using detailed electron microscopy, involving high-resolution imaging techniques and in-situ heating studies. Overall, the presence of these particles and their relative distribution result in strengthening of the
lamellar structure. The particular effect of each type of precipitate (silicides vs carbides) on creep has been assessed. New information about the nature of the light-element precipitation processes has been
obtained by studying the nucleation and growth of the carbide and silicide precipitates at the expense of dissolving α
2 laths during aging.
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
3.
L. Singheiser L. Niewolak V. Shemet W. J. Quadakkers U. Flesch 《Metallurgical and Materials Transactions A》2003,34(10):2247-2251
Alloys based on γ-TiAl are promising high-temperature materials that may replace conventional heat-resistant steels and superalloys in applications
where high strength in combination with low density is required. However, an important hindrance to the use of γ-TiAl alloys at high temperatures is their relatively poor oxidation resistance and sensitivity against environmentally induced
embrittlement. This material degradation is related to the poor protective properties of the mixed TiO2/Al2O3 surface scales which form on the surface during high-temperature exposure. Recently, it was shown that protective alumina
scale formation on γ-TiAl can be obtained by small additions of Ag. This effect was found to be related to the formation of Z phase in the subscale
depletion layer at the expense of α
2-Ti3Al. It was found that the beneficial effect of Ag can be suppressed if the alloys contain additional α
2-stabilizing elements, such as Nb, as is the case for most (semi)commercial, high-strength alloys. Therefore, recent efforts
have concentrated on developing Ag-containing γ-TiAl alloys as oxidation-resistant coatings for high-strength titanium aluminides. Preliminary results using magnetron sputtering
have shown that, due to the similarities in chemical and physical properties of the coating and base material, the Ag-containing
material offers promising potential to be qualified as a coating material for reducing the oxidation-induced degradation of
titanium aluminides.
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
4.
D. L. Davidson K. S. Chan D. L. Anton 《Metallurgical and Materials Transactions A》1996,27(10):3007-3018
Niobium-chromium alloys, both single and two phase, were alloyed with titanium in order to enhance fracture toughness and
fatigue crack growth resistance. The selection of titanium as an alloying element and the relationship of electronic bonding
to toughness are examined. The results indicated that toughness increased with a decreasing number of D +s electrons. Titanium was found to increase the toughness of solid-solution Nb-Cr alloys from ≈8 to 87 MPa√m, while for the
twophase “insitu composites,” toughness was increased from ≈5 to 20 MPa√m, although this is less than expected. Fracture toughness of the
composites correlated nonlinearly with the volume fraction of the phases. The evidence suggests that the toughness of the
composites is decreased due to fracture of the intermetallic particles and constraint on matrix deformation imposed by the
intermetallic. Fracture characteristics of the Nb-Cr-Ti materials are compared to those of Nb-Cr and Nb-Si materials. 相似文献
5.
M. Yoshihara S. Taniguchi Y. -C. Zhu 《Metallurgical and Materials Transactions A》2003,34(10):2253-2261
Ion implantation was applied to a gamma TiAl alloy, and the oxidation behavior of the alloy implanted with B, P, Fe, or W
was investigated through a cyclic oxidation test at 1200 K in a flow of purified oxygen under atmospheric pressure. Metallographic
examinations were performed for the implanted specimens and the oxidized specimens using X-ray diffractometry (XRD), Auger
electron spectroscopy (AES), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The β phase was detected along with γ-TiAl in the Fe- or W-implanted specimens, while γ-TiAl was the predominant phase for the B- or P-implanted specimens. The implantation of P, Fe, or W significantly improved
the oxidation resistance, provided the ion dose was sufficient, whereas the implantation of B enhanced scale spallation, resulting
in deteriorated oxidation resistance. The AES profiles for the specimens oxidized for a very short period strongly suggested
the incorporation of P or W in TiO2. The possible mechanisms for the improvement are discussed on the basis of the results obtained for the implanted alloys.
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
6.
