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1.
The effect of ordering on susceptibility to hydrogen embrittlement of a Ni-base superalloy (alloy C-276) has been investigated
by means of tensile tests in air and with hydrogen-charging in 1N-H2SO4 solution. The annealed specimen has exhibited intergranular fracture by hydrogen-charging, resulting in a marked reduction
in tensile elongation and ultimate tensile strength. The mode of fracture was changed by aging at 773 K, and the transgranular
fracture has been found to be dominant in the aged specimens. The susceptibility to hydrogen embrittlement, as identified
by the test method used in this study, seems to be reduced by short-term aging, though it turns out to be increased again
by further aging. The fractured boundaries have been characterized using electron channeling pattern (ECP) analysis of adjacent
grains. It is found that the misorientation of grain boundaries plays an important role in fracture, and ∑3 boundaries, twin
boundaries in a face-centered cubic (fcc) lattice, are most likely to fracture in the aged specimens. Transmission electron
microscopy (TEM) observation has shown that a short-range ordering reaction from a disordered fcc lattice into an ordered
Ni2(Cr, Mo) (Pt2Mo type) super-lattice takes place by aging, and hence, superdislocation triplets with APB (antiphase boundary) become predominant
when deformed. It is also seen that in the aged specimens, deformation twinning is another mode of deformation, and this leads
to the transgranular fracture at twin boundaries by hydrogen-charging. These results suggest that a change in the mode of
deformation after aging plays a major role in fracture due to hydrogen embrittlement as a consequence of the heterogeneous
interaction between slip dislocations and twin boundaries. 相似文献
2.
Hydrogen embrittlement in a Mg-Al alloy 总被引:1,自引:0,他引:1
Experiments are described which demonstrate that a Mg-7.5 wt pct Al alloy is embrittled by both cathodically-generated and
gaseous hydrogen. Immersion of unstressed specimens in an aqueous NaCl-K2CrO4 solution is shown to lead to absorption of hydrogen and to a form of internal hydrogen embrittlement similar to that observed
in BCC metals. Thus embrittlement was manifested by loss of ductility in tensile tests and by cleavage-like fracture surfaces;
vacuum annealing after immersion led to a reduction in hydrogen concentration and to a partial recovery of ductility; and
embrittlement was not observed at high strain rates. Embrittled specimens also exhibited delayed failure in both constant-load
tensile tests and constant-deflection bend tests. In a second series of experiments, slow crack growth was observed when edge-notched
tensile specimens were stressed in ~ lpsig (~ 6.9 × 103 N/m2) dry hydrogen; the fracture surfaces were again cleavage-like in appearance. The significance of these observations is discussed
in relation to the stress-corrosion failure of this alloy.
Formerly a Research Assistant in the Department of Metallurgy and Mining Engineering, University of Illinois, IL, 相似文献
3.
D. M. Symons 《Metallurgical and Materials Transactions A》1997,28(3):655-663
The purpose of this work was to investigate the role of chromium on hydrogen embrittlement of Ni-Cr-Fe alloys and thus to
develop a better understanding of the low-temperature stress corrosion cracking (SCC) phenomenon. The effect of chromium on
hydrogen embrittlement was examined using tensile tests followed by material evaluation via scanning electron microscopy (SEM) and light optical microscopy. Four alloys were prepared with chromium contents ranging
from 6 to 35 wt pct. In the uncharged condition, ductility, as measured by the percent elongation or reduction in area, increased
as the alloy chromium content increased. Hydrogen appeared to have only minor effects on the mechanical properties of the
low-chromium alloys. The addition of hydrogen had a marked effect on the ductility of the higher-chromium alloys. In the 26
pct chromium alloy, the elongation to failure was reduced from 53 to 14 pct, with a change in fracture mode from mixed ductile
dimple and ductile intergranular failure to a brittle appearing intergranular failure. A maximum in embrittlement was observed
in the 26 pct Cr alloy. The maximum in embrittlement coincided with the minimum in stacking-fault energy. It is proposed that
the increased hydrogen embrittlement in the high-chromium alloys is due to increased slip planarity caused by the lower stacking-fault
energy. Slip planarity did not appear to affect the fracture of the uncharged specimens. 相似文献
4.
