共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
R. J. H. Wanhill 《Metallurgical and Materials Transactions A》1976,7(9):1365-1373
A study was made of environmental fatigue crack propagation in 2.5 mm thick Ti-6A1-4V sheet conforming to AMS 4911, and 2.2 mm thick IMI 318 conforming to BS TA 10. The environments were dry argon, normal air, distilled water and 3.5 pct aqueous NaCl. There were three alloy/orientation combinations: Ti-6A1-4V L-T, IMI 318 L-T and IMI 318 T-L. Test frequencies were 30 and 50 Hz, at which there was a general trend of higher crack growth rates in the order: argon, air, distilled water, 3.5 pct aqueous NaCl. For both dry argon and 3.5 pct aqueous NaCl there were large differences in crack growth rates at low δK values between the three types of specimen. There was a correlation between the texture and cleavage fracture and crack growth rates in 3.5 pct aqueous NaCl. This result is of considerable practical importance. For dry argon the ranking of specimen types could be explained by the relative importance of mechanical and environmental crack growth, using the structure-sensitive to structure-insensitive transition concept of Irving and Beevers. 相似文献
3.
R. J. H. Wanhill 《Metallurgical and Materials Transactions A》1976,7(8):1365-1373
A study was made of environmental fatigue crack propagation in 2.5 mm thick Ti-6A1-4V sheet conforming to AMS 4911, and 2.2
mm thick IMI 318 conforming to BS TA 10. The environments were dry argon, normal air, distilled water and 3.5 pct aqueous
NaCl. There were three alloy/orientation combinations: Ti-6A1-4V L-T, IMI 318 L-T and IMI 318 T-L. Test frequencies were 30
and 50 Hz, at which there was a general trend of higher crack growth rates in the order: argon, air, distilled water, 3.5
pct aqueous NaCl. For both dry argon and 3.5 pct aqueous NaCl there were large differences in crack growth rates at low δK values between the three types of specimen. There was a correlation between the texture and cleavage fracture and crack growth
rates in 3.5 pct aqueous NaCl. This result is of considerable practical importance. For dry argon the ranking of specimen
types could be explained by the relative importance of mechanical and environmental crack growth, using the structure-sensitive
to structure-insensitive transition concept of Irving and Beevers. 相似文献
4.
The effects of environment and cyclic stress intensity factor on crack opening displacement and crack tip strain have been
measured, and discontinuous crack growth has been observed directly under high resolution conditions in the Scanning Electron
Microscope. This information is used in a crack tip failure model together with cyclic stress-strain, low cycle fatigue, and
microstructural characteristics of the material to derive the expected crack growth increment. Agreement with measured striation
spacings is reasonable. 相似文献
5.
W. C. Harrigan 《Metallurgical and Materials Transactions B》1974,5(3):565-572
Constant load creep tests were conducted with cast Ti-6Al-4 V bars in air and vacuum at 315† and 650†C. Some of the bars were
notched in their gauge section and heliarc-welded to simulate a weld repair in a casting. Results indicate that the welding
has little influence on the time to rupture of the bars. Fractographic analysis of the bars indicates minor differences in
the welded and unwelded fracture surfaces. However, these differences do not affect the microstructural influence on the creep
and fracture processes. The prior beta grain, size and the alpha platelet size are shown to control the creep fracture of
this alloy. These data show that weld repair of titanium castings for creep applications should be acceptable. 相似文献
6.
G. F. Pittinato 《Metallurgical and Materials Transactions B》1972,3(1):235-243
The effects of a hydrogen environment on the fatigue crack growth rates in Ti-6A1-4V ELI (STA) and weld material were determined
in the temperature range of ambient to -200°F. The hydrogen environment resulted in an acceleration of the crack growth rate
and a change in the fracture mode for both materials in the temperature range of ambient to -100°F. At -200°F, there was no
significant difference between the crack growth rates obtained in helium and hydrogen gas. The degree of hydrogén-enhanced
crack growth was found to be dependent on the crack tip stress-intensity range, temperature, and microstructure of the material.
The data is consistent with an embrittlement mechanism involving hydrogen diffusing ahead of the crack front. 相似文献
7.
