Title of Invention

"SUPER PLASTIC DIFFUSION BONDING PROCESS FOR BONDING TITANIUM ALLOYS"

Abstract Super plastic diffusion bonding process for bonding titanium alloys comprising the steps of preparing work pieces by reshaping titanium alloys work piece to make said work pieces complimentary to each other, treating with isopropyl alcohol and roughing with emery paper; etching for 5 to 30 second, the reshaped and roughened work pieces obtained from step (i) with reagent comprising about hydrofluoric acid and nitric acid in the preferred ratio of 1:3 or alternatively with Kalling's solution (H202+CHI) and washing with distilled water; loading the work pieces, obtained from step (ii) above in the hydraulic ram placing the gas muffle over the set of work pieces; purging the atmospheric gas from the work area by introducing argon gas of pure (medical grade) purity under pressure slightly above atmospheric; heating the said work pieces to about 800°C-825°C, below the alpha transition of titanium with the help of heat muffle; applying the hydraulic pressure over the work pieces maintaining the temperature to 800°C-825°C, raising the pressure on the work pieces to 2.5-3.0 Mpa and maintaining the pressure at the same level for about 3-3.5 hours, raising the temperature of the said work pieces to 925°C-950°C and reducing the hydraulic pressure to 2.0-2.5 Mpa and maintaining the said hydraulic pressure for about 15-20 minutes; lowering the temperature of the said work pieces at a regulated rate of about 250°C/hour to about 300°C and releasing the pressure and air quenching the said work pieces.
Full Text FIELD OF INVENTION:
This invention relates to a Super plastic diffusion bonding process for bonding titanium alloys, the joining of two similar or dissimilar metallic pieces can be made using the welding process. The conventional methods of welding rely on liquid formation, filling up of capillaries and solidification. All conventional methods rely on melting, flow and solidification to form a welded joint. The properties of the solidified liquid at the weld are different from those of the surrounding material.
In TIG Welding (Tungsten Inert Gas Welding), already known in the art, a skilled operator directs the welding tool at the joint. A flow of inert gas is directed at the joint and heat is produced with a plasma or arc source. The filler material can be used which melts and creates the bond. However, this method of joining two pieces, already known in the art, suffers from the following disadvantages.
One main disadvantage of this method of joining two pieces, known in the art, is that it depends upon the skill of the operator and it is hazardous to the operator.
Another disadvantage of this method of joining two pieces, known in the art, is that it requires huge energy in the form of electric energy to produce the arc.
Yet another disadvantage of this method of joining two pieces, known in the art, is that the characteristics of the joined piece are not uniform.
Electron Beam Welding is another method, known in the art, for joining two pieces. This operation is an improved process as it is an automatic process performed under vacuum. The welds, resulting from this process are of good quality. However, this process also suffers from the following disadvantages.
The main disadvantage of this method of joining two metallic pieces, known in the prior art, is that it consumes tremendous electrical energy and requires a large overhead expenditure for creating the facility for welding.
Another disadvantage of this method of joining two metallic pieces, known in the prior art, is that only lines and spots can be welded using this method.
Yet another disadvantage of this method of joining two metallic pieces, known in the prior art, is that this method can not be employed for joining large area (bigger pieces).


Still further disadvantage of this method of joining two metallic pieces, known in the prior art, is that this method can be utilized for welding materials with limited thickness as the electron beam can not penetrate very deep.
Yet further disadvantage of this method of joining two metallic pieces, known in the prior art, is that the weld suffers from the sputtering of the material.
Still further disadvantage of this method of joining two metallic pieces, known in the prior art, is that dissimilar metals, for example Ni and Ti., can not be readily welded using this method.
Yet further disadvantage of this method of joining two metallic pieces, known in the prior art, is that this method is particularly unsuitable for joining metals, which are relatively insoluble.
Diffusion Bonding is another process, known in the prior art, for joining two metallic pieces. Diffusion Bonding is a solid-state process wherein no liquid layer is formed at the joint, while in conventional welding methods, a layer of liquid forms and solidifies to form a welded joint. The joint in Diffusion Bonding is a 'Monolithic' one i.e. one unit homogenous with the original units and as such properties remain continuous across the joint.
One of the diffusion bonding method has been disclosed in US Patent No. 6129261. The diffusion bonding method, disclosed in the above prior art, uses vacuum and expensive setups for dies and jigs to position the parts to be joined. This process is particularly useful for constructing precise aerospace components. In this process, bonds are created along lines and spots joining two or more sheets or plates and then these lines are inflated with gas to produce the structure, for example, a 'honeycomb' structure.
However, the diffusion bonding method, as disclosed in the above mentioned prior art suffer from the disadvantage that this process can not be utilized for bonding large areas and this process is suitable for bonding arrays of lines. Further, a specific setup has to be specifically designed to bond only one particular component or sheet pattern utilizing above process..
Similarly, US Patent No 6177203 discloses a diffusion method for bonding multiple layers of metal. However, in the above process, super plastic deformation is not accomplished and, as such, profiling of the joined material can not be done through an external guide.
In the present method, the description includes bonding of multiple layers as well as allowing for super plastic deformation to a desired external profile by use of suitable restraining guides or molds.