Douglas M. Symons Anthony W. Thompson 《Metallurgical and Materials Transactions A》1996,27(1):101-110
The effect of hydrogen on the fracture of a nickel-base superalloy, alloy X-750, was investigated in the HTH condition. The
effect of hydrogen was examined through tensile testing incorporating observations from scanning electron microscopy and light
microscopy. The ductility at 25 °C, as measured by elongation to failure for tensile specimens, was reduced from 21 pct for
noncharged specimens to 7.3 pct for 5.7 ppm hydrogen and to 3.5 pct for 65 ppm hydrogen. The elongation to failure was a function
of the strain rate and test temperature. For hydrogen-charged specimens, the elongation decreased as the strain rate decreased
at a constant temperature, while for a constant strain rate and varying temperature, there was a maximum in embrittlement
near 25 °C and no embrittlement at -196 °C. For the noncharged specimens, the elongation monotonically increased as temperature
increased, while there was no noticeable effect of strain rate. Prestraining prior to charging dramatically decreased elongation
after hydrogen charging. When the strain rate was increased on the prestrained specimens, more plastic deformation was observed
prior to failure. Failure did not occur until the flow stress was reached, supporting the proposition that plasticity is required
for failure. The intergranular failure mechanism in alloy X-750 was a microvoid initiation process at grain boundary carbides
followed by void growth and coalescence. The void initiation strain, as determined from tensile data and from sectioning unfractured
specimens, was observed to be much lower in the hydrogen-charged specimens as compared to noncharged specimens. The reduced
ductility may be explained by either a reduction of the interfacial strength of the carbide-matrix interface or a local hydrogen
pressure at the carbide-matrix interface. 相似文献
5.
The effect of heat treatment on ductility loss in a boron-doped Ni3Al was studied by tensile tests of alloy specimens exposed to contaminated environments. Specimens heat-treated extensively
in evacuated quartz capsules at 1323 K exhibit only 3.3 pct ductility at 1033 K, whereas a previous study reported a tensile
ductility of about 24 pet for specimens heat-treated in a high vacuum system. Aluminum oxide and silicon-contaminated regions
were observed at and near external surfaces of capsule-annealed specimens. The reactions occurring during heat treatment are
interpreted in terms of thermodynamics. An Auger electron spectroscopy study revealed oxygen penetration along grain boundaries
during capsule annealing. Although the surface oxide layer and silicon contamination both contribute to some reductions in
ductility, the major cause for embrittlement comes from oxygen penetration along grain boundaries. 相似文献
6.
The mechanical properties and microstructures of commercial 11 to 29 pct Cr ferritic steels were examined as functions of
aging times to 1000 h at 371, 482, and 593°C. Of the properties evaluated, changes in impact transition temperatures were
the best measure of embrittlement. Embrittlement at 482°C occurs most rapidly in the 29 pct Cr alloy and somewhat more slowly
in the stabilized 26 pct Cr alloy. The stabilized 18 pct Cr alloy embrittles much more slowly while little, if any, embrittlement
was detected in a stabilizedll pct Cr alloy. Embrittlement at 482°C was characterized by a rapid change in properties followed
by a plateau region and then further property changes. The early property change is attributed to precipitation of interstitial
compounds and the later change to classic 475°C embrittlement. The onset of 475°C embrittlement in the two highest Cr alloys
was accompanied by clustering of Cr atoms along {100} planes indicative of spinodal decomposition. Concurrent with clustering
there was also a change from turbulent slip to a more planar slip along {110} planes. Some embrittlement was observed after
longer exposures at 371°C which was attributed to a combination of 475°C embrittlement and the precipitation of interstitial
compounds. Two of the alloys also embrittled at 593°C, accompanied by optically observable precipitates. The precipitate in
the stabilized 18 pct Cr alloy was identified as Laves (Fe2Ti) phase. One of the precipitates in the 29 pct Cr alloy was identified as sigma phase.
Formerly with Allegheny Ludlum Steel Corporation. 相似文献
7.
