共查询到20条相似文献,搜索用时 31 毫秒
1.
Martensitic transformations induced by plastic deformation are studied comparatively in various alloys of three types: Fe-30
pct Ni, Fe-20 pct Ni-7 pct Cr, and Fe-16 pet Cr-13 pct Ni, with carbon content up to 0.3 pct. For all these alloys the tensile
properties vary rapidly with temperature, but there are large differences in the value of the temperature rangeM
s toM
d, which strongly increases with substitution of chromium for nickel or with carbon addition. Using the node method, it is
found that the intrinsic stacking fault energy in the austenite drastically increases with temperature in all the chromium-bearing
alloys investigated. This variation is consistent with the observed influence of temperature on the appearance of twinning
or ε martensite during plastic deformation. Very different α’ martensite morphologies can result from spontaneous and plastic
deformation induced transformations, especially in Fe-20 pct Ni-7 pct Cr-type alloys where platelike and lath martensites
are respectively observed. As in the case of ε martensite, the nucleation process is analyzed as a deformation mode of the
material, using a dislocation model. It is then possible to account for the morphology of plastic deformation induced α’ martensite
in both Fe-20 pct Ni-7 pct Cr and Fe-16 pct Cr-13 pct Ni types alloys and for the largeM
s toM
d range in these alloys.
This paper is based upon a thesis submitted by F. LECROISEY in partial fulfillment of the degree of Doctor of Philosophy at
the University of Nancy. 相似文献
2.
The tensile deformation behavior of mechanically-stabilized austenite is investigated in Fe-Mn binary alloys. A 30 pct thickness
reduction by rolling at 673 K (above the Af temperature) largely suppresses the austenite (γ) to hcp epsilon martensite (ε) transformation in 17Mn and 25Mn steels. However,
the deformation behavior of the mechanically stabilized austenite in the two alloys differs significantly. In 25Mn steel,
the onset of plastic deformation is due to the stress-induced γ→ ε transformation and results in a positive temperature dependence of the yield strength. The uniform elongation is enhanced
by the γ → ε transformation during deformation. In 17Mn steel, bccα′ martensite is deformation-induced along with e and a plateau region similar to Lüders band deformation appears at the beginning
of the stress-strain curve. The mechanical stabilization of austenite also suppresses the intergranular fracture of 17Mn steel
at low temperatures.
M. STRUM, formerly Candidate for Ph.D. at the University of California at Berkeley 相似文献
3.
The influence of Mn content on the ductile-brittle transition in 16 to 36 wt pct Mn steels was investigated and interpreted
in light of the evolving microstructure. It was found that when hcp ε martensite is present in the as-quenched condition or
forms during deformation, it lowers the toughness. In 25Mn steel, the stress concentrations at e plate intersections result
in the formation of planar void sheets along the {111}γ planes. The deformation-induced α’ martensite in 16 to 20 pct Mn alloys enhances the toughness, but leads to a ductile-to-brittle
transition at low temperatures that is due to the intrusion of an intergranular fracture mode. Binary alloys with greater
than 31 pct Mn also fracture in an intergranular mode at 77 K although the impact energy remains quite high. Auger spectroscopy
of the fracture surfaces shows no evidence of significant impurity segregation, which suggests the importance of slip heterogeneity
in controlling intergranular fracture in these alloys. 相似文献
4.
The thermal cycling of an Fe-17 wt pct Mn alloy between 303 and 573 K was performed to investigate the effects of thermal
cycling on the kinetics of the γ → ε martensitic transformation in detail and to explain the previous, contrasting results of the change in the amount of ε martensite at room temperature with thermal cycling. It was observed that the shape of the γ → ε martensitic transformation curve (volume fraction vs temperature) changed gradually from a C to an S curve with an increasing number of thermal cycles. The amount of ε martensite of an Fe-17 wt pct Mn alloy at room temperature increased with thermal cycling, in spite of the decrease in the
martensitic start (M
s) temperature. This is due to the increase in transformation kinetics of ε martensite at numerous nucleation sites introduced in the austenite during thermal cycling. 相似文献
5.
A regular solution model for the difference of the chemical free energy between γ and ε phases during γ→ε martensitic transformation in the Fe-Mn binary system has been reexamined and partly modified based on many articles concerning
the M
s
and A
s
temperatures of Fe-Mn alloys. Using the regular solution model, the measured M
s
temperatures, and a thermodynamic model for the stacking fault energy (SFE) of austenite (γ), the driving force for γ→ε martensitic transformation, and the SFE of γ have been calculated. The driving force for γ→ε martensitic transformation increases linearly from − 68 to − 120 J/mole with increasing Mn content from 16 to 24 wt pct.
