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1.
A. B. Kamara A. J. Ardell C. N. J. Wagner 《Metallurgical and Materials Transactions A》1996,27(10):2888-2896
High-temperature X-ray diffractometry was used to determine thein situlattice parameters,a
γ anda
γ′, and lattice misfits, δ = (a
γ′, -a
γ)/a
γ, of the matrix (γ) and dispersed γ′-type (Ni3X) phases in polycrystalline binary Ni-Al, Ni-Ga, Ni-Ge, and Ni-Si alloys as functions of temperature, up to about 680 °C.
Concentrated alloys containing large volume fractions of theγ′ phase (∼0.40 to 0.50) were aged at 700 °C to produce large, elastically unconstrained precipitates. The room-temperature
misfits are 0.00474 (Ni-Al), 0.01005 (Ni-Ga), 0.00626 (Ni-Ge), and -0.00226 (Ni-Si), with an estimated error of ± 4 pct. The
absolute values of the lattice constants of theγ andγ′ phases, at compositions corresponding to thermodynamic equilibrium at about 700 °C, are in excellent agreement with data
from the literature, with the exception of Ni3Ga, the lattice constant of which is much larger than expected. In Ni-Ge alloys, δ decreases to 0.00612 at 679 °C, and in
Ni-Ga alloys, the decrease is to 0.0097. In Ni-Si and Ni-Al alloys, δ exhibits a stronger temperature dependence, changing
to-0.00285 at 683 °C (Ni-Si) and to 0.00424 at 680 °C (Ni-Al). Since the times required to complete the high-temperature X-ray
diffraction (XRD) scans were relatively short (2.5 hours at most), we believe that the changes in δ observed are attributable
to differences between the thermal expansion coefficients of theγ andγ′ phases, because the compositions of the phases in question reflect the equilibrium compositions at 700 δC. Empirical equations
are presented that accurately describe the temperature dependences ofa
γ,a
γ′, and δ over the range of temperatures of this investigation. 相似文献
2.
E. H. Du Marchie van Voorthuysen D. O. Boerma N. C. Chechenin 《Metallurgical and Materials Transactions A》2002,33(8):2593-2598
Iron layers are nitrided in mixtures of ammonia and hydrogen at low temperatures, using a thin nickel caplayer as a catalyst.
In the coordinate field of inverse temperature vs nitriding potential, we determined the boundaries between areas in which the α, γ′, or ε phases are in thermal equilibrium. Using these data, the Fe-N phase diagram is extended from 350 °C to 240 °C and extrapolated
down to 200 °C. The α, γ′, and ε phases probably coexist in a triple point in the Lehrer diagram around 214 °C. 相似文献
3.
D. B. Miracle K. A. Lark V. Srinivasan H. A. Lipsitt 《Metallurgical and Materials Transactions A》1984,15(3):481-486
Recent work on alloys based on the Ni-Al-Mo system has brought to light several inconsistencies with published equilibrium
phase diagrams for this system. Published diagrams have been based on theoretical computer models and on data gathered ostensibly
before equilibrium was achieved, especially at temperatures below 1100 °C. The intent of this effort was to produce an experimentally
validated ternary equilibrium phase diagram for the Ni-Al-Mo system. Specimens for this task were produced by both conventional
casting and powder metallurgy techniques. The temperatures studied included 1260, 1171, 1093, 1038, and 927 °C (2300, 2140,
2000, 1900, and 1700 °F) for times up to 2500 hours. Phases were identified using an electron probe microanalyzer and X-ray
diffraction. The results show significant deviations from the proposed phase diagrams published in the literature in the temperature
range investigated. In particular, a class II four-phase equilibrium reaction γ + α cooling // heating γ′+ δ has been shown to occur at 1127 ± 2 °C (2060 ± 4 °F).
Formerly NRC Senior Research Associate. 相似文献
4.