《Acta Metallurgica Materialia》1993,41(7):1979-1987
Hydrogen embrittlement has been studied in continuous cast sheet of an Ni3Al alloy (Ni77.83Al21.73Zr0.34B0.1). When tensile tests were performed at the initial strain rate of 5.8 × 10−5 s−, the elongation decreased from 32.7% for no charging to 1.9% for 330 min of cathodic charging with 50 mA/cm2 current, but the yield stress did not change. The fracture mode changed partially from dimple to intergranular and cleavage modes. At a faster strain rate of 5.8 × 10−3 s−1, hydrogen embrittlement was less pronounced, but the yield stress increased with hydrogen content and multiple cracks were generated. Plastically pre-deformed (2–26% elongations) and subsequently charged specimens failed after yielding, which occurred at the final pre-deformation stress. Our results suggest that the grain boundary or the interior of the grain was not weakened by hydrogen, rather hydrogen-enhanced localized plasticity caused the loss of ductility in B-doped Ni3Al alloy. 相似文献
8.
Xiang-Mingh He Li-Jian Rong Yi-Yi Li De-Sheng Yan Zhi-Min Jiang 《Metallurgical and Materials Transactions A》2004,35(9):2783-2788
The shape-memory characteristics in the Ni41.3Ti38.7Nb20 alloy have been investigated by means of cryogenic tensile tests and differential scanning calorimetry measurement. The martensite
start temperature M
s
could be adjusted to around the liquid nitrogen temperature by controlling the cooling condition. The reverse transformation
start temperature A′
s
rose to about 70 °C after the specimens were deformed to 16 pct at different temperatures, where the initial states of the
specimens were pure austenite phase, martensite phase, or duplex phase. The shape-memory effect and the reverse transformation
temperatures were studied on the specimens deformed at (M
s
+30 °C). It was found that once the specimens deformed to 16 pct, a transformation hysteresis width around 200 °C could be
attained and the shape recovery ratio could remain at about 50 pct. The Ni41.3Ti38.7Nb20 alloy is a promising candidate for the cryogenic engineering applications around the liquid nitrogen temperature. The experimental
results also indicated that the transformation temperature interval of the stress-induced martensite is smaller by about one
order of magnitude than that of the thermal-induced martensite. 相似文献
9.
The variation of the tensile mechanical properties and hardness (at 25‡C) of three Ni-Cr alloys has been determined as a function
of aging time (up to 4 months) in the range 290 to 530‡C. Aging has a negligible effect on the 10 pct Cr alloy, and only a
slight effect on the 20 pct Cr alloy. However, the 30 pct Cr alloy showed a marked sensitivity to aging; for example, at 479‡C
the yield strength doubled after about 1 month, then decreased slightly at 4 months. The effect in the 30 pct Cr alloy is
due to the formation of the Ni2Cr superlattice. 相似文献
10.
K. D. Sheffler R. H. Barkalow A. Yuen G. R. Leverant 《Metallurgical and Materials Transactions A》1977,8(1):83-89
The orientation dependence of deformation and fracture modes was investigated for a directionally-solidified Ni−Ni3Al−Ni3Cb lamellar eutectic alloy (Ni-20 wt pct Cb-2.5 wt pct al-6.0 wt pct Cr) using optical and transmission microscopy to examine
tensile and compression specimens tested at temperatures below the softening point of the δ (Ni3Cb) reinforcing phase (∼1050 K). In this temperature range there is a large difference between longitudinal and transverse
tensile ductibility (>5 pct longitudinalvs<1 pct transverse). No single preferred fracture path (such as interfacial delamination) could be found to account for the
low transverse tensile ductility. Analysis of the δ twinning geometry, however, indicated that the twinning strains for twins
of the type {211}, which operate copiously in longitudinal tension, are negative in most transverse orientations, with Schmid
factors being very low (<0.013) in the limited range of transverse orientations where {211} twin strains are positive. Examination
of transverse tension test specimens broken at 1033 K confirm the absence of {211} twins, with only limited {011} twinning
being found in selected grains, leading to the conclusion that the relatively low transverse tensile ductility of the eutectic
results from the very limited number of deformation systems which operate in the δ reinforcing phase below the softening temperature. 相似文献
11.
