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1.
Kinetics of phase evolution of Zn-Fe intermetallics 总被引:1,自引:0,他引:1
Z. T. Liu M. Boisson O. N. C. Uwakweh 《Metallurgical and Materials Transactions A》1996,27(10):2904-2910
The intermetallic phases, Γ (Fe33Zn10), Γ1, (Fe5Zn21), δ (FeZn7, and ζ (FeZn13), are mechanically alloyed through ball milling of pure elemental Fe and Zn powders under a controlled atmosphere of argon
gas. The state of the as-ball-milled materials was crystalline, except for the Γ phase, which was amorphous. Phase-evolution
kinetics through differential scanning calorimeter (DSC) measurements of the as-ball-milled powders show three characteristic
transition temperatures for the Γ1, and ζ phases, two for the Γ phase, and only one for the δ phase. The activation energies for the evolution of the milled
powders to their equilibrium crystalline phases are 170 ± 1, 251 ±2, 176± 1, and 737 ±4 kJ/mol for the Γ, Γ1, δ, and ζ phases, respectively. These values show that the mechanisms for the metastable-to-stable phase transition in these
intermetallics are different, whereas diffusion over short distances may be part of the entire process in all cases. 相似文献
2.
The ball milling of elemental powders corresponding to Γ (Fe3Zn10)+0.12 wt pct Si; Γ1 (Fe5Zn21) + 0.12 wt pct Si; δ (FeZn7)+0.12 wt pct Si; and ζ (FeZn13)+0.12 wt pct Si composition ratios yields crystalline, mechanically alloyed phases. Differential scanning calorimetry (DSC)
measurements of these materials show that they evolve differently, with well-defined characteristic stages. The activation
energies for processes corresponding to these stages, based on kinetic analyses, are determined and correlated to microstructural
evolvements. The processes occurring during the first stage below 250 °C, for all of the materials studied using X-ray diffraction
(XRD) analysis, are associated with release of strain, recovery, and limited atomic diffusion. The activation energies for
recovery processes are 120 kJ/mole for the Γ+0.12 wt pct Si, 131 kJ/mole for δ+0.12 wt pct Si, and 96 kJ/mole for ζ+0.12 wt pct Si alloys. At higher temperatures, recrystallization and other structural transformations occur with activation
energies of 130 and 278 kJ/mole for Γ+0.12 wt % Si; of 161 kJ/mole for Γ1+0.12 wt pct Si; of 167 and 244 kJ/mole for δ+0.12 wt pct Si; and of 641 kJ/mole for the ζ+0.12 wt pct Si. In addition, a eutectic reaction at 420 °C±3 °C, corresponding to the Zn-Si system, and a melting of Zn in
Fe-Zn systems are observed for the ζ+0.12 wt pct Si material. The relation of FeSi formation in the Sandelin process is discussed. 相似文献
3.
Fixed composition ratios of Fe and Zn corresponding to γ-(Fe3Zn110), Γ1-(Fe5Zn21), δ-(FeZn7), and ζ-(FeZn13) with the addition of 5 pct Al (wt) were ball milled in an argon gas atmosphere to form homogenous alloys. Nonisothermal
kinetic analyses of the mechanically alloyed materials, based on differential scanning calorimetry (DSC) measurements, revealed
two diffusion-controlled processes during the evolution of the δ+5 pct Al and ζ+5 pct Al compositions with activation energies of 227±2 and 159±1 kJ/mole, respectively. Other endothermic
and exothermic reactions detected for these compositions are consistent with the Fe-Zn-Al equilibrium phase systems with respect
to the formation of the Fe3Al, Fe2Al5, and δ-FeZn7 phases Based on the evidence of FeAl2 formation at 440 °C for the ζ+5 pct Al composition from X-ray diffraction (XRD) and DSC measurements, the revision/re-evaluation
of the Fe-Zn-Al equilibrium phase diagrams is proposed. The Γ+5 pct Al and Γ1+5 pct Al compositions evolved similarly through the same fields, except at 400 °C, where the former consisted of α-Fe + Γ + δ, while the later was without the Γ phase. 相似文献
4.