The SFE of γ decreases to approximately 13 at. pct Mn and then increases with increasing Mn content, which is in better agreement with
Schumann’s result rather than Volosevich et al.’s result. 相似文献
6.
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
7.
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
8.
Naresh C. Goel Sandeep Sangal Kris Tangri 《Metallurgical and Materials Transactions A》1985,16(11):2013-2021
A semi-mechanistic model for predicting the flow behavior of a typical commercial dual-phase steel containing 20 vol pct of
‘as quenched’ martensite and varying amounts of retained austenite has been developed in this paper. Assuming that up to 20
vol pct of austenite with different degrees of mechanical stability can be retained as a result of certain thermomechanical
treatments in a steel of appropriate low carbon low alloy chemistry, expressions for composite flow stress and strain have
been derived. The model takes into account the work hardening of the individual microconstituents(viz., ferrite-@#@ α, retained austenite- γ
r, and martensite -α′) and the extra hardening of ferrite caused by accommodation dislocations surrounding the ‘as quenched’
as well as the strain-induced(γ
r→ α′) martensite. Load transfer between the phases has been accounted for using an intermediate law of mixtures which also
considers the relative hardness of the soft and the hard phases. From the derived expressions, the flow behavior of dual phase
steels can be predicted if the properties of the individual microconstituents are known. Versatility of the model for application
to other commercial steels containing a metastable phase is discussed. 相似文献
9.
Thin foil transmission electron microscopy, X-ray diffraction and dilatometric techniques have been used to study the martensitic
γ → α transformation in three steels with nominal contents of 8 pct nickel and 0.2 pct beryllium and chromium contents of
12, 14 and 16 pct. In each case the martensite formed as laths with a habit plane close to {225}γ. With increasing chromium content and increasing cooling rate greater numbers of the laths were observed to be internally
twinned. Detailed analysis of the martensitic transformation suggested that the internally twinned laths are formed by a sequence
of γ→ ε or faulted γ→ ά. The orientation relationships between the three phases γ, ε and α, determined from selected area
diffraction analysis, corresponded to Kurdjumov-Sachs. 相似文献
10.
Bikas C. Maji Madangopal Krishnan Gouthama R. K. Ray 《Metallurgical and Materials Transactions A》2011,42(8):2153-2165
The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The
microstructural observations revealed that in these alloys the microstructure remains single-phase austenite (γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition
does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct
Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ε martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ε martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced
α′ martensite through γ-ε-α′ transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and
results in easy nucleation of stress-induced ε martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ε martensite formed during cooling is also observed to decrease with the increase in Si. 相似文献
11.
The variation of the kinetics of the martensite transformation with carbon content and martensite habit plane has been investigated
in several Fe−Ni based alloys. Transformation in an Fe-25 wt pct Ni-0.02 wt pct C alloy exhibits predominantly athermal features,
but some apparently isothermal transformation also occurs. In a decarburized alloy, on the other hand, the observed kinetic
features, such as the dependence ofM
s
on cooling rate, were characteristic of an isothermal transformation. In contrast, Fe-29.6 wt pct Ni-10.7 wt pct Co alloys
with carbon contents of 0.009 wt pct C and 0.003 wt pct C transform by burst kinetics to {259}γ plate. At both these carbon levels, theM
b
temperatures of the Fe−Ni−Co alloys are independent of cooling rate. It is proposed that the change in kinetic behavior of
the Fe-25 pct Ni alloy with the different carbon contents is due to the occurrence of dynamic thermal stabilization in the
higher carbon alloy. Dynamic thermal stabilization is relatively unimportant in the Fe−Ni−Co alloys which transform by burst
kinetics to {259}γ plate martensite.
P. J. FISHER, formerly with the University of New South Wales
D. J. H. CORDEROY, formerly with the University of New South Wales 相似文献
12.
Steels containing about 12 pct Cr, 10 pct Mn, and 0.2 pct N have been shown to have an unstable austenitic microstructure
and have good ductility, extreme work hardening, high fracture strength, excellent toughness, good wear resistance, and moderate
corrosion resistance. A series of alloys containing 9.5 to 12.8 pct Cr, 5.0 to 10.4 pct Mn, 0.16 to 0.32 pct N, 0.05 pct C,
and residual elements typical of stainless steels was investigated by microstructural examination and mechanical, abrasion,
and corrosion testing. Microstructures ranged from martensite to unstable austenite. The unstable austenitic steels transformed
to α martensite on deformation and displayed very high work hardening, exceeding that of Hadfield’s manganese steels. Fracture
strengths similar to high carbon martensitic stainless steels were obtained while ductility and toughness values were high,
similar to austenitic stainless steels. Resistance to abrasive wear exceeded that of commercial abrasion resistant steels
and other stainless steels. Corrosion resistance was similar to that of other 12 pct Cr steels. Properties were not much affected
by minor compositional variations or rolled-in nitrogen porosity. In 12 pct Cr-10 pct Mn alloys, ingot porosity was avoided
when nitrogen levels were below 0.19 pet, and austenitic microstructures were obtained when nitrogen levels exceeded 0.14
pct. 相似文献
13.