8.
Brittany Hamilton Scott Oppenheimer David C. Dunand Daniel Lewis 《Metallurgical and Materials Transactions B》2013,44(6):1554-1559
Advanced metallic bone implants are designed to have a porous surface to improve osseointegration and reduce risks of loosening. An alternative approach to existing surface treatments to create a porous surface is to bond separately produced metallic foams onto the implant. To assess the feasibility of this approach, a Ti-6Al-4V foam was diffusion bonded onto bulk Ti-6Al-4V in an argon atmosphere at temperatures between 1173 K and 1223 K (900 °C and 950 °C) for times between 45 and 75 minutes. These specimens were tested in tension to determine bond quality: failures occurred in the foam, indicating a strong diffusion-bonded interface. The quality of the bond was confirmed by metallographic studies, indicating that this approach, which can also be applied to creating of sandwich with porous cores, is successful. 相似文献
9.
Fracture toughness tests have been carried out on a wide range of specimen orientations from textured Ti-6A1-4V alloy plate.
The tests were instrumented to allow measurement of crack extension as well as stress intensity factors and COD data. Preferred
orientation of the dominant alpha phase was found to influence not only the toughness parameters but also the fracture surface
and propensity to shear lip formation. The anisotropic nature of plasticity in the material was demonstrated by direct measurement
of yield loci and by the variable shapes of plastic zones around crack tips. Results are discussed in terms of a qualitative
analysis of slip systems at the crack tip and also in a semiquantitative anisotropic upper bound slip line treatment. It is
found that stable crack extension starts at low values ofK and COD for specimens in which plastic flow can occur readily at the crack tip but toughness, assessed as resistance to unstable
crack propagation, is greatest in these cases. The magnitude of microstructure induced anisotropy is shown to be much smaller
than that originating in preferred crystallographic orientation. Troughlike features on some fracture surfaces were found
to be associated with regions of particularly strong local texture.
Formerly with the Department of Physical Metallurgy, University of Birmingham 相似文献
10.
11.
12.
J. H. Zhu P. K. Liaw J. M. Corum H. E. McCoy Jr. 《Metallurgical and Materials Transactions A》1999,30(6):1569-1578
Mechanical behaviors at 538 °C, including tensile and creep properties, were investigated for both the Ti-6Al-4V alloy and
the Ti-6Al-4V composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP). It
was shown that the yield strength (YS) and ultimate tensile strength (UTS) of the composite were greater than those of the
matrix alloy at the strain rates ranging from approximately 10−5 to 10−3 s−1. However, the elongation of the composite material was substantially lower than that of the matrix alloy. The creep resistance
of the composite was superior to that of the matrix alloy. The data of minimum creep strain rate vs applied stress for the composite can be fit to a power-law equation, and the stress exponent values of 5 and 8 were obtained
for applied stress ranges of 103 to 232 MPa and 232 to 379 MPa, respectively. The damage mechanisms were different for the
matrix alloy and the composite, as demonstrated by the scanning electron microscopy (SEM) observation of fracture surfaces
and the optical microscopy examination of the regions adjacent to the fracture surface. The tensile-tested matrix alloy showed
dimpled fracture, while the creep-tested matrix alloy exhibited preferentially interlath and intercolony cracking. The failure
of the tensile-tested and creep-tested composite material was controlled by the cleavage failure of the particulates, which
was followed by the ductile fracture of the matrix. 相似文献
13.