The effects of steel chemistry on the formation of Fe-Zn intermetallic compounds in the galvanneal coatings have been investigated
by examining the microstructure of galvanneal coat-ings on extra-low-carbon (ELC) steel, interstitial-free (IF) steel, and
interstitial-free rephos-phorized (IFP) steel. The layer structure of the coatings was revealed by chemical etching. Phases
present in each layer were then identified using electron diffraction in transmission elec-tron microscopy (TEM). A two-layer
structure, one consisting of the δ phase with a small fraction of the ζ, phase dispersed on the surface and Γ phases and another
consisting of the δ and Γ1 phases, was observed in the ELC sample and the IFP sample, respectively. A three-layer structure consisting of the δ, Γ1 + δ, and Γ phases was observed in the IF sample. The presence of C in the steel substrate retarded the alloying between Fe
and Zn; while P in the steel favored the formation of the Γ1, phase over the Γ phase by its surface segregation in the steel substrate. The orientation relationship between coating and
substrate was also studied by electron diffraction. Three α-Fe/Γ orientation relationships were frequently observed. 相似文献
5.
Microstructural study of galvanized coatings formed in pure as well as commercial grade zinc baths 总被引:1,自引:0,他引:1
G. K. Mandal D. Mandal S. K. Das R. Balasubramaniam S. P. Mehrotra 《Transactions of the Indian Institute of Metals》2009,62(1):35-40
This investigation is an effort to have a better understanding of the growth kinetics and morphology of the coating formed
during the galvanizing process in pure as well as commercial grade zinc baths. The protective coating that is formed during
hot dip galvanizing, normally between 450 and 480°C, consists of a series of Fe-Zn intermetallic layers, which have been identified
as gamma (Γ), delta (δ), zeta (ξ) and an outer eta (η) layer, highly rich in zinc. There is apparently no delay in the formation
of ξ or δ phases in both pure as well as the commercial grade zinc baths. The gamma (Γ) phase is formed after an incubation
time of about 30 s at a bath temperature of 470°C in the pure zinc bath. Its formation is further delayed in the commercial
grade zinc bath. The last morphological feature is the formation of a second ξ layer at the ξ/δ interface in the pure zinc
bath. In the commercial grade zinc bath two different morphologies of ξ phase are seen starting from the lowest dipping time,
and also the overall coating is considerably thicker due to formation of several iron-zinc intermetallics which degrade its
ductility and outward appearance. Commercial grade zinc also enhances the dross formation in the bath and deteriorates the
quality of the coating. Presence of transverse cracks as well as entrapment of dross particles in the coating is attributed
to the less compact coating that is formed in the commercial grade zinc bath. 相似文献
6.
The microstructures of multiphase intermetallic alloys with compositions Al70Ti10V20 and Al62Ti10V28 based on the trialuminide Al3Ti have been characterized, following chill casting and postsolidification heat treatment, using a combination of scanning
electron microscopy and transmission electron microscopy (TEM). Evidence of a eutectic reaction of the form L → δ-Al3(Ti, V)+ζ-Al8V5, not previously reported in the Al-Ti-V system, has been observed in both alloys solidified at sufficient levels of undercooling.
The ζ phase is replaced by metallic β-(Ti, V) phase during subsequent heat treatment in the range 1073 to 1273 K, and differential thermal analysis (DTA) of samples
prean-nealed at 1173 K revealed an endothermic peak at ∼1560 K, consistent with equilibrium eutectic melting of the form (δ+β) → L. Although the chill-cast alloys retained metastable intermediate high-temperature phases, duplex metallic-intermetallic
microstructures, containing uniform fine-scale distributions of metallic β-(Ti, V) solid solution in a δ-Al3(Ti, V) intermetallic matrix, have been produced in both alloys during isothermal heat treatments at temperatures in the range
1073 to 1273 K. For both alloys, the bulk Vickers hardness of such microstructures remained in excess of that of binary Al3Ti, while in the Al62Ti10V28 alloy, where the increased volume fraction of β phase took the form of a near-continuous network within δ matrix, there was evidence arising from indentation tests of a substantial improvement in the cracking resistance compared
to both chill-cast ternary alloy and binary Al3Ti. 相似文献
7.
