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1.
M. R. Jackson 《Metallurgical and Materials Transactions A》1977,8(6):905-913
The Ni−Ta−C ternary system has been studied at the Ni-rich end of the phase diagram. The investigation was directed toward
developing a detailed picture of γ+TaC composites. Alloys were melted with Ta/C atomic ratios of 0.79 to 3.33 in an attempt
to define the composition range that would produce two-phase γ+TaC eutectics. The liquidus trough rises in temperature across
the ternary diagram moving away from the Ni−C eutectic (1320°C) and toward the Ni−Ni3Ta eutectic (1380°C). Bulk chemistries were determined for aligned regions to map the liquidus trough compositions. Ratios
of Ta/C atoms varied from 1.3 to 8.8 in the aligned regions. Matrix composition was determined by electron microprobe analysis,
and lattice parameters of extracted TaC fibers were measured by X-ray diffraction. Fiber compositions ranged from TaC0.99 to TaC0.97 as the Ta/C ratio of the aligned region increased. The matrix compositions and TaC stoichiometries were used to map tie-lines
across the ternary diagram. Volume fraction and microstructural features of the TaC phase were also studied. The volume fraction
of TaC decreased from 6.7 vol pct to 1.7 vol pct as Ta/C increased from 1.3 to 8.8. The decreasing volume fraction can be
explained by a lever-arm rule application for the ternary phase diagram, based on the liquidus trough and tie-line compositions
determined in this study. The TaC growth axis was <111> in each case, but the carbide morphology changed progressively across
the phase diagram. The change in morphology is primarily a consequence of the change in volume fraction. Implications of the
findings of this study for more complex γ+MC eutectics will be discussed. 相似文献
2.
J. Zhang D. B. Williams J. I. Goldstein 《Metallurgical and Materials Transactions A》1994,25(8):1627-1637
The low-temperature (<500 °C) decomposition of Fe-Ni martensite was studied by aging martensitic Fe-Ni alloys at temperatures
between 300 °C and 450 °C and by measuring the composition of the matrix and precipitate phases using the analytical electron
microscope (AEM). For aging treatments between 300 °C and 450 °C, lath martensite in 15 and 25 wt pct Ni alloys decomposed
with γ [face-centered cubic (fcc)] precipitates forming intergranularly, and plate martensite in 30 wt pct Ni alloys decomposed
with γ (fcc) precipitates forming intragranularly. The habit plane for the intragranular precipitates is {111}fcc parallel to one of the {110}bcc planes in the martensite. The compositions of the γ intergranular and intragranular precipitates lie between 48 and 58 wt
pct Ni and generally increase in Ni content with decreasing aging temperature. Diffusion gradients are observed in the matrix
α [body-centered cubic (bcc)] with decreasing Ni contents close to the martensite grain boundaries and matrix/precipitate
boundaries. The Ni composition of the matrix α phase in decomposed martensite is significantly higher than the equilibrium
value of 4 to 5 wt pct Ni, suggesting that precipitate growth in Fe-Ni martensite is partially interface reaction controlled
at low temperatures (<500 °C). The results of the experimental studies modify the γ/α + γ phase boundary in the present low-temperature
Fe-Ni phase diagram and establish the eutectoid reaction in the temperature range between 400 °C and 450 °C.
Formerly Research Assistant, Department of Materials Science and Engineering, Lehigh University 相似文献
3.
The influence of cobalt,tantalum, and tungsten on the elevated temperature mechanical properties of single crystal nickel-base superalloys 总被引:4,自引:0,他引:4
The influence of composition on the tensile and creep strength of [001] oriented nickel-base superalloy single crystals at
temperatures near 1000 °C was investigated. Cobalt, tantalum, and tungsten concentrations were varied according to a matrix
of compositions based on the single crystal version of MAR-M247.* For alloys with the baseline refractory metal level of 3
wt pct Ta and 10 wt pct W, decreases in Co level from 10 to 0 wt pct resulted in increased tensile and creep strength. Substitution
of 2 wt pct W for 3 wt pct Ta resulted in decreased creep life at high stresses, but improved life at low stresses. Substitution
of Ni for Ta caused large reductions in tensile strength and creep resistance, and corresponding increases in ductility. For
these alloys with low Ta plus W totals, strength was independent of Co level. The effects of composition on properties were
related to the microstructural features of the alloys. In general, high creep strength was associated with high levels ofγ′ volume fraction,γ-γ′ lattice mismatch, and solid solution hardening. 相似文献
4.
