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1.
The near-α titanium alloy Ti-6Al-5Zr-0.5Mo-0.25Si has been rolled in the β- and (α+β)-phase fields. Texture studies have been performed on each of these materials in the as-rolled condition after air cooling
from the finish rolling pass, with a view to examining the transformation texture β/(α+β)→α. One of the materials from each of the β and (α+β) rolled conditions has been heat treated in the β-phase field and air cooled (AC) to α phase in order to study the nature of the α → β → α transformation texture. Results indicate that transformation textures of the α phase are significantly different for both the β as well as the (α+β) rolling conditions. Heat treatment of secondary (transformed) α in the β-phase field and its further cooling to α phase leads to relatively weak texture for the β rolled materials. The results have been discussed in relation to the microstructural features and consequent variant selections
and have been correlated with those observed in titanium and its alloys. 相似文献
2.
R. W. L. Fong R. Miller H. J. Saari S. C. Vogel 《Metallurgical and Materials Transactions A》2012,43(3):806-821
The phase transformations in an as-received Zr-2.5Nb pressure tube material were characterized in detail by neutron diffraction.
The texture and volume fraction of α and β phases were measured on heating at eight different temperatures 373 K to 1323 K (100 °C to 1050 °C) traversing across the
α/(α + β) and (α + β)/β solvus lines, and also upon cooling at 1173 K and 823 K (900 °C and 550 °C). The results indicate that the α-phase texture is quite stable, with little change in the {0002} and { 11[`2]0 } \left\{ {11\bar{2}0} \right\} pole figures during heating to 1123 K (850 °C). The β-phase volume fraction increased while a slight change in texture was observed until heating reached 973 K (700 °C). On further
heating to 1173 K (900 °C), there appears a previously unobserved α-phase texture component due to coarsening of the prior primary α grains; meanwhile the transformed β-phase texture evolved markedly. At 1323 K (1050 °C), the α phase disappeared with only 100 pct β phase remaining but with a different texture than that observed at lower temperatures. On cooling from the full β-phase regime, a different cooldown transformed α-phase texture was observed, with no resemblance of the original texture observed at 373 K (100 °C). The transformed α-phase texture shows that the {0002} plane normals are within the radial-longitudinal plane of the pressure tube following
the Burgers orientation relationship of (110)bcc//(0002)hcp and
[[`1]11]\textbcc //[11[`2]0]\texthcp [\bar{1}11]_{\text{bcc}} //[11\bar{2}0]_{\text{hcp}} with a memory of the precursor texture of the primary α grains observed on heating at 1173 K (900 °C). 相似文献
3.
The influence of solution-treatment temperature on the martensitic phase transformations observed in IMI 550 (Ti-4Al-4Mo-2Sn-0.5Si)
has been investigated. When solution treatment is conducted at temperatures above 1233 K, a hexagonal martensite (α′) is formed on rapid cooling. However solution treatment at temperatures between 1233 and 1123 K results in the formation
of an orthorhombic martensite (α″) on rapid cooling. Finally, below 1123 K, the β phase is stable—no martensitic transformation occurs on rapid cooling. This transition from α′ → α
primary + (α′ + β
retained) → α
primary + (α″ + β
retained) → α
primary + β
metastable + ω, with decreasing solution-treatment temperature, is shown to be a result of alloy partitioning during solution treatment.
Crystallographic analysis indicates that the transition in the martensite crystal structure with decreasing solution-treatment
temperature is related to chemical short-range ordering (CSRO) in the high-temperature β phase. 相似文献
4.
Phase transformation and microstructural evolution have been studied in Ti-44Al-4Nb-4Zr-0.2Si-0.1B alloys that were cooled
from theα +β phase region with various cooling rates. It has been shown that the cooling rates have different influence on the morphology
of the transformation products for the three phase transformations studied,α →α
2, B2 →ω, andα →γ. Under slow cooling, all three transformations can be fulfilled. Under rapid cooling, B2 →ω is partially detained and a diffuseω phase forms as metastable phase, butα →γ is almost completely suppressed, which supports that theγ lamellae formation is diffusion controlled. 相似文献
5.