Young-Kook Lee 《Metallurgical and Materials Transactions A》2001,32(2):229-237
This study was pursued to investigate the movement of γ/ε interfaces and the coalescence of ε martensite variants in an Fe-Mn binary system. An Fe-24 wt pct Mn tensile specimen was deformed with increasing tensile strain
at room temperature. The microstructural changes at a fixed area of the tensile specimen were continuously observed using
an optical microscope. Some of the γ/ε interfaces moved forward due to γ → ε transformation, and the others moved backward due to its reverse transformation during the tensile deformation, depending
on the orientation relationship between the tensile direction and each ε variant. The coalescence of ε martensite variants primarily occurs by the following three factors: (1) the reverse transformation of ε variants under an applied stress having a different direction from that of the ε variants’ shape change, (2) the nucleation and growth of new ε variants under an applied stress having the same direction as that of the ε variants’ shape change, and (3) the continuous growth of pre-existing ε variants under an applied stress having the same direction as that of the ε variants’ shape change. 相似文献
14.
The martensite phases in 304 stainless steel 总被引:3,自引:0,他引:3
A detailed analysis of martensite transformations in 18/8 (304) stainless steel, utilizing transmission electron microscopy
and diffraction in conjunction with X-ray and magnetization techniques, has established that the sequence of transformation
is γ → ∈ → α. ε is a thermodynamically stable hcp phase whose formation is greatly enhanced as a result of plastic deformation.
Comparison with the ε → α transformation in pure Fe-Mn alloys lends further support to the above sequence and suggests that
a transformation line between ε and α in Fe-Cr-Ni alloys can be expected. In the 304 stainless steel used in this investigation,
formation of α was induced only by plastic deformation and subsequent to formation of ε. Nucleation of α occurs heterogeneously
at intersections of ε bands or where ε bands abut twin or grain boundaries (which represent unilaterally compressed regions).
From electron diffraction, the Nishiyama relationship between γ and α phases appears to predominate at the start of the transformation,
but then changes to that of Kurdjumov-Sachs. Based on these observations, a sequence of atom movements from the hcp structure
to the bcc structure is proposed which has the basic geometric features of the martensitic transformation.
Formerly with Department of Materials Science and Engineering, University of California, Berkeley, Calif. 相似文献
15.
The eutectoid transformation of austenite in cast iron is known to proceed by both the meta-stable γ → α + Fe3C reaction common in Fe-C alloys of near eutectoid composition, and by the direct γ → α + Graphite reaction, with the graphite
phase functioning as a car-bon sink. In addition, the meta-stable cementite constituent of the pearlite can dissolve near
the graphite phase (Fe3C → α + Graphite), producing free ferrite. Isothermal trans-formation studies on a typical ductile iron (nodular cast iron)
confirmed that all of these reaction mechanisms are normally operative. The addition of 1.3 pct Mn was found to substantially
retard all stages of the transformation by retarding the onset of the eutectoid transformation, decreasing the diffusivity
of carbon in ferrite, and stabilizing the cemen-tite. Minor additions of Sb (0.08 pct) or Sn (0.12 pct) were found to inhibit
the γ →α + Graphite reaction path, as well as the Fe3C → α + Graphite dissolution step, but did not significantly affect the meta-stable γ → α + Fe3C reaction. Scanning Auger microprobe analysis indicated that Sn and Sb adsorb at the nodule/metal interphase boundaries during
solidification. This adsorbed layer acts as a barrier to the carbon flow necessary for the direct γ → α + Graphite and Fe3C → α + Graphite reactions. With the graphite phase dis-abled as a sink for the excess carbon, the metal transforms like a
nongraphitic steel. The effects of Mn, Sn, and Sb on the eutectoid transformation of ductile iron were shown to be consistent
with their behavior in malleable iron. 相似文献
16.
