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1.
Fabrication and properties of heavy section extrusions of Ti-6Al-6V-2Sn and Ti-8Mo-8V-2Fe-3AI alloys
This study is concerned with the fabrication in heavy section of the titanium alloys Ti-8Mo-8V-2Fe-3Al (Ti-8823) and Ti-6Al-6V-2Sn
(Ti-662). The technique utilized to achieve 84 pct reduction during the extrusion of heavy section cylindrical hollows is
given. The response to subsequent aging of both alloys is described in terms of the effect on important mechanical properties
such as yield and ultimate tensile strength, ductility and fracture toughness. For the Ti-8823 alloy extruded in heavy section,
it is shown that the optimum heat treatment consists of aging directly after hot working rather than the more common solution
treatment and age cycle. With the former heat treatment, uniform through the thickness mechanical properties are obtained.
Uniform mechanical properties are also obtained through the section of the Ti-662 extrusion with a solutionizing and overaging
heat treatment. 相似文献
2.
Alpha case thickness modeling in investment castings 总被引:1,自引:0,他引:1
W. J. Boettinger M. E. Williams S. R. Coriell U. R. Kattner B. A. Mueller 《Metallurgical and Materials Transactions B》2000,31(6):1419-1427
The alpha case thickness at the surface of a Ti-6Al-4V (wt pct) step wedge investment casting has been measured and successfully
predicted. The prediction uses temperature-time results obtained from a heat flow simulation of the casting. The temperature-time
results were coupled to a simple model for diffusion of oxygen into the beta phase during continuous cooling. Oxygen concentration
and microhardness profiles were measured from the surface in contact with the ZrO2 face coat of the shell mold into the interior of the casting. The oxygen content in the metal at the shell mold interface
was between 5 and 9.5 wt pct in general agreement with a thermodynamic calculation for bcc Ti in contact with ZrO2. At the limit of the alpha case region, as determined by standard metallographic technique, the oxygen concentration was
found to be no more than 0.02 wt pct above the level of oxygen in the bulk alloy. Using this information and one particular
literature value for the activation energy for diffusion of oxygen, a nearly linear relationship was obtained between the
measured and predicted alpha case thicknesses at various positions on the casting surface. Reduction of the prefactor of this
diffusion coefficient by a factor of 7.5 produces excellent agreement between predicted and measured alpha case thicknesses.
Such a reduction is not inconsistent with the scatter of literature values for the diffusion coefficient. 相似文献
3.
The phase transformation behavior of the metastable beta phase in hydrogen charged Ti-Mo alloys was investigated using electrical
resistivity and X-ray diffraction techniques. Hydrogen charging was found to have little effect on athermal omega phase formation
in a highly susceptible alloy (16 wt pct Mo) but suppressed athermal omega in alloys with compositions near the critical composition
for the transition to diffuse (incommensurate) type omega (∼20 wt pct Mo). No evidence was found for a hydrogen induced omega
phase in a concentrated alloy (30 wt pct Mo). The incipient stages of the beta + beta’ phase separation in Ti-30 wt pct Mo
were detected after aging slightly below the beta transus. 相似文献
4.
The phase transformation behavior of the metastable beta phase in hydrogen charged Ti-Mo alloys was investigated using electrical
resistivity and X-ray diffraction techniques. Hydrogen charging was found to have little effect on athermal omega phase formation
in a highly susceptible alloy (16 wt pct Mo) but suppressed athermal omega in alloys with compositions near the critical composition
for the transition to diffuse (incommensurate) type omega (∼20 wt pct Mo). No evidence was found for a hydrogen induced omega
phase in a concentrated alloy (30 wt pct Mo). The incipient stages of the beta + beta’ phase separation in Ti-30 wt pct Mo
were detected after aging slightly below the beta transus. 相似文献
5.
