共查询到20条相似文献,搜索用时 46 毫秒
1.
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
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.
R. Benedek D. N. Seidman C. Woodward 《Metallurgical and Materials Transactions A》2003,34(10):2097-2101
Among the additives to TiAl alloys that have been investigated in recent years with the objective of improving high-temperature
mechanical properties, particular attention has been given to carbon, which forms the carbide precipitates Ti3AlC (cubic perovskite) and Ti2AlC (hexagonal). Using the first-principles density-functional-theory code VASP, calculations of host-precipitate interface
energies were performed for these two carbides. Calculations were first applied to coherent interfaces to determine the favored
termination layers and parallel translation states. For the favored interface configurations, a correction is applied for
the effect of misfit, to obtain an estimated interface energy for semicoherent interfaces. The correction is based on an approximate
formulation recently presented by the authors. The perovskite is found to have a lower interface energy than the hexagonal
phase, consistent with the experimental finding that the former nucleates homogeneously and the latter inhomogeneously.
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.
N. N. Sereda L. N. Beloborodov I. A. Lavrinenko V. V. Poluyanskaya 《Powder Metallurgy and Metal Ceramics》1999,38(1-2):89-92
Wetting and contact interaction of (TiC−Mo2C)−(Ni−Mo) cemented carbides by molten copper, nickel, iron and their alloys and also by the cupronickel alloy, cast iron,
and steel melts is investigated. The results show that good wetting and intensive interfacial interaction for the cemented
carbides in question was observed in the case of iron and nickel, their alloys with copper, cast iron, and steel. These materials
are recommended for metallic binders in the preparation of composite materials—based on tungsten-free hard alloy.
Deceased.
Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya,
Nos. 1–2(405), pp. 98–101, January–February, 1999. 相似文献
5.
In situ observation of the bainite carbide precipitation processes in 40CrMnSiMoV steel by means of high-temperature transmission
electron microscopy (TEM) is conducted. It is evident that carbides can precipitate either in bainitic ferrite or from austenite
when carbide-free bainite (meta-bainite) obtained by isothermal transformation is tempered at higher temperatures. In view
of the quantity of carbides precipitated from ferrite in combination with the result of an X-ray diffraction analysis of the
bainitic ferrite carbon content, it can be concluded that bainitic ferrite growth involves supersaturation of carbon content
to some degree.
Formerly with Northwestern Polytechnical University
Formerly with Northwestern Polytechnical University
This paper is based on a presentation made in the symposium “International Conference on Bainite” presented at the 1988 World
Materials Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations
Committee and the TMS Ferrous Metallurgy Committee. 相似文献
6.
Peravudh Lowhaphandu John J. Lewandowski 《Metallurgical and Materials Transactions A》1999,30(2):325-334
The effects of Cu infiltration on the monotonic fracture resistance and fatigue crack growth behavior of a powder metallurgy
(P/M) processed, porous plain carbon steel were examined after systematically changing the matrix strength via heat treatment. After austenitization and quenching, three tempering temperatures were chosen (177 °C, 428 °C, and 704 °C)
to vary the strength level and steel microstructure. The reductions in strength which occurred after tempering at the highest
temperature were accompanied by the coarsening of carbides in the tempered martensitic steel matrix, as confirmed by optical
microscopy and by microhardness measurements of the steel. Each steel-Cu composite, containing approximately 10 vol pct infiltrated
Cu, had superior fracture toughness and fatigue properties compared to the porous matrix material given the same heat treatment.
Although the heat treatments given did not significantly change the fatigue behavior of the porous steel specimens, the fatigue
curves (da/dN vs ΔK) and fracture properties were distinctly different for the steel-Cu composites given the same three heat treatments. The
fracture toughness (K
IC
and J
IC
), tearing modulus, and ΔK
TH
values for the composites were highest after tempering at 704 °C and lowest after tempering at 177 °C. In addition, the fracture
morphology of both the fracture and fatigue specimens was affected by changes in strength level, toughness, and ΔK. These fractographic features in fatigue and overload are rationalized by comparing the size of the plastic zone to the microstructural
scale in the composite.
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
7.
