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1.
Two different pearlites after two separate eutectoid reactions were observed in an Fe-19.8 Mn-1.64 Al-1.03 C (wt pct) steel.
The steel specimens were processed under solution heat treatment at 1373 K (1100 °C) and received isothermal holding at temperatures
from 1073 K to 773 K (800 °C to 500 °C). The constituent phase of the steel is single austenite at temperatures between 1373 K
and 1073 K (1100 °C and 800 °C). At temperatures below 1048 K (775 °C), M 3C and M 23C 6 carbides coprecipitate at the austenitic grain boundaries. Two different pearlites appear in the austenite matrix simultaneously
at temperatures below 923 K (650 °C). One is lamellae of ferrite and M 3C carbide, and the other is lamellae of ferrite and M 23C 6 carbide. These two pearlites are product phases from two separate eutectoid reactions, i.e., austenite → ferrite + cementite and austenite → ferrite + M 23C 6. Therefore, the supersaturated austenite has decomposed into two different pearlites, separately. 相似文献
2.
Phase equilibria of the Cu-Fe-O-Si system have been investigated in equilibrium: (1) with air atmosphere at temperatures between 1373?K and 1673?K (1100?°C and 1400?°C) and (2) with metallic copper at temperatures between 1373?K and 1573?K (1100?°C and 1300?°C). High-temperature equilibration/quenching/electron-probe X-ray microanalysis (EPMA) techniques have been used to accurately determine the compositions of the phases in equilibrium in the system. The new experimental results are presented in the form of ??Cu 2O??-??Fe 2O 3??-SiO 2 ternary sections. The relationships between the activity of CuO 0.5(l) and the composition of slag in equilibrium with metallic copper are discussed. The phase equilibria information of the Cu-Fe-O-Si system is of practical importance for industrial copper production processes and for the improvement of the existing thermodynamic database of copper-containing slag systems. 相似文献
3.
We discovered a eutectoid reaction in an Fe-13.4Mn-3.0Al-0.63C (wt pct) steel after solution heat treatment at 1373 K (1100 °C)
and holding at temperatures below 923 K (650 °C). The steel is single austenite at temperatures from 1373 K to 923 K (1100 °C
to 650 °C). A eutectoid reaction involves the replacement of the metastable austenite by a more stable mixture of ferrite
and M 23C 6 phases at temperatures below 923 K (650 °C). The mixture of ferrite and M 23C 6 is in the form of pearlitic lamellae. The morphology of the lamellae of the product phases is similar to that of pearlite
in steels. Thus, we found a new pearlite from the eutectoid reaction of the Mn-Al steel featuring γ → α + M 23C 6. A Kurdjumov–Sachs (K-S) orientation relationship exists between the pearlitic ferrite (α) and M 23C 6 (C6) grains, i.e., (110) α // (111) C6 and [[`1] \overline{1} 11] α // [0[`1] \overline{1} 1] C6. The upper temperature limit for the eutectoid reaction is between 923 K and 898 K (650 °C and 625 °C). 相似文献
4.
Interfacial reactions between Al alloy and andalusite low-cement castables (LCCs) containing 5 wt pct B 2O 3, B 4C, and BN were analyzed at 1123 K and 1433 K (850 °C and 1160 °C) using the Alcoa cup test. The results showed that the addition
of boron-containing materials led to the formation of aluminoborate (9Al 2O 3.2B 2O 3) and glassy phase containing boron in the prefiring temperature (1373 K [1100 °C]), which consequently improved the corrosion
resistance of the refractories. The high heat of formation of the aluminoborate phase (which increased its stability to reactions
with molten Al alloy) and the low solubility of boron in molten Al were the major factors that contributed to the improvement
in the corrosion resistance of B-doped samples. 相似文献
5.
