U.S. patent application number 16/607592 was filed with the patent office on 2020-05-14 for titanium alloy-based sheet material for low-temperature superplastic deformation.
This patent application is currently assigned to The Boeing Company. The applicant listed for this patent is The Boeing Company Public Stock Company VSMPO-AVISMA Corporation. Invention is credited to Alexander Berestov, Robert D. Briggs, Michael Leder, Natalia G. Mitropolskaya, Igor Puzakov, Natalia Tarenkova.
Application Number | 20200149133 16/607592 |
Document ID | / |
Family ID | 63918626 |
Filed Date | 2020-05-14 |
United States Patent
Application |
20200149133 |
Kind Code |
A1 |
Leder; Michael ; et
al. |
May 14, 2020 |
TITANIUM ALLOY-BASED SHEET MATERIAL FOR LOW-TEMPERATURE
SUPERPLASTIC DEFORMATION
Abstract
Herein disclosed includes the manufacture of sheets from a
titanium alloy having a chemical composition efficiently balanced
with manufacturability based on known conventional manufacturing
techniques for finished products exhibiting low temperature
superplastic forming properties. The result is achieved by a sheet
material for low temperature superplastic made of titanium alloy
with the following content of element by % wt.: 4.5-5.5Al,
4.5-5.5V, 0.1-1.0Mo, 0.8-1.5Fe, 0.1-0.5Cr, 0.1-0.5Ni, 0.16-0.25O,
remainder is titanium and residual elements and having molybdenum
structural equivalent [Mo]eqiv.>5 and aluminum structural
equivalent [Al]equiv.<8; the equivalent values are calculated
from the expressions:
[Mo]eqiv.=[Mo]+[V]/1.5+[Cr].times.1.25+[Fe].times.2.5+[Ni]/0.8
[Al]eqiv.=[Al]+[O].times.10+[Zr]/6.
Inventors: |
Leder; Michael; (Verkhnyaya
Salda, RU) ; Puzakov; Igor; (Verkhnyaya Salda,
RU) ; Tarenkova; Natalia; (Verkhnyaya Salda, RU)
; Berestov; Alexander; (Verkhnyaya Salda, RU) ;
Mitropolskaya; Natalia G.; (Moscow, RU) ; Briggs;
Robert D.; (Auburn, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Boeing Company
Public Stock Company VSMPO-AVISMA Corporation |
Chicago
Verkhnyaya Salda, Sverdlovsk Region |
IL |
US
RU |
|
|
Assignee: |
The Boeing Company
Chicago
IL
Public Stock Company VSMPO-AVISMA Corporation
Verkhnyaya Salda, Sverdlovsk Region
|
Family ID: |
63918626 |
Appl. No.: |
16/607592 |
Filed: |
April 25, 2017 |
PCT Filed: |
April 25, 2017 |
PCT NO: |
PCT/RU2017/000266 |
371 Date: |
October 23, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/183 20130101;
C22C 14/00 20130101 |
International
Class: |
C22C 14/00 20060101
C22C014/00; C22F 1/18 20060101 C22F001/18 |
Claims
1-5. (canceled)
6. Sheet material for low temperature superplastic forming made of
titanium alloy with the following content of element by % wt.:
4.5-5.5Al, 4.5-5.5V, 0.1-1.0Mo, 0.8-1.5Fe, 0.1-0.5Cr, 0.1-0.5Ni,
0.16-0.25O, remainder is titanium and residual elements, having
molybdenum structural equivalent [Mo]eqiv.>5 and aluminum
structural equivalent [Al]equiv.<8; the equivalent values are
calculated from the expressions:
[Mo]eqiv.=[Mo]+[V]/1.5+[Cr].times.1.25+[Fe].times.2.5+[Ni]/0.8
[Al]eqiv.=[Al]+[O].times.10+[Zr]/6.
7. Sheet material for low temperature superplastic forming of claim
1 with the structure consisting of grains with the size below 8
.mu.m.
8. Sheet material for low temperature superplastic forming of claim
1 exhibiting superplastic properties at a temperature of
775.+-.10.degree. C.
9. Sheet material for low temperature superplastic forming of claim
1 exhibiting at a temperature of 775.+-.10.degree. C.
.alpha./.beta. phase ratio from 0.9 to 1.1.
