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1.
A pulsed laser technique was used to measure the polycrystalline elastic moduli of the martensite and austenite phases of
an Fe-30.1 wt pct Ni alloy between 298 and 900 K. The moduli of an Fe-29.5 wt pct Ni-0.1 wt pct C alloy were similarly determined
at 298 K. These data showed that the shear modulus and Young’s modulus of martensite were slightly decreased by carbon. The
moduli of austenite behaved in the expected manner, changing monotonically with temperature above the Curie temperature. The
moduli of the martensite changed monotonically with temperature from 298 K until the martensite-to-austenite transformation
temperature was reached at 650 K. At this temperature abrupt changes in moduli were observed. The same austenite start temperatures
were determined both from moduli measurements and from dilatometric measurements. No unusual decrease of the martensite elastic
constants was observed as a precursor to the reverse martensite-to-austenite transformation.
Formerly with Sandia Laboratories, Albuquerque, New Mexico 相似文献
2.
A Cahn Electrobalance has been used to determine directly and very accurately the carbon content of iron, iron-0.48 wt pct
molybdenum and iron-1.16 wt pct molybdenum specimens which were equilibrated with a series of methane-hydrogen gas mixtures
of constant composition. The equilibria investigated involved the austenite phases of the alloys at 783, 813 and 848‡C. The
experimental results permit direct calculation of the activities of carbon in the samples, relative to graphite as unity,
and of the enthalpy and entropy of solution of carbon. The results are compared with the experimental measurements of a number
of other investigators. The results are in excellent agreement with those of Smith and Schenck and Kaiser for the Fe-C system
at 800‡C, and indicate -H
C
/M
values of 9700 ± 500 cal/mole for pure Fe, 10,030 ± 500 cal/mole for an Fe-0.48 wt pct Mo alloy, and 10,150 ± 500 cal/mole
for an Fe-1.16 wt pct Mo alloy. The effect of molybdenum in austenite is to decrease the activity coefficient of carbon in
austenite. 相似文献
3.
A Cahn Electrobalance has been used to determine directly and very accurately the carbon content of iron, iron-0.48 wt pct
molybdenum and iron-1.16 wt pct molybdenum specimens which were equilibrated with a series of methane-hydrogen gas mixtures
of constant composition. The equilibria investigated involved the austenite phases of the alloys at 783, 813 and 848‡C. The
experimental results permit direct calculation of the activities of carbon in the samples, relative to graphite as unity,
and of the enthalpy and entropy of solution of carbon. The results are compared with the experimental measurements of a number
of other investigators. The results are in excellent agreement with those of Smith and Schenck and Kaiser for the Fe-C system
at 800‡C, and indicate -H
C
/M
values of 9700 ± 500 cal/mole for pure Fe, 10,030 ± 500 cal/mole for an Fe-0.48 wt pct Mo alloy, and 10,150 ± 500 cal/mole
for an Fe-1.16 wt pct Mo alloy. The effect of molybdenum in austenite is to decrease the activity coefficient of carbon in
austenite. 相似文献
4.
G. Spanos J. D. Ayers C. L. Vold I. E. Locci 《Metallurgical and Materials Transactions A》1993,24(4):809-818
The microstructural evolution, mechanisms of grain refinement, crystallography, and thermal processing of a rapidly solidified
Fe-1.85 pct C alloy have been studied by transmission electron microscopy (TEM). Melt-spun ribbons quenched in liquid nitrogen
consist of carbide-free highly twinned martensite plates between 0.5-and 2.0-μm long and 0.1-and 0.5 -μm thick, with approximately 40 pct retained austenite also present. Ribbons tempered at 600 °C for
10 seconds consist of ferrite of approximately the same grain size and both intragranular and intergranular cementite precipitates.
The intragranular cementite particles are about 0.1 /um or less in size and exhibit a single variant of the Bagaryatskii orientation
relationship with respect to a given ferrite grain; the intergranular particles are about 0.1 μm in thickness and can be as
long as 0.5 μm due to growth and/or coalescence along ferrite grain boundaries. A heat-treatment cycle investigated with a
view toward generating structures suited for superplastic consolidation of the rapidly solidified ribbons consists of quenching
the ribbon in liquid nitrogen, tempering at 600 °C for 10 seconds, “upquenching” to 750 °C (austenitizing) for 10 seconds,
and subsequently quenching again in liquid nitrogen. This treatment results in martensite grains highly misoriented with respect
to one another and typically 0.5 μm or less in both length and thickness and cementite particles 0.4 μm or less in size. (Occasionally,
longer martensite plates were observed; but they never exceeded 1 μm in length.) The microstructures produced here offer the
potential for producing fine-grained ultrahigh carbon steels of very high strength without the brittleness associated with
the formation of coarse carbide particles or the loss of strength due to graphite formation. This investigation has thus provided
the basis for follow-on studies currently underway in ultrahigh carbon Fe-C-Cr and Fe-C-Cr-Si steels, with the intent of producing
similar microstructures which will also exhibit enhanced high-temperature stability. 相似文献
5.