The results of a recent study of the effects of ternary alloying with Ti on the fatigue and fracture behavior of a new class
of forged damage-tolerant niobium aluminide (Nb3Al-xTi) intermetallics are presented in this article. The alloys studied have the following nominal compositions: Nb-15Al-10Ti
(10Ti alloy), Nb-15Al-25Ti (25Ti alloy), and Nb-15Al-40Ti (40Ti alloy). All compositions are quoted in atomic percentages
unless stated otherwise. The 10Ti and 25Ti alloys exhibit fracture toughness levels between 10 and 20 MPa√m at room temperature.
Fracture in these alloys occurs by brittle cleavage fracture modes. In contrast, a ductile dimpled fracture mode is observed
at room-temperature for the alloy containing 40 at. pct Ti. The 40Ti alloy also exhibits exceptional combinations of room-temperature
strength (695 to 904 MPa), ductility (4 to 30 pct), fracture toughness (40 to 100 MPa√m), and fatigue crack growth resistance
(comparable to Ti-6Al-4V, monolithic Nb, and inconnel 718). The implications of the results are discussed for potential structural
applications of the 40Ti alloy in the intermediate-temperature (∼700 °C to 750 °C) regime. 相似文献
6.
L. del Castillo H. M. Hu E. J. Lavernia Y. Wu 《Metallurgical and Materials Transactions A》1999,30(5):1381-1389
High-Li alloys, with the composition Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr, were synthesized using a spray deposition technique (wt. pct, X=0∼1.5). The microstructure of the spray-deposited Al-Li alloys consisted of equiaxed grains with an average grain size in
the range from 20 to 50 μm. The grain-boundary phases were fine and discrete. The spray-deposited and thermomechanically processed materials were isothermally
heat treated at 150 °C and 170 °C to investigate the age-hardening kinetics. It was noted that the spray-deposited Al-3.8Li-XCu-1.0Mg-0.4Ge-0.2Zr alloys exhibited relatively sluggish aging behavior. The peak-aged condition was achieved at 170 °C in
the range from 20 to 90 hours. It was noted that Cu increases the hardness of alloys during aging. Moreover, the influence
of Cu on age-hardening kinetics is marginal. The mechanical properties of the spray-deposited and extruded Al-Li alloys were
studied in the underaged, peak-aged, and overaged conditions. For example, the peak-aged yield strength, tensile strength,
and ductility of Al-3.8Li-1.0Cu-1.0Mg-0.4Ge-0.2Zr are 455 MPa, 601 MPa, and 3.1 pct, respectively. Moreover, an increase in
the Cu content of the alloy led to improvements in strength, with only slight changes in ductility, for Cu contents up to
1.0 wt pct. Beyond this range, an increase in Cu content led to decreases in both strength and ductility. 相似文献
7.
K. R. Ravi S. Manivannan G. Phanikumar B. S. Murty Suresh Sundarraj 《Metallurgical and Materials Transactions A》2011,42(7):2028-2039
Although the grain-refinement practice is well established for wrought Al alloys, in the case of foundry alloys such as near
eutectic Al-Si alloys, the underlying mechanisms and the use of grain refiners need better understanding. Conventional grain
refiners such as Al-5Ti-1B are not effective in grain refining the Al-Si alloys due to the poisoning effect of Si. In this
work, we report the results of a newly developed grain refiner, which can effectively grain refine as well as modify eutectic
and primary Si in near eutectic Al-Si alloys. Among the material choices, the grain refining response with Al-1Ti-3B master
alloy is found to be superior compared to the conventional Al-5Ti-1B master alloy. It was also found that magnesium additions
of 0.2 wt pct along with the Al-1Ti-3B master alloy further enhance the near eutectic Al-Si alloy’s grain refining efficiency,
thus leading to improved bulk mechanical properties. We have found that magnesium essentially scavenges the oxygen present
on the surface of nucleant particles, improves wettability, and reduces the agglomeration tendency of boride particles, thereby
enhancing grain refining efficiency. It allows the nucleant particles to act as potent and active nucleation sites even at
levels as low as 0.2 pct in the Al-1Ti-3B master alloy. 相似文献
8.