10. Sheet material for low temperature superplastic forming of
claim 1 with the amount of alloying elements diffusible between
.alpha.- and .beta.-phases during SPF process equal to 0.5% minimum
and which is determined from the following relation: where:
Q=.SIGMA..sub.j=1.sup.n|.DELTA.m|.gtoreq.0.5% wt. Q--amount of
diffusible alloying elements in the material during SPF, % wt.,
n--amount of alloying elements in the material,
|.DELTA.m|--absolute variation value of alloying element content in
.beta.- and .alpha.-phases, % wt. during SPF process,
|.DELTA.m|--is calculated from the formula:
|.DELTA.m|=(m.beta.1-m.alpha.1)-(m.beta.2-m.alpha.2), % wt. where:
m.beta.1--content of alloying element in .beta.-phase before SPF, %
wt., m.beta.2--content of alloying element in .beta.-phase after
SPF, % wt., m.alpha.1--content of alloying element in .alpha.-phase
before SPF, % wt., m.alpha.2--content of alloying element in
.alpha.-phase after SPF, % wt.
11. Sheet material for low temperature superplastic forming of
claim 1, wherein iron is present in an amount of 1.0% to 1.5%.
12. Sheet material for low temperature superplastic forming of
claim 1, wherein said sheet material has a thickness of about 2
mm.
13. Sheet material for low temperature superplastic forming of
claim 1, wherein said sheet material is used to make a
semi-finished aerospace product having grain size over 2 .mu.m.
14. Sheet material for low temperature superplastic forming of
claim 1, wherein said sheet material is in the form of a bar, tube,
section, open- and close-dye forging, plate, sheet, strip or
foil.
15. Sheet material for low temperature superplastic forming of
claim 1, wherein said sheet material is used in a structure used in
one of an airborne vehicle, a rocket or a medical implant.
Description
FIELD
[0001] Disclosed herein are materials and products, such as sheet
materials, and sheet semi-products, such materials and products
comprising titanium alloys, the materials being suitable for
product fabrication by methods including low temperature
superplastic forming (SPF) at a temperature of 775.degree. C. The
materials and products can be used as cost-effective options to
sheet products made of Ti-6Al-4V alloy.
BACKGROUND
[0002] The term "superplastic forming" is generally applicable to a
process in which a material (alloy) is being superplastically
formed under exceeded conventional limit of plastic strain (over
500%). SPF may be applied to certain materials exhibiting
superplastic properties within the limited ranges of temperatures
and strain rates. For example, titanium alloy sheets are normally
able to undergo superplastic forming (deformation) within the
temperature range of about 900 to 1010.degree. C. at the strain
rate of about 310.sup.-4 s.sup.-1.
[0003] From a production point of view, as a result of a decrease
in forming temperatures at SPF, significant advantages may be
gained. For example, a decrease in the SPF forming temperature may
result in a reduction of die cost, an increase of its life and may
potentially lead to an introduction of less expensive steel dyes.
Additionally, formation of an oxygen-rich layer (alpha case) and
scale may be mitigated, thus improving product yield and reducing
or eliminating the requirement of chemical etching. Additionally,
the advantage of retaining the presence of finer grains after
completion of SPF operations may result in lower deformation
temperatures, which may lead to restrain in grain growth.
[0004] Currently, there are two known approaches to improvement of
superplastic forming capability of sheet material from titanium
alloys. The first approach involves developing special-purpose
thermomechanical processing to produce fine grains with sizes just
between 2 .mu.m and 1 .mu.m and finer, thus resulting in
enhancement of grain boundary sliding. In particular, there is a
known method of manufacture of a sheet for deformation at the
temperature lower than that of conventional products formed from
Ti-6Al-4V material (Patent RF No. 2243833, IPC B21B1/38, published
10 Jan. 2005).
[0005] The second approach involves developing of new system of
titanium alloy sheet materials exhibiting superplasticity at
coarser material granularity because of: [0006] enhancement of two
phase volume fraction and morphology, [0007] faster diffusion
process which speeds up grain boundary sliding due to the content
of, i.e., Fe and Ni in the alloy as fast diffusers. [0008] lower
beta transus temperature (BTT).
[0009] Thus, in case of efficient selection of an alloy chemical
makeup it is possible to obtain satisfactory superplastic forming
(deformation) properties at low temperature without any use of
special-purpose processing techniques required for ultrafine grains
formation.
[0010] Two-phase (.alpha.+.beta.)-titanium alloys, depending on the
level of alloying elements addition, are classified as alloys
having molybdenum structural equivalents--[Mo]equiv.--equal to 2.5
up to 10%. (Kolachev B. A., Polkin I. S., Talalayev V. D. Titanium
alloys of various countries: Reference book. Moscow. VILS. 2000.
316 p.-p. 13-16). Such alloys are usually being alloyed with
aluminum and .beta.-stabilizers to retain the .beta.-phase. The
amount of .beta.-phase may vary from 5% to 50% in as-annealed
alloys belonging to this group. Therefore, mechanical properties
change over relatively wide range. These alloys had widespread use
in both Russia and foreign countries, in particular, Ti-6Al-4V
alloy due to successful addition of alloying elements. (Materials
Properties Handbook: Titanium Alloys. R. Boyer, G. Welsch, E.