Distribution of aluminum in hot-dip galvanized coatings 总被引:2,自引:0,他引:2
Valdemar Furdanowicz C. Ramadeva Shastry 《Metallurgical and Materials Transactions A》1999,30(12):3031-3044
Hot-dip galvanized panels of low-carbon (LC) and interstitial-free (IF) steels were produced in a laboratory simulator with
an average coating mass of 60 g/m2. Three pot aluminum levels were used, viz., 0.10 pct (by wt), 0.15 pct, and 0.18 pct. Metallography, scanning electron microscopy (SEM), and transmission electron microscopy
(TEM) were used to characterize coating and base steel microstructures. Wet chemical analysis and scanning transmission electron
microscopy (STEM) were employed for compositional analyses. The aluminum content of the melt was found to be the predominant
factor influencing the distribution of Al in the coating. At 0.18 pct melt aluminum, Al is partitioned between the aluminide
inhibition layer at the coating-steel interface (∼80 pct) and the zinc overlay (∼20 pct). At 0.15 pct, it is partitioned among
the aluminide layer (∼75 pct to 80 pct), zinc-iron (FeZn13, ζ) intermetallic layer (∼5 pct to 15 pct), and the coating overlay (∼10 pct). At 0.10 pct, the aluminum is divided almost equally
between the overlay and the zinc-iron intermetallics. At the two lower aluminum levels is the distribution marginally influenced
by the steel grade. The ζ was found to not preferentially nucleate at the ferrite grain boundaries. When both the aluminide and ζ occurred at the coating-steel interface, the ζ particles appeared near discontinuities and thinner regions in the aluminide layer. The coating, relative to the melt, is
enriched in aluminum because of its concentration in the aluminide and in the zinc-iron intermetallics. This enrichment increases
with melt aluminum through an increase in the aluminum content of the aluminide layer and not of its thickness. In addition,
a few tens-of-nanometers-thick layer enriched in aluminum, oxygen, and iron is observed on the outer surface of all coatings.
The aluminum content in this layer also increases with an increase in the melt aluminum, but it contributes negligibly to
the coatings’s content because of its extreme thinness. 相似文献
8.
W. Khalifa F. H. Samuel J. E. Gruzleski 《Metallurgical and Materials Transactions A》2003,34(3):807-825
The iron intermetallics observed in six dilute Al-Si-Fe alloys were studied using thermal analysis, optical microscopy, and
image, scanning electron microscopy/energy dispersive X-ray, and electron probe microanalysis/wavelength dispersive spectroscopy
(EPMA/WDS) analyses. The alloys were solidified in two different molds, a preheated graphite mold (600 °C) and a cylindrical
metallic mold (at room temperature), to obtain slow (∼0.2 °C/s) and rapid (∼15 °C/s) cooling rates. The results show that
the volume fraction of iron intermetallics obtained increases with the increase in the amount of Fe and Si added, as well
as with the decrease in cooling rate. The low cooling rate produces larger-sized intermetallics, whereas the high cooling
rate results in a higher density of intermetallics. Iron addition alone is more effective than either Si or Fe+Si additions
in producing intermetallics. The alloy composition and cooling rate control the stability of the intermetallic phases: binary
Al-Fe phases predominate at low cooling rates and a high Fe:Si ratio; the β-Al5FeSi phase is dominant at a high Si content and low cooling rate; the α-iron intermetallics (e.g., α-Al8Fe2Si) exist between these two; while Si-rich ternary phases such as the δ-iron Al4FeSi2 intermetallic are stabilized at high cooling rates and Si contents of 0.9 wt pct and higher. Calculations of the solidification
paths representing segregations of Fe and Si to the liquid using the Scheil equation did not conform to the actual solidification
paths, due to the fact that solid diffusion is not taken into account in the equation. The theoretical models of Brody and
Flemings[44] and Clyne and Kurz[45] also fail to explain the observed departure from the Scheil behavior, because these models give less weight to the effect
of solid back-diffusion. An adjusted 500 °C metastable isothermal section of the Al-Si-Fe phase diagram has been proposed
(in place of the equilibrium one), which correctly predicts the intermetallic phases that occur in this part of the system
at low cooling rates (∼0.2 °C/s). 相似文献
9.