F. S. Lin E. A. Starke S. B. Chakrabortty A. Gysler 《Metallurgical and Materials Transactions A》1984,15(6):1229-1246
An alpha + beta Ti-6Al-2Nb-lTa-0.8Mo alloy with an initial Widmanstätten structure was thermally treated to produce a wide range of microstructures. The effects of individual microstructural parameters on deformation behavior and mechanical properties were investigated. The results show that the Widmanstätten colony boundaries are major barriers to slip. However, the slip distance can be decreased to a distance equal to the thickness of acicular alpha by transforming the beta phase in the Widmanstätten structure to martensite by quenching from 950°C. The decrease in slip distance is accompanied by a 25 pct increase in yield strength with no loss in ductility. A large decrease in ductility occurs after excursions above the beta-transus. The development of both equiaxed beta grains during heating in the beta phase field and continuous grain boundary alpha during cooling in the alpha + beta phase field leads to strain localization along prior beta grain boundaries. 相似文献
9.
Dale J. McEldowney Seshacharyulu Tamirisakandala Daniel B. Miracle 《Metallurgical and Materials Transactions A》2010,41(4):1003-1015
The Ti-6Al-4V (Ti-64) alloys modified with two levels of boron (1B and 1.7B (wt pct)) representing hypoeutectic and hypereutectic
compositions, produced via a prealloyed powder metallurgy approach, were subjected to various standard heat treatments of Ti-64 to study the microstructural
evolution and its influence on tensile properties. Boron-modified Ti-64 (Ti-64B) alloys exhibited differences in microstructural
response to heat treatment compared to that of Ti-64 due to variations in constituent phase fractions and the influence of
TiB on the beta-to-alpha phase transformation kinetics. The tensile elastic modulus of Ti-64B alloys increased nearly linearly
with the boron content (or TiB volume fraction) and the increase could be satisfactorily predicted with an isostrain rule
of mixtures (ROMs) and the Halpin–Tsai model. The Ti-64-1B possessed a good combination of tensile strength (1200 to1370 MPa)
and ductility (10 to 13 pct), while Ti-64-1.7B exhibited high strength (1300 to 1695 MPa) and modest ductility (2 to 3.5 pct).
Coarse primary TiB particles present in Ti-64-1.7B were found to initiate premature failure. Strength modeling revealed that
load sharing by the micron-sized TiB whiskers provides the major contribution for the increase in yield strength. 相似文献
10.
Two nickel-base aligned eutectics, AG15 (Ni-8.1 wt pct Al-26.4 wt pct Mo) and AG34 (Ni-6.3 wt pct Al-31.2 wt pct Mo), have
been tested in high cycle fatigue at room temperature. Experimental variables were test environment and post-solidification
heat treatment. The fatigue lives of both alloys and the crack propagation resistance of AG15 improved substantially in tests
performed in vacuumvs those performed in air. AG34 had a higher fatigue limit than AGI5; both alloys showed surface initiation and stage I crack
propagation. Post-solidification heat treatment had a beneficial effect on the S-N lives of AG34 specimens. Fatigue resistance
of both alloys is compared with that of other nickel or cobalt base eutectics strengthened with brittle fibers. 相似文献
11.
12.
This work focuses on the effect of the second phase on the ambient temperature creep deformation mechanisms of titanium alloys, using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V with Widmanstätten microstructures as the model systems. In Part I it was observed that the presence of a second phase can affect the tensile deformation behavior. Likewise, the creep deformation mechanisms of the two-phase alloys differ from the mechanisms of single-phase alloys. These α-β deformation mechanisms include twinning in fine grains of the α phase and stress-induced hexagonal martensite in the β phase of Ti-8.1 V. This is the first time that twinning in the α phase and stress-induced martensite in the β phase are reported as creep deformation mechanisms in an α-β titanium alloy. Several factors, including elastic interaction effects, shear stress due to deformation products in adjacent phases, and the stability of the β phase, affect the creep deformation mechanisms in these alloys. Models for the time-dependent growth of martensite are suggested. In addition, the difference between tensile and creep deformation in regard to accumulation of stresses to reach the critical stresses is described. 相似文献
13.
