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1.
G. S. Ansell S. J. Donachie R. W. Messler 《Metallurgical and Materials Transactions B》1971,2(9):2443-2449
The effect of very high quench rates on the transformation kinetics of a series of Fe?C and low-alloy steels and the morphology of an Fe?14Ni-0.76C alloy was investigated. TheM S temperatures of the Fe?C and Fe?C?X alloys increased between 90° and 122°C in a sigmoidal fashion over a quench rate range from 2,750° to 24,800°C per sec. The sensitivity of theM s temperature to the quench rate from the austenitizing temperature to 315°C was shown to be related to the influence of the third alloying element on the diffusivity of carbon in austenite. Transmission electron microscopy and optical metallography showed that the morphology of an Fe?14Ni?0.76C martensite is changed from a lath structure in slow quenched samples to a plate structure in fast quenched samples. The substructure of the untransformed austenite adjacent to the martensite plates changed from planar dislocation arrays to dislocation tangles with increased quench rate. These results were explained using a model for ferrous martensite strengthening based upon the extent of carbon segregation to imperfections in the austenite during cooling. 相似文献
2.
《Acta Metallurgica Materialia》1993,41(6):1693-1699
The morphology and habit planes of deformation-induced lenticular martensite were investigated by optical and transmission electron microscopy in Fe30Ni and Fe30Ni0.11C alloys. Transitions in morphology were observed with progressive deformation levels going from lenticular to butterfly and to compact martensite for the Fe30Ni alloy and lenticular to butterfly and to small butterfly martensite for the Fe30Ni0.11C alloy. The habit planes changed from {225}f or {259}f for the thermal lenticular martensite to {111}f for the strain-induced martensite. The morphology and crystallography of the small butterfly martensites was also investigated. A change in the orientation relationships from K-S to N-W relations was also observed. These changes were attributed to the contribution of mobile dislocations which modified the shear mode from twinning to slip, and to a plastic accomodation of transformation strains. 相似文献
3.
Mössbauer Fe57 spectroscopy allows comparison of Fe?N and Fe?C interstitial solid solutions. The spectra of Fe?N retained austenite indicate that nitrogen atoms are randomly distributed on octahedral sites in the austenite and in the virgin martensite. On heating, austenite decomposes directly to the equilibrium phases α iron and Fe4N at temperatures above 160°C. Virgin martensite ages at room temperature by local ordering of nitrogen atoms. In that process, three new iron atom environments develop, characteristic of the Fe16N2 (α″) structure. However, the excessive width of the peaks indicate the perfect order of the Fe16N2 precipitate is not achieved, except after very long times. Further aging at 100°C leads to the complete decomposition of the virgin martensite to the discrete phases α iron and Fe16N2. This two phase structure is stable up to 160°C, above which the precipitation of Fe4N occurs. These results are in contrast to Fe?C data. Carbon atoms in retained austenite tend to be far apart in their octahedral sites, and this nonrandom distribution is inherited by the virgin martensite. Fe?C austenite decomposes by the formation of ∈ carbide below 160°C and precipitation of Fe3C above 180°C. The carbon atoms in virgin martensite agglomerate at room temperature and regions of ordered Fe4C are believed to result. Subsequently ∈ carbon is formed at 80°C and Fe3C precipitates above 160°C.1 相似文献
4.
《Acta Metallurgica Materialia》1991,39(6):1123-1131
In order to elucidate the origin of abnormally large tetragonality (c/a) of martensite in the FeNiC alloy system, a large number of alloys of which the Ni content is varied for a constant carbon content have been examined, using low temperature X-ray diffraction, optical and electron microscopy. The results show that the tetragonality of martensite in this alloy system is strongly dependent on martensite morphology. Namely, it is very large for a plate martensite, while it is normal or not so large for a lenticular martensite. In more physical words, the martensite tetragonality is dependent on the mode of the lattice invariant deformation in martensitic transformation. If the lattice invariant deformation is twinning, the resulting c/a is large, while in the case of slip it is small. 相似文献
5.
Bikas C. Maji Madangopal Krishnan V. V. Rama Rao 《Metallurgical and Materials Transactions A》2003,34(5):1029-1042
The microstructure and phase stability of the Fe-15Mn-7Si-9Cr-5Ni stainless steel shape memory alloy in the temperature range
of 600 °C to 1200 °C was investigated using optical and transmission electron microscopy, X-ray diffractometry (XRD), differential
scanning calorimetry (DSC), and chemical analysis techniques. The microstructural studies show that an austenite single-phase
field exists in the temperature range of 1000 °C to 1100 °C, above 1100 °C, there exists a three-phase field consisting of
austenite, δ-ferrite, and the (Fe,Mn)3Si intermetallic phase; within the temperature range of 700 °C to 1000 °C, a two-phase field consisting of austenite and the
Fe5Ni3Si2 type intermetallic phase exists; and below 700 °C, there exists a single austenite phase field. Apart from these equilibrium
phases, the austenite grains show the presence of athermal ɛ martensite. The athermal α′ martensite has also been observed for the first time in these stainless steel shape memory alloys and is produced through
the γ-ɛ-α′ transformation sequence. 相似文献
6.
