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1.
A Cu-15.0 at. pct Sn alloy has been chosen as a model alloy for the study of aging effects in copper-based shape memory alloys.
Different thermal aging treatments were carried out to determine the effects of both parent phase and martensite aging on
the amount of shape recovery and the characteristic transformation temperaturesM
s
,A
s
, andA
f
. Aging of the martensite reduces both the amount of shape recovery and the extent of the reverse martensite → parent transformation.
High martensite heating rates promote complete shape recovery and reverse transformation while the aging occurring during
slow heating can inhibit or prohibit both. But irrespective of the martensite heating rate the transformation temperature
hysteresis as given by (M
s
-A
s
) is large for the Cu-15 pct Sn alloy compared to other shape memory alloys exhibiting thermoelastic behavior. On the other
hand, some beneficial effects were noted when the Cu-15 pct Sn alloy was aged in the parent phase condition prior to subsequent
transformation to martensite. TheM
s
,A
s
, andA
f
were lowered following prior parent phase aging, possibly because of a change in long range order, but prior parent phase
aging was found to diminish the deleterious effect of martensite aging. Both shape recovery and the extent of the reverse
martensite → parent transformation are enhanced by prior parent phase aging. The enhancement is greater the higher the aging
temperature or the longer the aging time at a given temperature.
J. D. STICE, formerly Research Assistant at the University of Illinois 相似文献
2.
The relative effects of austenite stacking fault energy and austenite yield strength on martensite morphology have been investigated
in a series of three Fe-Ni-Cr-C alloys. Carbon content (0.3 wt pct) andM
6 temperature (− 15°) were held constant within the series. Austenite yield strength atM
s was measured by extrapolating elevated temperature tensile data. Austenite stacking fault energy was measured by the dislocation
node technique. Martensite morphologies were characterized by transmission electron microscopy and electron diffraction techniques.
A transition from plate to lath martensite occurred with decreasing austenite stacking fault energy. The austenite yield strength
atM
s for the low SFE, lath-forming alloy was found to be higher than previously reported for lath-forming alloys. The relative
effects of these variables on martensite morphologies in these alloys is discussed. 相似文献
3.
Fe3Pt austenites undergo an ordering reaction belowT
c
in addition to the martensite transformation at a much lower temperature. It is to be expected that theM
s
temperature will be affected by the degree of austenite order and the progress of austenite ordering can be conveniently
represented by the variation ofM
s
temperature. In this study it was found that heat treating the annealed austenites belowT
c
, a single-stage ordering reaction which followed first order kinetics was observed. The ordering rate or the rate ofM
s
temperature change was found to be composition dependent, faster for alloy closer to the stoichiometry. The reversed austenite
contains transformation induced defect structure. Consequently, heat treating the reversed austenites belowT
c
a two-stage reaction was observed. Annealing of defect structure was found to precede the ordering reaction. Both annealing
and ordering followed first order kinetics. The salient feature during annealing was that the initial rate ofM
s
temperature change appeared to be independent of alloy composition. 相似文献
4.
D. A. Colling 《Metallurgical and Materials Transactions B》1971,2(10):2889-2896
The martensite ⇌ austenite transformations were investigated in Fe-Ni-Co alloys containing about 65 wt pct Fe and up to 15
wt pct Co. A change in morphology of martensite from plate-like to lath-type occurred with increasing cobalt content; this
change in morphology correlates with the disappearance of the Invar anomaly in the austenite. The martensite-to-austenite
reverse transformation differed depending on martensite morphology. Reversion of plate-like martensite was found to occur
by simple disintegration of the martensite platelets. Reverse austenite formed from lath-type martensite was not retained
when quenched from much aboveA
s, with microcracks forming during theM→γ→M transformation. 相似文献
5.
Katsunari Oikawa Toshihiro Omori Yuji Sutou Haruhiko Morito Ryosuke Kainuma Kiyohito Ishida 《Metallurgical and Materials Transactions A》2007,38(4):767-776
Phase equilibria and martensitic and magnetic transitions of the β (B2 and L21) phase in the Ni–Fe–Ga system were investigated. The b phase was found to be in equilibrium with the γ (A1 structure) or
γ′ (L12 structure) phase. The Curie temperature, T
c
, equilibrium temperature, T
o
5 (Ms + Af)/2, martensitic transition starting temperature, M
s
, and reverse transition finishing temperature, Af , of the β single–phase alloys were sensitive to the Fe and Ga compositions.
