U.S. patent application number 10/935934 was filed with the patent office on 2006-01-19 for high strength, oxidation and wear resistant titanium-silicon base alloys and the use thereof.
This patent application is currently assigned to ELKEM ASA NORWEIGAN CORPORATION. Invention is credited to Karl Forwald, Georg Frommeyer, Gunnar Halvorsen, Kai Johansen, Oyvind Mikkelsen, Gunnar Schussler.
Application Number | 20060013721 10/935934 |
Document ID | / |
Family ID | 35013291 |
Filed Date | 2006-01-19 |
United States Patent
Application |
20060013721 |
Kind Code |
A1 |
Frommeyer; Georg ; et
al. |
January 19, 2006 |
High strength, oxidation and wear resistant titanium-silicon base
alloys and the use thereof
Abstract
The present invention relates to high strength, oxidation and
wear resistant titanium-silicon base alloy containing: 2.5-12 wt %
Si 0-5 wt % Al 0-0.5% B 0-2% Cr 0-1 wt % rare earth metals and/or
scandium balance Ti with unavoidable impurities.
Inventors: |
Frommeyer; Georg; (Ekrath,
DE) ; Forwald; Karl; (Kristiansand S, NO) ;
Halvorsen; Gunnar; (Kristiansand S, NO) ; Johansen;
Kai; (Kristiansand S, NO) ; Mikkelsen; Oyvind;
(Kristiansand S, NO) ; Schussler; Gunnar;
(Kristiansand S, NO) |
Correspondence
Address: |
LUCAS & MERCANTI, LLP
475 PARK AVENUE SOUTH
15TH FLOOR
NEW YORK
NY
10016
US
|
Assignee: |
ELKEM ASA NORWEIGAN
CORPORATION
Oslo
NO
|
Family ID: |
35013291 |
Appl. No.: |
10/935934 |
Filed: |
September 8, 2004 |
Current U.S.
Class: |
420/418 |
Current CPC
Class: |
C22C 14/00 20130101 |
Class at
Publication: |
420/418 |
International
Class: |
C22C 14/00 20060101
C22C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2004 |
NO |
NO/20042959 |
Claims
1. High strength, oxidation and wear resistant titanium-silicon
base alloy characterized in that the alloy contains: 2.5-12 wt %Si
0-5 wt % Al 0-0.5% B 0-2% Cr 0-1 wt % rare earth metals and/or
scandium balance Ti with unavoidable impurities.
2. Alloy according to claim 1, characterized in that the alloy
contains 0.3 to 3 wt % Al.
3. Alloy according to claim 1, characterized in that the alloy
contains 0.001-0.15 wt % rare earth metal and/or scandium.
4. Alloy according to claim 1, characterized in that the alloy
contains 0.5 to 2 wt % Cr.
5. Alloy according to claim 1, characterized in that the alloy
contains 0.01 to 0.03 wt % B.
6. Alloy according to claim 1, with near eutectic composition and
related microstructure, characterized in that the alloy contains
6-9 wt % Si 1.2-2.5 wt % Al 0.001-0.15 wt % rare earth metals with
yield strength of more than 700 Mpa at room temperature, fracture
toughness of more than K.sub.IC=15 MPa {square root over (m)}, and
improved wear and oxidation resistance.
7. Alloy according to claim 1, characterized in that the alloy
contains 1.1 to 3 wt. % Al.
Description
FIELD OF INVENTION
[0001] The present invention concerns high strength
silicon-containing titanium-based alloys with optionally additives
of aluminium, boron, chromium, scandium and rare earth metals (Y,
Er, and Ce and La containing misch metal).
BACKGROUND ART
[0002] A variety of two phase .alpha./.beta.-titanium and near
.alpha.-titanium alloys, such as Ti-6Al-4V, IMI 834
(Ti-5.8-Al-4Sn-3Zr-0.7Nb-0.5Mo-0.35Si-0.06C) and TIMET 1100
(Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si) show great potential application in
the air plane and space industry.
[0003] Among them Ti-6Al-4V exhibits the broadest application due
to an optimum combination of high strength and fracture toughness
and excellent fatigue properties at room and elevated temperature.
These alloys have, however, some disadvantages such as a poor
oxidation resistance above 475.degree. C. (.alpha.-case formation),
insufficient creep strength at 600.degree. C. and higher
temperatures and a poor wear resistance at room and elevated
temperatures. The .alpha.-case causes crevice formation on the
oxidised surface and has a detrimental effect on the fatigue
properties. The arc melting process of these relatively high
melting point alloy of about 1660.degree. C.) and the necessary
melt overheating to about 1750 to 1770.degree. C. is a very energy
consuming procedure for the manufacture of investment castings for
the air plane and automotive industry, and engineering purposes in
general.