Transition-metal trialuminide intermetallics such as Al3Zr and Al3Ti, having low densities and high elastic moduli, are good candidates for the in-situ reinforcement of light-metal matrices based on Al and Mg alloys. In this work, in-situ composites based on Al and Al-Mg matrices reinforced with an Al3Zr intermetallic were successfully processed by conventional ingot metallurgy. The microstructural studies showed that “needle”
or “feathery”-like particles of Al3Zr phase, whose volume fraction increased with increasing concentration of Zr, were formed in the Al matrix in the investigated
range of Zr contents from 0.9 to 11.6 at. pct. Properties of Al-Zr alloys were investigated as a function of volume fraction
of Al3Zr. It is shown that the density, hardness, and yield strength of the in-situ Al/Al3Zr composites can be quite adequately described by the composite rule-of-mixtures (ROM) behavior. Alloying of a binary Al-2.4
at. pct Zr alloy with Mg up to ∼25 at. pct reduces profoundly its density and, additionally, strengthens the matrix by a Mg
solid-solution strengthening mechanism. 相似文献
7.
F. Appel J. D. H. Paul M. Oehring U. Fröbel U. Lorenz 《Metallurgical and Materials Transactions A》2003,34(10):2149-2164
For high-temperature applications, creep strength is of major concern, in addition to oxidation and corrosion resistance,
and determines the application range of titanium aluminide alloys in competition with other structural materials. Thus, this
work was aimed at identifying mechanisms of creep deformation and microstructural degradation and at developing alloying concepts
with respect to an enhanced high-temperature capability. The analysis shows that dislocation climb controls deformation in
the range of the intended operation temperatures. Further, complex processes of phase transformations, recrystallization,
and microstructural coarsening were observed, which contribute to microstructural degradation and limit component life in
long-term service. By alloying with high contents of Nb, both room- and high-temperature strength properties can be improved
as Nb increases the activation energy of diffusion and increases the propensity for twinning at ambient temperature. For alloys
with enhanced high-temperature capability, microalloying with carbon is also of particular use, because carbide precipitates
effectively hinder dislocation motion and are thought to increase microstructural stability.
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
8.
M. Wenderoth U. Glatzel R. Völkl L. A. Cornish R. Süss S. Vorberg B. Fischer 《Metallurgical and Materials Transactions A》2005,36(3):567-575
The objective of this work is to mimic the microstructure and strengthening mechanisms of Ni-based superalloys in a new group
of high-temperature alloys based on the system Pt-Al. The elements Cr and Ni were chosen as further alloying components. Having
a face-centered cubic (fcc) crystal structure with an Ll2-ordered and coherently embedded phase, these new alloys should increase creep and corrosion resistance beyond Ni-based superalloys.
After arc melting and heat treatment, the alloys were investigated by means of scanning electron microscopy (SEM) and X-ray
diffraction (XRD). In the aged condition, the alloy composition 13 at. pct Al, 3 at. pct Cr, 7 at. pct Ni, and balance Pt
showed the most promising microstructure with cubical precipitates, 30 pct precipitate volume fraction, and a lattice misfit
of about −0.1 pct at room temperature.
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
9.
B. P. Bewlay M. R. Jackson H. A. Lipsitt 《Metallurgical and Materials Transactions A》1996,27(12):3801-3808
This article describes room-temperature and high-temperature mechanical properties, as well as oxidation behavior, of a niobium-niobium
silicide basedin situ composite directionally solidified from a Nb-Ti-Hf-Cr-Al-Si alloy. Room-temperature fracture toughness, high-temperature
tensile strength (up to 1200 °C), and tensile creep rupture (1100 °C) data are described. The composite shows an excellent
balance of high- and low-temperature mechanical properties with promising environmental resistance at temperatures above 1000
°C. The composite microstructures and phase chemistries are also described. Samples were prepared using directional solidification
in order to generate an aligned composite of a Nb-based solid solution with Nb3Si- and Nb5Si3-type silicides. The high-temperature mechanical properties and oxidation behavior are also compared with the most recent
Ni-based superalloys. This composite represents an excellent basis for the development of advanced Nb-based intermetallic
matrix composites that offer improved properties over Ni-based superalloys at temperatures in excess of 1000 °C. 相似文献
10.