The phase decomposition of two (Fe0.65Mn0.35)0.83Al0.17-xC (x=3 and 4 at. pct orx=0.74 and 0.98 wt pct) austenitic alloys prepared by rapid solidification (RS) has been investigated on aging at 823 and 923
K by means of X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Under low bulk carbon
supersaturation conditions (823 K aging of low carbon alloy and 923 K aging of high carbon alloy), zones formed preferentially
at the cellular boundaries and in the bands in the {100} planes, giving rise to line broadening in the X-ray diffraction patterns.
On the other hand, the initial aging under high, carbon supersaturation condition (823 K aging of high carbon alloy) resulted
in the sideband formation, resulting from homogeneous structural modulation in the <100>γ directions throughout the grain. The bulk carbon supersaturation dependence of initial decomposition modes indicates that
carbon atom fluctuations are crucial in the initial state of phase decomposition, and that the observed {100} modulated structure
corresponds to a structure consisting of alternate carbon-rich and carbon-poor zones. Together with the interstitial clustering
process, an fcc-based substitutional ordering reaction concurrently took place. Later on these zones were replaced by a coherent
metastable phase in the matrix, which was finally transformed into the cubic carbide (κ carbide) of (Fe, Mn)3AlCx chemical formula with the L'12 structure. However, at the end, a combined heterogeneous β-Mn and κ carbide precipitation seemed to finalize the decomposition
process over the matrix κ carbide precipitation. 相似文献
5.
R. V. Miner 《Metallurgical and Materials Transactions A》1997,28(4):1011-1020
Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements,
Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the γ′ phase, and
about 3 at. pct of X in the γ′. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured
at 760 °C, which is about the peak strength temperature. The CRSSOct and CRSScube are discussed in relation to those of Ni3 (Al, X) γ′ alloys taken from the literature and the γ′/γ lattice mismatch. The CRSSOct of the γ+γ′ alloys reflected a similar compositional dependence to that of both the CRSSOct of the γ′ phase and the γ′/γ lattice parameter mismatch. The CRSScube of the γ+γ′ alloys also reflected the compositional dependence of the γ′/γ mismatch, but bore no similarity to that of CRSScube for γ′ alloys since it is controlled by the γ matrix. The ratio of CRSScube/CRSSOct was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSScube/CRSSOct was related to the degree in which elements partition to the γ′ rather than the γ phase. 相似文献
6.
G. M. Janowski R. W. Heckel B. J. Pletka 《Metallurgical and Materials Transactions A》1986,17(11):1891-1905
Changes in the γ/γ'/carbide microstructure as a function of Ta content were studied in conventionally cast B-1900 + Hf and
both conventionally cast and directionally solidified MAR-M247.* The effects of tantalum on the microstructure were found
to be similar in both nickel-base superalloys. In particular, the γ' and carbide volume fractions increased approximately
linearly with tantalum additions in both alloys. The γ' phase compositions did not change as tantalum additions were made
with the exception of an increase in the tantalum level. Bulk tantalum additions increased the tantalum, chromium, and cobalt
levels of the γ phase in both alloy series. The increase in the concentrations of the latter two elements was attributed to
a decrease in the γ phase fraction with increasing bulk tantalum level and nearly constant γ' /γ partitioning ratios. It was
demonstrated that the large increase in the γ ' volume fraction was a result of tantalum not affecting the partitioning ratios
of the other alloying elements. The addition of tantalum led to a partial replacement of the hafnium in the MC carbides, although
the degree of replacement was reduced by the solutionizing and aging heat treat-ment. In addition, chromium-rich M23C6 carbides formed as a result of MC carbide decomposition during heat treatment. 相似文献
7.
The solubility of Nb + Al in the γ solid solution decreases markedly with decreasing temperature; thus alloys can be prepared
that are γ at 1200°C and yet contain 50 pct γ’ precipitate after aging at 800°C. Thermal stability of the γ’ precipitate is
related to the lattice mismatch between the γ and γ’ phases; the smaller the mismatch the lower is the interfacial elastic
energy and the more stable is the γ’. Upon aging certain alloys at 800°C a γ’ growth interface other than the normal (100)γll(100)γ’ is observed. The maximum solubility of the niobium in γ’ is ∼7 at. pct; the width of the γ’ field increases with increasing
niobium content but it is essentially independent of temperature. Replacing aluminum by niobium in γ’ gives hardnesses of
up to 400 Dpn. 相似文献
8.