OBJECTS OF THE INVENTION:
Primary object of the present invention is to provide a super plastic diffusion bonding process for bonding titanium alloys, which is particularly suitable for joining titanium alloy pieces.
Another object of the present invention is to provide an alternative process to conventional welding methods like electron beam welding and other methods, which processes are not suitable for joining titanium alloys.
Yet another object of the invention is to provide a super plastic diffusion bonding process for joining two or more titanium alloy pieces to a homogenous unit without melting the interface, as is the case in other welding processes.
Still another object of the invention is to provide super plastic diffusion bonding process for producing bonded surfaces with resultant molding to any exterior shape by use of outside or external holding mold vessel.
Yet further object of the invention is to provided a super plastic diffusion bonding process, wherein the shape of the bonded piece can be changed with the help external shape guides thereby allowing for 'Rapid Prototyping' or 'Rapid layer forming' as an alternative to powder metallurgy and Numerical controlled Technology forming.
Still another object of the invention is to provide super plastic diffusion bonding process wherein it is possible to achieve high strength bonds over and above that of the strength of formal titanium alloy.
Yet further object of the invention is to provide super plastic diffusion bonding process, which is a low cost alternative to Electron Beam Welding (EBW) and similar exotic techniques requiring high capital outlay and energy inputs.
Still further object of the invention is to provide super plastic diffusion bonding process, which is a low cost alternative to vacuum diffusion bonding requiring higher energy and time cost of vacuum production and maintenance.
Yet further object of the invention is to provide super plastic diffusion bonding process, which is able to produce a joint with properties different from that of the initial starting material.
Yet further object of the invention is to provide super plastic diffusion bonding process, which provides for large area contact in the bonded pieces.

Yet another object is to provide super plastic diffusion bonding process, which is an energy efficient process for joining metal-tometal, metal to ceramic and non metal and dissimilar alloys with appropriate inter layers, (e.g. Ni to Ti with suitable mutually compatible layer).
DESCRIPTION OF THE PROCESS
According to this invention there is provided super plastic diffusion bonding process for bonding titanium alloys comprising the steps of:
(i) preparing work pieces by reshaping titanium alloys work piece to make said work pieces complimentary to each other, treating with isopropyl alcohol and roughing with emery paper;
(ii) etching for 5 to 30 second, the reshaped and roughened work pieces obtained from step (i) with reagent comprising about hydrofluoric acid and nitric acid in the preferred ratio of 1:3 or alternatively with Railing's solution (H202+CHI) and washing with distilled water;
(iii) loading the work pieces, obtained from step (ii) above in the hydraulic ram placing the gas muffle over the set of work pieces;
(iv) purging the atmospheric gas from the work area by introducing argon gas of pure (medical grade) purity under pressure slightly above atmospheric;
(v) heating the said work pieces to about 800°C-825°C, below the alpha transition of titanium with the help of heat muffle;

(vi) applying the hydraulic pressure over the work pieces maintaining the temperature to 800°C-825°C, raising the pressure on the work pieces to 2.5-3.0 Mpa and maintaining the pressure at the same level for about 3-3.5 hours, raising the temperature of the said work pieces to 925°C-950°C and reducing the hydraulic pressure to 2.0-2.5 Mpa and maintaining the said hydraulic pressure for about 15-20 minutes;
(vii) lowering the temperature of the said work pieces at a regulated rate of about 250°C/hour to about 300°C and releasing the pressure and air quenching the said work pieces.
In accordance with the present invention the super plastic diffusion bonding process for bonding titanium alloys comprises following steps:
(i)Preparing work pieces:
The titanium alloys work pieces, to be bonded, are reshaped using milling machine to make these work pieces complimentary to each other. These work pieces are then treated with isopropyl alcohol and roughened with emery paper.
(ii)Chemically treating the work pieces:
The reshaped and roughened work pieces, obtained from step (I) are then etched for 5 to 30 second depending upon the size of the work pieces with KROLL's reagent comprising about 40% hydrofluoric acid and about 70% nitric acid in the preferred ratio of 1:3 or Kalling's solution (H2O2+HCI) and washed with distilled water.