The hot deformation behavior of 2101 grade lean duplex stainless steel (DSS, containing ~5 wt pct Mn, ~0.2 wt pct N, and ~1.4 wt pct Ni) and associated microstructural changes within δ-ferrite and austenite (γ) phases were investigated by hot-compression testing in a GLEEBLE 3500 simulator over a range of deformation temperatures, T
def [1073 K to 1373 K (800 °C to 1100 °C)], and applied strains, ε (0.25 to 0.80), at a constant true strain rate of 1/s. The microstructural softening inside γ was dictated by discontinuous dynamic recrystallization (DDRX) at a higher T
def [1273 K to 1373 K (1000 °C to 1100 °C)], while the same was dictated by continuous dynamic recrystallization (CDRX) at a lower T
def (1173 K (900 °C)]. Dynamic recovery (DRV) and CDRX dominated the softening inside δ-ferrite at T
def ≥ 1173 K (900 °C). The dynamic recrystallization (DRX) inside δ and γ could not take place upon deformation at 1073 K (800 °C). The average flow stress level increased 2 to 3 times as the T
def dropped from 1273 to 1173 K (1000 °C to 900 °C) and finally to 1073 K (800 °C). The average microhardness values taken from δ-ferrite and γ regions of the deformed samples showed a different trend. At T
def of 1373 K (1100 °C), microhardness decreased with the increase in strain, while at T
def of 1173 K (900 °C), microhardness increased with the increase in strain. The microstructural changes and hardness variation within individual phases of hot-deformed samples are explained in view of the chemical composition of the steel and deformation parameters (T
def and ε).
相似文献
6.
Continuous annealing treatment (austenitization for 4 hours followed by furnace cooling) and cyclic annealing treatment (four cycles of austenitization, each of 0.66 hours duration followed by forced air cooling) of 8.0 wt pct Cr white iron samples are undertaken at 1173 K, 1223 K, 1273 K, 1323 K, and 1373 K (900 °C, 950 °C, 1000 °C, 1050 °C, and 1100 °C) as steps of destabilizing the as-cast structure. Continuous annealing results in precipitation of secondary carbides on a matrix containing mainly pearlite, while cyclic annealing treatment causes similar precipitation of secondary carbides on a matrix containing martensite plus retained austenite. On continuous annealing, the hardness falls below the as-cast value (HV 556), while after cyclic annealing treatment there is about 70 pct increase in hardness, i.e., up to HV 960. Decrease in hardness with increasing annealing temperature is quite common after both heat treatments. The as-cast notched impact toughness (4.0 J) is nearly doubled by increasing to 7.0 J after both continuous and cyclic annealing treatment at 1173 K and 1223 K (900 °C and 950 °C). Cyclic annealing treatment gives rise to a maximum notched impact toughness of 10.0 J at 1373 K (1100 °C). Abrasive wear resistance after continuous annealing treatment degrades exhibiting wear loss greater than that of the as-cast alloy. In contrast, samples with cyclic annealing treatment show reasonably good wear resistance, thereby superseding the wear performance of Ni-Hard IV. 相似文献
7.
Initial-stage sintering kinetics of nanocrystalline tungsten has been studied in the temperature range of 1273–1473 K (1000–1200 °C).
Nanocrystalline tungsten sinters initially through a grain boundary diffusion mechanism. The calculated activation energy
was 388 ± 11 kJ/mol at low temperatures (1273–1373 K (1000–1100 °C)) and 409 ± 7 kJ/mol at high temperatures (1373–1473 K
(1100–1200 °C)), which are close to the experimentally measured activation energy for grain boundary diffusion (385 kJ/mol). 相似文献
8.
The oxidation behavior of sulfur in desulfurization slag generated from the secondary steelmaking process with air has been investigated in the temperature range of 973?K to 1373?K (700?°C to 1100?°C). Although a high removal rate of sulfur is not achieved at temperatures lower than 1273?K (1000?°C) because of the formation of CaSO 4, most of the sulfur is rapidly removed from slag as SO 2 gas in the 1273?K to 1373?K (700?°C to 1100?°C) range. This finding indicates that the desulfurization slag generated from the secondary steelmaking process can be reused as a desulfurized flux through air oxidation, making it possible to reduce significantly the amount of desulfurization slag for disposal. 相似文献
9.