The α + γ two-phase fields of the Fe-Ni and Fe-Ni (P saturated) phase diagrams have been determined in the composition range
0 to 60 wt pet Ni and in the temperature range 700 to 300 °C. The solubility of Ni in (FeNi)3P was measured in the same temperature range. Homogeneous alloys were austenitized and quenched to form α2, martensite, then heat treated to formα (ferrite) + γ (austenite). The compositions of the α and γ phases were determined
with electron microprobe and scanning transmission electron microscope techniques. Retrograde solubility for the α/(α + γ)
solvus line was demonstrated exper-imentally. P was shown to significantly decrease the size of the α + γ two-phase field.
The maximum solubility of Ni in α is 6.1 ± 0.5 wt pct at 475 °C and 7.8± 0.5 wt pct at 450 °C in the Fe-Ni and Fe-Ni (P saturated)
phase diagrams, respectively. The solubility of Ni in α is 4.2 ± 0.5 wt pct Ni and 4.9 ± 0.5 wt pct Ni at 300 °C in the Fe-Ni
and Fe-Ni (P saturated) phase diagrams. Ternary Fe-Ni-P isothermal sections were constructed between 700 and 300 °C.
Formerly Research Assistant in Department of Metallurgy & Materials Engineering, Lehigh University, Bethlehem, PA. 相似文献
9.
V. Biss G. N. Kirby D. L. Sponseller 《Metallurgical and Materials Transactions A》1976,7(8):1251-1261
Chromium, molybdenum, tungsten, and tantalum have been compared with each other in regard to their influence on the occurrence
of Σ phase in cast nickel-base superalloys. The compositions of the alloys were similar to the chromium-enriched matrix of
alloys strengthened by λ′ precipitate, but with systematic variations in refractory-metal content. To induce precipitation
of Σ phase, the alloys were aged for 3000 h at 1400‡F (760‡C), 1550‡F (845‡C), and 1700‡F (925‡C). Quantities of Σ phase were
determined with the aid of an image-analyzing computer. On an atomic percentage basis, molybdenum, tungsten, and tantalum
are equivalent with regard to the minimum concentration of each element that is necessary to cause Σ phase precipitation in
3000 h; their potency is slightly more than twice as high as that of further chromium additions above the 37.5 at. pct base
chromium level. At higher refractory metal concentrations, somewhat greater quantities of Σ phase are formed by specific atomic
concentrations of molybdenum and tungsten than by tantalum. Tantalum also forms large quantities of a tantalum-containing
Μ phase in the as-cast ingot and a (Ni, Co)3Ta phase on aging, the volume of all precipitate being much higher than the quantity of Σ phase for the molybdenum- and tungsten-containing
alloys. At any given atomic concentration of molybdenum, tungsten, or tantalum, considerably larger quantities of Σ phase
are formed than by a given increment of chromium above the 37.5 at. pct base chromium concentration in Mo-W-Ta-free alloys. 相似文献
10.
A melting and solidification study of alloy 625 总被引:1,自引:0,他引:1
M. J. Cieslak T. J. Headley A. D. Romig T. Kollie 《Metallurgical and Materials Transactions A》1988,19(9):2319-2331
The melting and solidification behavior of Alloy 625 has been investigated with differential thermal analysis (DTA) and electron
microscopy. A two-level full-factorial set of chemistries involving the elements Nb, C, and Si was studied. DTA results revealed
that all alloying additions decreased the liquidus and solidus temperatures and also increased the melting temperature range.
Terminal solidification reactions were observed in the Nb-bearing alloys. Solidification microstructures in gastungsten-arc
welds were characterized with transmission electron microscopy (TEM) techniques. All alloys solidified to an austenitic (γ)
matrix. The Nb-bearing alloys terminated solidification by forming various combinations of γ/MC(NbC), γ/Laves, and γ/M6C eutectic-like constituents. Carbon additions (0.035 wt pct) promoted the formation of the γ/MC(NbC) constituent at the expense
of the γ/Laves constituent. Silicon (0.4 wt pct) increased the formation of the yJLaves constituent and promoted formation
of the γ/M6C carbide constituent at low levels (<0.01 wt pct) of carbon. When both Si (0.4 wt pct) and C (0.035 wt pct) were present,
the γ/MC(NbC) and γ/Laves constituents were observed. Regression analysis was used to develop equations for the liquidus and
solidus temperatures as functions of alloy composition. Partial derivatives of these equations taken with respect to the alloying
variables (Nb, C, Si) yielded the liquidus and solidus slopes t(m
L
, m
S
) for these elements in the multicomponent system. Ratios of these liquidus to solidus slopes gave estimates of the distribution
coefficients (k) for these same elements in Alloy 625. 相似文献
11.