(iii) Loading of the work pieces in the hydraulic press:
loading the work pieces, obtained from step (ii) above in the hydraulic ram placing the gas muffle over the set of work pieces;
(iv) Introducing inert gas over the work pieces:
purging the atmospheric gas from the work area by introducing argon gas of pure (medical grade) purity under pressure slightly above atmospheric;
(v) Heating of the work pieces:
heating the said work pieces to about 800°C-825°C, below the alpha transition of titanium with the help of heat muffle;

(vi) Applying hydraulic pressure:
applying the hydraulic pressure over the work pieces maintaining the temperature to 800°C-825°C, raising the pressure on the work pieces to 2.5-3.0 Mpa and maintaining the pressure at the same level for about 3-3.5 hours, raising the temperature of the said work pieces to 925°C-950°C and reducing the hydraulic pressure to 2.0-2.5 Mpa and maintaining the said hydraulic pressure for about 15-20 minutes;
(vii) Cooling down of the bonded work pieces:
lowering the temperature of the said work pieces at a regulated rate of about 250°C/hour to about 300°C and releasing the pressure and air quenching the said work pieces.
In accordance with the present invention the super plastic diffusion bonding process for bonding titanium alloys comprises following steps:
(i) Preparing work pieces.
The titanium alloys work pieces, to be bonded, are reshaped using milling machine to make these work pieces complimentary to each other. These work pieces are then treated with isopropyl alcohol and roughened with emery paper.
(ii) Chemically treating the work pieces:
The reshaped and roughened work pieces, obtained from step (I) are then etched for 5 to 30 second depending upon the size of the work pieces with KROLL'S reagent comprising about 40% hydrofluoric acid and about 70% nitric acid in the preferred ratio of 1:3 or Railing's solution (H2O2+HCl) and washed with distilled water.
(iii). Loading of the Work Pieces in the Hydraulic Press:
The samples or work pieces, obtained from step (ii) above are placed symmetrically around the Hydraulic ram surfaces in three or more sets of pairs in equi- triangular form, or in any other symmetric form. Afterwards, the gas muffle is placed over the set of work pieces.
(iv) Introducing Inert Gas Over the Work Pieces:
Argon gas of 99.999 pure (medical grade) purity under pressure slightly above atmospheric is introduced over the work pieces which purges the atmospheric gas from the work area.
(v) Heating of the Work Pieces:
The work pieces are then heated to about 800 °C - 825 °C, below the alpha transition, with the help of heat muffle in an inert has atmosphere.
(vi) Applying Hydraulic Pressure:
Next, the hydraulic pressure is applied over the work pieces in two stages while maintaining the temperature to 800 °C - 825 °C. In the first stage (alpha titanium region), the pressure on the work pieces is raised to 2.5 - 3.0 Mpa and maintained at the same level for about 3- 3.5 hours. During this stage, the size of the alpha Titanium work pieces are reduced by half due to plastic deformation. In the next stage (beta titanium region), the temperature of the work pieces are raised to 925 °C - 950 °C and the hydraulic pressure is reduced to 2.0 - 2.5 Mpa This hydraulic pressure level on the work pieces is kept for about 15-20 minutes. After completion of the high temperature cycle, the Beta region Process is over and the bonding process is completed.
(vii) Cooling down of the Bonded Work pieces:
The temperature of the work pieces is lowered at a regulated rate of about 250 °C /hour and the pressure is also released. When the temperature is lowered to about 300 °C, the muffle and jacket are removed and the work pieces are air quenched to room temperature.
The invention shall now be illustrated with the following working example, which is intended to be a typical example to explain the technique of the present invention and which is not intended to be taken restrictively to imply any limitation to the scope of the present invention.
Working Example -1
A titanium alloy (TiAI4V) was prepared on the milling machine with milled finished faces. Two cylinders of lengths 50 mm and dia. 40 mm were bonded in sets of 3 pairs using argon gas atmosphere and hydraulic ram pressure. The cylinders were placed in contact, the chamber atmosphere purged with Argon gas while the temperature was raised. At 800 C the pressure was increased to 3 tonnes (3 Mpa) ad maintained for 3 hours. The size of the sample was reduced to 1/2 by plastic deformation at this time. Pressure was reduced to 2. 5 MPa while temperature was raised to 925 °C . The pressure was released and the temperature lowered to 300 °C . The muffle and hood was then opened and the samples allowed to cool in the air.
Resulting bonded samples were further test prepared by EDM wire cutting ad cylindrical specimens fabricated for test. Threads were made on the ends for attachment of adaptors. The samples were tested for tensile strength on a FRI Testing Machine. Ultimate tensile strengths were recorded and plotted with a recorder as stress versus strain on graph paper.
Specific results for three samples are as follows:
Sample No. Breaking Force (kN) U.T.S. (Mpa)
Sample 1 18.46 1161
Sample 2 20.08 1263
Sample3 25.75 1620
It is seen that the breaking stress is appreciably higher than the nominal breaking strength of unbonded Ti (around 900 Mpa).
It is to be understood that the process of the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention which is further set forth under the following claims:






WE CLAIM;
1. Super plastic diffusion bonding process for bonding titanium alloys
comprising the steps of:
(i) preparing work pieces by reshaping titanium alloys work piece to make said work pieces complimentary to each other, treating with isopropyl alcohol and roughing with emery paper;
(ii) etching for 5 to 30 second, the reshaped and roughened work pieces obtained from step (i) with reagent comprising about hydrofluoric acid and nitric acid in the preferred ratio of 1:3 or alternatively with Kalling's solution (H202+CHI) and washing with distilled water;
(iii) loading the work pieces, obtained from step (ii) above in the hydraulic ram placing the gas muffle over the set of work pieces;
(iv) purging the atmospheric gas from the work area by introducing argon gas of pure (medical grade) purity under pressure slightly above atmospheric;
(v) heating the said work pieces to about 800°C-825°C, below the alpha transition of titanium with the help of heat muffle;
(vi) applying the hydraulic pressure over the work pieces maintaining the temperature to 800°C-825°C, raising the pressure on the work pieces to 2.5-3.0 Mpa and maintaining the pressure at the same level for about 3-3.5 hours, raising the temperature of the said work pieces to 925°C-950°C and reducing the hydraulic pressure to 2.0-2.5 Mpa and maintaining the said hydraulic pressure for about 15-20 minutes;
(vii) lowering the temperature of the said work pieces at a regulated rate of about 250°C/hour to about 300°C and releasing the pressure and air quenching the said work pieces.
2. A super plastic diffusion bonding process for bonding titanium
alloys substantially as described.

Documents:

1370-DEL-2003-Abstract-(13-02-2009).pdf

1370-del-2003-abstract.pdf

1370-DEL-2003-Claims-(13-02-2009).pdf

1370-del-2003-claims.pdf

1370-DEL-2003-Correspondence-Others-(13-02-2009).pdf

1370-del-2003-correspondence-others.pdf

1370-del-2003-correspondence-po.pdf

1370-DEL-2003-Description (Complete)-(13-02-2009).pdf

1370-del-2003-description (complete).pdf

1370-DEL-2003-Form-1-(13-02-2009).pdf

1370-del-2003-form-1.pdf

1370-del-2003-form-18.pdf

1370-DEL-2003-Form-2-(13-02-2009).pdf

1370-del-2003-form-2.pdf


Patent Number 234880
Indian Patent Application Number 1370/DEL/2003
PG Journal Number 28/2009
Publication Date 10-Jul-2009
Grant Date 18-Jun-2009
Date of Filing 07-Nov-2003
Name of Patentee THE DIRECTOR GENERAL,
Applicant Address DEFENCE RESEARCH & DEVELOPMENT ORGANISATION MINISTRY OF DEFENCE, GOVT OF INDIA, B-341, SENA BHAWAN, DHQ P.O. NEW DELHI-110011
Inventors:
# Inventor's Name Inventor's Address
1 RAHUL BASU GTRE, CV RAMAN NAGAR, BANGALORE- 560093
PCT International Classification Number B23K 20/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA