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1.
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
2.
C. J. Boehlert D. S. Dickmann NY. N. C. Eisinger 《Metallurgical and Materials Transactions A》2006,37(1):27-40
The grain size, grain boundary character distribution (GBCD), creep, and tensile behavior of INCONEL alloy 718 (IN 718) were
characterized to identify processing-microstructure-property relationships. The alloy was sequentially cold rolled (CR) to
0, 10, 20, 30, 40, 60, and 80 pct followed by annealing at temperatures between 954 °C and 1050 °C and the traditional aging
schedule used for this alloy. In addition, this alloy can be superplastically formed (IN 718SPF) to a significantly finer
grain size and the corresponding microstructure and mechanical behavior were evaluated. The creep behavior was evaluated in
the applied stress (σ
a
) range of 300 to 758 MPa and the temperature range of 638 °C to 670 °C. Constant-load tensile creep experiments were used
to measure the values of the steady-state creep rate and the consecutive load reduction method was used to determine the values
of backstress (σ0). The values for the effective stress exponent and activation energy suggested that the transition between the rate-controlling
creep mechanisms was dependent on effective stresses (σ
e
=σ
a
σ0) and the transition occurred at σ
e
≅ 135 MPa. The 10 to 40 pct CR samples exhibited the greatest 650 °C strength, while IN 718SPF exhibited the greatest room-temperature
(RT) tensile strength (>1550 MPa) and ductility (ε
f
>16 pct). After the 954 °C annealing treatment, the 20 pct CR and 30 pct CR microstructures exhibited the most attractive
combination of elevated-temperature tensile and creep strength, while the most severely cold-rolled materials exhibited the
poorest elevated-temperature properties. After the 1050 °C annealing treatment, the IN 718SPF material exhibited the greatest
backstress and best creep resistance. Electron backscattered diffraction was performed to identify the GBCD as a function
of CR and annealing. The data indicated that annealing above 1010 °C increased the grain size and resulted in a greater fraction
of twin boundaries, which in turn increased the fraction of coincident site lattice boundaries. This result is discussed in
light of the potential to grain boundary engineer this alloy.
INCONEL is a registered trademark of Special Metals Corp., Huntington, WV.
This article is based on a presentation made in the symposium entitled “Processing and Properties of Structural Materials,”
which occurred during the Fall TMS meeting in Chicago, Illinois, November 9–12, 2003, under the auspices of the Structural
Materials Committee. 相似文献
3.
Mahsa Keyvani Reza Mahmudi Ghazal Nayyeri 《Metallurgical and Materials Transactions A》2011,42(7):1990-2003
The microstructure and creep behavior of a cast Mg-5Sn alloy with 1, 2, and 3 wt pct Bi additions were studied by impression
tests in the temperature range 423 K to 523 K (150 °C to 250 °C) under punching stresses in the range 125 to 475 MPa for dwell
times up to 3600 seconds. The alloy containing 3 wt pct Bi showed the lowest creep rates and, thus, the highest creep resistance
among all materials tested. This is attributed to the favorable formation of the more thermally stable Mg3Bi2 intermetallic compound, the reduction in the volume fraction of the less stable Mg2Sn phase, and the dissolution of Bi in the remaining Mg2Sn particles. These particles strengthen both the matrix and grain boundaries during creep deformation of the investigated
system. The creep behavior of the Mg-5Sn alloy can be divided into the low- and high-stress regimes, with the respective average
stress exponents of 5.5 and 10.5 and activation energies of 98.3 and 163.5 kJ mol−1. This is in contrast to the creep behavior of the Bi-containing alloys, which can be expressed by a single linear relationship
over the whole stress and temperature ranges studied, yielding stress exponents in the range 7 to 8 and activation energies
of 101.0 to 107.0 kJ mol−1. Based on the obtained stress exponents and activation energies, it is proposed that the dominant creep mechanism in Mg-5Sn
is pipe-diffusion controlled dislocation viscous glide the low-stress regime and dislocation climb creep with back stress
in the high-stress regime. For the Mg-5Sn-xBi alloys, however, the controlling creep mechanism is dislocation climb with an additional particle strengthening effect,
which is characterized by the higher stress exponent of 7 to 8. 相似文献
4.