The Fe substitution for Ni decreased and increased the T
o
and T
c
, respectively. The Ga substitution for Ni or Fe decreased both the T
o
and T
c
. The entropy change accompanying the reverse martensitic transition showed compositional dependence due to the magnetic contribution.
The saturation magnetization I
s
of the Ni–Fe–Ga system showed a strong dependence on the magnetic valence Z
M
. The Is values of the Ni–Fe–Ga alloys annealed at 1023 K showed the same Z
m
dependence as other ferromagnetic shape memory alloy (FSMA) systems.
This article is based on a presentation made in the symposium entitled "Phase Transformations in Magnetic Materials," which
occurred during the TMS Annual Meeting, March 12-16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS–MPMD
and ASMI–MSCTS Phase Transformations Committee. 相似文献
6.
Fe-Pt alloys near the composition Fe3Pt transform from fee austenite to bcc martensite at near ambient temperatures. The effect of austenite ordering in depressing
theM
s temperature has been reported previously, but more importantly the present work shows that ordering leads to a reversible
martensitic transformation. The characteristics of this reversible transformation have been investigated by optical metallography,
cinematography, and electrical resistivity measurements. It is concluded that in austenite ordered to an appropriate degree,
the transformation to martensite possesses all of the characteristics of a thermoelastic martensite transformation. This transformation
in ordered Fe~25 at. pct Pt alloys is the first thermoelastic martensite transformation reported for an iron-base alloy. The
present experiments indicate that martensite “nuclei” are not destroyed by the transformation, and are reactivated on each
cooling cycle at approximately the same temperature.
D. P. DUNNE, formerly with the University of Illinois at Urbana-Champaign, Urbana, 111. 61801 相似文献
7.
A series of dispersion strengthened Fe-Ni alloys has been prepared by powder metallurgical techniques. This series was designed
to permit evaluation of the relative effects of Ms temperature, chemical driving force, and austenite yield strength on resultant martensite morphology without altering matrix
chemistry. Using a carefully selected lath-forming Fe-27Ni-.025C base alloy, incremental additions of an inert oxide dispersion
resulted in a decrease in Ms temperature, an increase in the thermodynamic driving force at Ms, and an increase in the austenite yield strength at Ms to values beyond those previously associated with the lath-to-plate morphology transition. As the Ms temperature dropped below about 0 °C, martensite morphology shifted from lath to an intermediate “twinned lath” to plate,
while holding constant both matrix chemistry and thermal history. Previous correlations of thermodynamic driving force and
austenite yield strength with martensite morphology have been shown to break down. It is concluded that the observed transition
from lath to plate martensite in the present alloy series was induced primarily by the depression of Ms temperature into the plate-forming temperature regime of the Fe-Ni system. 相似文献
8.
The martensite start temperature (Ms), the martensite austenite re‐transformation start temperature (As) and the re‐transformation finish temperature (Af) of six high alloyed Cr‐Mn‐Ni steels with varying Ni and Mn contents in the wrought and as‐cast state were studied. The aim of this investigation is the development of the relationships between the Ms, As, Af, T0 temperatures and the chemical composition of a new type of Cr‐Mn‐Ni steels. The investigations show that the Ms, As and Af temperatures decrease with increasing nickel and manganese contents. The Af temperature depends on the amount of martensite. Regression equations for the transformation temperatures are given. The experimental results are based on dilatometer tests and microstructure investigations. 相似文献
9.
J. R. Strife M. J. Carr G. S. Ansell 《Metallurgical and Materials Transactions A》1977,8(9):1471-1484
The effect of austenite prestrain above theM
d
temperature on the structure and transformation kinetics of the martensitic transformation observed on cooling was determined
for a series of Fe-Ni-Cr-C alloys. The alloys exhibited a shift in martensite morphology in the nondeformed state from twinned
plate to lath while theM
s
temperature, carbon content, and austenite grain size were constant. The transformation behavior was observed over the temperature
range 0 to -196°C as a function of tensile prestrains performed above theM
d
temperature. A range of prestrains from 5 pct to 45 pct was investigated. It is concluded that the response of a given alloy
to austenite prestrain above theM
d
temperature can be correlated with the morphology of the martensite observed in the nondeformed, as-quenched state. For the
range of prestrains investigated, the transformation of austenite to lath martensite is much more susceptible to stabilization
by austenite prestrain above theM
d
temperature than is the transformation of austenite to plate martensite. 相似文献
10.
