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1.
The effect of deformation-induced transformation on the fracture toughness of commercial titanium alloys 总被引:2,自引:0,他引:2
M. Niinomi T. Kobayashi I. Inagaki A. W. Thompson 《Metallurgical and Materials Transactions A》1990,21(6):1733-1744
The effect of deformation-induced transformation of metastableβ phase on the ductility and toughness of four commercial titanium alloys was investigated. Tensile tests, Charpy impact tests,
and both static and dynamic fracture toughness tests were carried out at temperatures between 77 and 473 K on four titanium
alloys containing metastableβ phase. Deformation-inducedα″ (orthorhombic martensite) was observed in an (α + β)-type Ti-6Al-2Sn-4Zr-6Mo alloy. The dynamic fracture toughness of this
alloy increased considerably at 223 K compared to those at other temperatures. In another (α + β)-type Ti-6A1-4V alloy, the
static fracture toughness at 123 K and the dynamic fracture toughness at 223 K were increased considerably by the presence
of deformation-induced martensite compared to those at other temperatures. The strength increased as the temperature decreased
in this alloy. An abnormal elongation of aβ-type alloy, Ti-15V-3Al-3Sn-3Cr, at 123 K was attributed to the mechanical twinning of theβ phase. However, the effect of deformation-induced transformation on the fracture toughness of Ti-3Al-8V-6Cr-4Mo-4Zr alloy
was not observed.
Formerly Visiting Associate Professor, Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University,
Pittsburgh, PA.
Formerly with the Department of Production Systems Engineering, Toyohashi University of Technology. 相似文献
2.
P. N. Adler R. L. Schulte E. J. Schneid E. A. Kamykowski F. J. Kuehne 《Metallurgical and Materials Transactions A》1980,11(9):1617-1623
The change in hydrogen concentration as a function of applied strain has been studied in commercial titanium alloys that included
threeβ-phase, twoα-phase, and an (α + β)-phase Ti-6Al-4V alloy with differingα/β morphologies.Insitu measurements were made using a nondestructive nuclear technique on samples for which uniaxial compressive and tensile stresses
were applied by four-point bending.
Theβ-phase alloys exhibited hydrogen redistribution under an elastic stress gradient, but no further change was discernible accompanying
plastic deformation. The extent of hydrogen concentration change for theβ-phase alloys was of the order of 4 to 6 pct for a 620 MPa stress gradient. This is less than would be predicted based on
available data for the partial molal volume of hydrogen. Diffusion coefficients in a stress gradient were also determined
and are consistent with those measured inβ-phase titanium at elevated and room temperatures. Within the experimental sensitivities there was no evidence of hydrogen
redistribution with applied stress for theα-phase and Ti-6Al-4V alloys. 相似文献
3.
The present study compares the fatigue and fracture properties of the high-strength β titanium alloy β-Cez with the conventional α+β titanium alloy Ti-6Al-4V, because of increasing interest in replacing α+β titanium alloys with β titanium alloys for highly stressed airframe and jet engine components. This comparison study includes the Ti-6Al-4V alloy
in an α+ β-processed condition (for a typical turbine blade application) and the β-Cez alloy in two distinctly different α+β-processed and β-processed conditions (optimized for a combination of superior strength, ductility, and fracture toughness). The comparison
principally showed a much lower yield stress for Ti-6Al-4V (915 MPa) than for both β-Cez conditions (1200 MPa). The Ti-6Al-4V material also showed the significantly lower high-cycle fatigue strength (resistance
against crack initiation) of 375 MPa (R=−1) as compared to the β-Cez alloy (∼600 MPa, R=−1). Particularly in the presence of large cracks (>5 mm), the fatigue crack growth resistance and fracture toughness of
the Ti-6Al-4V material is superior when compared to both β-Cez conditions. However, for small crack sizes, the conditions of both the alloys under study show equivalent resistance
against fatigue crack growth. For the β-Cez material, where microstructures were optimized for high fracture toughness (conventional large crack sizes) by thermomechanical
processing, maximum K
Ic-values of 68 MPa√m of the β-processed β-Cez condition (tested in the longitudinal direction) decreased by ∼50 pct in the presence of small cracks (1 mm). A similar
decrease in fracture toughness was obtained by loading the β-processed β-Cez condition perpendicular to the flat surfaces of the pancake-shaped β grain structure (tested in the short transverse direction). These results were discussed in terms of the effectiveness of
the crack front geometry in hindering crack propagation. Further, the results of this study were considered for alloy selection
and optimized microstructures for fatigue and fracture critical applications. Finally, the advantage of the α+β-processed β-Cez condition in highly stressed engineering components is pointed out because of its overall superior combination of fatigue
crack initiation and propagation resistance (especially against small fatigue cracks). 相似文献
4.