Russell H. Jones V. F. Zackay E. R. Parker 《Metallurgical and Materials Transactions B》1972,3(11):2835-2842
Development of an iron-base alloy hardened by particles of an intermetallic compound rather than a carbide is a desirable goal because of the greater thermal stability of such a dispersion. As a first step in the development of iron-base alloys hardened with the Laves phase, structural studies of binary Fe-Ta alloys have been undertaken. The structures of two phase Fe-Ta alloys have been studied by means of optical and transmission electron microscopy, X-ray diffraction, electron beam microprobe analysis, and scanning electron microscopy. The hardness change as a function of time at 600°, 700°, and 800°C has been determined for binary alloys with 1 at. pct Ta and 2 at. pct Ta in iron. Also, the uniaxial tensile strengths of solution treated, quenched, and aged samples have been determined. These studies suggest that the compound, Fe2Ta, is isomorphous with the structure type, MgZn2, (C14) and has a range of compositional homogeneity. The latter results correspond with the predictions of the Engel-Brewer correlation. Also, it has been found that precipitation occurs at grain boundaries, dislocations, and randomly throughout the matrix. Particles which form at dislocations have a (100)α habit plane; whereas a (110)α habit plane has been reported by others1,3 for the hexagonal Laves phase in α iron. Hypereutectoid composition alloys quenched from the ö phase field have a completely retained § structure. Isothermal decomposition at 600°, 700°, and 800°C of alloys with the retained § structure results in a sizable hardness increase in 2 at. pct Ta alloys but only a modest increase in 1 at. pct Ta alloys. Brittle fracture of aged tensile specimens tested at room temperature reveals that the ductile-brittle transition temperature in tension is above room temperature. 相似文献
12.
13.
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
14.
M. Dilip Bhandarkar M. Shanthidas Bhat Victor F. Zackay Earl R. Parker 《Metallurgical and Materials Transactions A》1975,6(6):1281-1289
A Laves phase, Fe2Ta, was utilized to obtain good elevated temperature properties in a carbon-free iron alloy containing 1 at. pct Ta and 7
at. pct Cr. Room temperature embrittlement resulting from the precipitation of the Laves phase at grain boundaries was overcome
by spheroidizing the precipitate. This was accomplished by thermally cycling the alloys through theα →γ transformation. The short-time yield strength of the alloys decreased very slowly with increase in test temperature up to
600°C, but above this temperature, the strength decreased rapidly. Results of constant load creep and stress rupture tests
conducted at several temperatures and stresses indicated that the rupture and creep strengths of spheroidized 1 Ta−7 Cr alloy
were higher than those of several commercial steels containing chromium and/or molybdenum carbides but lower than those of
steels containing substantial amounts of tungsten and vanadium. When molybdenum was added to the base FeTa-Cr alloy, the rupture
and creep strengths were considerably increased.
Formerly with Lawrence Berkeley Laboratory. 相似文献
15.