A combined 3.5 wt pct Mo + 1.2 wt pct Ti imparted dynamic recrystallization in a 35 wt pct Fe-45 wt pct Ni-20 wt pct Cr alloy
system during creep at 700 °C, whereas 3.5 wt pct Mo addition alone did not initiate recrystallization. Dynamic recrystallization
substantially increased the creep elongation and produced a high ductile fracture topography in the present alloy system.
A subgrain coalescence nucleation mechanism for dynamic recrystallization mechanism was operative during creep. The critical
initiation strain requirements are also discussed. 相似文献
6.
Young-Kook Lee 《Metallurgical and Materials Transactions A》2002,33(7):1913-1917
The reason why thermal cycling decreases the martensite start (M
s
) temperature of an Fe-17 wt pct Mn alloy was quantitatively investigated, based on the nucleation model of ε martensite and a thermodynamic model for a martensitic transformation. The M
s
temperature decreased by about 22 K after nine cycles between 303 and 573 K, due to the increase in shear-strain energy (ΔG
sh
) required to advance the transformation dislocations through dislocation forests formed in austenite during thermal cycling.
The ΔG
sh
value increased from 19.3 to 28.8 MJ/m3 due to the increase in austenite dislocation density from 1.5 × 1012 to 3.8 × 1013/m2 with the number of thermal cycles (in this case, up to nine cycles). The austenite dislocation density increased rapidly
for up to five thermal cycles and then increased gradually with further thermal cycles, showing a good agreement with the
increase in austenite hardness with the number of thermal cycles. 相似文献
7.
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
8.
Li Zhao-Dong Miyamoto Goro Yang Zhi-Gang Furuhara Tadashi 《Metallurgical and Materials Transactions A》2011,42(6):1586-1596
Substitutional alloying effects on reversion kinetics from pearlite structure at 1073 K (800 °C) in an Fe-0.6 mass pct C binary
alloy and Fe-0.6C-1 or 2 mass pct M (M = Mn, Si, Cr) ternary alloys were studied. Reverse transformation in the Fe-0.6C binary
alloy at 1073 K (800 °C) was finished after holding for approximately 5.5 seconds. The reversion kinetics was accelerated
slightly by the addition of Mn but retarded by the addition of Si or Cr. The difference of acceleration effects by the addition
of the 1 and 2 mass pct Mn is small, whereas the retardation effect becomes more significant by increasing the amount of addition
of Si or Cr. It is clarified from the thermodynamic viewpoint of carbon diffusion that austenite can grow without partitioning
of Mn or Si in the Mn- or Si-added alloys. On the one hand, austenite growth is controlled by the carbon diffusion, whereas
the addition of them affects carbon activity gradient, resulting in changes in reversion kinetics. On the other hand, thermodynamic
calculation implies that the long-range diffusion of Cr is necessary for austenite growth in the Cr-added alloys. It is proposed
that austenite growth from pearlite in the Cr-added alloys is controlled by the diffusion of Cr along austenite/pearlite interface. 相似文献
9.
S. R. Goodman S. S. Brenner J. R. Low 《Metallurgical and Materials Transactions B》1973,4(10):2363-2369
The size and number density of precipitates formed during the early stage of precipitation of copper from Fe-1.4 at. pct Cu
at 500°C was determined with the field-ion microscope (FIM). While particles of less than 50 × 10−8 cm remain invisible in the electron microscope (ETM) they are clearly resolved with the FIM; particles as small as 8 × 10−8 cm in diameter could be detected. The growth rate of the particles can be accounted for by normal bulk diffusion. At its
peak strength, the alloy contains approximately 1018 particles per cu cm with an average diameter of 24 × 10−8 cm. The alloy reaches its peak strength well before precipitation is complete.
This paper is based on a thesis submitted by S. R. GOODMAN to Carnegie-Mellon University, in partial fulfillment of the requirements
of the Ph.D. degree. 相似文献
10.
