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1.
D. Hu A. Godfrey P. A. Blenkinsop M. H. Loretto 《Metallurgical and Materials Transactions A》1998,29(13):919-925
The influence of thermomechanical processing on the microstructure of a range of TiAl-based alloys has been assessed using
optical and electron microscopy, and the room-temperature mechanical properties have been determined. Long-term exposure at
high temperatures has been used to assess the thermal stability of some of the structures generated through the different
processing routes, and it has been found that the (gamma and alpha 2) lamellar structures, in some of the alloys, are unstable
at 700°C, a likely operating temperature. Addition of boron increases the stability of the lamellar structure. The influence
of the difficulty of slip transfer between gamma and alpha 2 has been assessed as one of the factors limiting ductility in
samples with this lamellar structure. In addition to the alloys produced via the ingot route, some atomized material has been produced and the microstructure and properties of hot-isostatically pressed
“hipped” material assessed. Regions, high in titanium, are present in all atomized powders that have been examined, and these
regions are found to initiate fracture at very low strains. These results are briefly discussed in terms of the factors that
control the room-temperature strength and fracture behavior of TiAl-based alloys.
This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the
TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations
Committees. 相似文献
2.
D. Hu A. Godfrey P. A. Blenkinsop M. H. Loretto 《Metallurgical and Materials Transactions A》1998,29(3):919-925
The influence of thermomechanical processing on the microstructure of a range of TiAl-based alloys has been assessed using
optical and electron microscopy, and the room-temperature mechanical properties have been determined. Long-term exposure at
high temperatures has been used to assess the thermal stability of some of the structures generated through the different
processing routes, and it has been found that the (gamma and alpha 2) lamellar structures, in some of the alloys, are unstable
at 700 °C, a likely operating temperature. Addition of boron increases the stability of the lamellar structure. The influence
of the difficulty of slip transfer between gamma and alpha 2 has been assessed as one of the factors limiting ductility in
samples with this lamellar structure. In addition to the alloys produced via the ingot route, some atomized material has been produced and the microstructure and properties of hot-isostatically pressed
“hipped” material assessed. Regions, high in titanium, are present in all atomized powders that have been examined, and these
regions are found to initiate fracture at very low strains. These results are briefly discussed in terms of the factors that
control the room-temperature strength and fracture behavior of TiAl-based alloys.
This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the
TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations
Committees. 相似文献
3.
The present article describes an investigation of the microstructure and tensile properties of cast Al-Li-Mg alloys with very
low densities, in the range 2.3 to 2.4 Mg/m3. Low density is achieved by adding Li and Mg in excess of the solubility limit, which prevents subsequent dissolution of
the Al2LiMg particles that form during solidification. A simple model developed during the course of this research allows prediction
of the volume fraction of Al2LiMg and alloy density from alloy composition. The model was used to select two alloy compositions for detailed investigation:
A112Li6Mg and A116Li8Mg. The microstructures of the cast alloys consist of coarse Al2LiMg particles embedded in an Al matrix containing Al3Li particles. Both alloys exhibit low tensile elongation in the as-cast condition. Additional processing steps were used to
modify the microstructural characteristics thought to be responsible for the low tensile elongation of the ascast alloys.
The A116Li8Mg alloy, with an Al2LiMg volume fraction of 0.25, does not exhibit increased tensile elongation as a result of processing, and the brittle nature
of this material is attributed to the high volume fraction of the Al2LiMg phase. The A112Li6Mg alloy, with an Al2LiMg volume fraction of 0.13, exhibits a remarkable increase in tensile elongation after extrusion, an effect attributed to
fragmentation and dispersal of a three-dimensional (3-D) network of the intermetallic phase in the as-cast alloy. 相似文献
4.
Measurements of the interface undercooling-growth velocity relationship for Al-CuAl2 eutectic alloys solidified horizontally and for Sn-Cd eutectic alloys solidified horizontally and vertically are presented.
All the measurements confirm the relationship ΔT =Kv
1/2. The value ofK for Al-CuAl2 alloys is 12.8°C cm-1/2 s1/2 and 13.3°C cm-1/2 s1/2 for Sn-Cd alloys for both modes of solidification. These values are much greater than those measured by Moore and Elliott.
Reasons for the discrepancy are discussed. TheK value for Al-CuAl2 alloys is only slightly greater than a recent measurement by Tassa and Hunt. The present measurements fit the extremum condition
of the Hunt and Jackson theory of eutectic growth. 相似文献
5.
X-ray diffraction study of isothermally annealed powder specimens of Fe-Al alloys with 18.75 to 32 at. pct Al indicates that
the α + FeAl two-phase field closes at around 662‡C where both phases have the same composition: 23.9 at. pct Al. X-ray diffraction
and magnetic data show that any twophase field that may exist between the FeAl and Fe3Al phases must be extremely narrow. It is probable that there is no two-phase field and that the transition is of a higher
than first order type. 相似文献
6.