Predictions for oxidation behavior of Ni-base superalloys become more difficult than before because of the complex alloy composition.
In this study, we focus on the initial oxidation behavior of Ni-base superalloys, and we suggest a new diagram to predict
the initial oxide morphology of Ni-base superalloys with 63 binary, ternary, and multicomponent Ni-base single-crystal superalloys
at 1373 K (1100 °C). As a comparison of observed and calculated weight changes after one cycle at 1373 K (1100 °C) obtained
by a regression analysis, 63 alloys demonstrated two distinct behaviors, which are divided heretofore into group A and group
B. Microstructural observation revealed that an oxide layer in the group A alloys consists of Al 2O 3 and/or spinel or complex oxide, whereas an oxide layer in the group B alloys consists of a thick NiO layer with an Al 2O 3 internal subscale. Thermodynamic properties can reflect more effects of alloy elements in Ni-base superalloys, and Al and
Cr activities, calculated by Thermo-Calc, were used as factors to predict initial oxidation morphology. Groups A and B alloys
can clearly be divided according to Al and Cr activities. This was suggested as a new diagram to predict the initial oxide
morphology of Ni-base superalloys, and possibly it can apply for any generation of Ni-base superalloys. 相似文献
10.
Deformation behavior of hot-rolled AISI 304 LN austenitic stainless steel was studied by hot axisymmetric compression tests at 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C) at strain rates of 0.01, 0.1, and 1 s ?1. The flow curves were examined to understand the deformation characteristics. The influence of Zener–Holloman parameter was analyzed using appropriate constitutive models. The activation energy for deformation was found to be 473 kJ/mol. Quantitative microstructural analysis was carried out using Electron backscattered diffraction. Compression at 1173 K (900 °C) at all true strain rates gave rise to partially dynamic recrystallized microstructure with strong α-fiber texture. The deformation texture is characterized by the formation of Brass component, and partial dynamic recrystallization (DRX) led to the development of Goss, S, and ube components. Necklace structure of small equiaxed recrystallized grains could be observed surrounding the large, elongated deformed grains. Compressions at 1273 K and 1373 K (1000 °C and 1100 °C) resulted in fully recrystallized microstructure consisting of mostly Σ3 and Σ9 coincidence site lattice high-angle boundaries. Compression at 1273 K (1000 °C) leads to the formation of low-intensity diffused α-fiber. DRX was confirmed by the presence of Goss, S, Cube, and rotated Cube components. Compression performed at 1373 K (1100 °C) resulted in nearly random texture with traces of α-fiber and prominent Cube/rotated Cube components. The microstructures of the 1173 K (900 °C)-compressed samples were partitioned using grain size and misorientation criteria to quantify DRX. 相似文献
11.
Vapor pressure measurements, in terms of a (non-)isothermal isopiestic method, were carried out in the system Cd-Pr between 749 K and 1067 K (476 °C and 794 °C). Thermodynamic activities of cadmium as a function of temperature were obtained directly for the composition ranging from 50.0 to 85.7 at. pct Cd. From these results, partial molar enthalpies of mixing of Cd were derived for the corresponding composition range. The activity values of Cd were converted to an average sample temperature of 823 K (550 °C) by applying an integrated form of the Gibbs–Helmholtz equation. These data indicate that Cd 2Pr and Cd 58Pr 13 are probably the most stable intermetallic compounds in this system. Using an activity value of Pr from the literature as integration constant, Gibbs–Duhem integration was performed, and integral Gibbs energies are presented at 823 K (550 °C), referred to Cd(l) and α-Pr(s). Gibbs energies of formation at the stoichiometric compositions of the phases Cd 6Pr, Cd 58Pr 13, Cd 45Pr 11, Cd 3Pr, and Cd 2Pr were determined to be about ?18.8, ?23.5, ?24.8, ?28.7, and ?33.8 kJ g-atom ?1 at 823 K (550 °C), respectively. 相似文献
12.