Tensile and creep tests were conducted to characterize the deformation behavior of four dilute SnBi alloys: SnBi0.5 at. pct,
SnBi1.5 at. pct, SnBi3 at. pct, and SnBi6 at. pct, the last two being supersaturated solid solutions at room temperature.
The test temperatures were − 20 °C, 23 °C, 90 °C, and 150 °C, and the strain rates ranged from approximately 10−8 to 10−1 1/s. In the tensile tests, all the alloys showed strain-hardening behavior up to room temperature. At higher temperatures,
only the higher-Bi-content alloys exhibited strain softening. The deformation behavior of the alloys can be divided into two
stress regimes, and the change from the low-stress regime to the high-stress regime occurred at around 6 × 10−4<σ/E<7.5 × 10−4. The results suggest that, at the low-stress regime, the rate-controlling deformation mechanism changes from dislocation
climb to viscous glide with the increasing Bi content of the alloy. At the high-stress regime, the activation energy of deformation
is about equal in all the alloys (∼60 kJ/mol) and the stress exponents are high (10<n<12.5). Unlike in the other alloys, bismuth precipitated at room temperature from the solution-annealed and quenched SnBi6
at. pct alloy by the discontinuous mechanism. This strongly affects the mechanical properties and makes the alloy brittle
at lower test temperatures. A comparison of the deformation behavior of the dilute SnBi alloys to that of the eutectic SnBi
alloy suggests that the deformation of eutectic structure is controlled by the Sn-rich phase containing the equilibrium amount
of dissolved Bi. 相似文献
11.
Three two-phase Fe-Mn-Al alloys with nominal compositions, Fe-24Mn-9Al, Fe-27Mn-9Al-3Cr,. and Fe-27Mn-9Al-6Cr, were prepared
in the solution-treated and cold-rolled conditions. The fractions of ferrite in the solution-treated condition were controlled
at 46 to 60 pct, mainly by adjusting the carbon content and the relative amounts of Mn and Al. The ferrite fractions were
reduced to 30 to 37 pct after 75 pct deformation by cold-rolling. Specimens were tensile tested at open circuit in aerated
3.5 pct NaCl solution at slow strain rates ranging from 4 × 10-7 to 4 × 10-5 s-1 at room temperature. All of the alloys were quite susceptible to environmentally assisted cracking (EAC). The deformed specimens
showed less susceptibility, presumably because the plasticity was already too limited. The EAC appeared to occur at or after
the onset of plastic deformation. In this alloy system, the ferritic phase was less resistant to EAC than the austenitic phase,
in contrast to the Fe-Cr-Ni stainless steels. The crack propagated preferentially through the ferrite grains or along the
ferrite/austenite grain boundaries. The addition of up to 6 pct Cr did not improve the EAC resistance.
Formerly Graduate Student, Department of Materials Science and Engineering, National Tsing Hua University 相似文献
12.
F. C. Levey M. B. Cortie L. A. Cornish 《Metallurgical and Materials Transactions A》2000,31(8):1917-1923
A gold alloy with 18 wt pct Cu and 6 wt pct Al undergoes a reversible displacive phase transformation between an incompletely
ordered L21 parent phase and a tetragonal product. The characteristics of these transformations were studied using acoustic emission,
dilatometry, X-ray diffraction, and metallography. The morphology of the transformation products, the structure of the parent
phase, and the generation of significant acoustic emission during the transformations indicate that they are at least quasi-martensitic,
if not martensitic, and that this system is an example of a β-phase shape-memory alloy (SMA). The onset temperatures of the transformations depend on the prior thermal history of the
sample. The martensite start (M
s
) temperature is between 30 °C and 20 °C. The system exhibits hysteresis and will revert to the parent phase when reheated,
with an austenite start (A
s
) temperature between 55 °C and 80 °C. However, freshly cast or solution-annealed and quenched samples of the alloy do not
transform to the tetragonal phase. Aging of such material at temperatures between 30 °C and 200 °C is required before they
will manifest the displacive transformation. The “martensite” phase is considerably more resistant to aging-induced stabilization
than that of most other SMAs. 相似文献
13.
The temperature dependence of fatigue crack propagation is considered in an Fe-1 pct Cr-0.5 pct Mo alloy steel. This material
was tested at temperatures between 425 and 550 °C, a frequency of 1 Hz, and anR-ratio of 0.1. It is shown that the effect of temperature can be explained in terms of a thermal activation energy for fatigue.