Evaluations of the (infrared)-brazed Ti-6Al-4V and niobium joints using three silver-base braze alloys have been extensively
studied. According to the dynamic wetting angle measurement results, the niobium substrate cannot be effectively wetted by
all three braze alloys. Because the dissolution of Ti-6Al-4V substrate causes transport of Ti into the molten braze, the molten
braze dissolved with Ti can effectively wet the niobium substrate during brazing. For infrared-brazed Ti-6Al-4V/Ag/Nb joint,
it is mainly comprised of the Ag-rich matrix. The TiAg reaction layer is observed at the interface between the braze and Ti-6Al-4V
substrate. In contrast, Ti-rich, Ag-rich, and interfacial TiAg phases are found in the furnace-brazed specimen. The dominated
Ti-rich phase in the joint is caused by enhanced dissolution between the molten braze and Ti-6Al-4V substrate. The infrared-brazed
Ti-6Al-4V/72Ag-28Cu/Nb joint is mainly comprised of the Ag-rich matrix and Ag-Cu eutectic. With increasing the brazing temperature
or time, the amount of Ag-Cu eutectic is decreased, and the interfacial Cu-Ti reaction layer(s) is increased. The infrared
brazed joint has the highest average shear strength of 224.1 MPa. The averaged shear strength of the brazed joint is decreased
with increasing brazing temperature or time, and its fracture location changes from the braze alloy into the interfacial reaction
layer(s) due to excessive growth of the Cu-Ti intermetallics. The infrared-brazed Ti-6Al-4V/95Ag-5Al/Nb joint is composed
of Ag-rich matrix and TiAl interfacial reaction layer. With increasing the brazing time, the amount of Ag-rich phase is greatly
decreased, and the interfacial reaction layer becomes Ti3Al due to enhanced dissolution of Ti-6Al-4V substrate into the molten braze. The average shear strength of the infrared-brazed
joint is 172.8 MPa. Additionally, the existence of an interfacial Ti3Al reaction layer significantly deteriorates the shear strength of the furnace-brazed specimen. 相似文献
14.
G. R. Yoder L. A. Cooley T. W. Crooker 《Metallurgical and Materials Transactions A》1978,9(10):1413-1420
Fatigue crack growth rates have been determined for beta-annealed Ti-6Al-4V alloys with respective oxygen contents of 0.06, 0.11, 0.18 and 0.20 wt pct. For each of these alloys, transitional crack growth behavior has been observed which appears to correlate with a critical value of the reversed plastic zone size,viz the Widmanstätten packet size. Moreover, growth rates below transitional levels order in terms of packet size, with lower growth rates associated with larger packets. The present results suggest that intersti-tial oxygen content and prior beta grain size significantly affect fatigue crack growth rates through control of the Widmanstätten packet size. 相似文献
15.
D. Essenmacher M. F. Prezkop D. E. Mikkola D. A. Koss 《Metallurgical and Materials Transactions A》1978,9(8):1069-1074
Cavitation-induced erosion has been examined in Ti-6A1-4V in the mill annealed, solution-treat and aged, and beta annealed
conditions. Weight loss data show only small differences between heat treatments with the solution-treat and aged microstructure
exhibiting the lowest weight loss rates. Sequential micrographs of the same specimen area as a function of erosion time show
that initial fracture occurs along the α-β interfaces and along crystallographic slip bands in the α-phase. The early stages of erosion are also dependent on the orientation
of the Widmanstatten colonies in the beta annealed condition. These observations strongly suggest that fatigue fracture is
important, at least in the early stages of the cavitation erosion process. Depression of the softer α- phase also occurs at short exposure times, and this facilitates fracture and removal of the exposed material;i.e., β-phase or tempered martensite. Examination of the eroded surfaces in the later stages where considerable material has been
removed shows little evidence of the underlying microstructure, despite the distinct differences in the micro-structures of
the samples tested.
Formaly Undergraduate Students at Michigan Technological University 相似文献
16.
17.
J. I. Qazi J. Rahim F. H. Fores O. N. Senkov A. Genc 《Metallurgical and Materials Transactions A》2001,32(10):2453-2463
Microstructures, phases, and phase transformations in Ti-6Al-4V alloy specimens containing 0, 10, 20, and 30 at. pct hydrogen
were investigated using optical microscopy (OM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and microhardness
testing. Alloying with hydrogen was achieved by holding the specimens in a pure hydrogen atmosphere of different pressures
at 780 °C for 24 hours. The phases present in the temperature range of 20 °C to 1000 °C were determined by microstructural
characterization of the specimens quenched from different temperatures. Increasing the hydrogen addition from 0 to 30 at.
pct lowered the beta-transus temperature of the alloy from 1005 °C to 815 °C, significantly slowed down the kinetics of the
beta-to-alpha transformation, and led to formation of an orthorhombic martensite instead of the hexagonal martensite found
in quenched specimens containing 0 pct H. A hydride phase was detected in specimens containing 20 and 30 at. pct hydrogen.