W. Salas N.G. Alba-Baena L.E. Murr 《Metallurgical and Materials Transactions A》2007,38(12):2928-2935
The formation of conventional metal-matrix composites reinforced with carbon nanotubes (CNTs) has proven difficult because
of the agglomeration and inability of CNTs to disperse. We have explored the explosive consolidation of 150-μm aluminum powder/multiwalled carbon nanotube (MWCNT) aggregates (including multiconcentric fullerenes) at volume percentages
of 2 and 5 pct. These consolidated mixtures formed two-phase, monolithic systems (TPSs) with the MWCNT aggregate material
spreading along the Al grains and forming carbon phases mainly at the Al particle triple points. The Al powder particle (or
grain) hardness increased from HRE 22 to HRE 40 for the consolidated Al, while the two-phase system hardness dropped from
HRE 40 to HRE 39 and 33, respectively, for 2 and 5 vol pct MWCNT aggregate additions. Transmission electron microscopy (TEM)
and scanning electron microscopy (SEM) observations illustrate a laminate-like structure of the consolidated MWCNT aggregate
material, which is easily delaminated, causing intergranular (Al) failure. The Al grains exhibited a shock-induced dislocation
substructure (0.5 to 3 μm) and recrystallized subgrains, which increased the individual particle/grain Vickers hardness from 24 to 43 HV.
This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during
the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals,
Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. 相似文献
8.
Xiaodan Zhang Wei Liu Dale Sun Youguo Li 《Metallurgical and Materials Transactions A》2007,38(3):499-505
The transformation of carbides with austenization time of a high speed steel (HSS) roll material, manufactured by a centrifugal
casting method, has been studied. The correlation between wear resistance and the type, morphology, volume fraction, and distribution
of the carbides has also been investigated. Microstructural observations, X-ray diffraction (XRD) analysis, hardness measurements,
and energy dispersive spectroscopy (EDS) have been used to characterize the carbides. The type and volume fraction of carbides
were found to change with austenizing time. During austenization, the transformation of the M3C carbides can be postulated as M3C + γ-Fe → M2C, with much finer nodular and rodlike MC carbides also forming through a solid-state transformation. The M2C carbide decomposes as M2C + γ-Fe → MC + M7C3 + M6C. The decomposed carbide substantially maintains a platelike shape until the end of decomposition. The most important finding
of this study is that austenization results in changes in the type, morphology, volume fraction, and distribution of carbides
and that it can be controlled to produced a homogeneous distribution of hard carbides, resulting in an improvement in the
wear resistance of HSS rolls. This finding may be of great use for the industrial production of HSS rolls. 相似文献
9.
10.
Harue Wada 《Metallurgical and Materials Transactions A》1986,17(3):391-398
The solubility of carbon and the composition of carbides in the ferritic Fe-Mo-C system were measured at 985 K by a gas flowing
method and a sealing method. The composition of alloys ranged from 0.24 pct to 2.93 pct Mo. An iron-carbon binary alloy was
included in the equilibration as a reference material. The molybdenum-carbon interaction in the α-phase was analyzed by the
central atoms model. The Wagner interaction coefficient was determined as ε
c
Mo
= •100 ± 2, which is a higher negative value than that in the Fe-Cr-C system at the same temperature. The carbide phase was
analyzed as a regular solution of two component carbides, FeC
x
and MoC
x
. M6C carbide was in equilibrium with α in the carbon activity range from 0.045 to 0.156, and M2C carbide was in equilibrium at the carbon activity 0.51. M6C and M2C carbides were present at the carbon activity 0.45. Molybdenum partitioning between α- and carbide phases was measured. The
standard free energies of formation of two component carbides and the interaction energy parameters were determined for M6C and M2C carbides. 相似文献
11.
S. C. Jha R. G. Delagi J. A. Forster P. D. Krotz 《Metallurgical and Materials Transactions A》1993,24(1):15-20
Copper-niobium microcomposites are a new class of high-strength high-conductivity materials that have attractive properties
for room- and elevated-temperature applications. Since Nb has little solid solubility in Cu, addition of Nb to Cu does not
affect its conductivity. Copper-niobium microcomposites are melted and cast so that the microstructure of cast Cu-Nb ingots
consists of 1-to 10μm Nb dendrites uniformly distributed within the copper matrix. Extensive wire drawing with a true processing strain (η > 12) of Cu-Nb alloy leads to refinement and elongation of Nb dendrites into 1-to 10 nm-thick filaments. The presence of
such fine Nb filaments causes a significant increase in the strength of Cu-Nb wires. The tensile strength of heavily drawn
Cu-Nb wires was determined to be significantly higher than the values predicted by the rule of mixtures. This article reports
the fabrication of high-strength Cu-Nb micro-composite sheet by multiple roll bonding. It is difficult and impractical to
attain high processing strains (η > 3) by simple cold rolling. In most practical cold-rolling operation, the thickness reduction does not exceed 90 pct (η ≅ 2). Therefore, innovative processing is required to generate high strength in Cu-Nb microcomposite sheet. Multiple roll
bonding of Cu-Nb has been utilized to store high processing strain (η > 10) in the material and refine the Nb particle size within the copper matrix. This article describes the microstructure,
mechanical properties, and thermal stability of roll-bonded Cu-Nb microcomposite sheet.
This article is based on a presentation made in the symposium “High Performance Copper-Base Materials” as part of the 1991
TMS Annual Meeting, February 17–21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee. 相似文献
12.
A mechanism for the formation of lower bainite 总被引:2,自引:0,他引:2
G. Spanos H. S. Fang H. I. Aaronson 《Metallurgical and Materials Transactions A》1990,21(6):1381-1390
A diffusional mechanism for the formation of lower bainite is proposed based primarily on transmission electron microscopy
(TEM) observations of isothermally reacted specimens of Fe-C-2 pct Mn alloys. The mechanism involves the initial precipitation
of a nearly carbide-free ferrite“spine,” followed by sympathetic nucleation of“secondary (ferrite) plates” which lie at an
angle to the initial“spine.” Carbide precipitation subsequently occurs in austenite at ferrite: austenite boundaries located
in small gaps between the“secondary plates.” An“annealing” process then occurs in which the gaps are filled in by further
growth of ferrite and additional carbide precipitation; the annealing out of ferrite: ferrite boundaries between impinged“secondary
plates” completes this process. This annealing stage contributes to the final appearance of lower bainite sheaves as monolithic
plates containing embedded carbides. The present mechanism accounts for the single variant of carbides oriented at an angle
to the sheaf axis repeatedly reported in lower bainite; it is also consistent with the previous observation of one“rough”
side and one“smooth” side of lower bainite“plates.”
Formerly Graduate Student, Carnegie Mellon University.
Formerly Visiting Professor, Carnegie Mellon University.
This paper is based on a presentation made in the symposium“International Conference on Bainite” presented at the 1988 World
Materials Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations
Committee and the TMS Ferrous Metallurgy Committee. 相似文献
13.
Feng Jiang Hongqi Li Guojiang Fan Yandong Wang Peter K. Liaw Hahn Choo 《Metallurgical and Materials Transactions A》2008,39(8):1817-1821
Three types of Ti-based alloys (an amorphous material, an amorphous composite with intermetallic crystals, and an intermetallic
compound) of the compositions Ti41.5Zr2.5Hf5Cu42.5−x
Ni7.5+x
Si1 (x = 0, 5, and 15) were fabricated to study the effect of composition on glass formability and microstructure, and the dependence
of mechanical properties on microstructure were investigated at room temperature. The results show that the amorphous composite
has an excellent combination of both ultrahigh strength (2245 MPa) and large plastic strain (9 pct), which is a significant
improvement compared to both the fully amorphous and intermetallic structures. In addition, it is also found that the crystal
phases in the amorphous matrix can obstruct the shearing-off of the shear bands by inducing them to interact, deflect, and
branch, resulting good plasticity in the amorphous composite.
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
14.
O. Muránsky P. Šittner J. Zrnik E.C. Oliver 《Metallurgical and Materials Transactions A》2008,39(13):3097-3104
Tensile deformation behavior of two transformation-induced plasticity (TRIP)–assisted multiphase steels with slightly different
microstructures due to different thermomechanical treatment conditions applied was investigated by in-situ neutron diffraction. The steel with lower austenite volume fraction (f
γ
= 0.04) and higher volume fraction of needlelike bainite in the α-matrix exhibits higher yield stress (sample B, 600 MPa) but considerably lower elongation in comparison to the steel with
higher austenite volume fraction (f
γ
= 0.08), granular bainite, and polygonal ferrite matrix (sample A, 500 MPa). The neutron diffraction results have shown that
the applied tensile load is redistributed at the yielding point in such a way that the retained austenite bears a significantly
larger load than the α matrix during the TRIP-assisted steel deformation.
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
15.
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
16.