J. Jung G. Ghosh D. Isheim G. B. Olson 《Metallurgical and Materials Transactions A》2003,34(6):1221-1235
The precipitation of Heusler phase (L21: Ni2TiAl) from a supersaturated B2 (TiNi-based) matrix at 600°C and 800°C is studied using transmission electron microscopy (TEM),
analytical electron microscopy (AEM), and three-dimensional atom-probe (3DAP) microscopy in Ni-Ti-Al and Ni-Ti-Al-X (X=Hf
and Zr) alloys. The B2/L21 two-phase system, with ordered structures based on the bcc lattice, is chosen for its microstructural analogy to the classical
γ/γ′ system with an fcc lattice. Knowledge of the temperature-dependent partitioning of alloying elements and their atomic volumes
in the B2-TiNi and L21 phases is desired to support design of high-performance shape-memory alloys (SMAs) with controlled misfit strain and transformation
temperatures. After aging at 600°C for up to 2000 hours, the L21 precipitates remain fully coherent at a particle diameter of ∼20 nm. The observed effects of a misfit strain of −1.9 pct
on the microstructure of the B2/L21 system are similar to those theoretically predicted and experimentally observed for the γ/γ′ system. The similarities are demonstrated in terms of the precipitate shape, spatial distribution, and minimum distance of
separation between L21 precipitates. However, all these effects disappear after aging the alloys at 800°C for 1000 hours, when the L21 precipitates become semicoherent at particle diameters above ∼400 nm. A simple analysis of the size evolution of L21 precipitates after an isochronal aging (1000 hours) experiment suggests that they follow coarsening kinetics at 600°C and
growth kinetics at 800°C, consistent with the Langer-Schwartz theory of precipitation kinetics, which predicts that a high
supersaturation suppresses the growth regime. Microanalysis using AEM and 3DAP microscopy define the TiNi-Ni2TiAl phase boundaries at 800°C and 600°C. At 800°C, Hf and Zr partition to the B2-TiNi, while at 600°C, they partition slightly
to the L21 phase, reducing the lattice misfit to −1.7 and −0.011 pct, respectively, and partition strongly to the metastable phase Ti2Ni3. To describe the composition dependence of the lattice parameter of multicomponent B2 and L21 phases, the atomic volumes of Al, Hf, Ni, Ti, and Zr in the B2-TiNi and L21 phases are determined. A simple model is proposed to predict the lattice parameters of these phases in multicomponent systems. 相似文献
16.
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
17.
M. Dilip Bhandarkar M. Shanthidas Bhat Victor F. Zackay Earl R. Parker 《Metallurgical and Materials Transactions A》1975,6(7):1281-1289
A Laves phase, Fe2Ta, was utilized to obtain good elevated temperature properties in a carbon-free iron alloy containing 1 at. pct Ta and 7
at. pct Cr. Room temperature embrittlement resulting from the precipitation of the Laves phase at grain boundaries was overcome
by spheroidizing the precipitate. This was accomplished by thermally cycling the alloys through the α→γ transformation. The short-time yield strength of the alloys decreased very slowly with increase in test temperature up to
600°C, but above this temperature, the strength decreased rapidly. Results of constant load creep and stress rupture tests
conducted at several temperatures and stresses indicated that the rupture and creep strengths of spheroidized 1 Ta-7 Cr alloy
were higher than those of several commercial steels containing chromium and/or molybdenum carbides but lower than those of
steels containing substantial amounts of tungsten and vanadium. When molybdenum was added to the base Fe-Ta-Cr alloy, the
rupture and creep strengths were considerably increased.
M. Dilip Bhandarkar, formerly with Lawrence Berkeley Laboratory. 相似文献
18.
Activity of carbon and solubility of carbides in the FCC Fe-Mo-C,Fe-Cr-C,and Fe-V-C alloys 总被引:1,自引:0,他引:1
T. Wada H. Wada J. F. Elliott J. Chipman 《Metallurgical and Materials Transactions B》1972,3(11):2865-2872
The activity of carbon in austenitic Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys has been studied by equilibration with controlled
CH4-H2 atmospheres at temperatures in the range 850° to 1200°C. The observations included a number of compositions in the two-phase
fields, γ + carbide. Equations are given for the activity coefficient of carbon as a function of temperature and composition
in the austenite field and from these the other thermodynamic properties of the solution may be computed as desired. The phase
boundaries γ/γ + carbide were determined by breaks in the isoactivity lines. This was supplemented in the case of Fe-Mo-C
alloys by metallographic linear analysis of equilibrated samples. The results confirm certain published phase diagrams and
discredit others.
T. WADA, formerly with Research Staff, Massachusetts Institute of Technology, Cambridge, Mass. 02139
H. WADA, formerly with Research Staff, Massachusetts Institute of Technology 相似文献
19.