The time-temperature-transformation (TTT) diagrams for beta-phase decomposition were determined at different hydrogen concentrations.
The nose temperature for the beginning of the transformation decreased from 725 °C to 580 °C, and the nose time increased
from 12 seconds to 42 minutes when the hydrogen concentration was increased from 0 to 30 at. pct. 相似文献
18.
M. Mubarak Ali S. Ganesh Sundara Raman S. D. Pathak R. Gnanamoorthy 《Transactions of the Indian Institute of Metals》2009,62(1):59-64
Ti-6Al-4V samples were plasma nitrided at 520°C in two environments (nitrogen and a mixture of nitrogen and hydrogen in the
ratio of 3:1) for two different time periods (4 h and 18 h). Fretting wear tests were conducted on unnitrided and nitrided
samples for 50,000 cycles using two counterbody materials (unnitrided Ti-6Al-4V and alumina). Gross slip prevailed at a normal
load of 4.9 N while mixed stick-slip prevailed at 9.8 N. Tangential force coefficient values of plasma nitrided samples were
lower than those of unnitrided samples. The tangential force coefficient nearly stabilised after thousand cycles in case of
samples tested against Ti-6Al-4V counterbody. On the other hand, it showed a continuously increasing trend in case of specimens
tested against alumina counterbody. The samples nitrided for 4 h exhibited higher hardness and lower tangential force coefficient
compared to the specimens nitrided for 18 h. The samples nitrided in nitrogen-hydrogen mixture environment exhibited higher
hardness and lower tangential force coefficient compared to the specimens nitrided in nitrogen. The samples plasma nitrided
in nitrogen-hydrogen mixture for 4 h exhibited the highest hardness and the lowest tangential force coefficient. The wear
volume of the plasma nitrided samples was lower than that of the unnitrided samples. Owing to tribochemical reactions, the
wear volume of unnitrided and nitrided samples fretted against alumina ball was higher than that of the samples fretted against
Ti-6Al-4V. A consistent trend was not observed regarding which nitriding condition would result in lower wear volume at different
loads. 相似文献
19.
The internal reactions associated with hydrogen absorbed at ambient temperature by Ti-6A1-4V having a transformedβ microstructure were determined by using X-ray diffraction analysis. Below 650 ppm, the absorbed hydrogen was concentrated
primarily in theβ phase causing an increase in the d(200) spacing and considerable X-ray line broadening. The a phase, however, was not significantly
affected by the absorbed hydrogen showing no change in the d(1120) and d(1012) spacings and only a finite amount of line broadening.
At approximately 650 ppm H, hydride precipitation began at thea-β interface. With increasing hydrogen content, theβ phase d(200) spacing continued to increase, the (200) X-ray line broadening reached a limiting value, and massive hydrides
were formed. The data indicates that low concentrations of hydrogen absorbed by a-β titanium alloys can be detected by examining
the X-ray line profile of theβ phase.
W. D. HANNA, formerly with the McDonnell Douglas Astronautics Co. 相似文献
20.
The alloy Ti-6-Al-4V deforms superplastically in the temperature range 750 to 950° The most important factor which is responsible
for superplastic behavior was found to be the very fine grain size. Strain rate has no direct effect on superplasticity, however
when the strain rate is very low (approximately 2 × 10 s), prolonged exposure to high temperature causes grain growth and
early failure. The strain rate sensitivity factorm = 0.5 and the apparent activation energyAH = 45,000 cal/mole, which is approximately the same as the activation energy for grain boundary self diffusion of titanium.
Both values are independent of strain rate within the range 10 - 2.5 × 10 s. All the experimental points fall in a straight
line when plotted as log (εkTd*
2/DgbGb3) vs log (σ/G) with a slopen = l/m = 2. This is in excellent agreement with the theory of grain boundary sliding accommodated by dislocation motion. 相似文献