Collings. ASM International, 1998. 1048 p.-p. 486-488). In this
alloy, the aluminum tends to increase the strength and heat
resisting properties, whereas the vanadium is among one of the few
elements that increases not only strength properties, but also
improves plasticity. Alloys belonging to Ti-6Al-4V group are used
to produce bars, tubes, sections, open- and close-dye forgings,
plates, sheets, strips and foil. They are used for fabrication of
welded and prefabricated structures in airborne vehicles, a number
of aviation and rocketry structural components, as well as for
fabrication of medical implants to be applied in traumatology,
orthopedics and odontology.
[0011] There is a known method of manufacture of titanium alloy
sheet semi-products suitable for low temperature superplastic
forming from VT5 alloy which is an analog of Ti-6Al-4V alloy
(Patent RF No. 2224047, IPC C22F1/18, B21B3/00, published 20 Feb.
2004). The method allows for the manufacture of titanium alloy
sheet semi-products having uniform submicrocrystalline structure
(grain size is below 1 .mu.m) suitable for low temperature
superplastic forming. The method can be costly, low-efficient and
require availability of special-purpose equipment.
[0012] Ti-6Al-4V alloy has been known to have a
sub-microcrystalline structure produced by severe plastic
deformation (SPD) with the use of all-round forging technique and
exhibiting superplastic properties. The alloy microstructure is
defined by .alpha.- and .beta.-phase grains and subgrains having an
average size of 0.4 .mu.m, high level of crystal lattice internal
stresses and elastic distortions as evidenced by non-uniform
diffraction contrast, and high density of dislocations on images of
the structure obtained by electron microscopy. (S. Zherebtsov, G.
Salishchev, R. Galeyev, K. Maekawa, Mechanical properties of
Ti-6Al-4V titanium alloy with submicrocrystalline structure
produced by severe plastic deformation.//Materials Transactions.
2005; V. 46(9): 2020-2025). To manufacture sheet semi-products from
this alloy, non-intensive and low-cost SPD operations with the use
of all-round forging technique are required that significantly
increase finished product value.
[0013] There is a known method of manufacture of thin sheets from
two-phase titanium alloy and for fabrication of products out of
said sheets. The method involves manufacture of sheet semi-products
from the alloy with the following content of element by % wt.:
3.5-6.5 Al, 4.0-5.5 V, 0.05-1.0 Mo, 0.5-1.5 Fe, 0.10-0.2 O,
0.01-0.03 C, 0.005-0.07 Cr, 0.01-0.5 Zr, 0.001-0.02 N, remainder is
titanium; at that chemical composition is adjusted with the values
of aluminum [Al].sub.equiv..sup.str.=6.0-11.55 and molybdenum
[Mo].sub.equiv..sup.str.=3.5-5.6 strength equivalents (Patent RF
No. 2555267, IPC C22F1/18 B21B3/00, published 10 Jul.
2015)--prototype.
[0014] Sheet semi-products with the thickness of <3 mm
manufactured within the patent may not be suitable for industrial
production due to the low stability of properties required for SPF.
The reason is that the use of strength equivalents as adjusters of
the alloy chemical composition does not allow the adjustment
required and appropriate relations between alloying elements in the
alloy and structural properties of the alloy required for
performance of SPF operations with sheet semi-products. Besides
that, the presence of Si and Zr in the alloy may form silicides on
the grain surfaces thereby hindering intergranular sliding and
resulting in process instability.
SUMMARY
[0015] Disclosed herein is manufacture of (.alpha.+.beta.)-titanium
alloy sheet material with the ability to lower temperature
superplastic forming with the grain size exceeding 2 .mu.m. The
sheet material exhibits stable properties and, in examples, is a
cost-effective option to sheet semi-products made of Ti-6Al-4V
alloy with finer grains.
[0016] Disclosed herein is the manufacture of sheets from titanium
alloy having chemical composition efficiently balanced with
manufacturability based on known conventional manufacturing
techniques for finished products exhibiting low temperature
superplastic forming properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1 and 2 show the alloys structure in initial
condition.
[0018] FIGS. 3, 4 and 5 are loading curves obtained during SPF.
[0019] FIG. 6 is a graph showing true stress vs. strain curve at
strain degree of 0.2 and 1.1 (in longitudinal direction) depending
on [Mo]equiv.