Masoud Atapour Adam L. Pilchak G.S. Frankel James C. Williams 《Metallurgical and Materials Transactions A》2010,41(9):2318-2327
The corrosion behavior of the investment-cast Ti-6Al-4V alloy in 5-pct HCl solution was investigated after gas tungsten arc
welding and friction stir (FS) processing. The FS-processed samples exhibited superior corrosion behavior compared with the
base metal and the arc-welded samples. The inferior corrosion resistance of the arc weldment was attributed to the acicular
α and β microstructure and the alloying element partitioning between the phases. This was confirmed by scanning electron microscopy
evaluations of the surface of specimens that had been immersed 50 hours in 20-pct HCl at 308 K (35 °C). In addition, the results
indicated that vanadium as an alloying element has a detrimental effect on the corrosion performance of Ti-6Al-4V alloy in
an HCl solution. 相似文献
5.
D. A. Meyn 《Metallurgical and Materials Transactions B》1974,5(11):2405-2414
The fracture toughness and resistance to inert-environment sustained load crack propagation of α-β titanium alloys are usually reduced by increased hydrogen contents. The range of hydrogen contents over which either fracture
toughness or threshold stress intensity for sustained load cracking was observed to decrease with hydrogen content is small
(0 to 50 ppm) for Ti-6 Al-4 V, but further increases in hydrogen content can cause an increase in cracking rates. Sustained
load crack propagation is characterized by a mixture of microvoid coalescence with cleavage, usually on a plane 12 to 15 deg
from {0001} of the hep α phase with some {000l} cleavage. Cleavage apparently initiates ahead of the main crack front within
a grains, usually near apparent α-β interfaces. Atmospheric moisture is inert with respect to sustained load cracking, that is, it does not cause stress corrosion
cracking. Sustained load cracking was demonstrated in Ti-8 Al-1 Mo-1 V, Ti-6 Al-6 V-2 Sn, and several grades of Ti-6 Al-4
V. 相似文献
6.
Shibayan Roy Vedavyas Tungala Satyam Suwas 《Metallurgical and Materials Transactions A》2011,42(9):2535-2541
In the present study, the β transus of boron-modified Ti-6Al-4V alloy was found to be almost equivalent to that of the normal alloy, although there is
a difference in interstitial element content large enough to produce significant change. Compositional analysis confirms the
scavenging ability of the boride particles that are present in the microstructure toward the interstitial elements. This factor
can successfully retard the α → β phase transformation locally and increase the overall β transus of boron-added material. 相似文献
7.
8.
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
9.
Observations have been made of cracking which develops after small plastic strains in the Ti-6Al-2Sn-4Zr-6Mo and Ti-6A1-4V
alloys at α-@#@ β interfaces, and a long slip band in α. Hydrogen and surface stresses and heat treat condition,i.e., solution treated or solution treated and aged have been ruled out. Cracking is attributed to intense slip commencing at
the α-@#@ β interfaces, and progressing into the α, or at martensite-matrix interfaces. 相似文献
10.
M. C. Brandes M. J. Mills J. C. Williams 《Metallurgical and Materials Transactions A》2010,41(13):3463-3472
The mechanical performance of engineering titanium alloys has long been known to be sensitive to the nature of applied load
waveform. Sustained load hold periods imposed during the fatigue loading of two-phase α + β alloys are detrimental to material performance. A number of factors, particularly material texture, phase morphologies, and
slip behavior, are thought to affect the dwell fatigue responses of these materials. This study examines the roles of slip
character and applied load waveform on an alloy with a simpler microstructure than the two-phase alloys studied previously.
It is found that planar slip has significant influence over the dwell, fatigue, and fracture behaviors of equiaxed-grained,
single-phase α Ti-7 wt pct Al. 相似文献
11.
The strong dependence of the superplastic behavior of metals and alloys on grain size has been demonstrated, and it is now
well known that a fine grain size is normally a requirement for superplasticity. However, the microstructure of certain alloy
systems such as Ti-6A1-4V cannot always be adequately characterized by a single parameter such as grain size. In two-phase
α β alloys such as Ti-6A1-4V, other microstructural parameters such as volume fractions of the two phases, grain aspect ratio,
grain size distribution and crystallographic texture may also influence superplasticity. For example, if “grain switching”
is an important deformation mechanism in superplastic flow as suggested by Ashby and Verall, then factors such as grain aspect
ratio and range of grain sizes would be expected to have an effect on superplastic behavior. In this study, these microstructural
features were determined for several different heats of Ti-6Al-4V, and the corresponding superplastic properties were evaluated
in terms of their fully characterized microstructure. The flow stress as a function of strain rate, strain rate sensitivity
exponent (m) as a function of strain rate and total elongation on properties were found to be strongly influenced by microstructural
parameters such as grain aspect ratios, grain size and grain size distribution. 相似文献
12.