K. Banerjee N. L. Richards M. C. Chaturvedi 《Metallurgical and Materials Transactions A》2005,36(7):1881-1890
The effect of filler alloys C-263, RENé-41, IN-718, and FM-92 on heat-affected zone (HAZ) cracking susceptibility of cast
IN-738 LC, which is a high-temperature Ni-based superalloy used at temperatures up to 980 °C and is precipitation hardened
by the γ′ (Ni3Al,Ti) phase, by gas-tungsten-arc (GTA) welding was studied. In addition, autogenous welds were also made on the IN-738 parent
material. The preweld treatments consisted of the standard solution treatment at 1120 °C for 2 hours followed by air cooling,
and a new heat treatment, which was developed to improve the HAZ cracking resistance of IN-738 LC. This heat treatment consisted
of solution treating at 1120 °C followed by air cooling then aging at 1025 °C for 16 hours followed by water quenching. Welds
were observed to suffer intergranular HAZ cracking, regardless of the filler alloy; however, the autogenous welds were most
susceptible to HAZ cracking. In general, the cracking tendency for both heat treatments was maximum for C-263 and RENE-41
fillers and decreased with the use of FM-92 and IN-718 filler alloys. The HAZ cracking was associated mainly with constitutional
liquation of γ′ and MC carbides. On some cracks, liquated low melting point containing Zr-carbosulfide and Cr-Mo borides were also observed
to be present. The cooling portion of the weld thermal cycle induced precipitation hardening via γ′ phase in the γ matrix of the weld metal. The HAZ cracking increased as the weld metal lattice mismatch between γ′ precipitates and γ matrix of the weld and its hardness (Ti + Al) increased. However, the weld-metal solidus and solidification temperature range,
determined by high-temperature differential scanning calorimetry, did not correlate with the HAZ cracking susceptibility.
It is suggested that the use of filler alloys with small γ′-γ lattice mismatch and slow age-hardening response would reduce the HAZ cracking in IN-738 LC superalloy welds. 相似文献
5.
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
6.
Compression yielding tests at 760 °C were performed on near [001]- and [lll]-oriented crystals of the Ni-base superalloys
René 150 and a modified MAR-M247, both having two different Co concentrations. Octahedral and cube slip occurred for the near
[001]- and [lll]-oriented crystals, respectively, for all compositions. For both alloy bases, increasing Co concentration
was found to decrease the critical resolved shear stress for octahedral slip but to have little effect on that for cube slip.
In the present work, phase analyses and variations in heat treatment indicated that the effects of Co concentration observed
were not due simply to changes in the volume fraction or size of theγ′ phase. It is suggested that decreasing complex stacking fault energy in theγ′ with increasing Co would lead to the observed effects based on current interpretations of the dislocation locking mechanism
by cube cross slip in theγ′. 相似文献
7.
S. M. Seo J. H. Lee Y. S. Yoo C. Y. Jo H. Miyahara K. Ogi 《Metallurgical and Materials Transactions A》2011,42(10):3150-3159
The evolution of γ/γ′ eutectic during the solidification of Ni-base superalloys CMSX-10 and CMSX-4 was investigated over a wide range of cooling
rates. The microsegregation behavior during solidification was also quantitatively examined to clarify the influence of elemental
segregation on the evolution of γ/γ′ eutectic. In the cooling rate ranges investigated (0.9 to 138.4 K/min (0.9 to 138.4 °C/min)), the γ/γ′ eutectic fraction in CMSX-10 was found to be more than 2 times higher than that in CMSX-4 at a given cooling rate. However,
the dependence of the γ/γ′ eutectic fraction on the cooling rate in both alloys showed a similar tendency; i.e., the γ/γ′ eutectic fraction increased with increasing the cooling rate and then exhibited a maximum plateau at and above the certain
critical cooling rate in both alloys. This critical cooling rate was found to be dependent on the alloy composition and was
estimated to be about 12 K/min (12 °C/min) and 25 K/min (25 °C/min) for CMSX-10 and CMSX-4, respectively. The calculated solid
compositions based on the modified Scheil model revealed that even a small compositional difference of total γ′ forming elements in the initial composition of the alloy can play a significant role in the as-cast eutectic fraction during
the solidification of Ni-base superalloys. The evolution of the γ/γ′ eutectic fraction with respect to the cooling rate could be rationalized by taking into account the effects of back-diffusion
in solid and dendrite arm coarsening on decreasing the extent of microsegregation. 相似文献
8.
Reaction synthesis of Ni-Al-based particle composite coatings 总被引:1,自引:0,他引:1
D. F. Susan W. Z. Misiolek A. R. Marder 《Metallurgical and Materials Transactions A》2001,32(2):379-390
Electrodeposited metal matrix/metal particle composite (EMMC) coatings were produced with a nickel matrix and aluminum particles.
