|Title of Invention||
"A NON-VACUUM DIFFUSION BONDING PROCESS FOR BONDING OF REFRACTORY METALS, ALLOYS AND SUPER ALLOYS"
|Abstract||This invention relates to a non-vacuum diffusion bonding process for bonding of refractory metals, alloys and super alloys comprising preparation of work piece by milling, cleaning and grinding Etching surface of said work piece chemically with KROLLS reagent comprising of 40% Hydrofluoric acid and 70% Nitric acid, preferably in the volume ratio of 1:3 or with Kallings reagent comprising hydrogen peroxide and hydrochloric acid, etching is carried out preferably for 5-30 second Loading, introducing inert gas such as Argon; heating the said work piece to 850-1000°C. Bonding pressurisation said work piece at 1 to 3 Mpa for 30 minutes to 1 hour. Cooling said work piece by lowering the temperature to 300°C, followed by air quenching from 300°C to room temperature.|
|Full Text||FIELD OF INVENTION
The invention relates to a non-vacuum diffusion bonding a process for bonding of refractory metals, alloys and super alloys of high melting point, with or without incipient melting, with or without pre-treatment, with of without filler materials and intermediary layers. Capable of being applied to parts of small or any larger length, being restricted only by the size of the treatment chamber.
Bonding of high temperature alloys is usually accomplished by melting of a thin layer of high temperature metal between the two surfaces to be joined. The thin layer of metal is melted by applying a focused electronic or laser beam or an electric are source. The solidification of the molten layer bonds the two surfaces. In Electronic welding, the bonding is by focused electronic beam. In Tungsten inert gas welding, melting of the layer is by electric are and the molten metal flows through the capillaries/cracks in the two surfaces to be joined and solidification of the intermediate liquid causes bonding of the two surfaces. In diffusion bonding known in the prior art, a monolithic joint is produced by formation of bonds as a result of local plastic deformation and inter-diffusion in the surface layers brought to contact. The diffusion bonding can be used with metals as well as non-metals.
According to one of the diffusion bonding process known in the art, the diffusion bonding is carried out under vacuum to prevent oxidation, the vacuum varying from l0-1 Pa to 10-3 Pa. The two surfaces to be bonded may be provided or may not be provided with intermediate filler between the surfaces, depending upon the material of the two surfaces to be bonded. These are then heated under vacuum by a power unit which may be induction, laser or and electronic beam, a flow of electronic current or any combination thereof.
A drawback of the above process it that it requires the process to be carried out under vacuum which in turn requires elaborate and expensive set up. To achiev.e high vacuum, takes long set up times and elaborate equipment for control, preliminary degassing, regulation and feedback of process parameters.
Another diffusion bonding process known in the art, as per US Patent 6,129,261, involves compression bonding of metal surfaces to be bonded; where-in increased pressure is applied to the areas of contact for diffusion bonding and heating with inflation of inert gas to prevent bonding in the areas where not required.
A drawback of above technique is that it requires gas pressurization which requires elaborate set up and needs inlet tubing to be welded to templates at certain points.
Another drawback of above technique is that it cannot form a large monolithic joint so bonding of large areas of surfaces is not possible.
Still another drawback of above technique is that it is designed for a specific component set up and is not adaptable for any general component fabrication by bonding.
Further drawback of above technique is that the two surfaces have to be precisely aligned at the locations where the surfaces are to be bonded, before subjecting to compression bonding.
OBJECTS OF PRESENT INVENTION
The primary object of the present invention is to provide a diffusion bonding process, which can be carried out under non-vacuum conditions.
Another object of the present invention is to provide a diffusion bonding process, which is relatively inexpensive.
Still another object of the present invention is to provide a diffusion bonding process which provides structurally strong large area bonded surfaces.
Further object of the present invention is to provide a diffusion bonding process to provide an energy-efficient method for bonding of two surfaces.
Yet further object of the present invention is to provide a diffusion bonding process which is faster.
Still further object of the present invention is to provide a diffusion bonding process, which provides an alternative to powder metallurgy or NC machining.
Even further object of the present invention is to provide a diffusion bonding process, which enables bonding of dissimilar metals.
Yet further object of the present invention is to provide a diffusion bonding process which enables manufacturing of layered objects.
DESCRIPTION OF PROCESS
According to this invention there is provided a non-vacuum diffusion bonding process for bonding of refractory metals, alloys and super alloys of high melting points, comprising preparation of work piece by milling, cleaning and grinding, etching by chemical treatment; loading; introduction of inert gas like Argon, heating and bonding pressurization, cooling followed by air-quenching.
The diffusion bonding of present invention consists of following steps: -
(a) Sample Preparation
Sample are prepared by using a milling machine to produce flat surfaces. These ae cleaned with alcohol and roughened with emery paper.