Chuan-Ming Tseng Wen-Ta Tsai Horng-Yih Liou 《Metallurgical and Materials Transactions A》2003,34(1):95-103
The effect of nitrogen content on the stress corrosion cracking (SCC) behavior of 22 pct Cr duplex stainless steel (DSS) in
chloride solutions was investigated in this study. Slow strain rate testing (SSRT) was employed to evaluate the SCC susceptibility.
The experimental results showed that the tensile strength and ductility of 22 pct Cr DSS increased with increasing amount
of nitrogen (in the range of 0.103 to 0.195 wt pct). Slow strain rate testing results indicated that 22 pct Cr DSSs were resistant
to SCC in 3.5 wt pct NaCl solution at 80 °C. However, environmentally assisted cracking occurred in 40 wt pct CaCl2 solution at 100 °C and in boiling 45 wt pct MgCl2 solution at 155 °C, respectively. The effects of environment and nitrogen content in DSS on the cracking susceptibility are
discussed in this article. Selective dissolution of ferrite phase was found to participate in the SCC process for tests in
CaCl2 solution. At temperatures above 80 °C, dynamic strain aging was found to occur in various environments at a strain beyond
plastic deformation. 相似文献
12.
《Acta Metallurgica Materialia》1994,42(10):3527-3534
The influence of residual hydrogen and hydrogen released from environment on the embrittlement of the Ni3(Al,Ti) single crystals with [001] orientation was investigated by the tensile tests at a room temperature both in air and vacuum, using specimens containing residual hydrogen in a wide range of contents (0.6–70 massppm). The tensile elongation and the UTS values of specimens deformed in air were primarily insensitive to the residual hydrogen contents, and the associated fractography exhibited the brittle fracture mode along the [001] plane. On the other hand, the tensile elongation and the UTS values of specimens deformed in vacuum were strongly sensitive to the residual hydrogen contents. With decreasing the residual hydrogen content, the tensile elongation and the UTS values increased, and the associated fractography changed from the brittle manner to the ductile manner. These results indicate that the ductility of the Ni3(Al,Ti) single crystals deformed in air is controlled by hydrogen released from moisture in air while that of the Ni3(Al,Ti) single crystals deformed in vacuum is controlled by residual hydrogen. 相似文献
13.
Iron alloys containing 20 and 30 pct Ni and 3 to 4 cu cm H per 100 g metal have been subjected to slow strain-rate tensile tests in a study of hydrogen embrittlement. In the lower nickel massive martensite alloy, embrittlement is manifest as the cracking of prior austenite grain boundaries and is severe at room temperature but less marked at -196°C; while in the higher nickel acicular martensite alloy, the embrittlement observed at 20°C does not occur at —196°C. Hydrogen embrittlement in these materials is believed to be the result of high hydrogen contents in the vicinity of the prior austenite grain boundaries combined with stress concentrations caused by boundary perturbations which result from the impact of the martensite shears. During deformation, microcracks form and propagate in the prior austenite grain boundaries, probably assisted by internal hydrogen pressure and the lowering of crack surface energy by hydrogen adsorption. The temperature dependence and the effect of the type of martensite on the embrittlement can be explained by their effects on the hydrogen content and stress concentrations at prior austenite grain boundaries during deformation. 相似文献
14.
Mine Yoji Tachibana Kazutaka Horita Zenji 《Metallurgical and Materials Transactions A》2011,42(6):1619-1629
This study addresses a hydrogen effect on the tensile properties of a type 310S austenitic stainless steel with ultrafine-grained
structures produced by high-pressure torsion (HPT) and subsequent annealing. The mean grain size was reduced to ~85 nm by
the HPT processing. The grain size was increased by the post-HPT annealing, but the grain size of ~265 nm was retained after
annealing at 1023 K (750 °C). The tensile strength of ~1.2 GPa, which is approximately twice as much as that of the solution-treated
specimen, was attained in the 1023 K (750 °C) post-HPT-annealed specimen. The elongation to failure was restored up to ~15 pct
by the post-HPT annealing, although it was still insufficient in comparison with the ~55 pct elongation of the solution-treated
specimen. There was no change in the tensile strength of the HPT-processed specimens and the post-HPT-annealed specimens by
hydrogen charging with the hydrogen content in the range of ~20 to 40 mass ppm. The HPT-processed and the 773 K (500 °C) post-HPT-annealed
specimens exhibited a ductility loss through the fully shear type fracture. The hydrogen charge into higher temperature post-HPT-annealed
specimens with σ-FeCr precipitates led to a mild hydrogen embrittlement. 相似文献
15.
