共查询到20条相似文献,搜索用时 15 毫秒
1.
The effects of air and vacuum on the fatigue behavior of a nickel-base superalloy, Mar-M200, in single crystal form were investigated.
Between 800° and 1400°F fracture is entirely in the Stage I mode in air and vacuum, and fatigue life is unaffected by environment.
At 1700° F in both environments, fracture is predominantly in the Stage II mode and fatigue life in air is greater than that
in vacuum. At both temperatures, fatigue cracking in air is internally initiated, whereas in vacuum cracking is generally
initiated at the specimen surface. Identical fatigue lives in air and in vacuum between 800° and 1400° F are attributed to
the fact that internally initiated cracks in air are actually propagating in a high vacuum, surface cracking being inhibited
by dynamic oxidation of emerging surface slip offsets. The subsurface portion of the Stage I fracture surface produced in
air tests and all of the Stage I fracture produced in vacuum tests shows a dimpled structure, whereas the Stage I fracture
surface produced while the crack propagation is in air shows a cleavage appearance. At 1700° F, bulk oxidation of surface
initiated cracks interferes with the plastic blunting mechanism of Stage II crack growth normally observed at this temperature,
internally initiated cracks causing ultimate failure. Shorter lives in vacuum are thought to result from enhanced Stage II
surface crack propagation.
Formerly with Materials Engineering and Research Laboratory, Pratt and Whitney Aircraft, Middletown, Conn. 相似文献
2.
Previous investigations have invariably observed strain rate related deformation effects as the fatigue frequency is raised to the ultrasonic range. Through room temperature tests on strain rate insensitive nickel-base superalloy single crystals of Mar-M200, we have shown that another effect of increasing the fatigue frequency to the ultrasonic range is in the suppression of the deleterious influence of environment. It was found that above a stress amplitude of 30,400 psi the fatigue lives of crystals ultrasonically fatiguedin air increase with decreasing stress in a manner which is functionally similar to, that of crystals conventionally fatiguedin vacuum. Similarly, the fracture surfaces of ultrasonically fatigued crystals have a dimpled appearance over most of their areas which is characteristic of locally ductile failure and identical to, the appearance of crystals failed at conventionally frequency in vacuum. These results, along with a kinetic analysis of gaseous adsorption, indicate that the major effect of increasing the fatigue frequency to the ultrasonic, range is in the suppression of the influence of oxygen in enhancing the rate of crack propagation. In addition, the short test times involved in running large numbers of cycles have allowed for the determination of the fatigue limit in a nickel-base superalloy. This is the first indication of no-fail behavior in this type of alloy. 相似文献
3.
C. L. Baker J. Chene I. M. Bernstein J. C. Williams 《Metallurgical and Materials Transactions A》1988,19(1):73-82
The entry and subsequent interaction of hydrogen on the mechanical properties of the single crystal nickel-base super alloy
CMSX-2 has been studied. Significant amounts of hydrogen were introduced by high temperature hydrogen charging in molten salts
which led to an increased lattice parameter and microhardness and to a degradation in tensile elongation to failure whose
extent scales with the depth of the hydrogenated zone. In this region a fracture mode change from a {111} to a {100} type
also occurred. The values of the binding energy of hydrogen to solidification voids and the effective hydrogen pressure in
the voids were estimate. 相似文献
4.
Carbon-free single crystals of Mar-M200 were tested in pulsating tension, stress-controlled fatigue at temperatures and frequencies
ranging from 1033 to 1255°K and 0.033 to 1058 Hz, respectively. The axis of loading was parallel to [001], the natural growth
direction for directionally-solidified nickel-base alloys. Except for the lowest frequency at the higher temperatures where
creep damage was extensive, crack initiation occurred at subsurface microporosity. Cracks initiated and propagated in the
Stage I mode (crystallographic cracking on the {111} slip planes) at the lower temperatures and higher frequencies, whereas
Stage (perpendicular to the principal stress axis) crack initiation and propagation was found at the higher temperatures and
lower frequencies. Often a transition from Stage II to Stage I crack propagation was observed. It was established that Stage
I cracking occurred under conditions of heterogeneous, planar slip and Stage II cracking under conditions of homogeneous,
wavy slip. A thermally activated recovery process with an activation energy of 368 KJ/mole (88 Kcal/mole) determined the instantaneous
slip character,i.e., wavy or planar, at the crack tip. In addition, it was found that an optimum frequency existed for maximizing fatigue life.
At frequencies below the optimum, creep damage was detrimental, while at frequencies greater than the optimum, intense, planar
slip was detrimental. The optimum frequency increased with increasing temperature. 相似文献
5.