DETAILED DESCRIPTION
[0020] Examples of sheet material for low temperature superplastic
forming can made of titanium alloy with the following content of
element by % wt.: 4.5-5.5Al, 4.5-5.5V, 0.1-1.0Mo, 0.8-1.5Fe,
0.1-0.5Cr, 0.1-0.5Ni, 0.16-0.25O, remainder is titanium and
residual elements and having molybdenum structural equivalent
[Mo]eqiv.>5 and aluminum structural equivalent [Al]equiv.<8;
the equivalent values are calculated from the expressions:
[Mo]eqiv.=[Mo]+[V]/1.5+[Cr].times.1.25+[Fe].times.2.5+[Ni]/0.8
[Al]eqiv.=[Al]+[O].times.10+[Zr]/6.
[0021] Sheet material for low temperature superplastic forming has
the structure consisting of grains with the size below 8 .mu.m.
[0022] Sheet material for low temperature superplastic forming may
exhibit superplastic properties at a temperature of
775.+-.10.degree. C.
[0023] Sheet material for low temperature superplastic forming at a
temperature of 775.+-.10.degree. C. exhibits .alpha./.beta. phase
ratio from 0.9 to 1.1.
[0024] Sheet material for low temperature superplastic forming with
the amount of alloying elements diffusible between .alpha.- and
.beta.-phases during SPF process equal to 0.5% minimum and which is
determined from the relation:
Q=.SIGMA..sub.j=1.sup.n|.DELTA.m|.gtoreq.0.5% wt.
where: [0025] Q--amount of diffusible alloying elements in the
material during SPF, % wt. [0026] n--amount of alloying elements in
the material, [0027] |.DELTA.m|--absolute variation value of
alloying element content in .beta.- and .alpha.-phases, % wt.
during SPF process. [0028] |.DELTA.m|--is calculated from the
formula:
[0028] |.DELTA.m|=(m.beta.1-m.alpha.1)-(m.beta.2-m.alpha.2), %
wt.
where: [0029] m.beta.1--content of alloying element in .beta.-phase
before SPF, % wt., [0030] m.beta.2--content of alloying element in
.beta.-phase after SPF, % wt., [0031] m.alpha.1--content of
alloying element in .alpha.-phase before SPF, % wt., [0032]
m.alpha.2--content of alloying element in .alpha.-phase after SPF,
% wt.
[0033] The provided sheet material, in examples herein, exhibits a
set of high processing and structural properties. This is achieved
by efficient selection of alloying elements and their ratio in the
material alloy.
[0034] Group of .alpha.-stabilizers.
[0035] Aluminum, which is used in substantially all commercial
alloys, is the most efficient strengthener and improves the
strength and heat resisting properties of titanium. Oxygen
increases the temperature of titanium allotropic transformation.
The presence of oxygen within the range of between 0.16% to 0.25%
increases the strength of the alloy and does not have a significant
negative impact on plasticity.
[0036] Group of .beta.-stabilizers (V, Mo, Cr, Fe, Ni) are widely
used in commercial alloys.
[0037] Vanadium in the amount of 4.5% to 5.5%, iron in the amount
of 0.8% to 1.5% and chromium in the amount of 0.1% to 0.5% increase
the alloy strength and have relatively little or no negative impact
on plasticity.
[0038] Introduction of molybdenum ranging between 0.1% to 1.0%
ensures its almost complete to complete dissolution in
.alpha.-phase, thus the required strength properties may be
achieved, in examples, with little to no negative impact on plastic
properties.
[0039] The provided alloy contains iron in the amount of 0.8% to
1.5, or 1.0% to 1.5% and nickel in the amount of 0.1% to 0.5%.
These elements are the most diffusible .beta.-stabilizers that have
a positive impact on intergranular sliding at SPF.
[0040] Among structural factors having an impact on SPF efficiency,
the first to be distinguished is the size of grain which is not to
exceed 8 .mu.m (experimental data) for the provided material.
[0041] It is known that superplastic flow of material may occur due
to phase transformations in two-phase titanium alloys provided that
.alpha./.beta. phase ratio at SPF temperature is close to 1
(Kaibyshev O. Superplastic properties of commercial alloys. Moscow.
Metallurgy. 1984. p. 179-218.). This facilitates formation of
equiaxial structure which contributes to intergranular sliding. The
driving force of structural spheroidizing is the trend of surface
energy degradation. The growth of intergranular boundary due to
increase of .beta.-phase results in a change of surface energy
level at the intergranular boundary that, in turn, results in
activation of spheroidizing. In order to have the required amount
of .beta.-phase during SPF process at .alpha./.beta. ratio close to
1, the value of molybdenum structural equivalent [Mo]equiv. shall
be greater than 5 and the value of aluminum structural equivalent
[Al]equiv. shall not exceed 8. Besides that aluminum equivalent
value above that stated above results in BTT increase and
consequently to increase of SPF temperature.
[0042] Optimum temperature to effect superplastic properties of the
provided material equals 775.+-.10.degree. C.