The mechanical properties of the Ll2-type intermetallic compound Ni2(Al0.4,Mn0.6), which exhibited enough deformability accompanied with the positive temperature dependence of yield stress, were examined
from the point of view of its susceptibility to hydrogen embrittlement. Remarkable and moderate increases of elongation and
ultimate tensile strength were observed by evacuating and with increasing strain rate, respectively, although the yield stress
was almost constant independent of not only testing environment but also strain rate. On the other hand, the cathodically
precharged hydrogen showed deteriorated elongations while the baking treatment resulted in restoration of elongation. Fractographic
observation revealed the expected correlation between elongation and fracture mode; with increasing elongation the transgranularly
fractured region increased. From this result, it is suggested that hydrogen can be removed from the specimen interior by evacuating
or baking, and also that hydrogen can be injected from the sample surface by hydrogen charging; that is to say, hydrogen permeation
is almost reversible for both processes. It is thus concluded that the present alloy has severe hydrogen embrittlement susceptibility,
both from the residual hydrogen in the specimens as well as from that penetrated from the environment.
formerly Graduate Student with Tohoku University, Sendai, Japan, 相似文献
16.
The apparent hydrogen compatibility of an age hardenable iron base superalloy (Fe + 30 pct Ni + 15 pct Cr + 2.0 pct Ti + 1.25
pct Mo) was affected by specimen preparation technique. Hydrogen induced ductility losses were significantly greater in specimens
which were machined before aging than in companion samples which were aged before being machined to shape. This difference
in susceptibility to hydrogen is attributed to the combined effects of the strain enhanced precipitation of Ni3Ti (ρ) in the near-surface, cold worked layer produced by the machining operation and the reduction in hydrogen compatibility
by ρ precipitation.
Is Member, Technical Staff, Sandia National Laboratories, Livermore, Livermore, CA 945 formerly Professor at SummerUniversity,
Sandia National Laboratories. 相似文献
17.
A eutectic alloy, Ag-32.2 at. pct Mg, has been directionally solidified at growth rates,R, ranging from 0.9 to 63.9 cm/h to produce an aligned lamellar structure. The alloy consists of AgMg, an ordered CsCl type
phase, and a solid solution of approximate composition Ag-27 at. pct Mg. The investigation consisted of studying ordering
effects in the Ag-27 pct Mg phase on creep behavior of the aligned eutectic at temperatures between 210 and 270°C. Ordering
of Ag-27 pet Mg markedly reduced creep rate and increased rupture life of the eutectic alloy. An increase in R resulted in
a finer interlamellar spacing and further reduced creep rate for both ordered and disordered material. An increase in the
apparent activation energy for creep with order is consistent with an increase in the activation energy for vacancy motion
in the Ag3Mg phase. Creep tests on a single-phase Ag3Mg alloy confirmed this conclusion. Both the ordered and disordered eutectic alloy exhibited a high sensitivity of steady-state
creep rate, ε, to stress. The stress dependence was analyzed in terms of a proposed mechanism of creep in this alloy. Slip
processes have been observed by optical microscopy, and fractographic techniques have been employed to explain the influence
of long range order on rupture. Implications of this work to design of creep-resistant eutectic composites are discussed. 相似文献
18.