(b) Chemical Treatment
After the metal surface is roughened with emery paper, it is then again cleaned with Iso- propyl alcohol or acetone. Subsequently, the surface are etched with KROLL's Regent comprising 40% Hydrofluoric aid and 70% Nitric acid in the preferred volume ratio of 1:3, and washed with distilled water. Other reagents could be used specific for the metal to be cleaned e.g. Kailing's solution comprising a mixture of H2O2 and HCL. Etching is done for a short duration 5 to 30 seconds depending upon the size of the sample.
The work piece are placed symmetrically around the ram surfaces in there set of pairs, in equi-triangular form. The gas muffle is placed over the three pair of work pieces.
(d) Introduction of Inert Gas
Argon gas of (99.999% purity) is introduced in the muffle, under pressure. The residual gas in the equipment gas supply lines is purged using Argon so that no oxygen or nitrogen is present. Subsequently, gas pressure above atmosphere pressure, is maintained.
The work piece is heated to a temperature from 850 to 1000°C preferably from 940 to 960°C.
(f) Bonding Pressurisation
At the onset of required temperature indicated by thermocouple, the pressure on the sample is raised to 1 Mpa to 3 Mpa, preferably 3 Mpa and maintained for about 30 minutes to 1 hour.
After about 30 minutes to 1 hours of bonding pressurisation, the temperature is lowered and pressure is released. The lowering of temperature is carried at the controlled rate of about 250°C/hour. When the temperature reaches to about 300°C, the muffle and the jacket are removed and the work pieces are air-quenched to room temperature.
The present invention will now be illustrated with a working example which is intended to illustrate the working of the invention and is not intended to be taken restrictively to imply any limitation on the scope of the present invention.
Cylindrical blocks of titanium alloy (Ti6 A14V) were prepared by milling and then emery roughening of samples. The surfaces were the etched with chemical and swabbed cleaned with alcohol. The samples were the mounted in a hot press in a equi-triangular arrangement in pairs to be bonded.
Argon gas atmosphere was applied and temperature raised to 950°C. At the onset of required temperature as indicated by thermocouple, the pressure on the sample was raised to 3 MPa and maintained for 30 minutes. After 30 minutes, the temperature was lowered and the pressure released. At 300°C the samples were allowed to cool in air after removing the muffle and the heating jacket.
EVALUATION OF PROPERTIES
Subsequently five tensile samples were prepared from the bonded blocks by wire cutting. 3 were tested as is and two were notched on the side at midpoint with a 1mm 45 degree V notch and a 2 mm 45 degree V notch. Breaking (UTS-ultimate tensile strength) strengths were noted and plotted with a recording attachment.
Results are as follows:
Breaking Strength Maximum Force
Sample 1 913 Mpa 50 KN range
Sample 2 972 Mpa
Sample 3 953 Mpa
Sample 4 (1 mm V notch) 696 Mpa
Sample 5 (2mm V notch) 914 Mpa
It can be seen that the bonding strength is very good and compares favourably with un-bonded parent material strengths (~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:
1. A non-vacuum diffusion bonding process for bonding of
refractory metals, alloys and super alloys comprising
preparation of work piece by milling, cleaning and grinding;
a) Etching surface of said work piece chemically with KROLLS reagent comprising of 40% Hydrofluoric acid and 70% Nitric acid, preferably in the volume ratio of 1:3 or with Kallings reagent comprising hydrogen peroxide and hydrochloric acid, etching is carried out preferably for 5-30 second;
b) Loading, introducing inert gas such as Argon; heating the said work piece to 850-1000°C.
c) Bonding pressurisation said work piece at 1 to 3 Mpa for 30
minutes to 1 hours.
d) Cooling said work piece by lowering the temperature to
300°C, followed by air quenching from 300°C to room
2. A non-vacuum diffusion bonding as claimed in claim 1 wherein heating of work piece is preferably carried from 940-960°C.
3. A non- vacuum diffusion bonding as claimed in claim 1 wherein bonding preessurisation is carried at preferably 3Mpa.
4. A non-vacuum diffusion bonding process as substantially described and illustrated herein.
|Indian Patent Application Number||585/DEL/2002|
|PG Journal Number||48/2008|
|Date of Filing||24-May-2002|
|Name of Patentee||THE ADDITIONAL DIRECTOR (IPR)|
|Applicant Address||DEFENCE RESEARCH & DEVELOPMENT ORGANISATION, MINISTRY OF DEFENCE, GOVT OF INDIA, B-341, SENA BHAWAN, DHQ P.O., NEW DELHI-110011, INDIA.|
|PCT International Classification Number||B21D 026/00|
|PCT International Application Number||N/A|
|PCT International Filing date|