Joo Hyun Park Geun-Ho Park Doo-Jin Paik Yoon Huh Moon-Hi Hong 《Metallurgical and Materials Transactions A》2012,43(1):195-207
The shape, size, and composition of dross particles as a function of aluminum content at a fixed temperature were investigated
for aluminum added to the premelted Zn-Fe melt simulating the hot-dip galvanizing bath by a sampling methodology. In the early
stage, less than 30 minutes after Al addition, local supersaturation and depletion of the aluminum concentration occurred
simultaneously in the bath, resulting in the nucleation and growth of both Fe2Al5Zn
x
and FeZn13. However, the aluminum was homogenized continuously as the reaction proceeded, and fine and stable FeZn10Al
x
formed after 30 minutes. An Al-depleted zone (ADZ) mechanism was newly proposed for the “η→η+ζ→δ” phase transformations. The ζ phase bottom dross partly survived for a relatively long period, i.e., 2 hours in this work, whereas the η phase disappeared after 30 minutes. In the early stage of dross formation, both Al-free large particles as well as high-Al
tiny particles were formed. The dross particle size decreased slightly with increased reaction time before reaching a plateau.
The opposite tendency was observed when the Al content was 0.130 mass pct; with a relatively high Al content, the nucleation
of tiny η phase dross was significantly enhanced because of the high degree of supersaturation. This unstable η phase dissolved continuously and underwent simple transformation to the stable δ phase. The relationship between nucleation
potential and supersaturation ratio of species is discussed based on the thermodynamics of classical nucleation theory. 相似文献
10.
W. Khalifa F. H. Samuel J. E. Gruzleski 《Metallurgical and Materials Transactions A》2003,34(13):807-825
The iron intermetallics observed in six dilute Al-Si-Fe alloys were studied using thermal analysis, optical microscopy, and
image, scanning electron microscopy/energy dispersive X-ray, and electron probe microanalysis/wavelength dispersive spectroscopy
(EPMA/WDS) analyses. The alloys were solidified in two different molds, a preheated graphite mold (600°C) and a cylindrical
metallic mold (at room temperature), to obtain slow (}0.2 °C/s) and rapid (}15 °C/s) cooling rates. The results show that
the volume fraction of iron intermetallics obtained increases with the increase in the amount of Fe and Si added, as well
as with the decrease in cooling rate. The low cooling rate produces larger-sized intermetallics, whereas the high cooling
rate results in a higher density of intermetallics. Iron addition alone is more effective than either Si or Fe+Si additions
in producing intermetallics. The alloy composition and cooling rate control the stability of the intermetallic phases: binary
Al-Fe phases predominate at low cooling rates and a high Fe:Si ratio; the β-Al5FeSi phase is dominant at a high Si content and low cooling rate; the α-iron intermetallics (e.g., α-Al8Fe2Si) exist between these two; while Si-rich ternary phases such as the δ-iron Al4FeSi2 intermetallic are stabilized at high cooling rates and Si contents of 0.9 wt pct and higher. Calculations of the solidification
paths representing segregations of Fe and Si to the liquid using the Scheil equation did not conform to the actual solidification
paths, due to the fact that solid diffusion is not taken into account in the equation. The theoretical models of Brody and
Flemings[44] and Clyne and Kurz[45] also fail to explain the observed departure from the Scheil behavior, because these models give less weight to the effect
of solid back-diffusion. An adjusted 500°C metastable isothermal section of the Al-Si-Fe phase diagram has been proposed (in
place of the equilibrium one), which correctly predicts the intermetallic phases that occur in this part of the system at
low cooling rates (}0.2 °C/s). 相似文献
11.