Carbon-free single crystals of Mar-M200 were tested in pulsating tension, stress-controlled fatigue at temperatures and frequencies ranging from 1033 to 1255°K and 0.033 to 1058 Hz, respectively. The axis of loading was parallel to [001], the natural growth direction for directionally-solidified nickel-base alloys. Except for the lowest frequency at the higher temperatures where creep damage was extensive, crack initiation occurred at subsurface microporosity. Cracks initiated and propagated in the Stage I mode (crystallographic cracking on the {111} slip planes) at the lower temperatures and higher frequencies, whereas Stage (perpendicular to the principal stress axis) crack initiation and propagation was found at the higher temperatures and lower frequencies. Often a transition from Stage II to Stage I crack propagation was observed. It was established that Stage I cracking occurred under conditions of heterogeneous, planar slip and Stage II cracking under conditions of homogeneous, wavy slip. A thermally activated recovery process with an activation energy of 368 KJ/mole (88 Kcal/mole) determined the instantaneous slip character,i.e., wavy or planar, at the crack tip. In addition, it was found that an optimum frequency existed for maximizing fatigue life. At frequencies below the optimum, creep damage was detrimental, while at frequencies greater than the optimum, intense, planar slip was detrimental. The optimum frequency increased with increasing temperature. 相似文献
6.
Influence of molybdenum on the creep properties of nickel-base superalloy single crystals 总被引:1,自引:0,他引:1
R. A. MacKay M. V. Nathal D. D. Pearson 《Metallurgical and Materials Transactions A》1990,21(1):381-388
The influence of Mo on the creep properties of single crystals of a model nickel-base superalloy has been investigated. The
Mo content was systematically varied from 9.8 to 14.6 wt pet in an alloy series based on Ni-6 wt pet Al-6 wt pet Ta. The optimum
initial γ-γ′ microstructure for raft development and creep strength was produced in each alloy prior to testing. The creep
lives at 982 °C and 234 MPa exhibited a steep peak as a function of Mo content, with the maximum in life occurring at about
14.0 wt pet Mo. Deviations of less than 1 wt pet Mo from the optimum composition resulted in an order of magnitude drop in
properties. As the Mo content was increased from 9.8 to 14.0 wt pct, the magnitude of lattice mismatch significantly increased,
which was believed to be beneficial because of stronger γ-γ′ interfaces. As the Mo content was increased further from 14.0
to 14.6 w/o, the mechanical properties degraded because of the precipitation of a deleterious third phase. The results suggest
that small variations in refractory metal content and initial gg′ size can have profound effects on mechanical properties.
Hence, composition ranges and microstructures for the attainment of optimum mechanical properties may be somewhat limited
and require close process control. 相似文献
7.
E. R. Golubovskiy I. L. Svetlov N. V. Petrushin S. A. Cherkasova M. E. Volkov 《Russian Metallurgy (Metally)》2010,(10):941-947
Single-crystal samples of nickel superalloys containing rhenium or rhenium plus ruthenium are subjected to low-cycle fatigue
(LCF) tests under rigid cycle conditions at temperatures of 850 and 1050°C. It is found that the single crystals of the alloy
containing rhenium with ruthenium have higher LCF resistance at 104 cycles as compared to the alloy containing only rhenium. At a test temperature of 850°C, volume stress concentrators in the
form of pores or their clusters represent fatigue crack nucleation zones; at 1050°C, surface corrosion cracks are the main
fracture zones. The fatigue microcrack growth rate is anisotropic: it is higher in the [001] direction and lower in the [011]
direction. 相似文献
8.
The influence of orientation on the stress rupture properties of nickel-base superalloy single crystals 总被引:1,自引:0,他引:1
The influence of orientation on the stress rapture properties of MAR-M247 single crystals was studied. Stress rupture tests
were performed at 724 MPa and 774 °C where the effect of anisotropy is prominent. The mechanical behavior of the single crystals
was rationalized on the basis of the Schmid factors for the operative slip systems and the lattice rotations which the crystals
underwent during deformation. The stress rupture lives at 774 °C were found to be greatly influenced by the lattice rotations
required to produce intersecting slip, because second-stage creep does not begin until after the onset of intersecting slip.
Crystals which required large rotations to become oriented for intersecting slip exhibited a large primary creep strain, a
large effective stress level at the onset of steady-state creep, and consequently, a short stress rupture life. Those crystals
having orientations within about 25° of the [001] exhibited significantly longer lives when their orientations were closer
to the [001]-[011] boundary of the stereographic triangle than to the [001]-[1l 1] boundary, because they required smaller
rotations to produce intersecting slip and the onset of second-stage creep. Thus, the direction off the [001], as well as
the number of degrees off the [001], has a major influence on the stress rapture lives of single crystals in this temperature
regime.
REBECCA A. MacKAY, formerly Graduate Assistant, Case Western Reserve University, Cleveland, OH
RALPH D. MAIER, formerly Assistant Professor, Case Western Reserve University 相似文献
9.