The deformation behavior of an extruded Ni-30 (at. pct) Al−20Fe−0.05Zr intermetallic alloy was studied in the temperature
range of 300 to 1300 K under initial tensile strain rates varying between about 10−6 and 2×10−3 s−1 and in constant load compression creep between 1073 and 1300 K. The deformation microstructures of the fractured specimens
were characterized by transmission electron microscopy (TEM). Three deformation regimes were observed: Region I consisted
of an athermal regime of low tensile ductility (less than 0.3 pct) occurring between 400 and 673 K, where the substructure
consisted of slip bands in a few grains. Exponential creep was dominant in region II between 673 and 1073 K, where the substructure
changed from a mixture of dislocation tangles, loops, and dipoles at 673 K to a microstructure consisting of subgrains and
dislocation tangles at 973 K. The tensile ductility was generally about 2.0 to 2.5 pct below 980 K in this region. A significant
improvement in tensile ductility was observed in region III, which occurred between 1073 and 1300 K. An analysis of the data
suggests that viscous glide creep with a stress exponent,n, of about 3 and high-temperature dislocation climb withn≈4.5 where the two dominant creep mechanisms in this region depending on stress and temperature. The average activation energy
for deformation in this region was about 310±30 kJ mol−1 for both processes. In this case, a transition from viscous glide creep to dislocation climb occurred when σ/E<1.7×10−4, where σ is the applied stress andE is the Young’s modulus. 相似文献
5.
R. Viswanathan 《Metallurgical and Materials Transactions A》1977,8(6):877-884
The creep and stress rupture behavior of a normalized 1.25 pct chromium-0.5 pct molybdenum steel has been investigated over
a temperature (T) range of 510 to 620°C and a stress(σ) range of 65 to 425 MN/m2. The creep rate (
) and time to rupture (t
r
) data have been analyzed in terms of the general expression
ort
r
-A σn exp (Q/RT), whereA is a constant,n is the power exponent of stress,Q is an empirical activation energy for the rate controlling process andR is the universal gas constant. At each temperature, the logarithmic plots of creep rate and time to rupture as functions
of stress consist of two linear segments, separating the data into low stress and high stress regimes. The stress exponent
has approximate values of 4 and 10 in the low stress and high stress regimes respectively in the appropriate expressions for
both creep rate and for time to rupture. The activation energy has values of 367 and 420 kJ/mole in the low stress regime
for time to rupture and creep rate respectively. In the high stress regime, the respective values of activation energy are
581 and 670 kJ/mole. Fractographic observations show that the changes from low stress to high stress behavior in creep rate
and time to rupture approximately coincide with the transition in fracture mode from intergranular to transgranular cracking
as well as with the transition in the rupture ductility from a region of linear variation with stress to one of constant ductility.
These observations suggest that the transition from low stress to high stress behavior may be associated with a change in
deformation mode from predominantly grain boundary sliding at low stress to transgranular matrix deformation at high stress.
Analysis of the creep rate data based on this premise enables calculation of the ratio of the contributions of the grain boundary
sliding mode to the total deformation (ε
gb
/ε
T
) at various values of stress and temperature. Results of this analysis are consistent with numerous experimental observations
reported in the literature. 相似文献
6.
The super α
2 Ti3Al-based alloy with a fine grain size of ∼2.2 μm exhibits superplastic elongations over 1000 pct at 920 °C to 1000 °C, 600 pct at 900 °C, 330 pct at 850 °C, and 140 pct
at 750 °C. Mechanical anisotropy is observed in this alloy, and relatively lower flow stresses and higher tensile elongations
are obtained in the 45 deg specimen loaded at 25 °C to 960 °C. The texture characteristics appear to impose significant influence
on the mechanical anisotropy at temperatures below 900 °C (under the dislocation creep condition), and the {111}〈2
〉 and {0001} basal textures evolve in the β and α
2 phases after tensile straining. At loading temperatures higher than 900 °C (under the superplastic flow condition), the anisotropy
effect is less pronounced and the grain orientation distribution becomes basically random in nature. Rationalizations for
the mechanical anisotropy in terms of the Schmid factor calculations for the major and minor texture components in the β and α
2 phases provide consistent explanations for the deformation behavior at lower temperatures as well as the initial straining
stage at higher temperatures. 相似文献
7.
8.
J. Wolfenstine H. K. Kim J. C. Earthman 《Metallurgical and Materials Transactions A》1994,25(11):2477-2482
The creep characteristics, including the nature of the creep transient after a stress reduction and activation energy for
creep of single crystalline Ni3Al(Ta,B) in the temperature range 1083 to 1388 K, were investigated. An inverse type of creep transient is exhibited during
stress reduction tests in the creep regime where the stress exponent is equal to 3.2. The activation energy for creep in this
regime is equal to 340 kJ mol−1. A normal type of creep transient is observed during stress reduction tests in the regime where the stress exponent is equal
to 4.3. The activation energy for creep in this regime is equal to 530 kJ mol−1. The different transient creep behavior and activation energies for creep observed in this investigation are consistent with
the previous suggestion that then = 4.3 regime is associated with creep controlled by dislocation climb, whereas then = 3.2 regime is associated with a viscous dislocation glide process for Ni3Al at high temperatures. 相似文献
9.
10.