G. Frommeyer W. Kowalski R. Rablbauer 《Metallurgical and Materials Transactions A》2006,37(12):3511-3517
A rapidly solidified and thermomechanically processed fine-grained eutectic NiAl−Cr alloy of the composition Ni33Al33Cr34 (at, pct) exhibits structural superplasticity in the temperature regime from 900°C to 1000°C at strain rates ranging from
10−5 to 10−3 s−1. The material consists of a B2-ordered intermetallic NiAl(Cr) solid solution matrix containing a fine dispersion of bcc chromium.
A high strain-rate-sensitivity exponent of m=0.55 was achieved in strain-rate-change tests at strain rates of about 10−4 s−1. Maximum uniform elongations up to 350 pct engineering strain were recorded in superplastic strain to failure tests. Activation
energy analysis of superplastic flow was performed in order to establish the diffusion-controlled dislocation accommodation
process of grain boundary sliding. An activation energy of Q
c=288±15 kJ/mole was determined. This value is comparable with the activation energy of 290 kJ/mole for lattice diffusion of
nickel and for 63Ni tracer selfdiffusion in B2-ordered NiAl. The principal deformation mechanism of superplastic flow in this material is grain-boundary
sliding accommodated by dislocation climb controlled by lattice diffusion, which is typical for class II solid-solution alloys.
Failure in superplastically strained tensile samples of the fine-grained eutectic alloy occurred by cavitation formations
along NiAl‖‖Cr interfaces. 相似文献
19.
R. S. Dutta G. K. Dey A. Lobo R. Purandare S. K. Kulkarni 《Metallurgical and Materials Transactions A》2002,33(5):1437-1447
The corrosion behavior of austenitic alloy 690 in a solution-annealed condition has been evaluated with the application of
anodic as well as cathodic potentials in an acidic chloride solution at room temperature (RT). In a 0.5M H2SO4 + 0.5M NaCl solution, the alloy displayed active-passive pitting behavior with the application of an anodic potential. Surface
films, formed at the onset and later stage of the passive region, were characterized using X-ray photoelectron spectroscopy
(XPS). The XPS revealed that the surface film formed at the onset of passivity (+ 100 mV SCE) consisted of Cr(OH)3, without any Fe+3/Fe+2. The presence of nickel in the film was found in a transition state of Ni+2 and Ni0. The passive film formed at the higher anodic potential (+ 700 mV SCE) consisted of Cr2O3 without any Fe+3/Fe+2 or even Ni+2/Ni0. Microscopic studies of alloy 690 after anodic polarization in an acidic chloride solution revealed pitting, which was found
to be initiated at large, faceted TiN-type inclusions. The susceptibility of the alloy to hydrogen embrittlement has been
investigated by conducting cathodic charging of the tensile samples in a 0.5M H2SO4 solution at RT and by subsequent tensile testing of the charged samples in air at a strain rate of 1.3 × 10−4 s−1 up to fracture. An indication toward hydrogen-induced ductility loss was noticed for the samples of the alloy, which is believed
to be attributable to a hydrogen-enhanced microvoid growth process. Since the microvoid growth process occurs at the last
stage of fracture, the effect of hydrogen on the ductility of the alloy is little. 相似文献
20.
W. Matuszyk G. Camus D. J. Duquette N. S. Stoloff 《Metallurgical and Materials Transactions A》1990,21(11):2967-2976
The effects of temperature, frequency, and environment on the tensile and cyclic deformation behavior of a nickel aluminide
alloy, Ni-9.0 wt pct Al-7.97 pct Cr-1.77 pct Zr (IC-221), have been determined. The tensile properties were obtained in vacuum
at elevated temperatures and in air at room temperature. The alloy was not notch sensitive at room temperature or at 600 °C,
unlike Cr-free Ni3Al + B alloys. In general, crack growth rates of IC-221 increased with increasing temperature, decreasing frequency, exposure
to air, or testing at higherR ratios. At 25 °C, crack growth rates were slightly higher than for a previously investigated Cr-free Ni3Al alloy. However, at 600 °C, the crack growth rates for IC-221 were lower than for the Cr-free alloy. Substantial frequency
effects were noted on crack growth of IC-221 at both 600 °C and 800 °C in both air and vacuum, especially at highK. The relative contributions of creep and environmental interactions to fatigue crack growth are discussed. 相似文献