A. Turnbull R. G. Ballinger I. S. Hwang M. M. Morra M. Psaila-Dombrowski R. M. Gates 《Metallurgical and Materials Transactions A》1992,23(12):3231-3244
The electrochemical permeation technique has been used to characterize hydrogen transport and trapping in pure nickel and
in alloys 600, X-750, and 718 at a temperature of 80 °C. The “effective diffusivity” of hydrogen atoms in alloy 600 is reduced
by a factor of about 5 compared to pure nickel. This is attributed to both compositional changes and the presence of [(Ti,
Nb)C] carbides. Aging of alloy 600, with subsequent M23C6 carbide precipitation, does not significantly influence the measured “effective diffusivity,” which is explained by the dominant
effect of preexisting [(Ti, Nb)C] carbides. The “effective diffusivity” of hydrogen atoms in solution-annealed alloy X-750
is reduced by a factor of about 9 compared to that of pure nickel. This is also attributed to compositional changes and [(Ti,Nb)C]
carbides. Aging of alloy X-750, which causes precipitation of γ’[Ni3(Al, Ti)], reduces the “effective diffusivity” by an additional factor of 5 or more. Double aging at 885 °C/24 hours, 704
°C/20 hours following hot working yields the greatest reduction in “effective diffusivity.” Analysis of permeation transients
using a diffusiontrapping model indicates a binding energy associated with trapping due to the γ’ phase of between-31 and
-37 kJ/mol. The “effective diffusivity” of hydrogen in alloy 718 is about 40 pct greater than for alloy X-750 for the same
double and direct aging treatments. The average “effective diffusivities” of the double-aged and direct-aged alloy 718 are
comparable, but the permeation transients for the double-aged treatment are significantly steeper. The double-aged treatment
with predominantly S phase (orthorhombic Ni3Nb) yields a binding energy of about-30 kJ/mol. Analysis of the direct aged-treated 718, which contains predominantly γ′ phase
(body-centered tetragonal Ni3Nb) gave a binding energy between -23 and -27 kJ/mol. Segregation of hydrogen atoms to the γ′/matrix interface, combined with
a large volume fraction ofγ at grain boundaries, provides the most likely explanation for the enhanced cracking associated
with the double-aging treatment in alloy X-750. 相似文献
20.
Gary N. Kirby D. L. Sponseller L. H. van Vlack 《Metallurgical and Materials Transactions B》1974,5(6):1477-1494
The relative effects of chromium, molybdenum, and tungsten on the occurrence of σ phase have been studied in Ni-Co-Cr alloys.
These alloys were designed to simulate the γ matrix in commercial nickel-base superalloys that are strengthened primarily
by precipitation of the γ phase, based on Ni3Al. Three alloy series were studied. The first series comprised four alloys varying in chromium content from 34.63 to 43.65
at. pct. The other two series contained separate molybdenum and tungsten additions of 1, 2, 3, and 4 at. pct at constant chromium
contents of 37.5 at. pct. In each of the 12 alloys, the atomic percentages of nickel and cobalt were equal. The alloys were
aged in both the annealed and cold-rolled conditions at 1400°F (760°C), 1550°F (845°C), and 1700°F (925°C) for times up to
3000 h. The contributions of the chromium-group elements to σ formation were evaluated both by measuring the volume percentage
of σ phase and by determining the final composition of the y matrix after σ precipitation. By these two techniques, critical
values of the average electron vacancy number, •N
v
, for σ formation at 1550°F (845°C) were found to be 2.518 and 2.512, respectively; σ precipitation was most rapid at 1550°F
(845°C). Both techniques in-dicated that under conditions approaching equilibrium, molybdenum and tungsten are equiv-alent
in inducing σ formation and about 1.5 to 2 times as potent as chromium. The approxi-mate electron vacancy coefficients(N
v
) for molybdenum and tungsten, as derived from volume-fraction measurements of σ phase, are as follows: 7.35 at 1400°F (760°C)
and 1550°F (845°C), and 8.7 at 1700°F (925°C). The values derived from final compositions of the γ matrix after σ precipitation
are 7.9 at 1550°F (845°C) and 8.6 at 1700°F (925°C). The bulk diffusion of aluminum into alloys that were otherwise not σ-prone
at 1700°F (925°C) caused extensive σ precipitation during aging. This was due to copious precipitation of γ-Ni3Al and β-NiAl, resulting in enrichment of the matrix in elements of the chromium group.
This paper is based on a dissertation submitted by GARY N. KIRBY in partial fulfillment of the requirements for the degree
of Doctor of Philosophy, Metallurgical Engineering, The University of Michigan, 1971. The study was conducted in the Ann Arbor
Research Labora-tory of the Climax Molybdenum Company of Michigan, a subsidiary of American Metal Climax, Inc. 相似文献