Chin Liu 《Metallurgical and Materials Transactions A》1986,17(4):679-684
In the fundamental equation of superplastic flow, σ = kέm, έ is the strain rate, σ is the flow stress,m is the strain-rate sensitivity index of flow stress, andk is a material constant. Bothm andk vary with increase in strain (δ). Therefore, we can have m0 (≠0), mI (mI1,m,I2,mI3,....), mF; k0 (≠0), kI (kI1,kI2,kI3,.... ), kF values corresponding to the initial strain δ0 (= 0.00 pct), the strain at any instant during stretching, δI (δI1, δI2, 8δI3,....), and the total elongation, δF, at fracture, respectively. The curves expressing the dependence ofm andk on δ can be called them-k- δ orm-C- δ or simply them- δ curves. All these curves can be classified into types and can be expressed by the C. L.m- δ equation derived by the present author: δ(pct) = [Cέ(m- m0 - 1] × 100 whereC = k0
+ dk0/k0,m = m0 andC = k0/k0
= 1, when δ = δ0;m = mI, andC = CI
= kI/k0 when δ= δI;m = mF andC = CF
= kF/k0, when δ = δF. By means of this equation, not only the total elongation at fracture but also the strains at any instant during stretching
of a material can be predicted, if the correspondingm values are known. 相似文献
12.
The oxygen potentials of several three- and two-phase equilibria in the Fe−Co−S−O quaternary system were measured atP
SO2=1, 0.1, and 0.01 atm over wide temperature ranges. The measurements were carried out using a solid oxide electrolyte emf
technique. The equilibria measured are sp+ε+δ, s+ε+ξ, sp+ξ+η, and sp+δ. The symbols sp, ε, δ, ξ, and η denote the spinel,
monoxide, monosulfide, metal sulfate, and Fe2O3 phases, respectively. Compositions for several of the equilibrated phases were measured using electron probe microanalysis.
The present results and literature data for the constituent ternary systems were used to obtain thermochemical solution parameters
for the sp, ε, δ and ξ solid solution phases. The calculated potential-composition stability diagrams for SO2 pressures of 1, 0.1, and 0.01 atm at 973, 1023, and 1073 K, respectively, are in good agreement with the experimental results.
OMRAN A. MUSBAH, formerly Research Associate at the University of Wisconsin-Madison 相似文献
13.
14.
The solubility of hydrogen was determined in the (Zr + 5 wt pct Nb)-H2, (Zr + 10 wt pct Nb)-H2, and (Zr + 20 wt pct Nb)-H2 systems as a function of composition, temperature (700° to 950°C) and hydrogen equilibrium pressure (0.5 to 760 mm Hg). The
position of boundariesβ - (β + δ) and(β + δ)-δ were determined in each of the above three systems. Niobium significantly reduces the solubility of hydrogen in theβ andδ phases and increases the equilibrium hydrogen pressure for any fixed concentration. The equilibrium pressure-temperature
relations in the two phase region (β + δ) were derived and the heat of formation ofδ-hydride from saturatedβ-Zr, ΔH
β → δ, were determined. The value of ΔH
β → δ increases up to about 5 wt pct Nb after which the effect of niobium seems to be insignificant. The maximum hydrogen pick-up
of zirconium at room temperature decreases with increasing niobium content of the alloy. 相似文献
15.
M. Ghosh S. Kundu S. Chatterjee B. Mishra 《Metallurgical and Materials Transactions A》2005,36(7):1891-1899
Solid-state diffusion bonding of Ti-6Al-4V and type 304 SS was investigated in the temperature range of 750 °C to 950 °C,
under a uniaxial load for 5.4 ks in vacuum. The diffusion bonds were characterized using light and scanning electron microscopy.
The scanning electron microscopic images in backscattered mode show the existence of different reaction layers in the diffusion
zone. The composition of these layers was determined by energy-dispersive X-ray spectroscopy (EDS) to contain the α-Fe, χ, λ, FeTi, β-Ti, and Fe2Ti4O phases. The presence of these intermetallics was confirmed by X-ray diffraction. The bond strength was evaluated, and the
maximum tensile strength of ∼342 MPa and the maximum shear strength of ∼237 MPa were obtained for the diffusion couple processed
at 800 °C due to the finer width of the brittle intermetallic layers. With a rise in joining temperature, the bond strength
drops owing to an increase in the width of the reaction layers. The activation energy and growth constant were calculated
in the temperature range of 750 °C to 950 °C for the reaction products. The χ phase showed the fastest growth rate. A fracture-surface observation in a scanning electron microscope (SEM) using EDS demonstrates
that failure takes place mainly through the β-Ti phase for the diffusion couples processed in the aforementioned temperature range. 相似文献
16.