Conclusions Of all the surfacing materials tested the greatest hardness at elevated temperatures is exhibited by electrodes made by the cermet method using chromium carbide as a base, i.e., GK-10 and GK-15 with a metal binder.Translated from Poroshkovaya Metallurgiya, No. 3 (51), pp. 80–83, March, 1967. 相似文献
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8.
C. A. V. de A. Rodrigues C. Prioul L. Hyspecka 《Metallurgical and Materials Transactions A》1984,15(12):2193-2203
A survey of experimental work on the isothermal martensitic transformation in the presence of prior martensite is given in
Fe-Ni and Fe-Ni-C alloys having subzero Ms (Mb) temperatures. Low temperature dilatometric measurements are correlated with
internal friction measurements in the 5 to 200 K temperature range. This study will show that this transformation can be discussed
in terms ofC-curve behavior as in Fe-Ni-Mn alloys. Nevertheless, in Fe-Ni and Fe-Ni-C alloys internal stresses created by the austenite-to-martensite
transformation during cooling play an important part in the development of the isothermal transformation. Furthermore, internal
friction is shown to be proportional to expansivity thus indicating that the internal friction technique can be applied successfully
for the study of phase transformations. 相似文献
9.
D. M. Kundrat 《Metallurgical and Materials Transactions A》1986,17(10):1825-1835
The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of
the quinary system Fe-Cr-Mn-Ni-C. Of the five quaternary systems that comprise the quinary system, this study was limited
to the three quaternary systems which contain both carbon and iron as two of the components;viz.: Fe-Cr-Mn-C, Fe-Cr-Ni-C, and Fe-Mn-Ni-C, as well as all of the binary and ternary subsystems that have iron as a component.
This paper discusses the modeling efforts for these systems, with particular emphasis on the ternary systems Fe-Cr-Mn and
Fe-Mn-Ni and the quaternary systems Fe-Cr-Mn-C and Fe-Mn-Ni-C. The experimental investigation consisted of measurements of
tie-lines for the liquid-delta (bcc) and the liquid-gamma (fcc) equilibria in the iron-rich corner of the Gibbs simplex bounded
by 0 to 25 wt pct Cr, 0 to 12 wt pct Mn, 0 to 25 wt pct Ni, and 0 to 1.2 wt pct C (bal. Fe). The temperature ranged from 1811
to about 1750 K. Compositions for the tie-lines were obtained from liquid-solid equilibrium couples, and the temperatures
for the equilibrium by differential thermal analysis (DTA). Parameters were selected in a thermodynamic model of the alloy
system to minimize the square of the difference between experimentally and calculated tie-lines, the latter being implicitly
a function of the derived parameters in the model. Binary and higher-order parameters were generally required. Ternary parameters
were obtained on ironcarbon base alloys Fe-Cr-C, Fe-Mn-C, and Fe-Ni-C, and for the Fe-Cr-Ni system, but not for the Fe-Cr-Mn
and Fe-Mn-Ni systems. Of the quaternary systems investigated, quaternary parameters were required only for theL/δ equilibrium in the Fe-Cr-Ni-C system; the Fe-Cr-Mn-C and Fe-Mn-Ni-C systems were found to be represented adequately by employing
only binary and ternary parameters. 相似文献
10.
The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of
the Fe-Cr-Ni system as part of a larger study of the Fe-Cr-Ni-C system. The investigation consisted of measurements and modeling
of tie-lines and the liquidus surfaces of the liquid-delta (bcc) and liquid-gamma (fcc) equilibria and the peritectic surface
involving all three phases in the iron-rich corner of the Gibbs triangle bounded by 0 to 25 wt pct Cr and 0 to 25 wt pct Ni
(bal Fe). The temperature ranged from the melting point of iron (1811 K) to about 1750 K. Compositions for tie-lines were
obtained from liquid-solid equilibrium couples and temperatures for the surfaces were obtained by differential thermal analysis.
Parameters for modeling the system were then selected in the subregular solution model to minimize the square of the difference
between experimental and calculated tie-lines. With one ternary parameter employed for each phase, calculations by the model
are in excellent agreement with the tie-line and liquidus measurements and in fair agreement with the temperatures for the
peritectic surfaceL + δ/L + δ + γ. The usefulness of the model is demonstrated by calculation of the solidification paths of selected alloys in the
composition field investigated for the limiting cases of (a) complete equilibrium followed by the alloy system, and (b) no
solid diffusion (i.e., segregation) with equilibrium maintained at the solidifying front and complete mixing in the liquid
phase. 相似文献
11.
D. M. Kundrat M. Chochol J. F. Elliott 《Metallurgical and Materials Transactions B》1984,15(4):663-676
The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of
the Fe-Cr-C system. The investigation consisted of measurements of tie-lines and the liquidus surface of the liquid-delta
(bcc) and liquid-gamma (fcc) equilibria in the Gibbs triangle, bounded by 0 to 1.4 wt pct C and 0 to 25 wt pct Cr (bal. Fe).
The peritectic surface of the three-phase equilibrium was also measured. The temperature ranged from 1811 to about 1750 K.