The effect of alloying additions on the superplastic properties of Ti-6 pct Al-4 pct V 总被引:1,自引:0,他引:1
The superplastic deformation properties of Ti-6 pct Al-4 pct V and modified alloys containing 1/4 pct, 1/2 pct, 1 pct, and
2 pct of either cobalt or nickel have been investigated in the temperature range 950 to 750 °C. The results show that both
cobalt and nickel modified alloys have reduced flow stresses, in comparison with Ti-6 pct Al-4 pct V, the reductions being
particularly marked at the lower temperatures and lower strain rates. The results are shown to be consistent with an isostress
model for the deformation of (α + β) two-phase alloys in which the varying β volume fractions and differing diffusivities
of titanium, cobalt, or nickel in the β phase are taken into account. 相似文献
14.
Toshikazu Akahori Mitsuo Niinomi Akihiro Suzuki 《Metallurgical and Materials Transactions A》2002,33(3):503-510
Hydrogenation and dehydrogenation, that is, thermochemical processing (THP) and its variation with a post-heat treatment (THPH),
are investigated in order to improve the balance of strength, elongation, and fatigue strength of cast Ti-6Al-7Nb and Ti-6Al-4V
for dental applications. Microstructures of both cast alloys change from coarse Widmanst?tten α structure to super fine α structure with an average diameter of 3 μm by conducting THP or THPH. Tensile strength and fatigue limit of cast Ti-6Al-7Nb and Ti-6Al-4V increase by around 10 and
40 pct, respectively, as compared with those of both as-cast alloys. The balance of strength and ductility of cast Ti-6Al-7Nb
is improved by conducting THPH as compared with the case where THP is conducted. This improvement is due to the plastic deformability
of unstable β phase because the lattice constant of β phase in each alloy conducted with THPH is much greater than that of each as-cast alloy. 相似文献
15.
The effects of α and β phase interactions on the room-temperature tensile and creep deformation behavior of α + β titanium
alloys with Widmanst?tten microstructures were studied using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V as the model two-phase alloy
systems. This article, Part I, deals with tensile deformation. It was found that when the α phase is present as thin (<10-μm)
plates in the α + β alloys, significant twinning occurs. No significant twinning was observed in single-phase alloys with
the same chemistry and similar grain size. Additionally, the β phase of Ti-8.1 V deforms by stress-induced hexagonal martensite
(α′), while only twinning occurs in the single-phase β alloy with the same chemistry. Twinning in the α phase in association
with stress-induced martensite (SIM) in the β phase was observed for the first time in a two-phase titanium alloy. This behavior
is explained in terms of a number of factors including elastic interaction stresses between the α and β phases, coherency
between the α phase and hexagonal martensite, and β phase stability. 相似文献
16.
The internal oxidation behavior of the bcc alloy TZM-Mo (Mo-0.5 wt pct Ti-0.08 wt pct Zr-0.02 wt pet C) was investigated in
low-pressure O2, CO, and H2O environments at 1098 and 1273 K. The results indicate that a diffusion process controls the kinetics of the oxygen absorption
at 1098 K, while bulk diffusion and gas-metal interaction at the specimen surface both affect the rate at 1273 K. The carbon
content of TZM in these experiments increased initially and then decreased. Decarburization became significant only after
extended exposure at 1273 K. The deformation and fracture behavior of both oxidized and heat-treated TZM specimens were studied
at temperatures to 1589 K. TZM specimens showed an increase in strength and a linear decrease in ductility with oxygen content.
Oxidized TZM lost its ductility completely at an oxygen level of 300 ppm at room temperature, 1366, and 1589 K, but 500 ppm
was required at 1098 K. The ductility of embrittled TZM was increased significantly with heat treatment at high temperatures
and was almost completely restored after annealing at 1973 K. The change in mechanical properties is discussed in terms of
internal oxidation and precipitation of oxides. 相似文献
17.