By optimizing the process parameters, coatings were deposited with 20 vol pct aluminum particles. Coating morphology and composition
were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM), and electron probe microanalysis
(EPMA). Differential thermal analysis (DTA) was employed to study reactive phase formation. The effect of heat treatment on
coating phase formation was studied in the temperature range 415 °C to 1000 °C. Long-time exposure at low temperature results
in the formation of several intermetallic phases at the Ni matrix/Al particle interfaces and concentrically around the original
Al particles. Upon heating to the 500 °C to 600 °C range, the aluminum particles react with the nickel matrix to form NiAl
islands within the Ni matrix. When exposed to higher temperatures (600 °C to 1000 °C), diffusional reaction between NiAl and
nickel produces (γ′)Ni3Al. The final equilibrium microstructure consists of blocks of (γ′)Ni3Al in a γ(Ni) solid solution matrix, with small pores also present. Pore formation is explained based on local density changes during
intermetallic phase formation, and microstructural development is discussed with reference to reaction synthesis of bulk nickel
aluminides. 相似文献
9.
The [001] oriented single crystals of nickel-base superalloy NASAIR 100 with the planar, cellular, coarse-dendritic, and fine-dendritic
solid/liquid (S/L) interfaces were prepared, respectively, and their microstructure and stress-rupture behavior at 1050 °C
were investigated in both as-cast and solution heat-treated conditions. It was found that in as-cast single crystals of NASAIR
100, microsegregation and γ/γ′ eutectic produced in the solidification process increased, γ′ size decreased, and γ′ shape tended progressively to be cuboidal, with the successive transition of the S/L interface from planar to cellular, then
to coarse-dendritic, and finally to fine-dendritic morphology. Furthermore, the solution temperature required to dissolve
all as-cast γ′ and most of the γ/γ′ eutectic increased with the aforementioned successive transition of S/L interfaces. The reprecipitated γ′, after solution heat treatment (SHT), was usually fine and cuboidal. However, some W-rich phase was present in the heat-treated
dendritic single crystals. Both the planar and the cellular single crystals of NASAIR 100 exhibited no superiority in stress-rupture
life, irrespective of the heat-treatment conditions. Instead, the single crystals with dendritic morphology possessed excellent
stress-rupture lives, after heat treatment at 1320 °C for 4 hours, followed by air cooling (AC). Perfect γ′ rafts with high-average aspect ratios formed during the stress-rupture tests of dendritic single crystals; in contrast, irregularly
coarsening structures appeared in both the planar and cellular single crystals. The microstructure and solution behavior were
illustrated in detail. Furthermore, the microstructural factors to affect the high-temperature stress-rupture life of the
single crystals of NASAIR 100 were also analyzed. 相似文献
10.
J.Y. Hwang S. Nag A.R.P. Singh R. Srinivasan J. Tiley G.B. Viswanathan H.L. Fraser R. Banerjee 《Metallurgical and Materials Transactions A》2009,40(13):3059-3068
The compositional and microstructural evolution of different generations of precipitates of the ordered γ′ phase during the continuous cooling, followed by isothermal aging, of a commercial nickel-base superalloy, Rene 88DT, has
been characterized by three-dimensional atom probe (3DAP) tomography coupled with energy-filtered transmission electron microscopy
(EFTEM) studies. After solutionizing in the single γ-phase field, during continuous cooling at a relatively slow rate (~24 °C/min), the first-generation primary γ′ precipitates, forming at relatively higher temperatures, exhibit near-equilibrium compositions, while the smaller-scale
secondary γ′ precipitates, forming at lower temperatures, exhibit nonequilibrium compositions often containing an excess of Co and Cr
while being depleted in Al and Ti content. The compositions of the γ matrix near these precipitates also exhibit similar trends, with the composition being closer to equilibrium near the primary
precipitates as compared to the secondary precipitates. Subsequent isothermal aging at 760 °C leads to coarsening of the primary
γ′ precipitates without affecting their composition significantly. In contrast, the composition of the secondary γ′ precipitates is driven toward equilibrium during the isothermal aging process. 相似文献
11.
Ricky L. Whelchel V. Siva Kumar G. Kelekanjeri Rosario A. Gerhardt Jan Ilavsky 《Metallurgical and Materials Transactions A》2011,42(5):1362-1372
The γ′ precipitation behavior of age-hardened WASPALOY, aged at 998 K, 1073 K, and 1148 K (725 °C, 800 °C, and 875 °C) for times
ranging from 0.5 to 263.5 hours, were evaluated via analysis of ultra small angle X-ray scattering (USAXS) curves and scanning electron microscopy (SEM) micrographs. The USAXS
spectra revealed a single precipitate size distribution at the earliest aging times, which evolves into a bimodal precipitate
size distribution at later aging times. The primary precipitate radius displayed t
1/3 coarsening dependence for aging at 1073 K and 1148 K (800 °C and 875 °C); however, the primary radius increased with t
0.4 dependence at 998 K (725 °C), most likely due to mixed growth and coarsening. A figure of merit, η′, consisting of two terms, one associated with precipitate size and volume fraction and the other with compositional fluctuations,
was proposed. η′ shows direct empirical correlations with changes in the measured electrical resistivity. 相似文献
12.