A Nb-stabilized Fe-15Cr-0.45Nb-0.010C-0.015N ferritic stainless steel is studied with transmission electron microscopy (TEM)
to investigate the morphology and kinetics of precipitation. Nb x(C,N) y\hbox{Nb}_{x}\hbox{(C,N)}_y and MnS precipitates are present in the steel in the initial condition. Ex-situ TEM analysis is performed on samples heat treated at 973 K, 1073 K, 1173 K, and 1273 K (700 °C, 800 °C, 900 °C, and 1000 °C).
Within this temperature range, both Fe 2Nb\hbox{Fe}_2\hbox{Nb} and Fe 3Nb 3X x\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x} (with X = C or N) precipitates form. Fe 2\hbox{Fe}_2Nb is observed at 1073 K (800 °C). Fe 3Nb 3X x\;\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x} precipitates form at the grain boundaries between 973 K and 1273 K (700 °C and 1000 °C). Up to at least 1173 K (900 °C)
their fraction increases with time and temperature, but at 1273 K (1000 °C) they lose stability with respect to Nb x(C,N) y.\hbox{Nb}_{x}\hbox{(C,N)}_{y}. With in-situ TEM, no phase transition is observed between room temperature and 1243 K (970 °C). At 1243 K (970 °C) the precipitation of
Fe 3Nb 3X x\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_{x} is observed in the neighborhood of a dissolving Nb 2\hbox{Nb}_2(C,N) precipitate. For sections of grain boundaries where no Nb x(C,N) y\hbox{Nb}_x\hbox{(C,N)}_y precipitates are present, Fe 3Nb 3X x\hbox{Fe}_3\hbox{Nb}_3\hbox{X}_{x} does not form. It is concluded that the precipitation of Fe 3Nb 3X x\hbox{Fe}_{3}\hbox{Nb}_{3}\hbox{X}_x is directly related to the dissolution of Nb 2\hbox{Nb}_2(C,N) through the redistribution of C or N. 相似文献
13.
An experimental study was conducted to investigate the interfacial phenomena between an Al alloy and andalusite low-cement
castables (LCCs) containing fixed contents of barium compounds (BaO, BaSO 4, and BaCO 3) at 1123 K and 1433 K (850 °C and 1160 °C) using the Alcoa cup test. Interfacial reaction products and phases formed during
heat treatment of the refractory samples were characterized using scanning electron microscopy (SEM) coupled with energy dispersive
spectrometry (EDS) and X-ray diffraction analysis (XRD). The addition of both BaO and BaSO 4 led to a significant reduction of alloy penetration into the refractory. Hexa-celsian formation was observed in both these
refractories, which drastically increased their corrosion resistance. Barite decomposition was observed at 1373 K (1100 °C)
in the presence of alumina and silica, which was the precursor for hexa-celsian formation. Barium silicates were formed in
all samples containing additives; however, this did not have any major influence on the corrosion resistance. Solidified eutectics
of BaSi 2 and α-BaAl 2Si 2 formed in all these samples, which acted as an interfacial barrier that prevented additional molten aluminum penetration;
however, the positive effect of intermetallic formation was offset by glassy phase formation in samples containing BaCO 3 as the additive. 相似文献
14.
Nanocrystalline TiO 2-AgO thin films and powders were prepared by an aqueous particulate sol-gel route at the low temperature of 573 K (300 °C).