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
18.
G. Sridhar V. V. Kutumbarao D. S. Sarma 《Metallurgical and Materials Transactions A》1987,18(6):877-891
The microstructure and tensile properties of a near-α titanium alloy, IMI-829 (Ti-6.1 wt pct Al-3.2 wt pct Zr-3.3 wt pct Sn-0.5 wt pct Mo-1 wt pct Nb-0.32 wt pct Si) have been studied after solutionizing (and no subsequent aging) at two different temperatures separately, one above the β transus (1050 °C) and another below the β transus (975 °C) followed by various cooling rates (furnace, air, oil, or water). While 1050 °C treatment resulted in coarse Widmanstätten structures on furnace or air cooling, fine Widmanstätten structure on oil quenching and martensitic structure on water quenching, 975 °C treatment produced duplex microstructures consisting of equiaxed alpha and partially transformed beta phases. Transmission electron microscopy studies revealed the morphology, size, and distribution of the α, β, and martensite phases and also the presence of small ellipsoidal suicide particles and an interface phase with fcc structure at almost all α-β interfaces. The oil quenched structure from 1050 °C has been found to be a mixture of fine Widmanstätten α coexisting with martensite laths and retained beta at the lath boundaries. Silicides with hcp structure of about 0.4 μm size were observed in specimens solution treated at 975 °C. The interface phase is seen in all slowly-cooled specimens. The YS and UTS are superior for 975 °C treatment compared to 1050 °C treatment after water quenching or oil quenching. The tensile ductility values are superior for any cooling rate after 975 °C solution treatment as compared to 1050 °C solution treatment. The specimens failed in tension diagonally by shear after 1050 °C treatment and by cup and cone fracture after 975 °C treatment. In all cases fracture has taken place by microvoid coalescence and in most cases, along the α-β boundaries. 相似文献
19.
Structure and properties of a β solution treated,quenched, and aged si-bearing near-α titanium alloy
The microstructure, tensile properties, and fractographic features of a near-α titanium alloy, IMI 829(Ti-6.1 wt pct Al-3.2
wt pct Zr-3.3 wt pct Sn-1 wt pct Nb-05 wt pct Mo-0.32 wt pct Si) have been studied after aging over a temperature range of
550°C to 950°C for 24 hours following solution treatment in the β phase field at 1050°C and water quenching. Transmission
electron microscopy studies revealed that aging at 625°C and above produced discrete silicides at α′ interplatelet boundaries.
However, aging at 900°C and above has also resulted in the precipitation of β phase along the lath boundaries of martensite.
The silicides have been found to have a hexagonal structure withc=0.36 nm anda=0.70 nm (designated as S2 by earlier workers). There is a significant improvement in yield and ultimate tensile strength after aging at 625°C, but
there is less improvement at higher aging temperatures. The tensile ductility is found to be drastically reduced. While the
fracture surface of the unaged specimen shows elongated dimples, the aged samples show a mixed mode of fracture, consisting
of facets, featureless parallel bands, and extremely fine dimples. 相似文献
20.
S. L. Semiatin T. M. Brown T. A. Goff P. N. Fagin R. E. Turner J. M. Murry D. R. Barker J. D. Miller F. Zhang 《Metallurgical and Materials Transactions A》2004,35(9):3015-3018
Values of the diffusivity of aluminum and vanadium that can be used for engineering-oriented calculations of the diffusional
growth of primary alpha during the heat treatment of Ti-6Al-4V were established using diffusion couples consisting of various
Ti-Al-V alloys. After taking compositional influences into account using thermodynamic correction factors, the pertinent diffusivities
in the ternary alloy were found to be approximately 80 pct of those previously estimated from tracer or impurity (binary)
diffusion experiments.
This work was conducted as part of the in-house research of the Metals Processing Group of the Air Force Research Laboratory’s
Materials and Manufacturing Directorate. 相似文献