Erdong Wu Jinchao Li Jun Zhang Sucheng Wang Guang Xie Jian Zhang Bo Chen Guangai Sun Vincent Ji Darren Hughes Thilo Pirling 《Metallurgical and Materials Transactions A》2008,39(13):3141-3148
The relationship between internal stress and thermomechanical fatigue (TMF) in a Ni-based single-crystal superalloy is studied
by neutron and X-ray diffraction. The extents of internal stress, deformation, lattice mismatch, and distortion during TMF
are characterized by the determined deviatoric stress invariants and lattice parameters and compared with relevant microstructural
information from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that, in
general, the macroscopic stress, plastic deformation, lattice mismatch, and distortion have all increased during TMF. The
lattice mismatches of the TMF samples are at a high level, where the values along [100]/[010] are negative, but those along
[001] are positive. The tetragonal lattice distortion of the γ matrix is slightly greater than that of the γ′ precipitates, where the c/a values of the γ matrix are smaller than 1, but that of the γ′ precipitate larger than 1. The γ matrix yields and becomes hardened at the initial TMF cycle and gradually loses most of its strength during the earlier TMF
cycles, associated with stress relaxation and homogenous deformation. However, the γ′ precipitates yield and become hardened later, bearing the most stress up to the necking of the superalloy. This process is
associated with a buildup of stress and significant concentrated and inhomogeneous distribution of deformation in the γ′ precipitate. The residual deformation states of the superalloy and its component phases at the earlier TMF are basically
shearing, and only become stretched at a later stage of TMF. The microstructure of the TMF samples shows an initial stage
of rafting, where the dislocations are accumulated at the
interfaces of the γ matrix channels, but both dislocation networks and stacking faults are inhomogeneously distributed in the γ′ precipitates.
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
13.
Y. H. Sohn A. Puccio M. A. Dayananda 《Metallurgical and Materials Transactions A》2005,36(9):2361-2370
Diffusion studies were carried out in the Fe-Ni-Al system at 1000 °C using solid-solid diffusion couples assembled with β (B2), γ (fcc) single phase, and (β + γ) two-phase alloys. The diffusion couples were encapsulated in quartz tubes under vacuum and annealed for 48 hours. The diffusion
structures were examined by optical and scanning electron microscopy. For all β vs (β + γ) couples, growth of the β phase was observed as the (β + γ) two-phase region recessed with the dissolution of the γ phase. For multiphase couples assembled with two (β + γ) terminal alloys, demixing of the (β + γ) two-phase alloys occurred with the formation of single-phase β and γ layers. The development of an interphase boundary between the (β + β′) two-phase region and the γ phase is reported for the first time for a Fe-Ni-Al diffusion couple assembled with single-phase, β, and γ terminal alloys. Various diffusion structures for the couples were related to their diffusion paths constructed from concentration
profiles determined by electron probe microanalysis. Interdiffusion fluxes of individual components were determined directly
from the experimental concentration profiles and examined in light of diffusional interactions and the development of zero-flux
planes and flux reversals. In addition, the boundaries for the miscibility gap between the ordered β and disordered β′ phases of the Fe-Ni-Al system at 1000 °C were determined with the aid of diffusion couples that developed β and β′ phases in the diffusion zone. 相似文献
14.
In order to provide the necessary phase equilibria data for understanding the development of the Widmanstatten pattern in
iron meteorites, we have redetermined the Fe-Ni-P phase diagram from 0 to 100 pct Ni, 0 to 16.5 wt pct P, in the temperature
range 1100° to 550°C. Long term heat treatments and 130 selected alloys were used. The electron microprobe was employed to
measure the composition of the coexisting phases directly. We found that the fourphase reaction isotherm, where α+ liq ⇌ γ+ Ph, occurs at 1000° ± 5°C. Above this temperature the ternary fields α+ Ph + liq and α+ γ+ liq are stable and below 1000°C, the ternary fields ⇌+ γ + Ph and γ + Ph + liq are stable. Below 875°C a eutectic reaction, liq → γ + Ph, occurs at the Ni-P edge of the diagram.