The Curie temperature of the austenite, the martensite-start temperature, and martensite morphology have been determined in a series of nil-carbon Fe?Ni and Fe?Ni?Co alloys. For these alloys, austenite ferromagnetism aboveM s is a necessary, but not sufficient, condition for the formation of lenticular rather than packet martensite. In contrast to Fe?Ni alloys where lenticular martensite only forms below ≈O°C, some of the Fe?Ni?Co alloys transform to this structure at temperatures up to ≈200°C. The results support the hypothesis that the resistance of austenite to plastic deformation affects the habit plane and thus morphology of the martensite which forms. 相似文献
11.
The effect of austenite yield strength on the transformation to martensite was investigated in Fe-10 pct Ni-0.6 pct C alloys.
The strength of the austenite was varied by 1) additions of yttrium oxide particles to the base alloy and 2) changing the
austenitizing temperature. The austenite strength was measured at three temperatures above theM
s temperature and the data extrapolated to the experimentally determinedM
s temperature. It is shown that the austenite yield strength is determined primarily by the austenite grain size and that the
yttrium oxide additions influence the effect of austenitizing temperature on grain size. As the austenite yield strength increases,
both theM
s temperature and the amount of transformation product at room temperature decrease. The effect of austenitizing temperature
on the transformation is to determine the austenite grain size. The results are consistent with the proposal1 that the energy required to overcome the resistance of the austenite to plastic deformation is a substantial portion of the
non-chemical free energy or restraining force opposing the transformation to martensite. 相似文献
12.
The effects of carbon content and ausaging on austenite γ ↔ martensite (α′) transformation behavior and reverse-transformed
structure were investigated in Fe-32Ni-12Co-4Al and Fe-(26,28)Ni-12Co-4Al-0.4C (wt pct) alloys. TheM
s
temperature, the hardness of γ phase, and the tetragonality of α′ increase with increasing ausaging time, and these values
are higher in the carbon-bearing alloys in most cases. The γ → α′ transformation behavior is similar to that of thermoelastic
martensite; that is, the width of α′ plate increases with decreasing temperature in all alloys. The αt’ → γ reverse transformation
temperature is lower in the carbon-bearing alloys, which means that the shape memory effect is improved by the addition of
carbon. The maximum shape recovery of 84 pct is obtained in Fe-28Ni-12Co-4Al-0.4C alloy when the ausaged specimen is deformed
at theM
s
temperature and heated to 1120 K. There are two types of reverse-transformed austenites in the carbon-bearing alloy. One
type is the reversed y containing many dislocations which were formed when the γ/α′ interface moved reversibly. The plane
on which dislocations lie is (01 l)γ if the twin plane is (112)α′. The other type of reverse-transformed austenite exhibits γ islands nucleated within the α′ plates. 相似文献
13.
Stress-Assisted and strain-induced martensites in FE-NI-C alloys 总被引:3,自引:0,他引:3
P. C. Maxwell A. Goldberg J. C. Shyne 《Metallurgical and Materials Transactions B》1974,5(6):1305-1318
A metallographic study was made of the martensite formed during plastic straining of metastable, austenitic Fe-Ni-C alloys
withM
s
temperatures below 0°C. A comparison was made between this martensite and that formed during the deformation of two TRIP
steels. In the Fe-Ni-C alloys two distinctly different types of martensite formed concurrently with plastic deformation. The
large differences in morphology, distribution, temperature dependence, and other characteristics indicate that the two martensites
form by different transformation mechanisms. The first type, stress-assisted martensite, is simply the same plate martensite
that forms spontaneously belowM
s
except that it is somewhat finer and less regularly shaped than that formed by a temperature drop alone. This difference
is due to the stress-assisted martensite forming from cold-worked austenite. The second type, strain-induced martensite, formed
along the slip bands of the austenite as sheaves of fine parallel laths less than 0.5μm wide strung out on the {111}γ planes of the austenite. Electron diffraction indicated a Kurdjumov-Sachs orientation for the strain-induced martensite relative
to the parent austenite. No stress-assisted, plate martensite formed in the TRIP steels; all of the martensite caused by deformation
of the TRIP steels appeared identical to the strain-induced martensite of the Fe-Ni-C alloys. It is concluded that the transformation-induced
ductility of the TRIP steels is a consequence of the formation of strain-induced martensite.