Titanium tetraisopropoxide and silver nitrate were used as precursors, and hydroxypropyl cellulose was used as a polymeric
fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy
(FTIR) revealed that the phase composition of the mixed oxide depends upon the annealing temperature, being a mixture of TiO 2 and AgO in the range 573 K to 773 K (300 °C to 500 °C) and a mixture of TiO 2, AgO, and Ag 2O at 973 K (700 °C). Furthermore, one of the smallest crystallite sizes was obtained for TiO 2-AgO mixed oxide, being 4 nm at 773 K (500 °C). Field emission–scanning electron microscopic (FE-SEM) and atomic force microscopic
(AFM) images revealed that the deposited thin films had nanostructured and nanoporous morphology with columnar topography.
Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They
exhibited a remarkable response toward low concentrations of CO gas ( i.e., 25 ppm) at low operating temperature of 473 K (200 °C), resulting in an increase of the thermal stability of sensing films
as well as a decrease in their power consumption. Furthermore, TiO 2-AgO sensors follow the power law for the detection of CO gas. 相似文献
15.
The tensile behavior of a directionally solidified (DS) Ni-base superalloy, namely, CM-247LC, was evaluated in the presence
of a Pt-aluminide bond coat. The effect of the thermal cycling exposure of the coated alloy at 1373 K (1100 °C) on its tensile
properties was examined. The tensile properties were evaluated at a temperature of 1143 K (870 °C). The presence of the bond
coating caused an approximately 8 pct drop in the strength of the alloy in the as-coated condition. However, the coating did
not appreciably affect the tensile ductility of the substrate alloy. The bond coat prevented oxidation-related surface damage
to the superalloy during thermal cycling exposure in air at 1373 K (1100 °C). Such cyclic oxidation exposure (up to 750 hours)
did not cause any further reduction in yield strength (YS) of the coated alloy. There was a marginal decrease in the ultimate
tensile strength (UTS) with increased exposure duration. Because of the oxidation protection provided by the bond coat, the
drastic loss in ductility of the alloy, which would have happened in the absence of the coating, was prevented. 相似文献
16.
This work describes the influence of secondary carbide precipitation at destabilizing heat treatment on kinetics of austenite phase transformation at a subcritical range of temperatures in high-Cr cast irons, alloyed with 4 to 6 wt pct of Mn or by complex Mn-Ni-Mo (Mn-Cu-Mo). The samples were soaked at 1073 K to 1373 K (800 °C to 1100 °C) (destabilization) or at 573 K to 973 K (300 °C to 700 °C) (subcritical treatment); the combination of destabilization and subcritical treatment was also used. The investigation was carried out with application of optical and electron microscopy and bulk hardness measurement. Time-temperature-transformation (TTT) curves of secondary carbide precipitation and pearlite transformation for as-cast austenite and destabilized austenite were built in this work. It was determined that the secondary carbide precipitation significantly inhibited the pearlite transformation rate at 823 K to 973 K (550 °C to 700 °C). The inhibition effect is more evident in cast irons alloyed with complex Mn-Ni-Mo or Mn-Cu-Mo. The possible reasons for transformation decelerating could be austenite chemical composition change (enriching by Ni, Si, and Cu, and depleting by Cr) and stresses induced by secondary carbide precipitation. 相似文献
17.
High temperature oxidation of alumina-forming MAX phases, Ti 2AlC and Cr 2AlC, were examined under turbine engine environments and coating configurations. Thermogravimetric furnace tests of Ti 2AlC showed a rapid initial transient due to non-protective TiO 2 growth. Subsequent well-behaved cubic kinetics for alumina scale growth were shown from 1273 K to 1673 K (1000 °C to 1400 °C). These possessed an activation energy of 335 kJ/mol, consistent with estimates of grain boundary diffusivity of oxygen (~375 kJ/mol). The durability of Ti 2AlC under combustion conditions was demonstrated by high pressure burner rig testing at 1373 K to 1573 K (1100 °C to 1300 °C). Here good stability and cubic kinetics also applied, but produced lower weight gains due to volatile TiO(OH) 2 formation in water vapor combustion gas. Excellent thermal stability was also shown for yttria-stabilized zirconia thermal barrier coatings deposited on Ti 2AlC substrates in 2500-hour furnace tests at 1373 K to 1573 K (1100 °C to 1300 °C). These sustained a record 35 µm of scale as compared to 7 μm observed at failure for typical superalloy systems. In contrast, scale and TBC spallation became prevalent on Cr 2AlC substrates above 1423 K (1150 °C). Cr 2AlC diffusion couples with superalloys exhibited good long-term mechanical/oxidative stability at 1073 K (800 °C), as would be needed for corrosion-resistant coatings. However, diffusion zones containing a NiAl-Cr 7C 3 matrix with MC and M 3B 2 particulates were commonly formed and became extensive at 1423 K (1150 °C). 相似文献
18.
