共查询到20条相似文献,搜索用时 16 毫秒
1.
R. T. Marlin F. Cosandey J. K. Tien 《Metallurgical and Materials Transactions A》1980,11(11):1771-1775
The effect of higher strain rate predeformation on creep behavior and stress rupture life of the oxide dispersion strengthened
nickel-base alloy MA 754 was studied. Both the predeformation and creep testing were conducted at 760 °C. It was found that
the minimum creep rate decreased as the amount of prestrain increased and was a factor of two lower at 1.2 pct prestrain.
Predeformation also shortened the duration of primary creep. Transmission electron microscopy revealed dislocations being
emitted from particle-matrix interfaces after prestraining and an increase in dislocation density with increasing prestrain.
These observations are discussed with respect to the mechanical results.
Formerly a Graduate Student at Columbia University 相似文献
2.
T. E. Howson J. E. Stulga J. K. Tien 《Metallurgical and Materials Transactions A》1980,11(9):1599-1607
The creep and stress rupture behavior of the mechanically alloyed oxide dispersion strengthened nickel-base alloy MA 754 was
studied at 760, 982 and 1093 °C. Using material with a fine, highly elongated grain structure, tensile specimens oriented
parallel and perpendicular to the longitudinal grain direction were tested at various stresses in air under constant load.
It was found that the apparent stress dependence was large, with power law exponents ranging from 19 to 33 over the temperature
range studied. The creep activation energy, after correction for the temperature dependence of the elastic modulus, was close
to but slightly larger than the activation energy for self diffusion. Rupture was intergranular and the rupture ductility
as measured by percentage elongation was generally low, with values ranging from 0.5 to 16 pct. The creep properties are rationalized
by describing the creep rates in terms of an effective stress which is the applied stress minus a resisting stress consistent
with the alloy microstructure. Values of the resisting stress obtained through a curve fitting procedure are found to be close
to the values of the particle by-pass stress for this ODS alloy, as calculated from the measured oxide particle distribution.
.nt]mis|Formerly at Columbia University 相似文献
3.
V. C. Nardone D. E. Matejczyk J. K. Tien 《Metallurgical and Materials Transactions A》1983,14(7):1435-1441
Cyclic creep and stress rupture results of Inconel MA 6000E are reported and discussed as a function of frequency. Inconel MA 6000E is a new alloy system developed for high creep resistance at intermediate as well as at high temperatures. It is a mechanically alloyed oxide dispersion (-2.5 vol pct) and y′ precipitation (-50 vol pct) strengthened nickel-base superalloy. A decrease in the minimum strain rate and increase in the rupture life were found to accompany cyclic frequency increase. The deceleration of the creep rate is related to the anelastic strains recovered during the off-load periods. The data are also discussed relative to those obtained for an alloy containing only the oxide dispersoids. 相似文献
4.
Fatigue crack growth behavior of oxide dispersion strengthened ferritic MA 956 alloy was studied at 25 °C and 1000 °C in air
at 0.17 Hz. The growth rates were analyzed using the linear elastic parameter ΔK and the elastic-plastic parameter ΔJ. Crack growth, although transgranular at both temperatures, increased by nearly three orders of magnitude with increase in
temperature from 25 to 1000 °C. The growth rates were essentially the same in terms of either ΔK or ΔJ parameters indicating that plasticity effects are small even at 1000 °C. Detailed fractographic analysis revealed the presence
of ductile striations in the ΔK range of 25 to 40 MPa√m at 25 °C and in a much narrower range at 1000 °C. Presence of voids could be detected at 1000 °C.