S. S. Babu E. D. Specht M. L. Santella G. E. Ice S. A. David 《Metallurgical and Materials Transactions A》2006,37(1):195-205
The effects of the as-cast microstructure on the oxidation characteristics of two Ni-Al-Cr alloys with either γ or γ′ primary
solidification were investigated with an in-situ, time-resolved X-ray diffraction (TRXRD) technique using synchrotron radiation. The measurements, carried out during rapid
heating and cooling, showed that a segregated microstructure in these cast alloys leads to the preferential formation of zirconium
oxide before the formation of aluminum oxides is detected. The oxidation leads to a change in the phase stability and to the
modification of surface microstructures. Computational thermodynamic models were used to explain the preferential formation
of oxides in the as-cast microstructure. 相似文献
11.
The microstructure and strength at 1473 and 2073 K and creep properties at 2073 K were investigated in three Ir-Nb-Zr alloys
with the fcc and L12 two-phase structure. The microstructure and lattice misfit were investigated using scanning electron microscopy (SEM), transmission
electron microscopy (TEM), and X-ray diffractometry (XRD). Compression and creep tests were performed, and their deformation
structures were observed using SEM and TEM. At 1473 K, the strength of the Ir-Nb-Zr alloys was higher than that of the binary
Ir-Nb and Ir-Zr alloys, but they were almost equivalent at 2073 K. However, the ternary alloys showed great improvement on
creep at 2073 K. The time for the 2 pct creep strain of the Ir-Nb-Zr alloy was about 100 hours, while it was 1 hour for the
binary alloys. The deformation mechanisms for compressive strength and creep resistance in these Ir-Nb-Zr alloys are discussed
in terms of the deformation structure.
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
12.
合金化及涂层技术提高铌基合金的抗高温氧化性能 总被引:1,自引:0,他引:1
综述了铌基合金的成分设计及抗高温氧化研究的现状,对铌基合金包埋渗法制备涂层研究的进展及存在的问题进行了阐述,提出了解决铌基合金抗高温氧化性能差的可能途径。 相似文献
13.
Robert V. Miner 《Metallurgical and Materials Transactions A》1977,8(12):1949-1954
Cast specimens of nickel-base superalloys 713C and Mar-M200 with nominal additions of 0, 0.5, and 1 wt pct Si were evaluated
for oxidation and corrosion resistance, tensile and stress-rupture properties, microstructure, and phase relations. Results
are com-pared with those of an earlier study of the effects of Si in B-1900. Si had similar effects on all three superalloys.
It improves oxidation resistance but the improvement in 713C and Mar-M200 was considerably less than in B-1900. Hot-corrosion
resistance is also improved somewhat. Si is, however, detrimental to mechanical properties, in particular, rupture strength
and tensile ductility. Si has two obvious microstructural effects. It in-creases the amount of γ precipitated in eutectie
nodules and promotes a Mo(Ni,Si)2 Laves phase in the alloys containing Mo. These microstructural effects do not appear responsible for the degradation of mechanical
properties, however. 相似文献
14.
A. D. Verkhoturov A. M. Shpilev P. S. Gordienko L. A. Konevtsov E. S. Panin I. A. Podchernyaeva A. D. Panasyuk 《Powder Metallurgy and Metal Ceramics》2008,47(1-2):112-115
The paper examines the contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys. It is established
that the oxidation of carbides results from their electronic structure. When WC and hard tungsten alloys are heated to 1000°C,
a brittle scale consisting of WO3 and CoWO4 rapidly forms. The oxidation resistance reduces as follows: TiC → Co → W → HTA (if TiC is more than 10%) → WC-Co → WC. The
oxidation rate of hard tungsten alloys may be a criterion of their serviceability. It is shown that the oxidation resistance
of hard tungsten alloys becomes much higher after their electrospark alloying with aluminum, titanium, and chromium and with
wear-resistant composite TsLAB-2 ceramics based on the ZrB2-ZrSi2-LaB6 system with Ni-Cr-Al (30 mole%) binder.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 145–150, 2008. 相似文献
15.
