FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Improved vacuum interrupter contact materials.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Jena Sushil Kumar and Nemade Janamejay Bhalchandra of Crompton Greaves Limited, Advanced Materials and Process Technology Centre, CG Global R&D Centre, Kanjur Marg (E), Mumbai, Maharashtra, India, both Indian Nationals
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Field of the Invention:
This invention relates to the field of alloys.
Particularly, this invention relates to the field of alloys for electrical contacts.
Still particularly, this invention relates to vacuum interrupter contacts.
More particularly, this invention relates to improved vacuum interrupter contact materials.
Background of the Invention:
Vacuum interrupter contacts desire the following properties, ideally, for improving the working parameters of the associated vacuum interrupters:
• Low gas content
• Minimal welding
• Low thermionic emission
• Optimum vapour pressure
• Optimum erosion
• Mechanical strength
• Voltage withstand
• High electrical conductivity
• High thermal conductivity

Previously, according to the prior art, many combinations of element have been tried, tested, and used for manufacturing contacts, preferably vacuum interrupter contacts. The following was observed:
For Cu-Cr contact material, the advantages include the following:
•After high current interruption the contact surface remains smooth
•The surface of the contact changes to very finely disperse Cr in a Cu matrix
• Excellent electrical endurance
• Excellent mechanical strength
• Excellent high-voltage performance
• Withstands high-speed TRVs
• Low cost
• Adequate resistance to contact welding in circuit breaker applications
• Excellent high, short-circuit interruption performance
• Butt contacts interrupt up to 10 kA
• Maximum chop current <6A
However, for- Cu-Cr contact material, the disadvantages include the
following:
•Excellent high-frequency current interruption can result in voltage
escalation in high inductance circuits
•Welding tendency too high for contactor applications
For Ag-WC contact material, the advantages include the following: ■Excellent load current electrical endurance (>106 electrical operations possible)

•Poor high-frequency current interruption, limits high-voltage escalation effects, that is, it is a "low surge" contact material •Excellent resistance to contact welding •Maximum chop current <2A
However, for Ag-WC contact material, the disadvantages include the
following:
•High cost
•Butt contact interruption limit 4-4.5 kA
•Requires an AMF design to reach higher short-circuit interruption values
•High-voltage performance generally limited to 15 kV or lower systems
•Use generally limited to contactor applications
For Cu-W contact material, the advantages include the following: •Excellent load current electrical endurance •High-frequency current interruption ability between that of Cu-Cr and Ag-WC •Excellent high-voltage performance
• Good resistance to contact welding
• Low cost
• Maximum chop current <8A
However, for Cu-W contact material, the disadvantages include the
following:
Butt contact interruption limit 2-3 kA
Use generally limited to load break switches

If Cu-Bi is chosen to alter the present contact materials, the element Bi is desirable for low chopping current. However, the Cu-Bi combination provides a mechanically weak contact material voltage withstand ability is low and erosion is high. With small addition of Bi to Cu, Bi migrates to the grain boundary of Cu during solidification. This makes contact more brittle than pure Cu. Inherent defect form.
If Cu-Ag is chosen to alter the current contact materials, it is observed that Silver is not used because of high cost and not real advantage over Cu in vacuum environment.
There is need for an improved contact material.
Objects of the Invention:
An object of the invention is to provide an improved vacuum interrupter contact materials with minimal welding.
Another object of the invention is to provide the improved vacuum interrupter contact materials with optimum erosion characteristics.
Yet another object of the invention is to provide the improved vacuum interrupter contact materials with enhanced mechanical strength.
Still another object of the invention is to provide the improved vacuum interrupter contact materials which withstand voltage.

An additional object of the invention is to provide the improved vacuum interrupter contact materials with high electrical conductivity.
Yet an additional object of the invention is to provide the improved vacuum interrupter contact materials with high thermal conductivity.
Summary of the Invention:
According to this invention, there is provided an improved vacuum interrupter contact materials comprising:
a. first element being copper matrix of a predetermined amount of said
contact weight;
b. second element being chromium of a predetermined amount of said
contact weight;
c. third element of a predetermined amount of said contact weight;
characterized in that, said second element and said third element are
mechanically milled and/or alloyed together and further milled onto said
first element.
Typically, said first element is used in the range of 45 to 80% by weight of Cu-Cr-third element.
Typically, said second element is used in the range of 20 to 55% by weight
of Cu-Cr-third element. I
Typically, said third element is used in the range of 0.1 to 5% by weight of Cu-Cr-third element.