Using the measured load-displacement hysteresis energies for a unit increment in crack length, crack growth rates were calculated
using cumulative damage models and were compared with the experimental data. At 1000 °C the predicted and the experimental
values agree within a factor of two and it is concluded that the growth occurs essentially by a damage accumulation process
except in a narrow range of ΔK where the plastic blunting process is superimposed, resulting in ductile striations that were observed. At 25 °C the predicted
and the experimental value reasonably agree for ΔK values greater than 40 MPa√m, and below this value the two diverge with predicted values being much lower. This divergence
is related to occurrence of the plastic blunting process in this ΔK range as confirmed by fractographic evidence. The cumulative damage process at 1000 °C was related to the environmentally
assisted void formation at dispersoid-matrix interfaces. At 25 °C the damage is related to the formation of microcracks ahead
of the crack tip. These results and interrelation between alloy microstructure and fatigue fracture path are discussed in
detail. 相似文献
5.
T. E. Howson D. A. Mervyn J. K. Tien 《Metallurgical and Materials Transactions A》1980,11(9):1609-1616
The creep and stress rupture behavior of a mechanically alloyed oxide dispersion strengthened (ODS) and γ′ precipitation strengthened
nickel-base alloy (alloy MA 6000E) was studied at intermediate and elevated temperatures. At 760 °C, MA 6000E exhibits the
high creep strength characteristic of nickel-base superalloys and at 1093 °C the creep strength is superior to other ODS nickel-base
alloys. The stress dependence of the creep rate is very sharp at both test temperatures and the apparent creep activation
energy measured around 760 °C is high, much larger in magnitude than the self-diffusion energy. Stress rupture in this large
grain size material is transgranular and crystallographic cracking is observed. The rupture ductility is dependent on creep
strain rate, but usually is low. These and accompanying microstructural results are discussed with respect to other ODS alloys
and superalloys and the creep behavior is rationalized by invoking a recently-developed resisting stress model of creep in
materials strengthened by second phase particles. The analysis indicates that at the intermediate temperature the creep strength
is controlled by the high volume fraction of γ′ precipitates and the contribution to the creep strength from the oxide dispersion
is small. At the elevated temperature, the creep strength is derived mainly from the inert oxide dispersoids.
Formerly at Columbia University. 相似文献
6.
V. C. Nardone D. E. Matejczyk J. K. Tien 《Metallurgical and Materials Transactions A》1985,16(6):1117-1122
In the paper we derive an expression for the cyclic minimum strain rate of cyclic creep in systems where anelastic relaxation
is a controlling mechanism. The cyclic creep behavior is modeled by assuming that the anelastic strain recovered during the
off-load periods must first be stored during the on-load periods before nonrecoverable creep results. To perform the derivation,
the time dependence of the anelastic relaxation is reported for two oxide dispersion strengthened alloys and shown to be adequately
described by a double exponential function. The time dependence of the anelastic relaxation is then incorporated into an expression,
generally used to describe static minimum strain rate data, to obtain the frequency dependence of the cyclic minimum strain
rate. The predicted values of the derived expression using results from static creep and strain relaxation tests are in excellent
agreement with the experimentally observed cyclic creep results with the use of no adjustable parameters. The proposed model
of anelastic strain storage delaying nonrecoverable creep is also shown to be consistent with the observed effects of temperature
and maximum load on the cyclic minimum strain rate. 相似文献
7.
8.
The influence of temperature, orientation, and environment on fatigue and creep crack growth behavior in oxide dispersion
strengthened INCONEL MA-754 was examined. With an increase in temperature, crack growth rates increase due largely to an increasing
creep contribution. Environment also may influence crack growth behavior, its effect depending on orientation. Orientation
has a marked effect on crack growth because of the propensity for creep void formation along particle stringers in the microstructure,
which form in the processing. The rate of crack growth can be enhanced if the aligned voids are parallel to the main crack
or retarded if these voids are normal to the direction of the crack. In the transverse-longitudinal (T-L) orimation crack
growth is faster on a time basis in creep than in fatigue; the reverse of this is true in the longitudinal-transverse (L-T)
orientation. Predicted fatigue crack growth rates based on a cumulative damage model agree with experimentally determined
growth rates. 相似文献
9.