The α-rhombohedral and β-rhombohedral crystal structures of pure elemental boron powders have been synthesized via gas phase thermal dissociation
of BCl 3 by H 2 on a quartz substrate. The parameters affecting the crystal structures of the final products and the process efficiency,
such as BCl 3/H 2 molar ratio (1/2 and 1/4) and reaction temperature (1173 K to 1373 K [900 °C to 1100 °C]), have been examined. The experimental
apparatus of original design has enabled boron powders to be obtained at temperatures lower than those in the literature.
The surface/powder separation problem encountered previously with different substrate materials has been avoided. Boron powders
have been synthesized with a minimum purity of 99.99 pct after repeated HF leaching. The qualitative analysis of exhaust gases
has been conducted using a Fourier transform infrared spectroscope (FTIR). The synthesized powders have been characterized
using an X-ray powder diffractometer (XRD) and scanning electron microscope (SEM) techniques. The results of the reactions
have been compared with equilibrium predictions performed using the FactSage 6.2 (Center for Research in Computational Thermochemistry,
Montreal, Canada) thermochemical software. 相似文献
19.
Dynamic recrystallization (DRX) behavior in hot deformed (by uniaxial compression in a thermomechanical simulator in the temperatures
range 1173 K to 1373 K [900 °C to 1100 °C]) Ti-modified austenitic stainless steel was studied using electron back scatter
diffraction. Grain orientation spread with a “cut off” of 1 deg was a suitable criterion to partition dynamically recrystallized
grains from the deformed matrix. The extent of DRX increased with strain and temperature, and a completely DRX microstructure
with a fine grain size ~4 μm (considering twins as grain boundaries) was obtained in the sample deformed to a strain of 0.8 at 1373 K (1100 °C). The
nucleation of new DRX grains occurred by the bulging of the parent grain boundary. The DRX grains were twinned, and a linear
relationship was observed between the area fraction of DRX grains and the number fraction of Σ3 boundaries. The deviation
from the ideal misorientation of Σ3 boundaries decreased with an increase in the fraction of Σ3 boundaries (as well as the
area fraction of DRX) signifying that most Σ3 boundaries are newly nucleated during DRX. The generation of these Σ3 boundaries
could account for the formation of annealing twins during DRX. The role of Σ3 twin boundaries on DRX is discussed. 相似文献
20.
Ti2AlNb-based alloys synthesized at 1223 K (950 °C) by spark plasma sintering were aged at 973 K, 1023 K, 1073 K, and 1123 K (700 °C, 750 °C, 800 °C, and 850 °C), respectively. Phase composition, microstructure, and microhardness of the aged alloys were investigated in this study. Equiaxed O grains and Widmanstätten B2/β + O laths were formed in the aged alloys, and the microhardness was improved in contrast with the spark plasma-sintered alloy without aging. The microhardness relies largely on the O-phase content, as well as the length and width of the O laths. In particular, complete Widmanstätten B2/β + O laths, with locally finely dispersed β precipitates, were obtained in the alloy aged at 1073 K (800 °C), and the alloy exhibited the best microhardness performance. Such fine structure is due to the temperature-dependent transformations Oequiaxed→Oprimary + B2/β
primary, Oprimary→Osecondary + B2/β
secondary, and B2/β
primary→O. 相似文献
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