Formerly a graduate student at Stanford University 相似文献
14.
Phase transformations and the kinetics of domain growth were studied in near stoichiometric Ti3Al and in a similar alloy containing about 5 at. pct Nb (Cb). The alloys were quenched from the β and from the α+ β fields and were subsequently annealed in the α2 field to study the ordering transformation. The critical temperature (T
c) for ordering was found to be between 1125 and 1150° for both alloys. When quenched from aboveT
c the microstructure of the stoichiometric compound contained massive martensite with small antiphase domains of average size
8 × 10— μm. On annealing the quenched structures in the range 700 to 1000°, domain coalescence occurred, the domains growing approximately
as the square root of the annealing time. The activation energy for the domain growth process was found to be 64.6 ± 6 Kcal/mole
(2.68 ± 0.25 × 105 J/mole). On quenching the alloy containing Nb the β transforms to a fine acicular martensite. On annealing, antiphase domain
coalescence within the martensite plates and the simultaneous recrystallization of the martensite resulted in a fine subgrain
structure even after annealing at 900° for up to 3 h. The mechanical properties and the fracture modes of the two alloys tested
at 700° were correlated with the observed microstructural changes. The effects of Nb in this alloy are to slow the domain
growth kinetics, to reduce the planarity of slip, and to increase nonbasal slip activity.
Formerly NRC Research Associate in the Air Force Materials Laboratory, Wright-Patterson Air Force Base, OH 相似文献
15.
T. M. Heil M. A. Willard W. T. Reynolds Jr. 《Metallurgical and Materials Transactions A》2007,38(4):752-758
The martensite and magnetic transformations in Ni-Fe-Ga ferromagnetic shape memory alloys are very sensitive to both alloy
chemistry and thermal history. A series of Ni-Fe-Ga alloys near the prototype Heusler composition (X2YZ) were used to investigate how the martensite and magnetic transitions change with alloy composition and isothermal aging
above and below the B2/L21 ordering temperature. Calorimetry and magnetometry were employed to measure the martensite transformation temperatures and
Curie temperatures. Compositional variations of only a few atomic percent result in martensite start temperatures and Curie
temperatures that differ by about 230 and 35 K, respectively. Aging a Ni53Fe19Ga28 alloy for 3600 seconds at various temperatures shifts the martensite start temperature and the Curie temperature by almost
70 K. Transmission electron microscopy investigations were conducted on the aged Ni53Fe19Ga28 alloy. The considerable variations in the martensite and magnetic transformations in these alloys are discussed in terms
of microstructural differences resulting from alloy chemistry and aging treatments.
This article is based on a presentation made in the symposium “Phase Transformations in Magnetic Materials: Magnetic Shape
Memory Alloys which occurred March 14, 2006, during the TMS Spring Meeting in San Antonio, TX, under the auspices of the ASMI/MPMD-Phase
Transformations, EMPMD/SMD-Chemistry & Physics of Materials, and EMPMDNanomaterials Committees." 相似文献
16.
A. M. Thakur N. N. Thadhani R. B. Schwarz 《Metallurgical and Materials Transactions A》1997,28(7):1445-1455
Shock-impact generated tensile-stress pulses were used to induce B2-to-monoclinic martensitic transformations in two near-equiatomic
NiTi alloys having different martensite transformation start (M
s
) temperatures. The NiTi-I alloy (M
s
≈+27 °C) impacted at room temperature at 2.0 and 2.7 GPa tensile stress-pulse magnitude, showed acicular martensite morphology.
These martensite needles had a substructure containing microtwins, typical of “stress-assisted” martensite. The NiTi-II alloy
(M
s
≈−45 °C) showed no martensite formation when shocked with tensile-stress pulses of 2 GPa. For tensile stresses of 4.1 GPa,
the alloy showed spall initiation near the region of maximum tensile-stress duration. In addition, monoclinic martensite needles,
with a well-defined dislocation substructure, typical of “strain-induced” martensite, were seen clustering around the spall
region. No stress-assisted martensite was formed in this alloy due to its very low M
s
temperature. The present article documents results of the use of a metallurgical technique for generating large-amplitude
tensile stress pulses of finite duration for studies of phase transformations involving changes from a high density to a low
density state. 相似文献
17.