An electron fractrographic study was made of opposing crystallographic (Stage I) fatigue fracture surfaces of specimens of a single crystal nickel-base superalloy, low carbon MAR-M200, that were tested at room temperature. In regions near the crack initiation site, features on both surfaces are the same. In regions at some distance from the initiation site significant differences in the type and extent of microfeatures were observed. For a crack propagating in an upward direction, irregular markings were observed on the upper fracture surface and regularly spaced slip offsets and slip band cracks were observed on the lower surface. These observations are explained by a consideration of the elastic stress field and the resultant glide forces on all possible slip systems surrounding a crack growing at an angle to the principal stress direction. Additionally the results are used to support a previously proposed model for Stage I fatigue crack propagation. 相似文献
10.
11.
12.
The recrystallization behavior of a single crystal nickel-base superalloy was investigated by shot peening and subsequent annealing. Two kinds of recrystallization microstructures, which are intensively dependent on the annealing temperature, are shown in the nickel-base superalloy after shot peening and subsequent annealing. Surface recrystallized grains are obtained when the superalloy is anparticles occurs. Cellular recrystallization is observed after annealing at lower temperatures. Cellular structures induced by high diffusivity of the shot-peened alloy annealed at 1050℃ accords with the Johnson-Mehl-Avrami-Kolmogorov equation. The low Avrami exponent is caused by the inhomogeneous distribution of stored energy, the decreasing of stored energy during recovery, and the strong resistance of boundary migration yb γ' particles. 相似文献
13.
The thermal-mechanical fatigue (TMF) behavior of IN-100, a cast nickel-base superalloy, was investigated with a basic mechanical
strain-temperature loop applied in a temperature range from 600 °C to 1050 °C (873 to 1323 K). Peak strains were applied at
intermediate temperatures, giving a faithful simulation of real component parts. Tests with or without a mean strain were
used; other tests involved a longer period or a tensile hold time, and they were compared with conventional “in-phase” TMF
cycles. An interrupted test procedure was used with a plastic replication technique to define a conventional TMF life to 0.3-mm
crack depth, as well as a life to 50-μm, crack depth, to characterize the crack initiation period. Some stress-strain hysteresis
loops were reported. Thermal-mechanical fatigue life was found to be dependent upon test parameters, while the life to crack
initiation was not. Oxidation of specimens and micro-cracks was found to be important in all the tests. These results were
then discussed and compared with those under low cycle fatigue at high temperature.
Formerly with the Centre des Matériaux 相似文献
14.
The hydrogen-induced fracture behavior of notched single crystals of the PWA 1480E nickel-based superalloy was studied. Notched
single crystals with seven different crystal orientations near [100], [110], [111], [013], [112], [123], and [223] were tensile
tested at 22 °C in an hydrogen atmosphere at 34 MPa. The notch tensile strength degradation in hydrogen was orientation dependent.
The specimen with the [100] orientation had the greatest strength degradation, while the crystal with the [111] orientation
had the least. A stereoscopic technique combined with the use of planar γ′ morphologies was applied to identify cleavage plane
orientations. All specimens failed predominately by {100}-type cleavage within about 0.5 mm of the notch and {111}-type cleavage
toward the center of the crystal. Cleavage on {111}-type planes in the center of the crystals was not related to testing in
hydrogen. Microcracking along the {100} γ/γ′ interfaces was observed in the area near the fractured surface. Both scanning
electron microscopy (SEM) and transmission electron microscopy (TEM) studies indicated that {100}-type cleavage within the
notch region controlled the hydrogen-induced cleavage fracture in notched single crystals.
Formerly graduate Student, Auburn University 相似文献
15.
The fracture behavior of single crystals of the PWA 1480E nickel-base superalloy was studied using both scanning electron
microscopy (SEM) and transmission electron microscopy (TEM) techniques. Notched single crystals with seven different crystal
growth orientations near [100], [110], [111], [013], [112], [123], and [223] were tensile tested at 22 °C in a helium atmosphere
at 34 MPa. Gamma prime particles were orderly and closely aligned with the cube edges along the [100], [010], and [001] directions
of theγ matrix. The cuboid morphology of theγ’ precipitate was not influenced by the crystal growth orientation. The specimen with the [110] orientation was the strongest,
while the crystal with the [100] orientation was the weakest. A stereoscopic technique, combined with the use of planary’ morphologies, was applied to identify the cleavage plane orientation. All specimens failed predominately by {lll}-type cleavage
which originated from combined slip on various {111} planes. In most cases, deformation was found to occur inhomogeneously
in intense slip bands lying on {111} planes and aligned parallel to the different slip directions. Both SEM and TEM studies
indicated that {lll}-type slip was the controlling factor during cleavage fracture of single crystals of the PWA 1480E nickel-base
superalloy.