The relationship between heat-treatment parameters and microstructure in titanium alloys has so far been mainly studied empirically,
using characterization techniques such as microscopy. Calculation and modeling of the kinetics of phase transformation have
not yet been widely used for these alloys. Differential scanning calorimetry (DSC) has been widely used for the study of a
variety of phase transformations. There has been much work done on the calculation and modeling of the kinetics of phase transformations
for different systems based on the results from DSC study. In the present work, the kinetics of the β ⇒ α transformation in a Ti-6Al-4V titanium alloy were studied using DSC, at continuous cooling conditions with constant cooling
rates of 5 °C, 10 °C, 20 °C, 30 °C, 40 °C, and 50 °C/min. The results from calorimetry were then used to trace and model the
transformation kinetics in continuous cooling conditions. Based on suitably interpreted DSC results, continuous cooling-transformation
(CCT) diagrams were calculated with lines of isotransformed fraction. The kinetics of transformation were modeled using the
Johnson-Mehl-Avrami (JMA) theory and by applying the “concept of additivity.” The JMA kinetic parameters were derived. Good
agreement between the calculated and experimental transformed fractions is demonstrated. Using the derived kinetic parameters,
the β ⇒ α transformation in a Ti-6Al-4V alloy can be described for any cooling path and condition. An interpretation of the results
from the point of view of activation energy for nucleation is also presented. 相似文献
13.
Bing Ye Marc R. Matsen David C. Dunand 《Metallurgical and Materials Transactions A》2012,43(1):381-390
A powder-level, finite-element model is created to describe densification, as a function of applied stress during uniaxial
hot pressing, of CP-Ti and Ti-6Al-4V powders with spherical or spheroidal shapes for various packing geometries. Two cases
are considered: (1) isothermal densification (in the α- or β-fields of CP-Ti and in the β-field of Ti-6Al-4V) where power-law creep dominates and (2) thermal cycling densification (across the α/β-phase transformation of Ti-6Al-4V) where transformation mismatch plasticity controls deformation at low stresses. Reasonable
agreement is achieved between numerical results and previously published experimental measurements and continuum modeling
predictions. 相似文献
14.
15.
Ji Sik Kim Young Won Chang Chong Soo Lee 《Metallurgical and Materials Transactions A》1998,29(1):217-226
A study has been made to investigate boundary sliding and its accommodation mode with respect to the variation of grain size
and α/β volume fraction during superplastic deformation of a two-phase Ti-6Al-4V alloy. A load relaxation test has been performed
at 600 °C and 800 °C to obtain the flow stress curves and to analyze the deformation characteristics by the theory of inelastic
deformation. The results show that grain matrix deformation (GMD) is found to be dominant at 600 °C and is well described
by the plastic state equation. Whereas, at 800 °C, phase/grain boundary sliding (P/GBS) becomes dominant and is fitted well
with the viscous flow equation. The accommodation mode for fine-grained microstructures (3 μm) well agrees with the isostress model, while that for large-grained structures (11 μm) is a mixed mode of the isostress and isostrain-rate models. The sliding resistance analyzed for the different boundaries
is lowest in the α/β boundary, and increases on the order of α/β≪α/α≈β/β, which plays an important role in controlling the superplasticity of the alloys with various α/β phase ratios. 相似文献
16.
I. A. Akmoulin M. Niinomi T. Kobayashi 《Metallurgical and Materials Transactions A》1994,25(8):1655-1666
The effect of stability of the body-centered cubic (bcc) β phase on the dynamic fracture behavior of Ti-6Al-4V alloy at room
temperature and 77 K has been studied. The presence of a highly unstable β phase in the quenched alloy leads to a decrease
in both the dynamic fracture toughness and the crack propagation energy, and this decrease bccomes more pronounced when test
temperature is reduced to 77 K. Somewhat improved fracture characteristics were obtained by applying anneal procedure to receive
a fully stable β phase. The highest fracture toughness as well as the greatest crack propagation resistance were observed
in the air-cooled grade, where the lattice parameter of the bcc phase was intermediate between those pertaining to quenched
and annealed Ti-6Al-4V alloys. The effect is attributed to the vanadium content in the β phase, which is sufficiently high
to suppress deformation-induced transformation. On the other hand, the V content should be low enough to retard ductile-brittle
transition, typical for the bcc metals at cryogenic temperatures. As a result, marked toughening can be achieved, so that
the lowest application temperature of high-strength titanium alloys containing the bcc phase can be decreased significantly.