J. Daniel Whittenberger 《Metallurgical and Materials Transactions A》1978,9(1):101-110
A study of the 1365 K tensile properties, creep characteristics and residual room temperature properties after creep testing
of the experimental oxide dispersion strengthened iron-base alloy MA-956E (Fe-20Cr-4.5Al-0.5Ti-0.5Y2O3) was conducted. The 1365 K tensile properties, particularly ductility, are strongly dependent on strain rate. It appears
that MA-956E does not easily undergo slow plastic deformation. Rather than deform under creep loading conditions, the alloy
apparently fails by a crack nucleation and growth mechanism. Fortunately, there appears to be a threshold stress below which
crack nucleation andJor growth does not occur. 相似文献
10.
The effects of interstitial sinks on the structure and creep behavior of the dispersion-strengthened columbium base alloy., D43 were examined. Interstitial sinks change the structure of the alloy and render it less creep resistant by reducing the carbon concentration and, therefore, the volume fraction of the dispersed phase. Where the interparticle spacing is small (<≈1 μ) the alloy is strengthened by the direct interaction of dislocations with particles. Where the interparticle spacing is large, subgrains are probably a more important structural feature strengthening the alloy. The creep rate can be described by the empirical expression \(\dot \varepsilon = A\sigma ^n e^{ - H/RT} \) , whereH (106 to 112 kcal per mole) andn (7.7 to 8.3) are independent of the amount of dispersed phase, andA is proportional to the reciprocal carbon concentrations in the range 100 to 800 ppm. 相似文献
11.
Two models of constrained cavity growth are developed to describe the long-term longitudinal creep behavior of nickel based
oxide dispersion strengthened (ODS) alloys. For both models the rupture time is taken as the time for a transverse grain boundary
to cavitate fully. A diffusive cavity growth law is assumed to govern cavitation. The applicability of the respective models
is determined by the particular grain morphology achieved by thermal-mechanical processing. The first model assumes that longitudinal
grain boundaries are unable to slide; hence displacements due to cavitation must be matched by displacements due to dislocation
creep in adjoining grains. This model predicts a low stress exponent at the transition from single crystal to cavitation creep
behavior, and higher stress exponents at stresses below this transition. Good agreement is found between the model predictions
and creep data for MA 754 at 1000 and 1093 °C. A second model considers a grain morphology wherein longitudinal grain boundaries
are able to slide by means of deformation of pockets of fine grains. Cavitation of transverse grain boundaries is thus controlled
by grain boundary sliding. This model predicts a stress exponent of 1 at low stresses, and serves as an upper bound for the
creep rate when a duplex grain morphology is present. Model predictions are in good agreement with creep data for a heat of
MA 754 with a duplex grain morphology.
Formerly Graduate Research Assistant in the Department of Materials Science and Engineering at Stanford University 相似文献
12.
13.
Robert Blickensderfer 《Metallurgical and Materials Transactions B》1974,5(11):2347-2350
The creep behavior of a dispersion strengthened tungsten alloy was studied over a temperature range of 1820 to 2160 K or 0.45
to 0.56 Tm and a stress range of 24 to 138 MPa. The activation energy for creepwas determined as 2.37 ± 0.07 MJ/kgK and was not a function
of stress. The steady-state creep rate varied linearly with stress at stresses below 80 MPa and as the 4.6 ± 0.1 power of
stress at stresses above 100 MPa. The stress dependency did not satisfy an exponential relationship. The creep behavior satisfied
the functional dependency of the Ansell-Weertman model, but the creep rates were in error by a factor of about 103. Nabarro-Herring creep in the low-stress region and a modification of the Ansell-Weertman theory in the high-stress region
provide satisfactory agreement with experiment for this tungsten alloy as well as the SAP alloy of Ansell and Lenel. 相似文献
14.