John W. Elmer Joe Wong Thorsten Ressler 《Metallurgical and Materials Transactions A》1998,29(11):2761-2773
Spatially resolved X-ray diffraction (SRXRD) is used to map the α → β → α phase transformation in the heat-affected zone (HAZ) of commercially pure titanium gas tungsten arc welds. In situ SRXRD experiments were conducted using a 180-μm-diameter X-ray beam at the Stanford Synchrotron Radiation Laboratory (SSRL)
(Stanford, CA) to probe the phases present in the HAZ of a 1.9 kW weld moving at 1.1 mm/s. Results of sequential linear X-ray
diffraction scans made perpendicular to the weld direction were combined to construct a phase transformation map around the
liquid weld pool. This map identifies six HAZ microstructural regions between the liquid weld pool and the base metal: (1)
α-Ti that is undergoing annealing and recrystallization; (2) completely recrystallized α-Ti; (3) partially transformed α-Ti, where α-Ti and β-Ti coexist; (4) single-phase β-Ti; (5) back-transformed α-Ti; and (6) recrystallized α-Ti plus back-transformed α-Ti. Although the microstructure consisted predominantly of α-Ti, both prior to and after the weld, the crystallographically textured starting material was altered during welding to produce
different α-Ti textures within the resulting HAZ. Based on the travel speed of the weld, the α → β transformation was measured to take 1.83 seconds during heating, while the β → α transformation was measured to take 0.91 seconds during cooling. The α → β transformation was characterized to be dominated by long-range diffusional growth on the leading (heating) side of the weld,
while the β → α transformation was characterized to be predominantly massive on the trailing (cooling) side of the weld, with a massive growth
rate on the order of 100 μm/s. 相似文献
6.
S. Saroja M. Vijayalakshmi Baldev Raj 《Transactions of the Indian Institute of Metals》2008,61(5):389-398
An alloy of Titanium with 5% Tantalum and 1.8% Niobium has been developed which possesses high corrosion resistance in highly
oxidising environments. The microstructural basis that enabled design of optimum thermo-mechanical treatments has been established
for this alloy. The classification of the alloy, transformation temperatures and different types of phase transformations
were evaluated for the first time by experimental methods like metallography and calorimetry and empirical methods. Systematic
microstructural modifications were introduced by thermo-mechanical treatments to improve corrosion resistance and mechanical
properties. The Ti-5Ta-1.8Nb alloy exhibited interesting texturing behaviour. Deformation and transformation textures exhibited
during unidirectional cold rolling and subsequent β→α+β transformation were studied using XRD and Electron Back Scatter Diffraction
techniques. The cross section of a wire drawn specimen exhibited (1 0–1 0)α texture while a cold rolled specimen showed (0 0 0 2)α deformation texture along the length — width direction. The transformation texture by itself was found to be dependent on
the type of deformation texture, (1 1 −2 0)α in cold rolled and (1 1 −2 2)α texture in the case of wire drawn alloy. A new method has been proposed to determine theoretical misorientation angle and
axis between variants of hcp a product transforming from a parent bcc crystal, obeying Burgers Orientation Relationship. The
role of variant selection mechanisms in the final texture of the alloy has been demonstrated by comparison of texture maps
obtained by X-ray Diffraction with those computed. 相似文献
7.
8.
T. F. Liu G. C. Uen C. Y. Chao Y. L. Lin C. C. Wu 《Metallurgical and Materials Transactions A》1991,22(6):1407-1415
The microstructure of an (α + γ) duplex Fe-9.0Al-29.5Mn-l.2Si alloy has been investigated by means of transmission electron
microscopy. In the as-quenched condition, extremely fine D03 particles were formed within the ferrite matrix by a continuous ordering transition during quenching. After being aged at
550 °C, the extremely fine D03 particles existing in the as-quenched specimen grew preferentially along (100) directions. With increasing the aging time
at 550 °C, a (Si, Mn)-rich phase (designated as “L phase”) began to appear at the regions contiguous to the D03 particles. The L phase has never been observed in various Fe-Al-Mn, Fe-Al-Si, Fe-Mn-Si, and Mn-Al-Si alloy systems before.