Altogether nineteen isotherms were determined in this study. The phase boundary compositions of the two-and three-phase fields
are listed and are compared with the three binary diagrams. The α + γ + Ph field expands in area in each isotherm as the temperature
decreases from 1000°C. Below 800°C the nickel content in all three phases increases with decreasing temperature. The phosphorus
solubility in α and γ decreases from 2.7 and 1.4 wt pct at 1000°C to 0.25 and 0.08 wt pct at 550°C. The addition of phosphorus
to binary Fe-Ni greatly affects the α/α + γ and γ/α + γ boundaries below 900°C. It stabilizes the α phase by increasing the
solubility of nickel (α/α +γ boundary) and above 700°C, it decreases the stability field of the γ phase by decreasing the
solubility of nickel(@#@ γ/α + γ boundary). However below 700°C, phosphorus reverses its role in γ and acts as a γ stabilizer, increasing the nickel
solubility range. The addition of phosphorus to Fe-Ni caused significant changes in the nucleation and growth processes. Phosphorus
contents of 0.1 wt pct or more allow the direct precipitation ofa from the parent γ phase by the reaction γ ⇌ α + γ. The growth rate of the α phase is substantially higher than that predicted
from the binary diffusion coefficients.
Formerly at Planetology Branch, Goddard Space Flight Center 相似文献
15.
E. L. Hall Y. M. Kouh M. R. Jackson R. L. Mehan 《Metallurgical and Materials Transactions A》1983,14(4):781-790
Aspects of the solid state reaction between SiC and a model superalloy consisting of Ni-20 at. pct Cr-10 at. pct Al at 1150
°C are studied in detail using analytical electron microscopy. The metal reaction zone formed on the metal side of the original
metal/ceramic interface is found to consist of a complex mixture of four phases: γ′-Ni3Al, β-NiAl, α-Cr, and Ξ, a ternary Ni-Si-Al phase. The chemistry of each phase is determined using X-ray spectroscopy in the
analytical electron microscope. The effect of silicon on the γ —γ′ microstructure of the model superalloy is described, and is shown to alter the chemistry, morphology, and size of the γ′
phase. The γ-γ′ lattice parameter mismatch is calculated from the chemistry data, and changes in this mismatch caused by silicon
correlate well with γ′ morphology changes. Finally, phase equilibria concepts are used to explain the presence and distribution
of phases in the metal reaction zone.
Department of Materials Science and Engineering, and during the course of this work was employed at the General Electric Corporate
Research and Development Center as part of the Cornell University Engineering Cooperative Program. 相似文献
16.
Two oxide dispersion strengthening (ODS) nickel-base superalloys, a solely dispersion-strengthened alloy (PM 1000) and an
additionally γ′-strengthened alloy (PM 3030) are investigated regarding creep resistance at temperatures between 600 °C and 1000 °C. The
creep strength advantage of PM 3030 over PM 1000 decreases as the temperature increases due to the thermal instability of
the γ′ phase. The particle strengthening contribution in both alloys increases linearly with load. However, solid solution softening
leads to an apparent drop in particle strengthening in PM 1000. Deformation concentration in slip bands is more accentuated
in PM 3030-R34 due to additional γ′ strengthening combined with strongly textured coarse and elongated grain structure. Finer, equiaxed grains reduce creep strength
at higher temperatures due to grain boundary deformation processes and premature pore formation, but have only minor impact
at low and intermediate temperatures. 相似文献
17.
Phase equilibria between γ (Al), γ′ (Ll2), and β (B2) phases in the Ni-rich portions of the Ni-Al-X ternary systems were investigated over a temperature range of
800 °C to 1300 °C. The tie lines and phase boundaries were accurately determined by the diffusion couple technique. It was
established that Co, Cu, Mn, Fe, and Cr concentrated more into the γ phase than into the γ′ phase, while Ta, Nb, Ti, V, and
Si mostly partitioned to the γ′ phase. The partition coefficients for alloying elements between γ and γ′ phases varied as
a function of temperature for most of the elements and also as a function of concentration for some of the elements, such
as Mo, W, and V. In the equilibrium between γ′ and β phases, Mn, Fe, Co, and Cu partitioned to the β phase rather than to
the γ′ phase, whereas Nb, Mo, Ta, Ti, W, V, Cu, and Si concentrated into the γ′ phase. The partition of alloying elements
in the metastable equilibrium between γ and β phases, in the Ni-Al binary system, was estimated from the data on γ/γ′ and
γ′/β equilibria. Based on these data, the relative stabilizing effects of alloying elements on γ, γ′, and β phases are also
discussed. 相似文献
18.
19.