Rishi Raj 《Metallurgical and Materials Transactions A》1975,6(8):1499-1509
Steady state solutions to three types of diffusion problems: creep, grain boundary sliding and intergranular crack growth, have been published in the literature. This paper considers, in detail, the events which occur between the time when the external stress is applied and the time when the steady state is eventually reached. The time constant of the transient has been calculated. It is shown how the grain boundary tractions change with time from the initial “elastic” configuration (when sliding has been elastically accommodated) to the steady state “diffusional” configuration (when the sliding rate is diffusionally accommodated). This requires infusion of excess grain boundary dislocations; the distribution of these dislocations is calculated. The results are applied to problems of diffusional creep, grain boundary sliding and intergranular crack growth. 相似文献
15.
Rishi Raj 《Metallurgical and Materials Transactions A》1975,6(9):1499-1509
Steady state solutions to three types of diffusion problems: creep, grain boundary sliding and intergranular crack growth,
have been published in the literature. This paper considers, in detail, the events which occur between the time when the external
stress is applied and the time when the steady state is eventually reached. The time constant of the transient has been calculated.
It is shown how the grain boundary tractions change with time from the initial “elastic” configuration (when sliding has been
elastically accommodated) to the steady state “diffusional” configuration (when the sliding rate is diffusionally accommodated).
This requires infusion of excess grain boundary dislocations; the distribution of these dislocations is calculated. The results
are applied to problems of diffusional creep, grain boundary sliding and intergranular crack growth. 相似文献
16.
17.
采用粉末冶金法制备出成分为Fe-12.5Cr-2.5W-0.4Ti-0.02V-0.4Y2O3(12Cr-ODS,质量分数,%)的铁素体钢.通过电镜观察及力学性能测试等手段研究了12Cr-ODS铁素体钢的组织与性能,并定量计算了不同强化机制对合金屈服强度的贡献.电镜观察发现12Cr-ODS钢为等轴的铁素体组织,平均晶粒尺寸为1.5μm,不同尺寸氧化物在基体中均匀分布.力学性能测试结果表明12Cr-ODS钢具有优异的室温拉伸性能,屈服强度达到738 MPa.合金主要强化机制为氧化物弥散强化、氧化物弥散强化钢加工强化、热错配位错强化和晶界强化机制,各种强化机制计算得到的理论屈服强度为750 MPa,与实测值吻合较好. 相似文献
18.
The high cycle fatigue (HCF) behavior of the oxide dispersion strengthened (ODS) MA 754 alloy has been determined as a function
of specimen orientation. The fatigue life showed anisotropic behavior with the longest and shortest lives in the longitudinal
and short transverse directions, respectively. Surface porosity, due to oxidation, was found to affect fatigue life in the
long transverse orientation more than in the longitudinal orientation. The fatigue crack growth behavior in MA 754 exhibited
a directional dependence. In general, the crack growth rates in the longitudinal direction were lower than those in the long
transverse direction. The ΔK
th
was ∼11 MN ·-3/2 and 9 MN · m-3/2 for the longitudinal and the long transverse orientation, respectively. This behavior was explained on the basis of the unusual
grain structure and the texture exhibited by this alloy as well as different crack closure effects. It was found that a consideration
based on the crack growth rates results, obtained from fracture mechanics specimens, could not explain the anisotropic behavior
of the HCF properties of MA 754. However, the anisotropic HCF properties could be rationalized on the basis of the differences
in the modes of crack initiation. 相似文献
19.
20.
The behavior of wrought and cast polycrystalline Udimet 700 tested in static tension at 1200 K (1700†F) has been determined.
An air environment decreases rupture life and ductility, except in very coarse-grained cast specimens, because of premature
failure by stress-assisted grain boundary oxidation and cracking. In very coarse-grained cast specimens greater life and ductility
are found in air than in vacuum, presumably due to the paucity of transverse grain boundaries and to some type of surface
hardening effect. Wrought specimens exhibit greater grain boundary sliding, hence more cracking, shorter life, and lower ductility,
than cast specimens in any environment. This is attributed to differences in grain boundary topography.
Formerly Research Fellow, Department of Metallurgy and Materials Science and LRSM, University of Pennsylvania, Philadelphia 相似文献