[0043] The amount of alloying elements diffusible between .alpha.-
and .beta.-phases shall not be less than 0.5%. This is due to the
fact that the activation energy of grain-boundary diffusion is less
than the activation energy of volume diffusion, and the diffusion
transport of atoms is being carried out at grain boundaries. Those
areas of grain boundaries being influenced by normal tension stress
and exhibit increased concentration of vacancies. Those areas being
influenced by compressive stress exhibit less concentration of
vacancies: resulting in a difference in concentrations causing
direct diffusion of vacancies. Since migration of vacancies
involves interchange with atoms, the latter will move in opposite
direction thus causing intensification of intergranular
sliding.
Examples
[0044] For investigation purposes, sheet semi-products having
thickness of 2 mm were used. To manufacture sheet materials, six
experimental alloys of various chemical compositions given in Table
1 were melted.
[0045] Sheet materials of 2 mm thick were manufactured against
known method of manufacture and intended for superplastic forming.
Before being tested for superplastic properties, the materials were
subject to annealing at a temperature of 720.degree. C. during 30
minutes and then subjected to subsequent air cooling. After the
processing steps were completed, samples were taken from the sheets
in longitudinal and transverse direction for tensile strength
testing at room and elevated temperatures, and then the samples
were subjected to typical testing at room temperature to determine
strength, elastic and plastic properties.
TABLE-US-00001 TABLE 1 Chemical Composition of Sheet Materials
under Investigation Heat Chemical Composition No. Al Mo V Cr Fe Ni
O [Al]equiv [Mo]equiv 1 top 5.42 0.31 4.92 0.18 0.87 0.017 0.152
6.83 6.03 bottom 5.2 0.34 4.69 0.16 0.76 0.017 2 top 4.05 0.11 4.09
0.12 0.85 0.017 0.147 5.54 5.19 bottom 4.09 0.1 4.04 0.11 0.76
0.016 3 top 5.03 0.42 5.06 0.28 1.25 0.017 0.140 6.39 7.26 bottom
4.95 0.36 4.87 0.23 1.14 0.017 4 top 5.13 0.43 5.15 0.27 1.24 0.30
0.160 6.66 7.67 bottom 4.99 0.41 4.9 0.24 1.14 0.29 5 top 5.07
0.0032 5.18 0.27 1.26 0.02 0.146 6.54 6.93 bottom 5.09 0.0015 4.96
0.24 1.11 0.018 6 top 5.18 0.42 5.06 0.01 1.22 0.016 0.138 6.53
6.89 bottom 5.12 0.38 4.79 0.012 1.13 0.018
[0046] Evaluation of material structure in initial condition (FIG.
1 and FIG. 2) showed that the structure is similar to equiaxial
structure and predominantly consists of alternating grains of
.alpha.- and .beta.-phases that look like darker (.alpha.) or
lighter (.beta.) elements. It should be noted that with increase of
[Mo]equiv in the alloy, volume fraction of .beta.-phase grain tends
to increase from estimated .alpha./.beta. ratio of 2/1 in Alloy 2
up to the value approaching to 1/1 in Alloy 3 and Alloy 4. Average
size of phase grains measured on microstructure photographs by
intercept method tends to increase some with the increase of
[Mo]equiv. and is within the range of 2.8 to 3.8 .mu.m (minimum
grain size is determined for Alloy 2). It should be noted that
grain structure of Material 1 in initial condition is less uniform
compared with other experimental alloys. Besides equiaxed grains,
Material 1 demonstrates areas consisting of sufficiently bulk
elongated grains. It also can be noted that morphology of
.beta.-phase varies in some way from alloy to alloy. Alloy 2 has
minimum amount of alloying elements and .beta.-phase is
predominantly located as individual groups between .alpha.-phase
particles; but beginning from Alloy 5 .beta.-phase has definite
coherency and besides grain texture it is shaped as relatively thin
layers between .alpha.-phase grains. With [Mo]equiv. increase,
these layers tend to thickening.
Comparative Example
[0047] Comparative analysis of material structure in wrought
(reduced section) and unwrought (head area) conditions after SPF
(at a temperature of 775.degree. C. and strain rate of
3.times.10.sup.-4 s.sup.-1, longwise the sheet) showed that
deformation in reduced section induces some grain growth compared
with almost unwrought head as well as evolution of conglomerates
from .alpha.- and .beta.-phase grains of more complex shapes.
[0048] Evaluation of grain size showed that addition of alloying
elements does not significantly affect the size of phase grains in
alloys with maximum addition of .beta.-stabilizers and it ranges
between 3.5.+-.0.5 .mu.m (unwrought section) and 4.+-.0.5 .mu.m
(wrought section). At the same time in case of Alloy 2 with minimum
content of alloying elements, size of grains in reduced section
increases almost twice up to 5 .mu.m and greater compared with
initial condition.