《Acta Metallurgica Materialia》1994,42(12):4117-4133
The stabilization effect of retained austenite has been studied using FeNiC alloys with Ms temperatures below 0°C via a two-step cooling procedure, i.e. the samples were first cooled to a temperature (Ta) below Ms temperature and then heated to room temperature (RT), after being held at RT for a while, the samples were recooled to low temperatures (23 or 82 K) and then heated to RT. It was found that, during the second step of cooling, the martensitic transformation occurred at a temperature of Ms′ which was lower than Ta. With increasing the amount of martensite formed during the first cooling, the difference in the martensitic transformation starting temperatures, ΔMs = Ms − Ms′, increased. The mechanism of the stabilization of retained austenite during the second step of cooling is proposed to be mainly due to the inhibition effect produced by the previously formed martensite. The aging processes, which retard the growth of the previously formed martensite plates and reduce the number of the available nucleation sites, are the necessary conditions for the above mechanism to operate. By simplifying the internal resisting stress acting on the retained austenite due to the existence of martensite phase as a hydrostatic compressive stress, which increases with increasing the amount of martensite, the change in ΔMs is discussed from a thermodynamic point of view. 相似文献
7.
M. J. Cieslak C. R. Hills P. F. Hlava S. A. David 《Metallurgical and Materials Transactions A》1990,21(9):2465-2475
Differential thermal analysis (DTA), high-temperature water-quench (WQ) experiments, and optical and electron microscopy were used to establish the near-solidus and solidification microstructures in PH 13-8 Mo. On heating at a rate of 0. 33 °C/s, this alloy begins to transform from austenite to δ-ferrite at ≈1350 °C. Transformation is complete by ≈1435 °C. The solidus is reached at ≈1447 °C, and the liquidus is ≈1493 °C. On cooling from the liquid state at a rate of 0. 33 °C/s, solidification is completed as δ-ferrite with subsequent transformation to austenite beginning in the solid state at ≈1364 °C. Insufficient time at temperature is available for complete transformation and the resulting room-temperature microstructure consists of matrix martensite (derived from the shear decomposition of the austenite) and residual δ-ferrite. The residual δ-ferrite in the DTA sample is enriched in Cr (≈16 wt pct), Mo (≈4 wt pct), and Al (≈1. 5 wt pct) and depleted in Ni (≈4 wt pct) relative to the martensite (≈12. 5 wt pct Cr, ≈2 wt pct Mo, ≈1 wt pct Al, ≈9 wt pct Ni). Solid-state transformation of δσ γ was found to be quench-rate sensitive with large grain, fully ferritic microstructures undergoing a massive transformation as a result of water quenching, while a diffusionally controlled Widmanstätten structure was produced in air-cooled samples. 相似文献
8.
Bikas C. Maji Madangopal Krishnan M. Sujata Gouthama Ranjit K. Ray 《Metallurgical and Materials Transactions A》2013,44(1):172-185
The effect of Co addition has been studied in Fe-30Mn-6Si-xCo (x = 0 to 9 wt pct) shape memory alloys in terms of their microstructure, martensitic transformation and shape recovery. Microstructural investigations reveal that in Fe-Mn-Si-Co alloys, the microstructure remains single-phase austenite (??) up to 5 pct Co and beyond that becomes two-phase comprising ?? and off-stoichiometric (Fe,Co)5Mn3Si2 intermetallic ??-phases. The forward ??-?? martensite transformation start temperature (M S) decreases with the addition of Co up to 5 pct, and alloys containing more than 5 pct Co, show slightly higher M S possibly on account of two-phase microstructure. Unlike M S, the ??-?? reverse transformation start temperature (A S) has been found to remain almost unaltered by Co addition. In general, addition of Co to Fe-Mn-Si alloys deteriorates shape recovery due to decreasing resistance to plastic yielding concomitant with the formation of stress induced ?? martensite. However, there is an improvement in shape recovery beyond 5 pct Co addition, possibly due to the strengthening effect arising from the presence of (Fe,Co)5Mn3Si2 precipitates within the two-phase microstructure and due to higher amount of stress induced ?? martensite. 相似文献
9.
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
10.
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
11.
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
12.