[0004] Low silicon-containing titanium-based alloys are well known.
Thus JP 2002060871 A describes a titanium alloy containing 0.2-2.3
wt % Si, 0.1-0.7 wt % O (total content oxygen), and 0.16-1.12 wt %
N and 0.001-0.3 wt % B and remainder of titanium including
unavoidable impurities, used for as cast products.
[0005] These are e.g. golf club heads, fishing tackles and medical
components such as tooth root, implants, bone plates, joints and
crowns. The low silicon-containing titanium-based alloy does,
however, suffer from a disadvantage, by forming small needle like
Ti.sub.3Si precipates along grain boundaries, which decrease the
fracture toughness and ductility of this material.
[0006] There is thus a need for an alloy that has a high strength
at high temperatures, has a lower melting point than the Ti--Al--V
alloys and has good casting properties.
DESCRIPTION OF INVENTION
[0007] By the present invention it is provided Ti--Si alloys with
relatively high silicon contents which exhibit a relatively low
melting point due to their eutectic constitution, good casting
properties and high strength at higher temperatures as well as a
very high resistance to oxidation and creep deformation at high
temperatures.
[0008] The present invention thus relates to a Ti--Si alloy
comprising 2.5-12 wt % Si, 0-5 wt % Al, 0-2 wt % Cr, 0-0.5 wt % B,
0-1 wt % rare earth metals and/or Sc, the remaining except for
impurities being Ti.
[0009] According to a preferred embodiment the alloy contains 0.3-3
wt % Al, and more preferably 1.1 to 3 wt % Al.
[0010] According to another preferred embodiment the Ti--Si alloy
contains 6-9 wt % Si and 1.2-2.5 wt % Al.
[0011] A particularly preferred alloy is the eutectic alloy
containing about 8.5 wt % Si.
[0012] According to yet another preferred embodiment the alloy
contains 0.001 to 0.15 wt % rare earth metals and/or scandium.
[0013] It has been found that the addition of rare earth metals or
scandium improves the warm strength and creep strength of the
Ti--Si alloy up to at least 675.degree. C.,
[0014] The rare earths and scandium additions form a fine
dispersion of thermo-dynamically stable oxides, such as
Er.sub.2O.sub.3, Y.sub.2O.sub.3 etc. in the Ti--Si alloy.
[0015] The alloy may further contains 0.1 to 1.5 wt % Cr. The
addition of Cr will enhances solid solution hardening and therefore
increases the strength and will further increase the oxidation
resistance of the alloy.
[0016] In the as cast state, the Ti--Si alloy possesses
fine-grained hypoeutectic, eutectic or slightly hypereutectic
microstructures depending upon the silicon content. The
microstructure of the eutectic Ti--Si alloy consists of finely
dispersed Ti.sub.5Si.sub.3 silicide particles of discontinuous rod
like shape within the hexagonal close-packed .alpha.-Ti(Si) solid
solution matrix. The hypoeutectic microstructure consists of
primary solidified .alpha.-Ti(Si) crystals and the surrounding
eutectic.
[0017] The Ti--Si alloy according to the invention has with a yield
stress of at least 700 MPa, a Brinell hardness of at least 320 HB
and sufficient ductility and fracture toughness -stress intensity
factor K.sub.IC of more than 20 MPa {square root over (m)}.
[0018] The Ti--Si alloy according to the invention further exhibits
excellent oxidation resistance up to 650.degree. C. and above
depending upon the Si content and improved wear resistance both at
room and elevated temperature. The yield strength at 650.degree. C.
will be of at least R.sub.P.sub.0.2.gtoreq.250 MPa and the tensile
strength exceeds R.sub.m=450 MPa.
[0019] The hypereutectic microstructures consist of primary
solidified Ti.sub.5Si.sub.3 crystals of hexagonal shape within the
fine-grained eutectic microstructure.
[0020] In the as cast state the hypoeutectic Ti--Si alloys exhibit
at room temperature fractures toughness--K.sub.IC-values-- of more
than 20 MPa {square root over (m)}, yield stress of more than 500
MPa with a plastic strain of more than 1.5 to 3%.
[0021] The eutectic alloy shows a fracture toughness of K.sub.IC of
15-18 MPa {square root over (m)} and the yield stress exceeds 850
MPa at room temperature. At 600.degree. C. and above the fracture
toughness is increased to 30 MPa {square root over (m)} and the
strength is of the order of at least Rm=450 MPa.
[0022] Oxidation tests with exposure to air at 600.degree. C. have
resulted in an increase in mass of less than 5 mg/cm.sup.2 after
500 hours. In comparison the conventional Ti--Al6-V4 alloy exhibits
alpha case formation at 475.degree. C. during long term exposure on
air.