When the as-quenched specimen was aged at temperatures ranging from 550 °C to 950 °C, the phase transformation sequence occurring
within the (α + D03) region as the aging temperature increases was found to be (α + D03 + L phase) → (α + D03 + A13 β-Mn)→ (B2 + D03 + A13 β-Mn)→ (B2 + A13β-Mn)→ (α + A13 β-Mn)→ (α +γ)→α. 相似文献
9.
Tatsuya Fukino Sadahiro Tsurekawa Yasuhiro Morizono 《Metallurgical and Materials Transactions A》2011,42(3):587-593
This article presents in-situ observation of ferrite (α)/austenite (γ) phase transformation in an Fe-8.5 at. pct Ni alloy deformed by rolling using an automated scanning electron microscopy/energy
backscattered diffraction (SEM/EBSD) system. During heating, recrystallization in α phase and α → γ phase transformation independently occurred. The γ grains nucleated in unrecrystallized α grains were most probably incorporated into the grain interior of recrystallized α grains. They did not have any specific orientation relation (OR) with recrystallized α grains and grew in an isotropic manner. On the other hand, the intragranular γ grains nucleated in recrystallized α grains had a Kurdjumov–Sachs (K-S) OR with the α grains and grew in a considerably anisotropic manner. They preferentially grew along the common direction of surface traces
of {110}
α
/{111}
γ
. Approximately half of grain boundary (GB) allotriomorphs had either the K-S OR or the Nishiyama–Wasserman (N-W) OR with
the parent α grains. The γ allotriomorphs predominantly grew into the α grain having the special OR with themselves. The GB character distribution of γ phase at high temperatures was measured. The fraction of CSL boundaries was as high as 63 pct, particularly that of Σ3 grain
boundaries (GBs) was 54 pct. 相似文献
10.
Juho Talonen Hannu Hänninen Pertti Nenonen Gersom Pape 《Metallurgical and Materials Transactions A》2005,36(2):421-432
The effect of strain rate on strain-induced γ → α′-martensite transformation and mechanical behavior of austenitic stainless steel grades EN 1.4318 (AISI 301LN) and EN 1.4301
(AISI 304) was studied at strain rates ranging between 3×10−4 and 200 s−1. The most important effect of the strain rate was found to be the adiabatic heating that suppresses the strain-induced γ → α′ transformation. A correlation between the work-hardening rate and the rate of γ → α′ transformation was found. Therefore, the changes in the extent of the α′-martensite formation strongly affected the work-hardening rate and the ultimate tensile strength of the materials. Changes
in the martensite formation and work-hardening rate affected also the ductility of the studied steels. Furthermore, it was
shown that the square root of the α′-martensite fraction is a linear function of flow stress. This indicates that the formation of α′-martensite affects the stress by influencing the dislocation density of the austenite phase. Olson-Cohen analysis of the
martensite measurement results did not indicate any effect of strain rate on shear band formation, which was contrary to the
transmission electron microscopy (TEM) examinations. The β parameter decreased with increasing strain rate, which indicates a decrease in the chemical driving force of the α → α′ transformation. 相似文献
11.
Shibayan Roy Vedavyas Tungala Satyam Suwas 《Metallurgical and Materials Transactions A》2011,42(9):2535-2541
In the present study, the β transus of boron-modified Ti-6Al-4V alloy was found to be almost equivalent to that of the normal alloy, although there is
a difference in interstitial element content large enough to produce significant change. Compositional analysis confirms the
scavenging ability of the boride particles that are present in the microstructure toward the interstitial elements. This factor
can successfully retard the α → β phase transformation locally and increase the overall β transus of boron-added material. 相似文献
12.