Formerly Graduate Student, Auburn University 相似文献
16.
K. Sugimoto T. Sakaki T. Horie K. Kuramoto O. Miyagawa 《Metallurgical and Materials Transactions A》1985,16(8):1457-1466
The effects of crystallographic orientation and thickness of specimen on the notch-tensile creep strength of single crystals
of a nickel-base superalloy UDIMET∗520 has been examined at 700°, 850°, and 900 °C. It was found that the notch-tensile creep
strength of thin specimens depended on the crystallographic orientations not only in the tensile direction but also in the
normal direction of the specimens, and that the creep strength was superior in the thin specimens with the [011] tensile and
the [011] normal orientations or the [001] tensile and the [110] normal orientations. The thick-notched specimens exhibited
great creep resistance regardless of the crystallographic orientations.
Formerly Graduate Student
Formerly Graduate Student, Tokyo Metropolitan University 相似文献
17.
Dislocation structure in a single-crystal nickel-base superalloy during low cycle fatigue 总被引:1,自引:0,他引:1
J. H. Zhang Z. Q. Hu Y. B. Xu Z. G. Wang 《Metallurgical and Materials Transactions A》1992,23(4):1253-1258
An investigation of dislocation structure in a single crystal nickel-base superalloy during low cycle fatigue (LCF) at 760
°C has been conducted. Dislocation bands are found to be produced first in the matrix in some defined directions. With an
increase in cycle numbers, there is an increase in dislocation density in the bands and a decrease in the spacing between
the bands, leading to the formation of the dislocation walls or cells. Sometimes, three-dimensional (3-D) networks are formed
also by the interaction between two sets of parallel dislocations. The Burgers vectors of the dislocations in the network
are 1/2 〈110〉. Clustering of dislocations eventually occurs at γ′/γ interfaces because of the obstruction of the γ′-particles
to moving dislocations. Most of the dislocations observed in the γ′-phases are in the form of superdislocations. Dislocation
shearing through theγ′-phase was found occasionally. Reprecipitation of γ′-phase induced by strain was also observed in the
present study. 相似文献
18.
M. Dollar I. M. Bernstein A. Domnanovitch W. Kromp H. Pinczolits 《Metallurgical and Materials Transactions A》1991,22(11):2597-2603
The effects of hydrogen on the low-cycle fatigue behavior of CMSX-2 [001]-oriented single crystals were examined. Fatigue
tests were conducted under constant plastic strain amplitude control. Cyclic stress-strain curves and fatigue life data at
different plastic strain amplitudes were determined for hydrogen-free and hydrogen-charged specimens. Two charging procedures,
leading to different hydrogen concentrations, were applied. Hydrogen was found to decrease significantly the number of cycles
to failure under the various experimental conditions. The increasing hydrogen concentration and ratio of the hydrogen to nonhydrogen-containing
volume were found to shorten fatigue life in hydrogen-charged specimens. Based on the analysis of cyclic stress-strain curves
and optical and transmission electron microscopy (TEM), it was established that hydrogen enhanced strain localization and
promoted crystallographic, stage I cracking, leading to embrittlement. The overall fracture mechanism is discussed in conjunction
with Duquette and Gell’s stage I fracture model.[16] 相似文献
19.
通过测定一种单晶镍基合金的高温拉伸蠕变曲线及位错运动的内摩擦应力σ0,建立了综合蠕变方程,计算出稳态蠕变期间的表观蠕变激活能及相关参数.结果表明:在蠕变期间,位错运动的内摩擦应力σ0,随外加应力的提高略有提高,随温度的升高而明显降低.蠕变后期,由于缩径使样品不同位置承受不同的有效的应力,导致筏状γ'相具有不同的粗化特征,在近断口处,载荷的有效应力增大,使筏状γ'相扭曲且粗化加剧.界面位错网对形变硬化和回复软化具有协调作用,并减缓位错切入γ'相,因此有利于合金蠕变抗力的提高. 相似文献
20.
通过蠕变曲线测定及组织形貌观察,研究了一种镍基单晶合金的蠕变行为和变形特征.结果表明:单晶合金在试验的温度和应力范围内,对施加应力和温度有明显的敏感性.由所得数据测算出合金的蠕变激活能和应力指数.蠕变初期在施加温度和应力场的作用下,立方γ′相逐渐转变成与施加应力轴方向垂直的N型筏状结构.稳态蠕变期间,合金的变形机制是位错攀移越过筏状γ′相,由于高温蠕变稳态阶段形成的N型γ′相筏状组织厚度较小,位错易于攀移,因而合金具有较大的应变速率.蠕变后期,由于塑性变形,在近断口处筏形γ′相转变成与应力轴方向呈45°角的形貌,合金的变形机制是位错剪切筏状γ′相. 相似文献