Yung-Fu Hsu Wen-Hsing Wang C. M. Wayman 《Metallurgical and Materials Transactions A》1991,22(7):1479-1490
The shape memory effect (SME), superelasticity (SE), and cyclic deformation behavior of two-phase α/β brasses have been investigated
at various temperatures, using tensile tests andin situ optical microscopic observations. The morphology and characteristics of the (thermoelastic) martensitic transformation and
the mechanism of the SME are similar to those for single-phase β-brass, but the amount of irrecoverable strain is larger in
the two-phase alloys due to plastic deformation of the α particles. After unloading and heating, the slipbands in the discrete
a particles remain, whereas the martensite almost disappears; thus, the higher the volume fraction of α particles, the larger
the amount of irrecoverable strain. The deformation behavior of alloy A at temperatures above the martensite start (Ms) temperature (with 26 pct α phase) is dominated by deformation of the α phase, so complete SE cannot be obtained after cyclic
deformation, both at room temperature and at -40 °C. While in alloy B (containing 15 pct α phase), the deformation behavior
is dominated by the formation of stress-induced martensite (SIM). The α particles are deformed before SIM formation on loading
at room temperature, but on the contrary, SIM forms before the α particles are deformed on loading at -40 °C (>Ms). Complete SE can be obtained in alloy B after cyclic deformation at room temperature to a given strain but does not occur
at -40 °C because the a particles are deformed along with the growth of pre-existing SIM under larger strain during cycling
at this temperature. 相似文献
17.
Void nucleation and growth was studied in three binary equiaxed α-β Ti-Mn alloys containing 1.8 wt pct Mn (alloy 2), 3.9 wt
pct Mn (alloy 3), and 5.8 wt pct Mn (alloy 4) given heat treatments to vary the alpha size at constant volume fraction of
alpha. Void nucleation rates expressed as number of voids per unit volume,N
v, increased exponentially with true strain, ε. WhenN
v was normalized with respect to the number of alpha particles or grains per unit volume, Nα
T,N
v/Nα
T was found to be largest for the largest alpha size in each alloy series. Void size distributions as a function of strain
for one alloy containing 3.9 wt pct Mn (alloy 3 given heat treatment B,3B) were presented and, as expected, the largest number
of voids occurred at the smallest void sizes. Void growth rates for alloys 3 and 4 were found to increase with increasing
particle size and this was ascribed to decreasing constraints to slip with increasing particle size. For alloy 2C with the
largestα grain size void growth rates were smallest and this behavior was attributed to the growth inhibiting effects of multiple
twinning. Evidence was adduced to show that nucleating voids grow more rapidly than established voids.
T. V. Vijayaraghavan, Formerly Graduate Student, Polytechnic University, Brooklyn, NY 相似文献
18.
A. A. Hussein L. I. El-Menawati H. J. Klaar 《Metallurgical and Materials Transactions A》1978,9(12):1783-1788
The temper hardening of quench-induced Cu-Al martensite was investigated via trans-mission electron microscopy, differential
thermal analysis, microhardness and yield strength measurements. The results obtained are also viewed in conjunction with
inde-pendent set of experimental data dealing with anneal hardening of the α-phase without prior martensitic transformation.
A substantial low temperature hardening of a 10 pct Al martensite is indicated and attributed to the formation of small ordered
clusters, en-hanced by stacking faults already existing in martensite. In the 11 pct Al martensite hardening is also linked
with ordering though less pronounced due to the larger domain size reached. On the other hand the tempering of 11.8 pct Al
martensite is associated with phase separation leading to the(α + γ2) state via continuous and discontinuous pre-cipitation. 相似文献
19.
20.
Transformation behavior of TRIP steels 总被引:2,自引:0,他引:2
True-stress (σ), true-strain (ε) and volume fraction martensite(f) were measured during both uniform and localized flow as a function of temperature on TRIP steels in both the solution-treated
and warm-rolled conditions. The transformation curves(f vs ε) of materials in both conditions have a sigmoidal shape at temperatures above Ms
σ (maximum temperature at which transformation is induced by elastic stress) but approach initially linear behavior at temperatures
below Ms
σ where the flow is controlled by transformation plasticity. The martensite which forms spontaneously on cooling or by stress-assisted
transformation below Ms
σ exhibits a plate morphology. Additional martensite units produced by strain-induced nucleation at shear-band intersections
become important above Ms
σ. Comparison of σ-ε andf-ε curves indicate that a “rule of mixtures” relation based on the “static” strengthening effect of the transformation product
describes the plastic flow behavior reasonably well above Ms
σ, but there is also a dynamic “transformation softening” contribution which becomes dominant below Ms
σ due to the operation of transformation plasticity as a deformation mechanism. Temperature sensitivity of the transformation
kinetics and associated flow behavior is greatest above Ms
σ. Less temperature-sensitive TRIP steels could be obtained by designing alloys to operate with optimum mechanical properties
below Ms
σ. 相似文献