The primary characteristics of the creep of metal matrix composites (MMCs) are reviewed, including the shapes of the creep
curves, the origin of the threshold stresses, and the nature of the rate-controlling processes. A detailed analysis of two
representative MMCs provides no support for the concept of a constant substructure model for creep with a stress exponent
(n) of 8. Analysis of the data demonstrates that creep is controlled by deformation in the matrix alloys and, as in solid solution
alloys, there is a division into control by viscous glide (class A) and climb (class M), respectively.
This article is based on a presentation made in the symposium “Fatigue and Creep of Composite Materials” presented at the
TMS Fall Meeting in Indianapolis, Indiana, September 14–18, 1997, under the auspices of the TMS/ASM Composite Materials Committee. 相似文献
16.
Gang Wang Yan-Dong Wang Yang Ren Yandong Liu Peter K. Liaw 《Metallurgical and Materials Transactions A》2008,39(13):3184-3190
The full information on the changes in many crystallographic aspects, including the structural and microstructural characterizations,
during the phase transformation is essential for understanding the phase transition and “memory” behavior in the ferromagnetic
shape-memory alloys. In the present article, the defects-related microstructural features connected to the premartensitic
and martensitic transition of a Ni2MnGa single crystal under a uniaxial pressure of 50 MPa applied along the [110] crystallographic direction were studied by
the in-situ high-energy X-ray diffuse-scattering experiments. The analysis of the characteristics of diffuse-scattering patterns around
different sharp Bragg spots suggests that the influences of some defect clusters on the pressure-induced phase-transition
sequences of Ni2MnGa are significant. Our experiments show that an intermediate phase is produced during the premartensitic transition in
the Ni2MnGa single crystal, which is favorable for the nucleation of a martensitic phase. The compression stress along the [110]
direction of the Heusler phase can promote the premartensitic and martensitic transition of the Ni2MnGa single crystal.
This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,”
which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science
Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee. 相似文献
17.
Abdulhaqq A. Hamid S. C. Jain P. K. Ghosh Subrata Ray 《Metallurgical and Materials Transactions B》2006,37(4):519-529
Aluminum alloy—based cast in-situ composite has been synthesized by dispersion of externally added molybdenum trioxide particles (MoO3) in molten aluminum at the processing temperature of 850 °C. During processing, the displacement reaction between molten
aluminum and MoO3 particles results in formation of alumina particles in situ and also releases molybdenum into molten aluminum. A part of this molybdenum forms solid solution with aluminum and the remaining
part reacts with aluminum to form intermetallic phase Mo(Al1−x
Fe
x
)12 of different morphologies. Magnesium (Mg) is added to the melt in order to help wetting of alumina particles generated in situ, by oxidation of molten aluminum by molybdenum trioxide, and helps to retain these particles inside the melt. The mechanical
properties of the cast in-situ composite, as indicated by ultimate tensile stress, yield stress, percentage elongation, and hardness, are relatively higher
than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The wear and friction of the resulting cast
in-situ Al(Mg,Mo)-Al2O3(MoO3) composites have been investigated using a pin-on-disc wear testing machine under dry sliding conditions at different normal
loads of 9.8N, 14.7N, 19.6N, 24.5N, 29.4N, 34.3N, and 39.2 N and a constant sliding speed of 1.05 m/s. The results of the
current investigation indicate that the cumulative volume loss and wear rate of cast in-situ composites are significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy, under similar
load and sliding conditions. Beyond about 30 to 35 N loads, there appears to be a higher rate of increase in the wear rate
in the cast in-situ composite as well as in cast commercial aluminum and cast Al-Mo alloy. For a given normal load, the coefficient of friction
of cast in-situ composite is significantly lower than those observed either in cast commercial aluminum or in cast Al-Mo alloy. The coefficient
of friction of cast in-situ composite increases gradually with increasing normal load while those observed in cast commercial aluminum or in cast Al-Mo
alloy remain more or less the same. Beyond a critical normal load of about 30 to 35 N, the coefficient of friction decreases
with increasing normal load in all the three materials. 相似文献
18.