Formerly Assistant Professor, Department of Production Systems Engineering, Toyohashi University of Technology 相似文献
17.
Hiroaki Matsumoto Sadao Watanabe Naoya Masahashi Shuji Hanada 《Metallurgical and Materials Transactions A》2006,37(11):3239-3249
The Young’s modulus of Ti-V and Ti-V-Sn alloys quenched from the β-phase region after solution treatment and cold rolling
was investigated in relation to alloy compositions, microstructures, and constituent phases. The composition dependence of
the Young’s modulus for quenched Ti-V binary alloys shows two minima of 69 GPa at Ti-10 mass pct V and 72 GPa at Ti-26 mass
pct V. Between the two compositions, athermalω or stress-induced ω is introduced in retainedβ phase and increases Young’s modulus. That is, a low Young’s modulus is attained unless alloys undergoω transformation. In Ti-5 and -8 mass pct V, which under goα′ (hcp) martensitic transformation on quenching, the Young’s modulus further decreases by cold rolling, which can be reasonably
explained by the formation ofα′ rolling texture. Comparing Young’s modulus in Ti-V binary alloy with that in Ti-Nb binary alloy, it is found that Young’s
modulus is remarkably increased by athermal- or stress inducedω phase, and it shows a minimum when both martensitic andω transformation are suppressed during quenching in metastableβ alloys. The Sn addition to Ti-V binary alloy retards or suppresses athermal and stress-inducedω transformation, thereby decreasing Young’s modulus. Young’s modulus exhibits minimum values of 51 GPa in quenched (Ti-12
pct V)-2 pct Sn and of 57 GPa in cold-rolled (Ti-12 pct V)-6 pct Sn. 相似文献
18.
The near-α titanium alloy Ti-6Al-5Zr-0.5Mo-0.25Si has been rolled in the β- and (α+β)-phase fields. Texture studies have been performed on each of these materials in the as-rolled condition after air cooling
from the finish rolling pass, with a view to examining the transformation texture β/(α+β)→α. One of the materials from each of the β and (α+β) rolled conditions has been heat treated in the β-phase field and air cooled (AC) to α phase in order to study the nature of the α → β → α transformation texture. Results indicate that transformation textures of the α phase are significantly different for both the β as well as the (α+β) rolling conditions. Heat treatment of secondary (transformed) α in the β-phase field and its further cooling to α phase leads to relatively weak texture for the β rolled materials. The results have been discussed in relation to the microstructural features and consequent variant selections
and have been correlated with those observed in titanium and its alloys. 相似文献
19.
20.
J. R. Kennedy P. N. Adler H. Margolin 《Metallurgical and Materials Transactions A》1993,24(12):2763-2771
The effect of alloy composition on hydrogen activity was measured for seven titanium alloys as a means to determine the tendency
for hydrogen migration within dissimilar metal welds. The alloys were: Ti-CP, Ti-3A1-2.5V, Ti-3Al-2.5V-3Zr, Ti-3Al-2Nb-lTa,
Ti-6A1, Ti-6A1-4V, and Ti-6Al-2Nb-lTa-0.8Mo. Hydrogen pressure-hydrogen concentration relationships were determined for temperatures
from 600 ‡C to 800 ‡C and hydrogen concentrations up to approximately 3.5 at. pct (750 wppm). Fusion welds were made between
Ti-CP and Ti-CP and between Ti-CP and Ti-6A1-4V to observe directly the hydrogen redistribution in similar and dissimilar
metal couples. Hydrogen activity was found to be significantly affected by alloying elements, particularly Al in solid solution.
At a constant Al content and temperature, an increase in the volume fraction ofΒ reduced the activity of hydrogen in α-@#@ Β alloys. Activity was also found to be strongly affected by temperature. The effect of temperature differences on hydrogen
activity was much greater than the effects resulting from alloy composition differences at a given temperature. Thus, hydrogen
redistribution should be expected within similar metal couples subjected to extreme temperature gradients, such as those peculiar
to fusion welding. Significant hydrogen redistribution in dissimilar alloy weldments also can be expected for many of the
compositions in this study. Hydride formation stemming from these driving forces was observed in the dissimilar couple fusion
welds. In addition, a basis for estimating hydrogen migration in titanium welds, based on hydrogen activity data, is described. 相似文献