[0049] By method of electron microprobe analysis (EMPA)
distribution of alloying elements between .alpha.- and
.beta.-phases was examined in the materials under investigation in
initial condition and after testing of superplastic properties; the
examination was performed on wrought reduced section and heads of
longitudinal specimens, the results are given in Tables 2, 3 and
4.
TABLE-US-00002 TABLE 2 Average Chemical Composition of
.quadrature..quadrature.phase (% wt.) in Sheet Materials after
Various Processing based on EMPA results Alloy Al Ti V Cr Fe Ni Mo
Initial Condition 2 4.17 93.00 2.74 0.00 0.10 0.00 0.00 1 5.71
90.79 3.35 0.00 0.15 0.00 0.00 6 5.28 89.48 4.33 0.00 0.65 0.00
0.27 5 6.03 91.67 2.31 0.00 0.00 0.00 0.00 3 5.45 90.77 3.78 0.00
0.00 0.00 0.00 4 5.54 91.01 3.21 0.00 0.24 0.00 0.00 Reduced
Section after SPF in Longitudinal Direction 2 4.32 93.35 2.22 0.00
0.11 0.00 0.00 1 5.72 91.90 2.25 0.07 0.06 0.00 0.00 6 5.49 91.50
2.80 0.00 0.21 0.00 0.00 5 5.30 91.53 3.01 0.00 0.15 0.00 0.00 3
5.61 91.44 2.77 0.00 0.08 0.00 0.10 4 5.77 91.78 2.29 0.00 0.00
0.00 0.16 Reduced Section after SPF in Transverse Direction 2 4.47
93.13 2.40 0.00 0.00 0.00 0.00 1 5.58 91.30 2.87 0.05 0.00 0.11
0.09 3 5.79 91.17 2.74 0.00 0.07 0.12 0.12 4 5.79 91.86 2.27 0.00
0.08 0.00 0.00 Specimen Head after SPF in Longitudinal Direction 2
4.21 92.62 2.99 0.00 0.19 0.00 0.00 1 5.99 91.21 2.51 0.00 0.19
0.09 0.00 6 5.52 91.41 2.71 0.06 0.30 0.00 0.00 5 5.20 89.88 4.22
0.00 0.59 0.11 0.00 3 5.36 91.02 3.19 0.00 0.32 0.11 0.00 4 5.65
91.51 2.51 0.00 0.25 0.08 0.00 Specimen Head after SPF in in
Transverse Direction 2 4.27 93.05 2.40 0.00 0.18 0.00 0.10 1 4.59
89.81 4.64 0.00 0.59 0.26 0.12 3 5.18 90.26 3.93 0.00 0.46 0.00
0.18 4 5.50 91.35 2.87 0.00 0.17 0.00 0.11
TABLE-US-00003 TABLE 3 Average Chemical Composition of
.quadrature..quadrature.phase (% wt.) in Sheet Materials after
Various Processing based on EMPA results Alloy Al Ti V Cr Fe Ni Mo
Initial Condition 2 3.11 88.17 6.91 0.10 1.73 0.00 0.00 1 3.76
84.87 9.04 0.00 1.85 0.00 0.48 6 3.61 85.65 7.19 0.00 2.66 0.00
0.89 5 3.72 84.83 8.28 0.64 2.53 0.00 0.00 3 3.54 84.79 8.43 0.12
2.35 0.00 0.79 4 3.65 85.05 7.67 0.16 2.09 0.66 0.74 Reduced
Section after SPF in Longitudinal Direction 2 2.80 87.72 7.74 0.00
1.74 0.00 0.00 1 3.70 84.58 8.90 0.12 2.06 0.00 0.66 6 3.61 84.34
8.43 0.00 2.79 0.08 0.75 5 3.58 85.44 8.16 0.20 2.55 0.07 0.00 3
3.57 84.99 7.96 0.38 2.37 0.00 0.73 4 3.83 84.46 8.15 0.21 1.91
0.75 0.70 Reduced Section after SPF in Transverse Direction 2 2.72
87.25 7.90 0.00 1.93 0.00 0.20 1 4.00 85.52 7.95 0.00 1.89 0.00
0.64 3 3.99 85.10 7.79 0.29 2.23 0.00 0.61 4 3.81 84.64 8.21 0.13
2.06 0.57 0.59 Specimen Head after SPF in Longitudinal Direction 2
2.79 88.09 7.15 0.00 1.71 0.00 0.27 1 3.96 86.06 7.53 0.14 1.90
0.00 0.40 6 3.70 85.43 7.70 0.00 2.49 0.14 0.54 5 3.82 86.76 7.58
0.00 1.83 0.00 0.00 3 3.66 85.19 7.97 0.08 2.34 0.00 0.76 4 3.77
85.92 7.13 0.28 1.86 0.36 0.69 Specimen Head after SPF in
Transverse Direction 2 2.99 87.68 7.48 0.00 1.86 0.00 0.00 1 3.74
85.20 9.03 0.00 1.78 0.25 0.00 3 3.39 85.65 7.91 0.17 2.29 0.00
0.60 4 3.67 85.52 7.52 0.10 1.92 0.45 0.82
[0050] The amount of diffusible alloying elements in the material
during SPF is determined from the formula:
Q=.SIGMA..sub.j=1.sup.n|.DELTA.m|% wt.