The transverse stress-strain behavior of several titanium metal-matrix composites (TiMMCs) has been studied in-situ. Debonding of 1140+/Ti-6-4 composites occurs over a range of stresses. The sharpness of the first “knee” is affected by the
fiber volume fraction and by the relative moduli of the matrix regions and the reinforced composite. It has been observed
that debonding occurs mainly at the interface between two sublayers of carbon/carbon coatings in 1140+/Ti-6-4 composites and
mainly at the interface between the carbon/reaction zone in the as-processed and peak-aged 35 pct SCS-6/Tiβ21s composites. At surface positions, this process starts at very low stresses (≥50 MPa) from the positions with sharp changes
of curvatures (or undulations), voids, or debris at the periphery of the interface. Cracking of the outermost carbon sublayer
and of the reaction zone in the 1140+/Ti-6-4 composites and the reaction zone in the SCS-6/Tiβ21s composites occurs during elastic deformation of the matrix. This has been directly observed in a field-emission gun (FEG)-scanning
electron microscope (SEM) under incremental loading. Although these cracks are arrested and blunted by the matrix material,
they cause local stresses and, thus, stimulate local plastic deformation of the matrix and subsequent development of a second
knee on the stress-strain curve. The in-situ observations are discussed in terms of the effects of fiber volume fraction and fiber type on the loci and dynamic processes
of interfacial debonding, cracking of carbon coatings and reaction zones, and plastic deformation of the matrix. 相似文献
19.
Kwangjun Euh Jung-Moo Lee Duk-Hyun Nam Sunghak Lee 《Metallurgical and Materials Transactions A》2011,42(13):3961-3968
The fracture property improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile γ particles was explained by direct observation of microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable
amount of γ particles in β grains after the homogenization treatment at 1073 K to 1373 K (800 °C to 1100 °C). With increasing homogenization temperature,
γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains. According to the in-situ microfracture observation, γ particles effectively acted as blocking sites of crack propagation and provided the stable crack growth, which could be confirmed
by the R-curve analysis. The increase in fracture resistance with increasing crack length improved overall fracture properties of
the Ni-Mn-Ga-Fe alloys. This improvement could be explained by mechanisms of blocking of crack propagation and crack blunting
and bridging. 相似文献
20.
C. Huang Y. Yamabe-Mitarai S. Nakazawa H. Harada X. H. Yu 《Metallurgical and Materials Transactions A》2005,36(3):539-545
Two quanternary systems, Ir-Nb-Ni-Al and Ir-Nb-Pt-Al, were successively investigated to assess their possible use in ultra-high-temperature
applications. The phase relationships concentrated on the fcc/L12 two-phase region were primarily established, and the mechanical properties were studied. Ir-Nb-Ni-Al quaternary alloys around
the Ir-rich or Ni-rich corners of the Ir-Nb-Ni-Al tetrahedron showed a coherent fcc/L12 two-phase structure, analogous to that of Ni-base superalloys; however, most of the alloys presented three or four phases
with two types of L12 phases. Although these alloys showed a high compressive strength at high temperature, they exhibited a higher creep rate
than Ir-base binary and ternary alloys. Another quanternary system, Ir-Nb-Pt-Al, showed promising results. Only an fcc/L12 two-phase structure was found in all the alloys investigated with compositions ranging from the Ir-rich side to the Pt-rich
side, and the lattice misfit between the fcc and L12 phases was small. The high-temperature strength at 1200 °C of Ir-Nb-Pt-Al alloys was higher than that of Ir-Nb-Ni-Al alloys
with the same Ir content (at. pct). Moreover, Ir-Nb-Pt-Al alloys exhibited excellent creep resistance at 1400 °C and 100 MPa.
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