The graded material of Ti6Al4V-Rene88DT superalloy, which has shown the potential to be applied in aeroengines, was fabricated
from prealloyed metal powders using the technique of laser rapid forming (LRF). A compositional gradient, from 100 pct Ti6Al4V
to Ti6Al4V-38 pct Rene88DT, was achieved within a thickness of laser deposit of 54 mm. The solidification behavior and the
phase evolution of the compositionally graded material were studied. The results of the X-ray diffraction (XRD) analysis together
with the metallographic study showed that a series of phase evolutions, α + β → α + β + Ti2Ni → β + Ti2Ni, along the compositional gradient have occurred. The hardness value of the graded material was measured along the compositional
gradient, and the results were explained in terms of the various phases present. The condition for columnar-to-equiaxed transition
observed in the graded material was explained, based on Hunt’s criterion. Finally, the morphology of β + Ti2Ni anomalous eutectic is discussed.
相似文献
T.M. Yue (Professor)Email: |
13.
Satish C. Gupta K.D. Joshi S. Banerjee 《Metallurgical and Materials Transactions A》2008,39(7):1593-1601
The pressure-induced electron transfer from sp to d band in transition elements, and spd to f band in the light actinides significantly influences the stability of crystal structures in these metals. Although α → ω → β phase transition with increasing pressure in group IV transition elements is well documented, the β → ω transition under pressure has not been reported until recently. Our experimental study on the β-stabilized Zr-20Nb alloy reveals that it transforms to ω phase on shock compression, whereas this transition is not seen in a hydrostatic pressure condition. The platelike morphology
of ω formed under shock compression is in contrast to the fine particle morphology seen in this system under thermal treatment,
which clearly indicates that the mechanism of the β → ω transformation under shock treatment involves a large shear component. In this article, we have analyzed why the ω → β transition pressures in Ti, Zr, and Hf do not follow the trend implied by the principle of corresponding states. Our analysis
shows that the ω → β transition depends on how the increased d population caused by the sp → d transfer of electron is distributed among various d substates. In Th, we have analyzed the role of 5f electrons in determining the mechanical stability of fcc and bct structures under hydrostatic compressions. Our analysis
shows that the fcc to bct transition in this metal, which has been reported by high-pressure experiments, occurs because of
softening of the tetragonal shear modulus C′ = (C
11 – C
12)/2 under compression. From the total energy calculated as a function of specific volume, we have determined the 0 K isotherm,
which is then used to deduce the shock Hugoniot. The theoretical Hugoniot compares well with the experimental data.
This article is based on a presentation given in the symposium entitled "Materials Behavior: Far from Equilibrium" as part
of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India. 相似文献
14.
A model has been developed to describe the microscopic behavior of phase transformation of carbon steels in the range of cooling
rate occurring in continuous casting. In the liquid-to solidphase transformation, this model simulates the phenomena of dendrite
nucleation and growth during solidification. Both δ- and γ-dendrites are involved. The nucleation and growth model has been established on the basis of published experimental
data and previous work. Also, a model of the peritectic transformation of carbon steels has been included. In the solid-to
solidphase transformation, the model considers the δ→ γ, γ→ α, and γ→ α + Fe3C phase transformations. The δ→ γ and γ→ α phase transformations have been modeled by using the Johnson-Mehl equation, also known as the Avrami equation. For the
pearlite transformation, a nucleation law, as well as the growth kinetics, has been established. Good agreement has been found
between the prediction of the model and the experimental data. 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.
The β → α transformation kinetics of CP-Ti during continuous cooling was measured using a fully computer-controlled resistivity-temperature
real-time measurement apparatus. Unlike the pure Ti case, the massive transformation occurs at medium cooling rates, about
90 °C/s to 600 °C/s. Its start temperature is estimated to be about 890 °C, which is close to the T
0 temperature. The reason for the appearance of massive transformation in CP-Ti is because CP-Ti contains a significant amount
of Fe as an impurity, which leads to the T
0(β → α) vs composition curve being parallel to the composition axis due to its retrograde solubility. The martensitic transformation
starts to occur at a cooling rate of about 500 °C/s, which is much slower than that (about 3000 °C/s) reported in a pure Ti
case. This retardation effect of martensitic transformation is also believed to arise from the presence of Fe in CP-Ti, which
is a strong β stabilizer. 相似文献
17.
