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1.
Zhihong Zhong Yuefeng Gu Yong Yuan Toshio Osada Chuanyong Cui Tadaharu Yokokawa Toshimitsu Tetsui Hiroshi Harada 《Metallurgical and Materials Transactions A》2012,43(3):1017-1025
The influence of solution temperature on the microstructure and mechanical properties of TMW-4M3 superalloy has been investigated.
Comparisons of mechanical properties have also been made between the heat-treated TMW-4M3 variants and the commercial U720Li.
The key microstructural variables examined were grain size and the volume fraction and size of the strengthening γ′ precipitates that control the mechanical properties of these alloys. By increasing the solution temperature from 1373 K
to 1393 K (1100 °C to 1120 °C), the volume fraction of primary gamma prime dropped from 16.9 pct to 14.5 pct, whereas the
average grain size increased from 8.7 μm to 10.6 μm. Compared with an alloy with a smaller grain size, the alloy with a larger grain size exhibited superior resistances to
creep and fatigue crack growth without the expense of reduced tensile strength and low-cycle fatigue resistance. This suggested
that a higher solution temperature may benefit TMW-4M3 in terms of superior overall properties. The greater overall properties
of TMW-4M3 variants than that of commercial U720Li were also demonstrated experimentally. The possible explanations for the
improvement of mechanical properties were discussed. 相似文献
2.
C. Y. Cui A. Sato Y. F. Gu D. H. Ping H. Harada 《Metallurgical and Materials Transactions A》2006,37(11):3183-3190
Ni-base superalloys containing high Co (>20 wt pct) and Ti (>5.5 wt pct) were designed in order to study the effects of Co16.9
wt pct Ti addition on phase stability and mechanical property. These new alloys, though they contained high Ti, mainly consisted
of γ and γ′ phases. Ni3Ti (η) phase was observed along the grain boundaries in some of the alloys. The formation of η phase was mainly related to
the Ti/Al ratio, Ti content, and alloy composition. Tensile and compression tests showed that these new alloys exhibited higher
yield stress than that of the baseline alloy, TMW-1(U720LI). The possible strengthening mechanisms were discussed in terms
of solid-solution and precipitation strengthening effects by the Co16.9 wt pct Ti additions. Preliminary results show promising
trends for the development of new superalloys for turbine disc applications. 相似文献
3.
Chuanyong Gui Akihiro Sato Yuefeng Gu Hiroshi Harada 《Metallurgical and Materials Transactions A》2005,36(11):2921-2927
We proposed a new method for developing Ni-base turbine disc alloy for application at temperatures above 700 °C by mixing
a Ni-base superalloy U720LI with a two-phase alloy Co-16.9 wt pct Ti in various contents. The microstructure and phase stability
of the alloys were analyzed using an optical microscope, a scanning electron microscope, energy-dispersive spectroscopy, and
an X-ray diffractometer. The yield strength was studied by compression tests at temperatures ranging from 25 °C to 1200 °C.
The results show that all the alloys had a dendritic structure. Ni3Ti (η) phase was formed in the interdendritic region in the alloys with the addition of Co-16.9 wt pct Ti, and its volume fraction
increased with the increase in the addition of Co-16.9 wt pct Ti. The results of exposure at 750 °C show that the addition
of Co-16.9 wt pct Ti to U720LI had a great effect on suppressing the formation of σ phase due to the reduced Cr content in the γ matrix. Compared to U720LI, the alloys with the addition of Co-16.9 wt pct Ti possessed higher yield strength. The solid-solution
strengthening of γ and γ′ and higher volume fraction of γ′ were assumed to cause this strength increase. 相似文献
4.
Some second-, third-, and fourth-generation single-crystal Ni-base superalloys (i.e., Re-containing alloys) have demonstrated the propensity for excessive primary creep at intermediate temperatures. This behavior
has been attributed to the presence of secondary gamma-prime precipitates in the gamma channels as well as on the Re content
of the alloys. This investigation examined creep behavior for a common first-generation alloy, PWA 1480, a common second-generation
alloy, PWA 1484, as well as a modified first-generation alloy, PWA 1480, with 3 wt pct rhenium added. In addition, two different
aging heat treatments were given to each alloy to either precipitate or prevent the formation of fine (nanometer-scale) secondary
gamma-prime in the gamma channels. The intermediate creep properties and tensile properties of the alloys were determined
for both conditions. The microstructures of these samples were characterized by scanning electron microscopy (SEM), transmission
electron microscopy (TEM), and X-ray diffraction (XRD), and then the role of the fine-scale microstructure and the alloy composition
on the primary creep deformation was determined. 相似文献
5.
A. Suzuki M.F.X. Gigliotti B.T. Hazel D.G. Konitzer T.M. Pollock 《Metallurgical and Materials Transactions A》2010,41(4):947-956
Crack progression during compressive sustained-peak low-cycle fatigue (SPLCF) was examined in vapor phase aluminide coated
single-crystal Ni-base superalloy René N5. Strain-controlled tests with a 120-second hold at compression were conducted at
1366 K (1093 °C) with A = –1 (R = –∞) and 0.35 pct total strain range, and were terminated at selected fractions of predicted life. Crack lengths on the
surface and crack depth in longitudinal sections were examined for each specimen. All cracks appeared to have initiated at
the coating surface. Failed specimens showed that cracks initially grew on (001), perpendicular to the stress axis, and then
deflected to other crystallographic planes. Interrupted test specimens showed crevices initiated on the coating surface at
less than 10 pct of the predicted life. The depths of crevices into the coating increased with cyclic exposure, but they did
not penetrate into the substrate through the interdiffusion zone (IDZ) until about 80 pct of predicted life. Stress relaxation
during compressive hold results in residual tension upon unloading. These results suggest that improving creep resistance
of the substrate alloy and developing a coating system that can delay crack penetration into the substrate are keys for improved
SPLCF life. 相似文献
6.
7.
8.
The effect of the addition of 5 at. pct boron on the microstructure and creep behavior of a nominally Ti-22Al-26Nb (at. pct)
alloy was investigated. The boron-modified alloy contained boride needles enriched in titanium and niobium, and because to
these borides, this material was considered to be a discontinuously reinforced metal matrix composite. These needle-shaped
borides made up to 2 pct of the volume and were up to 158-μm long and 22-μm wide. The effect of boron on the mechanical properties
was evaluated through in-situ creep testing and tensile testing at room temperature (RT) and 650 °C. Overall, the addition of 5 at. pct boron proved to
be detrimental to the tensile and creep behavior. The composite exhibited a brittle failure and lower elongations-to-failure
than the monolithic material. The in-situ tensile and creep experiments revealed that the deformation process initiated in the boride needles, which cracked extensively,
and significantly greater primary creep strains and creep rates were exhibited by the composite.
相似文献
C.J. Cowen (Graduate Assistant)Email: |
9.
Jiangbo Sha Hisatoshi Hirai Hidetoshi Ueno Tatsuo Tabaru Akira Kitahara Shuji Hanada 《Metallurgical and Materials Transactions A》2003,34(1):85-94
To improve the high-temperature strength of Nb-Mo-Ti-Si in-situ composites, alloying with W and a directional solidification technique were employed. The alloy composition of Nb-xMo-10Ti-18Si (x=10 or 20) was used as the base, and Nb was further replaced by 0, 5, 10 and 15 mol pct W. For samples without W, the as-cast
microstructure was a eutectic mixture of fine Nb solid solution (Nb
SS
) and (Nb, Me)5 Si3 silicide (Me = Mo, W, or Ti), while large primary Nb
SS
particles appeared besides the eutectic mixture as a result of replacing Nb by W. The directionally solidified samples consisted
of coarse Nb
SS
and (Nb,Me)5 Si3 silicides, and the microstructure showed a slight orientation in the direction of growth. The maximum compressive ductility
(ɛ
max) at room temperature decreased with increasing W content and was in the range of 0.8 to 2.3 pct, in contrast to the Vickers
hardness (HV), which increased with W content. The 0.2 pct yield compressive strength (σ
0.2) and the specific 0.2 pct yield compressive strength (σ
0.2S
) (σ
0.2 divided by the density of sample) at elevated temperatures were markedly improved by the W addition. The directionally solidified
samples always showed higher σ
0.2 and σ
0.2S
values than the as-cast samples. At elevated temperatures, the directionally solidified sample with 10 mol pct Mo and 15
mol pct W had the highest σ
0.2 and σ
0.2S
values; even at 1770 K, σ
0.2 was as high as 650 MPa. The directionally solidified materials alloyed with W exhibited excellent compressive creep performance.
The sample with 10 mol pct Mo and 15 mol pct W had a minimum creep rate
of 1.4×10−7s−1 and retained steady creep deformation at 1670 K and an initial stress of 200 MPa. Under compression, the damage and failure
of these in-situ composites were dominated by decohesion of interfaces between the Nb
SS
and silicide matrix. 相似文献
10.
11.
J. Daniel Whittenberger 《Metallurgical and Materials Transactions A》1977,8(12):1863-1870
A study was undertaken to determine if oxide dispersion strengthened (ODS) Ni-base alloys in wrought bar form are subject
to a loss of room temperature tensile properties after elevated temperature creep similar to that found in a thin gage ODS
alloy sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and advanced ODS-NiCrAl types. Tensile type test specimens
were creep exposed in air at various stress levels at 1365 K and then tensile tested at room temperature. Low residual tensile
properties, change in fracture mode, the appearance of dispersoid free bands, grain boundary cavitation, and/or internal oxidation
in the microstructure were interpreted as creep degradation effects. This work has shown that many ODS alloys are subject
to creep damage. Degradation of tensile properties occurs after very small amounts (≲0.2 pct) of creep strain; ductility being
the most sensitive property. The amount of degradation is dependent on the creep strain and is essentially independent of
the alloy system. All the ODS alloys which were creep damaged possessed a large grain size (>100 μm). Creep damage appears
to be due to diffusional creep which produces dispersoid free bands around boundaries acting as vacancy sources. Low angle
and, possibly, twin boundaries were found to act as vacancy sources. The residual tensile properties of two alloys were not
affected by prior creep parallel to the extrusion axis. One of these alloys, DS-NiCr(S), was single crystalline. The other
alloy, TD-Ni, possessed a small, elongated grain structure which minimized the thickness of the dispersoid free bands produced
by diffusional creep. 相似文献
12.
13.
Sujoy S. Hazra Azdiar A. Gazder Andrew Carman Elena V. Pereloma 《Metallurgical and Materials Transactions A》2011,42(5):1334-1348
Ti-stabilized interstitial free steel subjected to eight passes, route BC room temperature equal channel angular pressing (ECAP) additionally was cold rolled (CR) up to 95 pct thickness reduction.
Electron back-scattering diffraction and transmission electron microscopy characterized microstructural refinement and microtexture
evolution, whereas the mechanical properties were assessed by uniaxial tensile tests. After 95 pct CR, the average high-angle
grain boundary spacing reduces to 0.14 μm, whereas the high-angle boundary fraction increases to ~81 pct. The ECAP negative simple shear texture components rotate by ~15 deg around the transverse direction toward the rolling direction for up to
50 pct CR, with typical rolling textures observed at 95 pct CR. The decrease in boundary spacing produces a ~500 MPa gain
in 0.2 pct proof stress, a ~600 MPa increase in ultimate tensile strength (UTS), and a ~4 pct loss in total elongation after
95 pct CR. Similar rates of decrease in work hardening correspond to comparable rates of cross and/or multiple slip events
irrespective of the processing regime and substructural refinement. The fracture mode of the tensile samples changes from
ductile to brittle type between ECAP and 95 pct CR and is attributed to the reduced work hardening capacity of the latter.
The modified Hall–Petch equation shows that the convergence of high-angle boundary spacing values with their low-angle counterparts
results in an increased contribution via boundary strengthening to the 0.2 pct proof stress and UTS. 相似文献
14.
C. H. Caceres Gemma E. Mann J. R. Griffiths 《Metallurgical and Materials Transactions A》2011,42(7):1950-1959
Cast specimens of Mg and of several Mg-Zn binary alloys with a wide range of grain sizes were deformed in tension and compression.
The k values calculated from the Hall–Petch (H-P) plots of the tensile 0.2 pct proof stress increased with the Zn content, from
0.24 MPa m1/2 for pure Mg to ~0.66 MPa m1/2 for the 2.3 at. pct Zn alloy; k values measured from compression tests were larger, typically by 0.05 MPa m1/2. When the strength measurements were corrected for the pseudoelastic strain resulting from elastic twinning, the k values generally increased, and the difference between tension and compression was eliminated. This showed that the larger
k values obtained in compression using uncorrected data were an artifact of the pseudoelastic effect. The apparent friction
stress varied between about 14 MPa for pure Mg to very low or negative values for the most dilute alloy, increasing again
to about 8 MPa for the most concentrated alloy. The use of strength data corrected for pseudoelasticity effects is necessary
for a consistent analysis of the grain size hardening. 相似文献
15.
B. Nami H. Razavi S. Mirdamadi S.G. Shabestari S.M. Miresmaeili 《Metallurgical and Materials Transactions A》2010,41(8):1973-1982
Creep properties of AZ91 magnesium alloy and AZRC91 (AZ91 + 1 wt pct RE + 1.2 wt pct Ca) alloy were investigated using the
impression creep method. It was shown that the creep properties of AZ91 alloy are significantly improved by adding Ca and
rare earth (RE) elements. The improvement in creep resistance is mainly attributed to the reduction in the amount and continuity
of eutectic β(Mg17Al12) phase as well as the formation of new Al11RE3 and Al2Ca intermetallic compounds at interdendritic regions. It was found that the stress exponent of minimum creep rate, n, varies between 5.69 and 6 for AZ91 alloy and varies between 5.81 and 6.46 for AZRC91 alloy. Activation energies of 120.9 ± 8.9 kJ/mol
and 100.6 ± 7.1 kJ/mol were obtained for AZ91 and AZRC91 alloys, respectively. It was shown that the lattice and pipe-diffusion-controlled
dislocation climb are the dominant creep mechanisms for AZ91 and AZRC91 alloys, respectively. The constitutive equations,
correlating the minimum creep rate with temperature and stress, were also developed for both alloys. 相似文献
16.
Sang-Bok Lee Kyuhong Lee Sang-Kwan Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2009,40(13):3159-3170
An STS304-continuous-fiber-reinforced Zr-based amorphous alloy matrix composite with excellent fiber/matrix interfaces was
fabricated without pores and misinfiltration by liquid pressing process. Approximately 60 vol pct of continuous fibers were
homogeneously distributed in the matrix, in which considerable amounts of polygonal and dendritic crystalline phases were
formed by the diffusion of metallic elements from the fibers. The ductility of the composite under compressive or tensile
loading was drastically improved over that of the monolithic amorphous alloy. According to the compressive test results, a
strength of 700 to 830 MPa was sustained until reaching a strain of 40 pct, because fibers interrupted the propagation of
shear bands initiated in the matrix and took over a considerable amount of load. Under tensile loading, the deformation and
fracture occurred by crack formation and opening at matrices, necking of fibers, fiber/matrix interfacial separation, and
cup-and-cone–type fracture of fibers, thereby resulting in a high tensile elongation of 27 pct. 相似文献
17.
18.
Wen-Fan Xu Yu Zhang Jessica Renae TerBush Li-Ming Peng Wen-Jiang Ding Jian-Feng Nie 《Metallurgical and Materials Transactions A》2014,45(9):4103-4116
The minimum creep rate and microstructures of aged samples of Mg-Gd-Zr alloys, with and without alloying additions of Zn and/or Y, have been investigated in the present work. The creep tests were performed at 523 K (250 °C) and under 80 to 120 MPa, and the microstructures before and after creep tests were characterized using scanning electron microscopy, transmission electron microscopy, and the high-angle annular dark-field imaging technique. It is found that dislocation creep predominates in the steady-state creep stage for all alloys. The Mg-2.5Gd-0.1Zr (at. pct) alloy, strengthened by the β′ precipitates, has minimum creep rates in the range 1.0 × 10?8 to 3.8 × 10?8 s?1 under 80 to 120 MPa. The addition of 1.0 at. pct Zn to the Mg-2.5Gd-0.1Zr alloy reduces the 0.2 pct proof strength and increases the minimum creep rate, resulting from the formation of γ′ basal plates at the expense of β′ precipitates. The replacement of 1.0 at. pct Gd by Y in the Mg-2.5Gd-1.0Zn-0.1Zr alloy leads to a substantial reduction in the minimum creep rate, even though it does not cause much change to the 0.2 pct proof strength. The reduced minimum creep rate is attributed to a much lower diffusivity of Y atoms than Gd in the solid magnesium matrix. An increase in the Gd content from Mg-1.5Gd-1.0Y-1.0Zn-0.1Zr to Mg-2.5Gd-1.0Y-1.0Zn-0.1Zr leads to a denser distribution of precipitates, a higher 0.2 pct proof strength, and a further reduction in the minimum creep rate. 相似文献
19.
Shogo Komura Zenji Horita Minoru Furukawa Minoru Nemoto Terence G. Langdon 《Metallurgical and Materials Transactions A》2001,32(3):707-716
An Al-3 pct Mg-0.2 pct Sc alloy was fabricated by casting and subjected to equal-channel angular pressing to reduce the grain
size to ∼0.2 μm. Very high tensile elongations were achieved in this alloy at temperatures over the range from 573 to 723 K, with elongations
up to >2000 pct at temperatures of 673 and 723 K and strain rates at and above 10−2 s−1. By contrast, samples of the same alloy subjected to cold rolling (CR) yielded elongations to failure of <400 pct at 673
K. An analysis of the experimental data for the equal-channel angular (ECA)-pressed samples shows consistency with conventional
superplasticity including an activation energy for superplastic flow which is within the range anticipated for grain boundary
diffusion in pure Al and interdiffusion in Al-Mg solid solution alloys. 相似文献