D. A. Colling 《Metallurgical and Materials Transactions B》1970,1(6):1677-1682
The reverse martensitic transformation was investigated in three Fe-Ni-Co alloys containing acicular martensite by means of
dilatometry and coercive force (Hc) measurements. Two maxima were observed in the Hc
-T relationships: the first Hc peak occurred at the Curie temperature of the austenite and is attributable to magnetic effects in a material containing
two ferromagnetic phases; the second Hc peak, with values near 400 oe, is caused by reverse transformation wherein the remaining ferromagnetic martensite has increased
coercivity due to decreased particle size and increased shape anisotropy. Dilatometric measurements display a gradual decrease
in expansivity in the early stages of reversal. This observation is explained by a two-step process for shear-type transformation
in which the first austenite formed has high magnetostriction and low expansivity. As the magnetostriction is lost by further
heating, a large expansion occurs which counteracts contraction due to the crystallographic phase change. 相似文献
18.
A. I. Uvarov V. A. Kazantsev N. F. Vil’danova E. I. Anufrieva 《Russian Metallurgy (Metally)》2010,(3):223-228
The N30K10T3 invar that has a temperature of the onset of martensite transformation of austenite M
s ≈ −80°C and a Curie point θC ≈ 200°C after water-quenching from 1150°C is studied. The decomposition of a supersaturated solid solution is shown to substantially
influence the linear thermal expansion coefficient. The alloy is studied in the following three initial states: after quenching,
after phase transformation-induced hardening (γ → αm → γp.h), and after cold (20°C) plastic deformation by 30%. 相似文献
19.
Three stabilization mechanisms—the shortage of nuclei, the partitioning of alloying elements, and the fine grain size—of the
remaining metastable austenite in transformation-induced plasticity (TRIP) steels have been studied by choosing a model alloy
Fe-0.2C-1.5Mn-1.5Si. An examination of the nucleus density required for an athermal nucleation mechanism indicates that such
a mechanism needs a nucleus density as large as 2.5 · 1017 m−3 when the dispersed austenite grain size is down to 1 μm. Whether the random nucleation on various heterogeneities is likely
to dominate the reaction kinetics depends on the heterogeneous embryo density. Chemical stabilization due to the enrichment
of carbon in the retained austenite is the most important operational mechanism for the austenite retention. Based on the
analysis of 57 engineering steels and some systematic experimental results, an exponential equation describing the influence
of carbon concentration on the martensite start (M
s) temperature has been determined to be M
s (K)=273+545.8 · e
−1.362w
c(mass pct). A function describing the M
s temperature and the energy change of the system has been found, which has been used to study the influence of the grain size
on the M
s temperature. The decrease in the grain size of the dispersed residual austenite gives rise to a significant decrease in the
M
s temperature when the grain size is as small as 0.1 μm. It is concluded that the influence of the grain size of the retained
austenite can become an important factor in decreasing the M
s temperature with respect to the TRIP steels. 相似文献
20.
W. Ito Y. Imano R. Kainuma Y. Sutou K. Oikawa K. Ishida 《Metallurgical and Materials Transactions A》2007,38(4):759-766
Martensitic and magnetic transformation behaviors of Ni50MnIn, Ni45Co5MnIn, and Ni42.5Co7.5MnIn Heusler alloys were investigated by differential scanning calorimetry (DSC), vibrating sample magnetometry (VSM), and
transmission electron microscopy (TEM). The martensitic transformation starting temperature (M
s
) decreases with increasing In composition, while the Curie temperatures (T
c
) of the parent phase are almost independent in each alloy series. On the other hand, the addition of Co resulted in a decrease
of the M
s
and an increase of the T
c
, and the degree of the decline of M
s
was accelerated by magnetic transformation of the parent phase. The M
s
temperature change induced by the magnetic field was also confirmed. It was found that the degree of M
s
change is strongly related to the entropy change by the martensitic transformation, which shows a correlation with T
c
-M
s
. These behaviors can be qualitatively explained on the basis of thermodynamic considerations.
This article is based on a presentation made in the symposium entitled “Phase Transformations in Magnetic Materials,” which
occurred during the TMS Annual Meeting, March 12–16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS-MPMD
and ASMI-MSCTS Phase Transformations Committee. 相似文献