Plastic flow during the austenite ? martensite transformation under constant load has been studied in two Fe?Ni alloys (15.4 pct Ni; 32.9 pct Ni). Transformation plasticity, characterized by the typical linear relationship between the transformation strain per cycle and the externally applied stress,i.e., a quasiviscous behavior, was observed for both alloys. The plastic transformation strain on heating was larger than that on cooling for the 15.4 pct Ni alloy and equal to that on cooling for the 32.9 pct Ni alloy. Transformation plasticity results for both alloys are in quantitative agreement with the pseudo-creep theory of Greenwood and Johnson except for the martensite to austenite transformation in the 32.9 pct Ni alloy where the result is an order of magnitude too low. A dislocation model is proposed which considers the superposition of the large shear stresses generated by the martensite plate formation and the externally applied stress. The model quantitatively predicts the stress dependence of the transformation strain per cycle for transformation plasticity. 相似文献
13.
Dieter Isheim Allen H. Hunter Xian J. Zhang David N. Seidman 《Metallurgical and Materials Transactions A》2013,44(7):3046-3059
Austenite reversion in martensitic steels is known to improve fracture toughness. This research focuses on characterizing mechanical properties and the microstructure of low-carbon, high-nickel steels containing 4.5 and 10 wt pct Ni after a QLT-type austenite reversion heat treatment: first, martensite is formed by quenching (Q) from a temperature in the single-phase austenite field, then austenite is precipitated by annealing in the upper part of the intercritical region in a lamellarization step (L), followed by a tempering (T) step at lower temperatures. For the 10 wt pct Ni steel, the tensile strength after the QLT heat treatment is 910 MPa (132 ksi) at 293 K (20 °C), and the Charpy V-notch impact toughness is 144 J (106 ft-lb) at 188.8 K (?84.4 °C, ?120 °F). For the 4.5 wt pct Ni steel, the tensile strength is 731 MPa (106 ksi) at 293 K (20 °C) and the impact toughness is 209 J (154 ft-lb) at 188.8 K (?84.4 °C, ?120 °F). Light optical microscopy, scanning electron and transmission electron microscopies, synchrotron X-ray diffraction, and local-electrode atom-probe tomography (APT) are utilized to determine the morphologies, volume fractions, and local chemical compositions of the precipitated phases with sub-nanometer spatial resolution. The austenite lamellae are up to 200 nm in thickness, and up to several micrometers in length. In addition to the expected partitioning of Ni to austenite, APT reveals a substantial segregation of Ni at the austenite/martensite interface with concentration maxima of 10 and 23 wt pct Ni for the austenite lamellae in the 4.5 and 10 wt pct Ni steels, respectively. Copper-rich and M2C-type metal carbide precipitates were detected both at the austenite/martensite interface and within the bulk of the austenite lamellae. Thermodynamic phase stability, equilibrium compositions, and volume fractions are discussed in the context of Thermo-Calc calculations. 相似文献
14.
When analyzing the ternary Ni–Al–M phase diagrams, where M is a group VI–VIII transition metal, we chose the Ni–Al–Co system, where the γ′ and γ phases are in equilibrium with the β phase, as a base for designing alloys with the following physicochemical properties: a moderate density (≤7.2 g/cm3) and satisfactory heat resistance at temperatures up to 1300°C. The structure formation in heterophase β + γ′ alloys during directional solidification is studied. It is found that, in contrast to cobalt-free β + γ′ alloys (where the γ′-Ni3Al aluminide forms according to the peritectic reaction L + β ? γ′), the alloys with 8–10 at % Co studied in this work during directional solidification at 1370°C contain the degenerate eutectic L ? β + γ. The transition from the β + γ field to the β + γ′ + γ field occurs in the temperature range 1323–1334°C, and the γ′ phase then forms according to the reaction β + γ ? γ′. 相似文献
15.
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
16.
It is well known that the morphologies of the α martensite formed from the γ phase in ferrous alloys are classified into five types of lath, butterfly, (225)A type plate,lenticular and thin-plate. Among those α martensites, onlythe thinplate martensite, which is characterized by containing a high density of transformation twins, has a potential of exhibiting a perfect shape memory (SM) effect.Recently the present authors found in Fe-Ni-Si alloys that the thin-plate martensite is formed by the introduction of fine and coherent γ-(Ni,Fe)3Si particles with a L12 ordered structure in the austenite matrix due to ausaging. In the present study, the SM properties of the ausaged Fe-Ni-Si alloys with the thin-plate martensite are investigated by a conventional bending-test. The effects of the addition of Co to the Fe-Ni-Si alloys on the martensitic transformation and the SM properties are also investigated. It is shown that while the ausaged Fe-Ni-Si ternary alloys exhibit an imperfect SM effect due to reverse transformation from stress-induced thin-plate martensite to austenite, the SM properties are improved by the addition of Co. An almost perfect SM effect is confirmed in the Fe-Ni-Si-Co alloys by heating to 1 100 ℃ after deformation at -196 ℃. 相似文献
17.