The magnitude of this activation energy is a function of ΔK and varies from more than 150 kJ/mole at 15 MPa√m to 30 kJ/mole
above 30 MPa√m. The magnitude of these activation energies supports the idea that oxidation, and not creep, is the rate-controlling
time-dependent process for the test conditions studied. 相似文献
14.
Isothermal transformation from austenite in an Fe-9.14 pct Ni alloy has been studied by optical metallography and examination
by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the temperature range 565 °C and 545
°C, massive ferrite (α
q
) forms first at prior austenite grain boundaries, followed by Widmanst?tten ferrite (α
W
) growing from this grain boundary ferrite. Between 495 °C and 535 °C, Widmanst?tten ferrite is thought to grow directly from
the austenite grain boundaries. Both these transformations do not go to completion and reasons for this are discussed. These
composition invariant transformations occur below T
0 in the two-phase field (α+γ). Previous work on the same alloy showed that transformation occurred to α
q
> and α
W
on furnace cooling, while analytical TEM showed an increase of Ni at the massive ferrite grain boundaries, indicating local
partitioning of Ni at the transformation interface. An Fe-3.47 pct Ni alloy transformed to equiaxed ferrite at 707 °C ±5 °C
inside the single-phase field on air cooling. This is in agreement with data from other sources, although equiaxed ferrite
in Fe-C alloys forms in the two-phase region. The application of theories of growth of two types of massive transformation
by Hillert and his colleagues are discussed.
This article is based on a presentation made at the symposium entitled “The Mechanisms of the Massive Transformation,” a part
of the Fall 2000 TMS Meeting held October 16–19, 2000, in St. Louis, Missouri, under the auspices of the ASM Phase Transformations
Committee. 相似文献
15.
Shinwoo Kim W. F. Flanagan B. D. Lichter R. N. Grugel 《Metallurgical and Materials Transactions A》1993,24(4):975-979
Composites consisting of aligned copper dendrites in a lead matrix have been produced by directional solidification processing
for potential application as grids in lead-acid batteries. To promote a uniform composite of aligned copper dendrites in a
protective lead matrix, two alloy compositions, Pb-9 and -20 wt pct Cu, have been directionally solidified through a temperature
gradient,G
l of 4.5 Kmm-1 at constant growth velocities which ranged from 1 to 100 μm s-1. With slow growth rates (≲10 μm s-1 ), the copper dendrites were generally columnar and continuous along the sample length; at higher velocities (≳60 μm s-1), they assumed an intricate and equiaxed morphology. In accordance with copper content and growth rate, the electrical conductivity
of the directionally solidified composites was found to be as much as a 2.5 times that of pure lead. The results are compared
with that predicted by a model based on a geometrical dendrite.
Formerly Doctoral Student, Department of Materials Science and Engineering, Vanderbilt University.Seoul Korea.
This paper is based on work leading to the successful completion of his Ph.D. degree at Vanderbilt University. 相似文献
16.
T. F. Liu S. W. Peng Y. L. Lin C. C. Wu 《Metallurgical and Materials Transactions A》1990,21(2):567-574
Both M23C6 and Mi6C carbides were observed to precipitate within the austenite phase in an Fe-24.6 pct Mn-6.6 pct Al-3.1 pct Mo-1.0 pct alloy
after being quenched from 1200 °C and aged at 700 °C. By means of transmission electron microscopy and diffraction techniques,
the orientation relationships among M23C6, M6C, and the austenite phase were determined as follows: {fx567-1} The present result of the orientation relationship between
M6C and the austenite phase is in disagreement with that reported by Maziasz[14] for M6C in an austenitic stainless steel. 相似文献
17.
Joonyeon Chang Inge Moon Chongsool Choi 《Metallurgical and Materials Transactions A》1998,29(7):1873-1882
Analytical transmission electron microscopy and thermal analysis of as-extruded Al-4.7 pct Zn-2.5 pct Mg-0.2 pct Zr-X wt pct Mn alloys, with Mn contents ranging from 0.5 to 2.5 wt pct, were carried out to elucidate the microstructural change
and accompanying mechanical properties during subsequent heat treatments. The as-extruded alloy was fabricated from rapidly
solidified powder and consisted of a fine, metastable manganese dispersoid and the ternary eutectic T phase (Al2Mg3Zn3). Solution heat treatment resulted in the formation of the stable Al6Mn phase and complete dissolution of the T phase. Formation of stable Al6Mn was made by two routes: by phase transition from metastable Mn dispersoids which already existed, and from the supersaturated
solid solution by homogeneous nucleation. The density of the Al6Mn phase increased with the addition of manganese, while the shape and average size remained unchanged. A significant increase
in the hardness was observed to coincide with the formation of the Al6Mn phase. Similarly, the tensile strength increased further after the aging treatment, and the increment was constant over
the content of Mn in the alloy, which was explained by the contribution from the same amount of precipitates, MgZn2. Results of thermal analysis indicated that the dissolution of the T phase started near 180 °C and that formation of Al6Mn occurred at about 400 °C, suggesting that further enhancement of strength is possible with the modification of the heat-treatment
schedule. 相似文献
18.