P. J. Mcginn P. Kumar A. E. Miller A. J. Hickl 《Metallurgical and Materials Transactions A》1984,15(6):1099-1102
Constitutive liquid phase sintering is used to obtain fully dense parts of powdered STELLITE Alloy No. 6 PM (Co-29Cr-4.5W-l.2C-
< 1B) with excellent wear resistance at elevated temperature. This alloy is characterized by a cobalt-rich fcc solid solution
and interdendritic carbide phases in the as-atomized state. Compositional changes in the carbides prior to, and during, the
liquid phase sintering were investigatedvia X-ray diffraction, optical microscopy, and Auger electron spectroscopy. The rejection of boron and cobalt by an M23C6-type carbide was identified as leading to the local formation of the liquid phase. A mechanism for the interactive role of
the carbide composition change and the constitutive liquid phase sintering is proposed.
This paper is based on a presentation delivered at the symposium “Activated and Liquid Phase Sintering of Refractory Metals
and Their Compounds” held at the annual meeting of the AIME in Atlanta, Georgia on March 9, 1983, under the sponsorship of
the TMS Refractory Metals Committee of AIME. 相似文献
17.
Successful application of “transformation-toughening” to cemented carbides is demonstrated in the system WC-(Fe, Ni, C). Strict
control of the chemical composition of the binder and careful consideration to the effects of thermal residual stress and
the constraint imposed by the surrounding carbide grains are essential for achieving the desired degree of metastability of
the binder phase that can lead to enhancements in the hardness/fracture toughness behavior of this class of cemented carbides.
Formerly Manager, Research-Development, Reed Tool Company, Houston, TX. 相似文献
18.
19.
S. Kar T. Searles E. Lee G. B. Viswanathan H. L. Fraser J. Tiley R. Banerjee 《Metallurgical and Materials Transactions A》2006,37(3):559-566
The development of a set of computational tools that permit microstructurally based predictions for the tensile properties
of commercially important titanium alloys, such as Ti-6Al-4V, is a valuable step toward the accelerated maturation of materials.
This paper will discuss the development of neural network models based on a Bayesian framework to predict the yield and ultimate
tensile strengths of Ti-6Al-4V at room temperature. The development of such rules-based model requires the population of extensive
databases, which in the present case are microstructurally based. The steps involved in database development include producing
controlled variations of the microstructure using novel approaches to heat treatments, the use of standardized stereology
protocols to characterize and quantify microstructural features rapidly, and mechanical testing of the heat-treated specimens.
These databases have been used to train and test neural network models for prediction of tensile properties. In addition,
these models have been used to identify the influence of individual microstructural features on the tensile properties, consequently
guiding the efforts toward development of more robust mechanistically based models. Based on the neural network model, it
is possible to investigate the influence of individual microstructural features on the tensile properties, and in certain
cases these dependencies can point toward unrecognized phenomena. For example, the apparently unexpected trend of increase
in tensile strength with increasing prior β-grain size has led to the determination of the pronounced role of the basketweave microstructure in strengthening these alloys,
especially in case of larger prior β grains.
This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,”
which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational
Materials Science & Engineering (Jt. ASM-MSCTS) Committee. 相似文献
20.
Placid Rodriguez 《Metallurgical and Materials Transactions A》2004,35(9):2697-2705
A critical review of available results on the dependence of grain size on the activation parameters for deformation, specifically,
the activation volume, V*, and the thermal component of flow stress, σ*, has been carried out with a view to verifying the Armstrong prediction that identifies the Hall-Petch (H-P) intercept with
the easy slip system and the H-P slope with the most difficult system in polycrystals. The influence of slip system choice
is demonstrated using results on Cd and Zr. The Armstrong prediction is valid for basal slip hcp metals, such as Cd and Zn,
with V* and σ* determined by the difficult pyramidal slip. For the prism slip metals such as Zr and Ti, V* and σ* are controlled by interstitial solutes and are independent of grain size. The results on Zr are used to highlight the influence
of dynamic strain aging on the H-P parameters. In bcc metals, in which the Peierls-Nabarro barrier is the rate-controlling
obstacle, V* and σ* are again independent of grain size. For fcc metals, correlation of the H-P slope with the cross-slip stress, predicted
by the Armstrong model, has been demonstrated for a few cases. The variation of V* with grain size in Ni as reported by Narutani and Takamura (Acta Metall. Mater., 1991, vol. 227, pp. 2037–49) is newly interpreted in terms of the Armstrong model that associates the H-P intercept in fcc
metals with dislocation intersections and the H-P slope with cross-slip, and provides realistic results for the activation
volumes for the two processes.
This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and
Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California,
under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee. 相似文献