where: [0051] Q--amount of diffusible alloying elements in the
material during SPF, % wt. [0052] n--amount of alloying elements in
the material, [0053] |.DELTA.m|--absolute variation value of
alloying element content in .alpha.- and .beta.-phases, % wt.
during SPF process. [0054] |.DELTA.m|--is calculated from the
formula:
[0054] |.DELTA.m|=(m.beta.1-m.alpha.1)-(m/.beta.2-m.alpha.2), %
wt.
where: [0055] m.beta.1--content of alloying element in .beta.-phase
before SPF, % wt., [0056] m.beta.2--content of alloying element in
.beta.-phase after SPF, % wt., [0057] m.alpha.1--content of
alloying element in .alpha.-phase before SPF, % wt., [0058]
m.alpha.2--content of alloying element in .alpha.-phase after SPF,
% wt.
[0059] Included in Table 4 are calculation data related to the
amount of alloying elements diffusible during SPF process.
[0060] Analysis of change in .alpha.- and .beta.-phases in wrought
sheet materials under investigation demonstrated greater difference
in the alloying elements content between .alpha.- and .beta.-phases
in reduced sections of specimens compared to that in heads of
specimens that were not subject to plastic deformation (Tables 2, 3
and 4).
[0061] The obtained EMPA results were also used for assessment of
phase volume fraction in the material under superplastic properties
test temperature of 775.degree. C. and are given in Table 5.
TABLE-US-00004 TABLE 4 Total difference in variation of alloying
elements Al- content between loy Al Ti V Cr Fe Ni Mo .alpha.- and
.beta.-phases Data on specimen tested in longitudinal direction 2
-0.10 -1.10 1.36 0.00 0.11 0.00 -0.27 1.84 1 0.01 -2.16 1.63 -0.10
0.28 0.09 0.25 2.36 6 -0.06 -1.18 0.63 0.06 0.39 -0.06 0.21 1.41 5
-0.35 -2.98 1.78 0.20 1.16 0.18 0.00 3.67 3 -0.34 -0.62 0.40 0.29
0.28 0.11 -0.13 1.55 4 -0.06 -1.72 1.24 -0.07 0.29 0.46 -0.15 2.27
Data on specimen tested in transverse direction 2 -0.47 -0.51 0.43
0.00 0.25 0.00 0.30 1.45 1 -0.73 -1.18 0.69 -0.05 0.70 -0.10 0.68
2.95 3 0.00 -1.46 1.07 0.12 0.33 -0.12 0.07 1.71 4 -0.15 -1.39 1.29
0.02 0.23 0.12 -0.12 1.93
TABLE-US-00005 TABLE 5 .alpha./.beta. volume fraction at a
temperature of 775.degree. C. based on EMPA results obtained after
completion of testing in different directions (reduced section).
Alloy [Mo]equiv longitudinal transverse average 2 5.19 66/34 70/30
68/32 1 6.03 62/38 62/38 62/38 6 6.89 61/39 -- 61/39 5 6.93 60/40
-- 60/40 3 7.26 58/42 56/44 57/43 4 7.67 46/54 54/46 50/50
[0062] Loading curves obtained during testing are shown in FIGS. 3,
4 and 5.
[0063] Properties of alloys at superplastic testing are given in
Table 6.
[0064] True stress vs. strain curve at strain rates of 0.2 and 1.1
(in longitudinal direction) depending on [Mo]equiv is shown in FIG.
6.