Jianqing Su Srinivasan Swaminathan Sarath K. Menon Terry R. McNelley 《Metallurgical and Materials Transactions A》2011,42(8):2420-2430
Equivalent strains up to a value of ≈2.7 were determined by evaluation of the shape changes of the phases in a duplex α(fcc)/β(bcc) microstructure formed ahead of the pin tool extraction site during the friction stir processing (FSP) thermomechanical
cycle in a cast NiAl bronze alloy. Correlation of the local strains with volume fractions of the various microstructure constituents
in this alloy shows that the concurrent straining of FSP results in acceleration of the α + β → β reaction in the thermomechanically affected zone (TMAZ) ahead of the pin extraction site. The resulting volume fraction of
β (as determined by the volume fraction of its transformation products formed during post-FSP cooling) corresponds closely
to the volume fraction expected for the peak stir zone temperature measured separately by means of thermocouples embedded
within the tool pin profile along the tool path. The stir zone (SZ) in this material exhibits near-equilibrium microstructures
despite brief dwells near the peak temperature (T
peak ≈ 0.95T
melt), reflecting large local strains and strain rates associated with this process. 相似文献
18.
The phenomenological double-shear theory of martensite crystallography has been applied to the β → α′ martensitic transformation
in the U-1.6 at. pct Ga alloy. A correspondence matrix for the β → α′ transformation was derived from the experimentally determined
β/α′ orientation relationship, and the double lattice invariant shear was considered as a combination of the principal slip
(010) [100]a with one of the minor slips in the α-uranium structure. The theoretical predictions of the habit plane are in good agreement
with the experimental observations.
Formerly Graduate Student, Ben-Gurion University of the Negev. 相似文献
19.
P. Vizcaíno A. D. Banchik J. P. Abriata 《Metallurgical and Materials Transactions A》2004,35(8):2343-2349
In this work, the dissolution enthalpy, ΔH
δ→α, of the δ hydride phase in the αZr matrix in ZIRCALOY-4 has been determined with a differential scanning calorimeter (DSC)
in two different ways: by means of a van’t Hoff equation, measuring the terminal solubility temperature in dissolution, TSSd,
and by direct measurement of the dissolution heat, Q
δ→α, as the area between the base line and the calorimetric curve. The application of the DSC technique to the hydride dissolution
heat measurements, a transformation which covers an extended temperature range, is completely original and requires a special
treatment of the calorimetric curve. These measurements were done on samples that practically cover the entire solubility
range of hydrogen in αZr phase (80 to 640 ppm). The values obtained, 36.9 and 39.3 kJ/mol H, respectively, are self-consistent
and in good agreement with the values of the more recent revisions, but reduces considerably the scatter of the literature
data. 相似文献
20.
An investigation of the influence of processing variables on mechanical properties and phase development for a Ti-60 wt pct
Ta (Ti-28.5 at. pct Ta) alloy was conducted. The alloy was hot-rolled, subjected to heat-treatment temperatures above the
β (bcc) transus (1 hour at 700 °C, 800 °C, or 900 °C), and water quenched. All heat treatment produced a combination of metastable
β (bcc) and metastable α″ (orthorhombic martensite), with the amount of retained β essentially independent of heat treatment, ranging from 20 to 33 vol pct. Deformation of as-rolled and heat-treated tension
specimens showed an anomalous leveling of the stress-strain curve in the stress-strain curves at low strains. X-ray diffraction
(both simple 2ϑ diffractometry and texture analysis) on both deformed and undeformed material determined that the leveling of the stress-strain
curve was a result of the β→α″ martensitic transformation. The stress required to initiate the transformation increased with prequench temperature. This
was determined to be due to the presence of athermal ω. Grain growth kinetics have been determined in the course of this work. 相似文献