The substructure of AISI 316 stainless steel resulting from creep deformation has been quantitatively characterized using
transmission electron microscopy. The specimens were tested at temperatures and stresses ranging from 593° to 816°C and 8000
to 35,000 psi, respectively. Subgrains whose boundaries are predominantly (111) twist boundaries were formed in all tests
at and above 704°C but were observed very infrequently at 650°C and were completely absent after creep at 593°C. The subgrain
diameter,d, and the mobile dislocation density, ρ, were found to vary with the applied stress, σa, according to:d =kσa
-1 and ρα σa
2. Subgrain misorientation varys from less than 0.1 to 1 deg in each specimen seemingly independent of all parameters evaluated.
A double triple node dislocation configuration was frequently observed in all specimens. Its relation to the deformation process
is discussed in a mechanism involving the breaking of attractive dislocation nodes.
Formerly Graduate Student, Materials, Science and Metallurgical Engineering Department, University of Cincinnati, Cincinnati,
Ohio 45221 相似文献
11.
G. W. King 《Metallurgical and Materials Transactions B》1972,3(4):941-945
Constant-load creep tests were conducted with pure tungsten and a W-2 wt pct ThO2 alloy at temperatures between 1600° and 2200°C and at strain rates of about 1 × 10-8 to 4 × 10-5 sec-1. The results were evaluated by the empirical correlations of Robinson and Sherby and also Mukherjeeet al. which describe the stress dependence of the creep of metals and alloys. The agreement of the present experimental data with
these correlations was found to be poor. However, when the following empirical relationship was used: •ε
c
=A’(σ
c
/σ
f
)
n
the present creep data for tungsten and the tungsten alloy at various temperatures were much better correlated. Here, •ε
c
is the experimental creep rate, σc is the applied stress for creep, σf is the flow stress of the material at the same temperature in a constant strain rate tensile test, andA’ is function of temperature, structure, and strain rate. 相似文献
12.
The mechanisms of deformation of a rapidly solidified and compacted Al-8.8Fe-3.7Ce (wt pct) alloy were investigated in the
stress range 20 to 115 MPa and temperature range 523 to 623 K. The stress dependence of the steady state strain rates indicated
a transition from diffusional creep to power law creep, the transition stress decreasing with increasing temperature from
70 MPa (σ/G = 3.1 × 10-3) at 523 K to 40 MPa (σ/G = 1.9 × 10-3) at 623 K. The activation energy in the power law creep regime was close to that of bulk self-diffusion in aluminum, while
the activation energy in the diffusional creep regime was close to that of grain boundary self-diffusion in Al. The creep
strain rates in the power law creep regime were found to be predicted much better by the substructure-invariant creep law
(Sherby, 1981) than by the semi-empirical Dorn equation for Al, with the inclusion of a “threshold” stress. In the Coble creep
regime, it was found that the cell/subgrain boundaries are inefficient vacancy sources/sinks and that their contribution to
Coble creep is totally suppressed in this alloy. The Coble creep rates could be explained by using the average diameter of
the powder particles as the effective grain size in the Coble creep equation. 相似文献
13.
Troy A. Hayes M. E. Kassner Robert S. Rosen 《Metallurgical and Materials Transactions A》2002,33(2):337-343
Cumulative zirconium creep data over a broad range of stresses (0.1 to 115 MPa) and temperatures (300 °C to 850 °C) were analyzed
based on an extensive literature review. Zirconium obeys traditional power-law creep with a stress exponent of approximately
6.4 over stain rates and temperatures usually associated with the conventional “five-power-law” regime. Thus, dislocation
climb, rather than the often assumed glide mechanism, may be rate controlling. Power-law breakdown occurs at values of
greater than approximately 109 cm−2, consistent with most traditional five-power-law materials. The creep rate of zirconium at low values of σ/G varies proportionally to the applied stress. The rate-controlling mechanism(s) for creep within this regime is unclear. A
grain-size dependency may exist, particularly at small (<90 μm) sizes, suggesting a diffusional mechanism. A grain-size independence at larger grain sizes supports a Harper-Dorn mechanism,
but the low observed activation energy (∼90 kJ/mol) is not consistent with those observed at similar temperatures at higher
stresses in the five-power-law regime (270 kJ/mol) where creep is also believed to be lattice self-diffusion controlled. The
stress dependence in this regime is not consistent with traditional grain-boundary sliding mechanisms.
This article is based on a presentation made in the workshop entitled “Mechanisms of Elevated Temperature Plasticity and Fracture”,
which was held June 27–29, 2001, in San Diego, CA, concurrent with the 2001 Joint Applied Mechanics and Materials Summer Conference.
The workshop was sponsored by Basic Energy Sciences of the United States Department of Energy. 相似文献
14.
15.
The effects of 0.2, 0.6, and 1.0 wt pct Zr additions on the microstructure and creep behavior of AZ91 Mg alloy were investigated
by impression tests carried out under constant punching stress (σ
imp) in the range 100 to 650 MPa, corresponding to the modulus-compensated stress levels of
0.007 £ s\textimp \mathord