TABLE-US-00006 TABLE 6 True Stress, MPa Longitudinal Transverse
Direction Direction Strain Strain Strain Strain Structural Degree
Degree Degree Degree Equivalents Alloy 0.2 1.1 0.2 1.1 [Al]equiv
[Mo]equiv 2 25.32 27.25 25.01 28.81 5.54 5.19 1 23.22 29.01 24.88
29.11 6.83 6.03 6 20.81 26.08 20.93 26.37 6.53 6.89 5 21.77 26.82
21.06 28.72 6.54 6.93 3 21.82 26.52 21.24 26.83 6.39 7.26 4 19.71
26.78 19.32 27.12 6.66 7.67
[0065] Material 1 (FIG. 3) with the minimum content of alloying
elements has the most unstable SPF process at a temperature of
775.degree. C. that is described by typical waviness of
stress-strain curves caused by formation of floating neck. Such
material behavior at SPF is attributed to relatively bulk initial
grain (over 2.5 .mu.m) which has high growth rate at SPF (up to 5
.mu.m), at that .alpha./.beta. phase ratio (2/1) is not efficient
and leads to activation of intragranular sliding which is less
preferable for SPF instead of efficient intergranular slipping.
[0066] Material 2 (FIG. 3) has more additions of
.beta.-stabilizers, thus instability of SPF process in form of
stress-strain curve waviness decreased compared with Alloy 1 due to
increase in .beta.-phase volume fraction in the structure. At that,
no significant hardening was noted in the case of strain degree
ranging from 0.6 to 0.8, due to the evolution of dynamic
recrystallization within the areas of incompletely processed
structure (presence of elongated grains) and this is not typical
for all other alloys subjected to investigation.
[0067] Materials 3, 5 and 6 (FIGS. 4, 5) with the maximum content
of .beta.-stabilizers, except for molybdenum (Alloy 5), chromium
(Alloy 6), due to increase in .beta.-phase in the alloys structure
with improved coherence and easier intergranular slipping are
described with stress-strain curves having less waviness compared
with Materials 1 and 2; also hardening becomes more prominent with
the increase of degree of true strain (Table 3, FIG. 6). At that
waviness is retained at degrees of strain of up to 0.6,
specifically at testing in transverse direction that may be
attributed to sheet initial texture as well as with not enough
efficient .alpha./.beta. phase ratio .beta. close to 3 to 2).
Absence of chromium in Material 6 impacts stress-strain curves to
the lesser extent than absence of molybdenum in Material 5 compared
with Material 3. One of the causes may be in the result of a
stronger impact of molybdenum additions on stability of SPF process
compared with chromium addition which is from 2 to 2.5 times
less.
[0068] Material 4 contains maximum amount of .beta.-stabilizers and
is additionally alloyed with 0.3% of nickel; it exhibited more
stable superplastic behavior at a temperature of 775.degree. C. in
both transverse and longitudinal directions, minimum stress at the
beginning of the flow, absence of prominent curve waviness and
monotonic hardening with the increase of strain degree. This is
attributed to almost efficient .alpha./.beta. phase ratio (1/1) at
deformation temperature as well as to maximum content of diffusible
.beta.-stabilizers (nickel, iron) compared with all the alloys
under investigation, thus facilitating mass transport processes at
intergranular slipping (total difference in change of alloying
elements content between .alpha.- and .beta.-phases during SPF
process exceeds 1.9% wt.).
[0069] Among the investigated alloys, Material 4 demonstrated the
best results in full compliance with the material requirements
(Table 7). Tensile tests at constant strain rate and test
temperature of (775.+-.7.degree.) C. (3.times.10.sup.-4 inch/inch/s
of strain) are shown below in Table 7.
TABLE-US-00007 TABLE 7 Longitudinal Direction Transverse Direction
Actual Stress Actual Stress Difference at True Strain Increase in
at True Strain Increase in between (maximum) Actual (maximum)
Actual Longitudinal 0.2 0.9 Stress between 0.2 0.9 Stress between
and Transverse psi psi 0.4 and 0.9 psi psi 0.4 and 0.9 Directions
.ltoreq.600 psi Material 4500 7400 yes 4500 7400 yes yes
Requirements Alloy 4 2859 3884 yes 2802 3934 yes yes
[0070] Comparison of as-annealed sheet mechanical properties is
given in Table 8.
TABLE-US-00008 TABLE 8 Longitudinal Direction Transverse Direction
.sigma..sub.0.2, .sigma..sub.B, .sigma..sub.0.2, .sigma..sub.B,
Material MPa MPa .delta., % MPa MPa .delta., % Material 4 963 999
10.8 988 1017 9.8 Requirements 866 920 8 866 920 8 to Ti--6Al--4V
Material
[0071] The data given in Tables 7 and 8 shows that as a result of
an exemplary embodiment, sheet material was manufactured from
titanium alloy with chemical composition efficiently balanced with
manufacturability based on known conventional manufacturing
techniques for semi-finished products having grain size over 2
.mu.m and compliant with the requirements applicable to aerospace
material.
[0072] It should be noted that the products manufactured in
accordance herein may have various designs. The designs provided in
the description shall be considered as exemplary and not as
limiting ones and the limits of this invention are established by
the provided claims.
* * * * *