Chunsheng Wen Ph.D. Zi Chen Baoxu Huang Ph.D. Yonghua Rong 《Metallurgical and Materials Transactions A》2006,37(5):1413-1421
A nanostructured surface layer was formed in Fe-30 wt pct Ni alloy by surface mechanical attrition treatment (SMAT). The microstructure
of the surface layer after SMAT was investigated using optical microscopy, X-ray diffraction, and transmission electron microscopy.
The analysis shows that the nanocrystallization process at the surface layer starts from dislocation tangles, dislocation
cells, and subgrains to highly misoriented grains in both original austenite and martensite phases induced by strain from
SMAT. The magnetic properties were measured for SMAT Fe-30 wt pct Ni alloy. The saturation magnetization (M
s
) and coercivity (H
c
) of the nanostructured surface layers increase significantly compared to the coarse grains sample prior to SMAT. The increase
of M
s
for SMAT Fe-30 wt pct Ni alloy was attributed to the change of lattice structure resulting from strain-induced martensitic
transformation. Meanwhile, H
c
was further increased from residual microstress and superfined grains. These were verified by experiments on SMAT pure Ni
and Co metal as well as liquid nitrogen-quenched Fe-30 wt pct Ni alloy. 相似文献
19.
The effect of quenching condition on the mechanical properties of an A356 (Al-7 wt pct Si-0.4 wt pct Mg) casting alloy has
been studied using a combination of mechanical testing, differential scanning calorimetry (DSC), and transmission electron
microscopy (TEM). As the quench rate decreases from 250 °C/s to 0.5 °C/s, the ultimate tensile strength (UTS) and yield strength
decrease by approximately 27 and 33 pct, respectively. The ductility also decreases with decreasing quench rate. It appears
that with the peak-aged condition, both the UTS and yield strength are a logarithmic function of the quench rate,i.e., UTS orσ
y
=A logR +B. The termA is a measure of quench sensitivity. For both UTS and yield strength of the peak-aged A356 alloy,A is approximately 32 to 33 MPa/log (°C/s). The peak-aged A356 alloy is more quench sensitive than the aluminum alloy 6063.
For 6063,A is approximately 10 MPa/log (°C/s). The higher quench sensitivity of A356 is probably due to the high level of excess Si.
A lower quench rate results in a lower level of solute supersaturation in the α-Al matrix and a decreased amount of excess
Si in the matrix after quenching. Both of these mechanisms play important roles in causing the decrease in the strength of
the peak-aged A356 with decreasing the quench rate. 相似文献
20.
The compressive strength at -196°C of martensites in Fe-0.26 pct C-24 pct Ni, Fe-0.4 pct C-21 pct Ni, and Fe-0.4 pct C-18 pct Ni-3 pct Mo alloys, all with subzero M temperatures, has been determined in the virgin condition and after one hour at temperatures from -80 to +400 °C. The effects of ausforming (20 pct reduction in area of the austenite by swaging at room temperature prior to the martensitic transformation) were also investigated. For the unausformed martensites, aging at temperatures up to 0 °C results in relatively small increases in strength. Above 0 °C, the age hardening increment increases rapidly, reaching a maximum at 100 °C. Above 100 °C, the strength decreases continuously with increasing tempering temperature except for the molybdenum-containing alloy, which exhibits secondary hardening on tempering at 400 °C. For the ausformed martensites, the response to aging at subzero temperatures is greater than for unausformed material. Strength again passes through a maximum on aging at 100 °C. However, on tempering just above 100 °C, the ausformed materials show a slower rate of softening than the unausformed martensites. The strengthening produced by the ausforming treatment is largest for the Fe-0.4 pct C-18 pct Ni-3 pct Mo alloy, but there is no evidence of carbide precipitation in the deformed austenite to a°Count for this effect of molybdenum. 相似文献