[0023] The creep stress (applied stress at given temperature where
the creep rate is {dot over (.epsilon.)}=10.sup.7 s.sup.-1) of the
eutectic Ti--Si alloy according to the invention is higher than 200
MPa at 600.degree. C. In contrast the Ti--Al6-V4 alloy with
potential application in the air plane and space industry exhibits
a creep stress of about 150 MPa at 450.degree. C.
[0024] The Ti--Si alloy according to the invention has a low
melting point of between about 1330 and about 1380.degree. C. The
alloy according to the invention has further excellent casting
properties making it possible to cast virtually any size and
shape.
[0025] As a result of its spectrum of characteristics properties
presented above, the Ti--Si alloy according to this invention are
advantageously suitable for the manufacture of diverse components,
such as:
[0026] connecting rods, piston crowns, piston pins, inlet and
outlet valves and manifolds of exhaust gas mains in internal
combustion engines and diesel engines;
[0027] static blades in axial flow compressors and fan blades in
jet engines;
[0028] wear resistant parts in textile machines--weaving
looms--like shuttles and connecting shafts;
[0029] surgical implants, bone plates, joints;
[0030] hard facings and surface alloys used as coatings in surface
engineering for improving wear resistance and to avoid
fretting;
[0031] watch cases;
[0032] pump cases and impellers for the chemical and oil
industry.
[0033] The Ti--Si alloy according to the invention is particularly
suitable for as cast components because of their relatively low
melting temperatures of about 1330 to 1380.degree. C. and excellent
castability.
[0034] The Ti--Si alloy according to the invention can be produced
in conventional way, such as by arc melting in a water cooled
copper hearth.
DETAILED DESCRIPTION OF INVENTION
EXAMPLE 1
[0035] A hypoeutectic Ti-6Si-2Al alloy according to the invention
was produced by arc melting using a non consumable tungsten
electrode. Titanium sponge with a purity of more than 99.8 wt %,
metallurgical grade silicon and aluminium granules with a purity of
more than 99.8 wt % were used as starting materials. The alloy was
kept during arc melting in a water cooled copper hearth by forming
a thin solid skull on the copper hearth and was then cast into a
copper mould in order to achieve rod like ingots. These were
machined by turning and grinding to cylindrical compression and
tensile test samples exhibiting a smooth surface finish.
[0036] The Brinell hardness was determined to be about 336.+-.3 HB
187.5/2.5 applying a testing load of 187.5 kp. The flow stress was
determined at room temperature in compression test to be about
R.sub.P.sub.0.2.apprxeq.725 to 750 MPa and the plastic strain
exceeds -.epsilon..sub.pi 10%. The fracture toughness was measured
in a four point bend test. The stress intensity factor K.sub.IC
varies between 19.ltoreq.K.sub.IC.ltoreq.21 MPa m. At higher
temperature of 650.degree. C. the flow stress is still 260
R.sub.P.sub.O.2 275 MPa and the fracture toughness is about
32.ltoreq.K.sub.IC.ltoreq.34 MPa m. The weight gain in an oxidation
test on air at 600.degree. C. was 4.5 mg/cm.sup.2 after 525
hrs.
EXAMPLE 2
[0037] A hypereutectic Ti-10Si alloy containing 0.2 wt % Al was
also produced by arc melting technique as described above in
Example 1.
[0038] The macrohardness--Brinell--of this alloy was determined to
be about 365 HB 187.5/2.5 and the yield stress at room temperature
ranges between 930.ltoreq.R.sub.P.sub.0.2.ltoreq.965 MPa depending
upon the grain size of the alloy. The plastic strain in compression
is about 6 to 8% and the fracture toughness is in between
K.sub.IC=16 and 19 MPa m.
[0039] At higher temperature of 650.degree. C. the yield stress is
about 330 to 360 MPa. The fracture toughness is in between 25 and
28 MPa m. The creep strength was determined at 600.degree. C. and
exhibits values of 215 to 230 MPa in the coarse-grained state.
[0040] The oxidation on air at 650.degree. C. leads to a weight
gain of about 3.8 mg/cm.sup.3 at 500 hrs exposure time.
EXAMPLE 3
[0041] A hypoeutectic (near eutectic) oxide dispersion strengthened
Ti-7Si-2Al alloy with addition of 0.07 mass-% Y was also produced
by the arc melting technique described in example 1. Metallic
Yttrium was added to the melt and formed Y.sub.2O.sub.3 with the
dissolved oxygen of about 1200 ppm. The Brinell hardness was
determined to be 347.+-.2 HB 187.5/2.5. The measured yield strength
was about 960 to 990 MPa. First creep experiments at 600.degree. C.
with the creep rate of {dot over (.epsilon.)}=10.sup.-7 s.sup.-1
showed a creep strength in between 235 and 255 MPa.
* * * * *