Recent research suggest that the iron-rich intermetallic phases, such as α-Fe Al15(Fe,Mn)3Si2 and β-Fe Al5FeSi, nucleate on oxide films entrained in aluminum casting alloys. This is evidenced by the presence of crack-like defects
within these iron-rich intermetallics. In an attempt to verify the role of oxides in nucleating iron-rich intermetallics,
experiments have been conducted under conditions where in-situ entrained oxide films and deliberately added oxide particles were present. Iron-rich intermetallics are observed to be associated
with the oxides in the final microstructure, and crack-like defects are often observed in the β-Fe plates. The physical association of the Fe-rich intermetallic phases with these solid oxides, either formed in situ or added, is in accordance with the mechanism suggesting that iron-rich intermetallics nucleate upon the wetted sides of
double oxide films.
This article is based on a presentation made in the John Campbell Symposium on Shape Casting, held during the TMS Annual Meeting,
February 13–17, 2005, in San Francisco, CA. 相似文献
17.
Keith J. Leonard Joseph C. Mishurda Vijay K. Vasudevan 《Metallurgical and Materials Transactions B》2000,31(6):1305-1321
The solidification pathways, subsequent solid-state transformations, and the liquidus surface in the Nb-Ti-Al system have
been examined as part of a larger investigation of phase equilibria in Nb-Ti-Al intermetallic alloys. Fifteen alloys ranging
in composition from 15 to 40 at. pct Al, with Nb to Ti ratios of 4:1, 2:1, 1.5:1, 1:1, and 1:1.5, were prepared by arc melting
and the as-cast microstructures were characterized by optical microscopy (OM), microhardness, X-ray diffraction (XRD), differential
thermal analysis (DTA), backscattered electron imaging (BSEI), electron probe microanalysis (EPMA), and transmission electron
microscopy (TEM). The results indicate that the range of primary β solidification is much wider than that indicated in previously reported liquidus surfaces, both experimental and calculated.
Differential thermal analysis has identified the existence of a β to σ+γ transformation in three alloys where it was previously thought not to exist; confirmation was provided by high-temperature
vacuum heat treatments in the single-phase β region followed by rapid quenching. The location of the boundary between the β, σ, and δ primary solidification fields has been redefined. A massive β → δ transformation, which was observed in the cast microstructure of a Nb-25Ti-25Al alloy, was repeatable through cooling following
homogenization. A β → δ+σ eutectoid-like transformation in the 25 at. pct Al alloys, was detected by DTA and evaluated through microstructural analysis
of heat-treated samples. Trends in the β phase with variations in composition were established for both lattice parameters and microhardness. As a result of this
wider extent of the primary β solidification field, a greater possibility exists for microstructural control through thermal processing for alloys consisting
of either σ+γ, β+σ, or β+δ phases.
An erratum to this article is available at . 相似文献
18.
19.
20.
It has recently been suggested that the β-Al5FeSi and ϑ-Al2Cu intermetallic particles are refined and dispersed in the presence of high silicon, thereby improving the ductility of Al-Si-Cu-Mg
alloys. However, limited metallographic evidence was presented to support these claims. Therefore, a study of the effect of
Si content in the range of 4.5 to 9 pct on the morphology and distribution of Fe-rich and Cu-rich intermetallic phases has
now been conducted. It is shown that Si, indeed, exerts a refining effect on the iron-containing particles (α and β) and disperses clusters of intermetallics (including the Cu-rich particles). In alloys with low Si content, the Fe- and Cu-rich
particles form long and closely intertwined clusters. Microcracks originating from cracked intermetallic particles extend
and propagate along the clusters with little plasticity, resulting in the low ductility of the alloys. At a high Si content,
the intermetallic phases appear more dispersed and the clusters of particles are small and isolated from each other. Microcracks
resulting from the cracked intermetallics are short and are isolated, as well, thereby increasing the ductility of the alloys.
The mechanisms by which the refinement and dispersion of intermetallic phases occur are discussed.
This article is based on a presentation made in the John Campbell Symposium on Shape Casting, held during the TMS Annual Meeting,
February 13–17, 2005, in San Francisco, CA. 相似文献