The tie-lines were obtained from liquid-solid equilibrium couples, and the liquidus and peritectic surfaces, by differential
thermal analysis (DTA). A statistical procedure was applied to determine from the experimental results the parameters required
for a thermodynamic model of the system. Calculations by the model are in good agreement with the experimental results. As
a consequence the model can be used to interpolate and extrapolate properties and compositions of phases in equilibrium in
the system within the composition and temperature field investigated.
D.M. KUNDRAT, formerly Research Fellow at Massachusetts Institute of Technology
M. CHOCHOL, formerly Research Assistant, Massachusetts Institute of Technology 相似文献
12.
J. Glazer S. L. Verzasconi R. R. Sawtell J. W. Morris 《Metallurgical and Materials Transactions A》1987,18(10):1695-1701
The cryogenic mechanical properties of aluminum-lithium alloys are of interest because these alloys are attractive candidate
materials for cryogenic tankage. Previous work indicates that the strength-toughness relationship for alloy 2090-T81 (Al-2.7Cu-2.2Li-0.12Zr
by weight) improves significantly as temperature decreases. The subject of this investigation is the mechanism of this improvement.
Deformation behavior was studied since the fracture morphology did not change with temperature. Tensile failures in 2090-T81
and -T4 occur at plastic instability. In contrast, in the binary aluminum-lithium alloy studied here they occur well before
plastic instability. For all three materials, the strain hardening rate in the longitudinal direction increases as temperature
decreases. This increase is associated with an improvement in tensile elongation at low temperatures. In alloy 2090-T4, these
results correlate with a decrease in planar slip at low temperatures. The improved toughness at low temperatures is believed
to be due to increased stable deformation prior to fracture. 相似文献
13.
Intergranular fracture in some precipitation-hardened aluminum alloys at low temperatures 总被引:1,自引:0,他引:1
Intergranular fracture at low temperatures from room temperature down to 4.2 K has been studied in some precipitation-hardened
aluminum alloys. Microscopic appearance of intergranular facets is revealed to be greatly affected by the microstructure adjacent
to the grain boundaries (GBs). When large precipitates on GBs and wide precipitation-free zones (PFZs) are present, coalescence
of microvoids initiated at the GB precipitates causes the intergranular fracture with dimples. This fracture process is found
to be unaffected by deformation temperature. On the other hand, in the presence of fine precipitates on GBs and narrow PFZs,
matrix slip localization exerts significant influence on the fracture behavior. At low temperatures, large stress concentration
at GBs leads to intergranular fracture, forming sharp ledges on the fracture surfaces, while at room temperature, the dynamic
recovery process is thought to relax such stress concentration, resulting in a transgranular “uctile” rupture.
formerly Graduate Student, the Department of Materials Science, University of Tokyo 相似文献
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17.
The effect of substitutional solutes on the solution of hydrogen gas has been studied by means of hydrogen pressure-composition
isotherms in vanadium alloyed with niobium, chromium, or titanium. An isopiestic solubility technique was employed to measure
the hydrogen equilibrium pressures for the vanadium alloys from 223 to 473 K. In all the alloys studied, the reaction of hydrogen
with the metal phase was exothermic and hydrogen followed Sieverts' law over a considerable range of hydrogen concentration.
Additions of titanium to vanadium dramatically enhanced the isopiestic solubility of hydrogen, chromium significantly reduced
the solubility, and niobium moderately in-creased the solubility. Sieverts' law behavior for hydrogen in the vanadium alloys
showed that substitutional atoms did not act as local, deep traps for hydrogen.
Former Graduate Student, Department of Materials Science and Engineering, Iowa State University 相似文献
18.
M. S. Grewal S. A. Sastri N. J. Grant 《Metallurgical and Materials Transactions A》1975,6(7):1393-1404
BeO dispersed nickel alloys, produced by powder metallurgy techniques, were studied extensively in stress rupture at 815, 982, and 1093°C (1088, 1255, and 1366 K) and by transmission electron microscopy. The alloys were subjected to a variety of thermomechanical treatments (TMT) to determine the benefits of TMT on properties. It is shown that the use of intermediate annealing treatments after 10 pct reduction steps is highly beneficial on both low and high temperature properties. It is indicated that the high temperature strength is not primarily dependent on the grain aspect ratio or texture but depends strongly on the dislocation density and distribution of dislocations in a stable substructure which is pinned by the fine oxide dispersion. 相似文献
19.
M. S. Grewal S. A. Sastri N. J. Grant 《Metallurgical and Materials Transactions A》1975,6(8):1393-1404
BeO dispersed nickel alloys, produced by powder metallurgy techniques, were studied extensively in stress rupture at 815,
982, and 1093°C (1088, 1255, and 1366 K) and by transmission electron microscopy. The alloys were subjected to a variety of
thermomechanical treatments (TMT) to determine the benefits of TMT on properties. It is shown that the use of intermediate
annealing treatments after 10 pct reduction steps is highly beneficial on both low and high temperature properties. It is
indicated that the high temperature strength is not primarily dependent on the grain aspect ratio or texture but depends strongly
on the dislocation density and distribution of dislocations in a stable substructure which is pinned by the fine oxide dispersion. 相似文献