An investigation of the phase transformation and the austenite stabilization in a high strength austenite has been made. An Fe?29Ni?4.3Ti austenite age-hardened by γ′(Ni3Ti) precipitates showed a further increase of strength after martensitic and reverse martensitic phase transformations. The stability of ausaged austenite as well as ausaged and transformation-strengthened austenite was improved significantly through an isothermal treatment at 500°C. TheM s temperature of the strengthened austenite was restored to nearly that of annealed austenite while the austenite was hardened toR C 41 through precipitation and phase transformations. The observed austenite stabilization is attributed to the formation of G.P. zones or short-range order of less than ~10Å size. 相似文献
18.
Huseyin Sehitoglu X. Y. Zhang T. Kotil D. Canadinc Y. Chumlyakov H. J. Maier 《Metallurgical and Materials Transactions A》2002,33(12):3661-3672
We present experimental and theoretical evidence of thermoelastic martensites in Fe29Ni18Co4Ti alloys. In this class of alloys,
the high strength in the austenite domains limits the slip deformation as verified with transmission electron microscopy.
The restriction of slip permits a higher degree of recoverability of the transformation. Using both single crystals with [123]
orientation and polycrystals, the appearance of martensite plates upon deformation, and their reversion back to austenite
upon heating (the shape memory effect), is revealed with in-situ optical microscopy. Theoretical results for the transformation strains and the detwinning of martensite are presented, which
demonstrate convincingly the potential of these classes of alloys. Electrical resistance measurements identified the stress
and temperature levels at the onset of forward and reverse transformations in isothermal deformation and thermal cycling experiments,
respectively. The return of the electrical resistance to its reference value, upon austenite to martensite followed by martensite
to austenite transformation, verified the recovery in the transformation strains measured in the experiments. 相似文献
19.
《Acta Metallurgica Materialia》1992,40(10):2471-2482
Evidence for a coherent bond at the interfaces between retained austenite and as-quenched martensite in FeNiC alloys and the relation of coherent interfaces to the abnormally high tetragonality of martensite are presented. The iron based alloys with 20 Ni-0.73 C, 28 Ni-0.2 C, 20 Ni-1.2 C, 25 Ni-0.7 C, 30 Ni-0.37 C, 33.5 Ni-0.01 C (in wt%) were studied by means of X-ray and neutron diffraction, Mössbauer spectroscopy, internal friction, electrical resistivity and magnetic susceptibility. It is shown that the break of coherency occurs during heating of the freshly formed twinned martensite in the temperature range of 100–200 K and it is accompanied by a relaxation of stresses in the retained austenite and a decrease of tetragonality. A new internal friction peak centered at 145 K was observed and attributed to movement of coherent interfaces and to the subsequent break of coherency. The relation between abnormally high tetragonality and coherency at the interface was confirmed in experiments with external deformation of virgin martensite at temperatures around 100 K. It is shown that the plate morphology of martensite is a necessary condition for a coherent bond at the interface. A possible role of atomic ordering of austenite in abnormally high tetragonality is discussed. Mössbauer measurements gave evidence for nickel-rich regions in initial austenite. During quenching the regions with the highest nickel content were assumed to remain austenitic inside the martensite plates. The conclusion about the coherency at the interface between the freshly formed martensite and the ordered regions in the retained austenite and at the interface along the martensite plates as a reason for high tetragonality of the FeNiC martensite with plate morphology is made. 相似文献
20.
The effect of high quench rate on theM s temperature, percent transformed, martensite morphology and austenite hardness has been studied for several Fe-Ni-C steels. For these steels the quench rate was varied only in the austenite region. TheM s temperature was found to increase with increased quench rate for both high- and low carbon steels while the percent transformation increased or decreased depending upon the morphology of the steel. No variations in martensite hardness were found in the as-quenched condition, but a difference in tempering rate was found between fast and slow quenched specimens. Austenite hardness decreased slightly with increasing quench rate while the martensite morphology changed from lath to plate. Parallel aligned plate structures were observed which resemble a twinned lath morphology. It was demonstrated that the actual difference between this morphology and a true lath morphology is the self-accommodating nature of the lath structure. The morphology changes were compared to the measured changes in martensite properties in order to identify the mechanism of the morphology shift. It was concluded that for these alloys the morphology was controlled by the austenite shear mode. 相似文献