Typically, said third element is selected from a group of elements consisting of Nb, V, Fe, Mo, Ta, and W. Preferably, said third element is Nb.
Typically, said first element is milled into alloyed second element - third element in an end cycle, preferably lasting for 5 to 30 minutes, more preferably for 5 to 15 minutes.
Preferably, Copper (Cu) is milled into alloyed Cr-Nb in an end cycle, preferably lasting for 5 to 30 minutes, more preferably for 5 to 15 minutes.
Brief Description of the Accompanying Drawings:
Figures 1 to 4 illustrate images of microstructures of the material made by mechanically alloying and/or mechanically milling Cu, Cr, and Nb.
Detailed Description of Invention:
According to this invention, there is provided improved vacuum interrupter contact materials.
The improved vacuum interrupter contact materials comprises Copper (Cu) being first element, Chromium (Cr) being second element, and third element selected. The third element is selected from Nb, V, Fe, Mo, Ta, and W.
The improved vacuum interrupter contact materials is prepared by the processes of mechanical milling (MM) and mechanical alloying (MA), the

microstructural changes occur to provide a new material. Thus, this provides a microstructurally changed material comprising Cu, Cr, and third element.
This vacuum interrupter performance directly depends on the microstructural distribution and arrangement of Cr and Cr-Nb on Cu matrix.
For better contact properties, it is important to have a fine and uniform distribution of Cr phase on the Cu matrix. For the fine and uniform microstructure, the manufacturing process of mechanically alloying Cr and Nb is followed.
Mechanical milled and/or alloying process achieves sub-micron to nano-scale homogenous distribution and solid solubility.
Preferably, Cu being first element is milled with Cr-third element in the last 5 to 30 minutes of preparation of Cu-Cr-third element. This easily disperses Cu.
Typically, said third element is selected from a group of elements consisting of Nb, V, Fe, Mo, Ta, and W. More particularly, third element is Nb.
The first element is used in the range of 45 to 80% by weight of Cu-Cr-third element.
The second element is used in the range of 20 to 55% by weight of Cu-Cr-third element.

The third element is used in the range of 0.1 to 5% by weight of Cu-Cr-third element.
This vacuum, interrupter performance directly depends on the microstructural distribution and arrangement of Cr and Cr-Nb on Cu matrix.
For better contact properties, it is important to have a fine and uniform distribution of Cr phase on the Cu matrix.
Fine and uniform distribution of Cr and Nb on Cu decreases the chopping current, improve welding properties, and wear resistance. The addition of Nb to Cu-Cr forms Cr2Nb phase. The negligible solubility of refractory Cr and Cu in liquid Body Cubic Centre up to 1000° C, their complete solubility above solvus, and their Cr2Nb formation provide thermodynamic design. Due to better electrical properties, it increases the rating of vacuum interrupter without any change in design of VI.
One of the advantages of the current invention is that Cu-Cr-Nb has high strength at elevated temperatures, corrosion resistance, and also maintains thermal and electrical conductivity at high temperatures. Another advantage of the current invention is that Cu—Cr—Nb alloys have finer grain size at higher temperatures. Further, Cu—Cr—Nb has much better hydrogen embrittlement resistance. Mechanical milling (MM) of Cu-Cr-Nb increase hardness due to Cu grain size refinement. The negligible solubility of refractory Cr and Cu in liquid Body Cubic Centre up to 1200K, their completely solubility above solvus, and their Cr2Nb formation provide thermodynamic design. The Cu-Nb alloy shows the best mechanical

strength among the family of Body Cubic Centre. In thermodynamic equilibrium the mutual solubility of niobium and copper is negligibly small, since their melting points differ strongly.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
Example 1:
Copper (Cu) and Chromium (Cr) was mechanically milled in the ratio of 75:25 to form milled mixture Cu-Cr for 6 hours. The milling was carried out in the presence of Nitrogen atmosphere and toluene medium. The attrition mill container was cooled by chilled water at 20° C continuously through out the milling. The Cu-Cr obtained was sintered at 1075° C to obtained contact material. The material was tested for its roundness, elongation, distribution, directionality, conductivity and hardness. The results obtained are listed in table 1. Figure 1 illustrates images of microstructures of the material made by mechanically alloying and mechanically milling Cu, and Cr.
Example 2:
Chromium (Cr) was blended with Copper (Cu) and Niobium (Nb) in the ratio of 75:24:1 to form blend of Cr-Cu-Nb. The blend of Cr-Cu-Nb obtained was sintered at 1075° C to obtained contact material. The.material was tested for its roundness, elongation, distribution, directionality, conductivity and hardness. The results obtained are listed in table 1. Figure 2 illustrates images of microstructures of the blend of Cu, Cr, and Nb.

Example 3:
Chromium (Cr) was mechanically milled with Niobium (Nb) in the ratio of 24:1 to form milled mixture Cr- Nb for 5 hours and 45 minutes. The milling was carried out in the presence of Nitrogen atmosphere and toluene medium. 75 % of Copper (Cu) was added and was milled into mixture Cr-Nb at the end of the cycle for last 15 minutes. The attrition mill container was cooled by chilled water at 20° C continuously throughout the milling. The Cr-Cu-Nb obtained was sintered at 1075° C to obtained contact material. The material was tested for its roundness, elongation, distribution, directionality, conductivity and hardness. The results obtained are listed in table 1. Figure 3 illustrates images of microstructures of the material made by mechanically alloying and mechanically milling Cu, Cr, and Nb.
Example 4;
Chromium (Cr) was mechanically milled with Niobium (Nb) in the ratio of 23:2 to form milled mixture Cr- Nb for 5 hours and 45 minutes. The milling was carried out in the presence of Nitrogen atmosphere and toluene medium. 75 % of Copper (Cu) was added and was milled into mixture Cr-Nb at the end of the cycle for last 15 minutes. The attrition mill container was cooled by chilled water at 20° C continuously throughout the milling. The Cr-Cu-Nb obtained was sintered at 1075°C to obtained contact material. The material was tested for its roundness, elongation, distribution, directionality, conductivity and hardness. The results obtained are listed in table 1. Figure 4

illustrates images of microstructures of the material made by mechanically alloying and mechanically milling Cu, Cr, and Nb.
It can be observed from the table 1 that the elongation and roundness of the microstructures changes.
Table 1: Properties in accordance with the process parameters adopted and observed microstructure from the image, according to the examples 1 to 4:

Figure 1 Milling hours : 6
Sintering temperature : 1075° C
Roundness : 3
Elongation : 2
Distribution : 4
Directionality : 4 The conductivity is 44.74 %IACS and hardness is 65.87 HRF of the sample.
Figure 2 Milling hours : 0
Sintering temperature : 1075° C
Roundness : 5
Elongation : 1
Distribution : 4
Directionality : 3 The conductivity is 54.12 %IACS and hardness is 55.37 HRF of the sample.
Figure 3 Milling hours : 6
Sintering temperature : 1075° C
Roundness : 4
Elongation : 3
Distribution : 4 The conductivity is 43.22 %IACS and hardness is 67.47 HRF of the sample.

Directionality : 5
Figure 4 Milling hours : 6
Sintering temperature : 1075° C
Roundness : 4
Elongation : 3

Distribution : 4 Directionality :5 The conductivity is 43.53 %IACS and hardness is 63.43 HRF of the sample.
Example 5:
The Cu and Cr were mixed (i.e. unmilled) and milled in different proportions as shown in table 2 and their conductivity and hardness has been studied. The results obtained for the same are illustrated in table 2. The Cu, Cr and Nb were milled in different proportions as shown in table 2 and their conductivity and hardness has been studied. The results obtained for the same are illustrated in table 2.
Table 2: The results of conductivity and hardness in relation to treatment of Mechanical milling like alloying, the composition of Cu, Cr and Nb, milling time, compaction pressure, and sintering temperature.

Powder Composition (Cu:Cr:Nb) Milling
tine
(hours) Compaction Pressure
(kN) Peak
sintering
temp.
(°C) Conductivity
(%IACS) Hardness (HRB)
Unmilled Cu-Unmilled Cr 75:25:0 0 120 1075 53.21 63
Unmilled Cu- milled Cr 75:25:0 36 300 1075 ,42.55 98
Unmilled Cu- milled Cr 75:25:0 36 120 1075 40.63 79

Unmilled Cu- milled Cr 75:25:0 12 120 1075 39.45 75
milled Cu- Unmilled Cr 75:25:0 12 300 975 13.57 48
milled Cu- Unmilled Cr 75:25:0 36 300 1075 12.34 75.5
milled Cu- Unmilled Cr 75:25:0 12 120 1075 20.71 36.5
milled Cu- Unmilled Cr 75:25:0 12 300 1075 21.76 85
milled Cu- Unmilled Cr 75:25:0 36 300 975 5.24 46
milled Cu- Unmilled Cr 75:25:0 36 120 1075 10.64 65
milled Cu- milled Cr 75:25:0 36 300 975 16.46 93.5
milled Cu- milled Cr 75:25:0 36 120 1075 16.12 99
milled Cu- milled Cr 75:25:0 36 120 975 11,00 52.5
Cu-(Milled/alloyed Cr andNb) 75:25:0.5 6 120 1075 43,28 69.3
Cu-(Milled/alloyed Cr and Nb) 75:25:1 6 120 1075 43.22 67.4
Cu-(Milled/alloyed Cr andNb) 75:25:2 6 120 1075 43.53 63.4
It can be seen that Milling of copper decreases the conductivity.

We claim,
1. An improved vacuum interrupter contact materials comprising:
a. first element being copper matrix of a predetermined amount of said
contact weight;
b. second element being chromium of a predetermined amount of said
contact weight;
c. third element of a predetermined amount of said contact weight;
characterized in that, said second element and said third element are
mechanically milled and/or alloyed together and further milled onto
said first element.
2. The improved vacuum interrupter contact materials as claimed in claim 1 wherein, said Copper (Cu) is 45 to 80% by weight of said contact weight.
3. The improved vacuum interrupter contact materials as claimed in claim 1 wherein, said Chromium (Cr) is 20 to 55% by weight of said contact weight.
4. The improved vacuum interrupter contact materials as claimed in claim 1 wherein, said third element is 0.1 to 5% by weight of said contact weight.
5. The improved vacuum interrupter contact materials as claimed in claim 1 wherein, said third element is selected from a group of element consisting of Nb, V, Fe, Mo, Ta, and W.

6. The improved vacuum interrupter contact materials as claimed in claim 1 wherein, said first element is mixed into mechanically alloyed second element - third element in an end cycle.
7. The improved vacuum interrupter contact materials as claimed in claim 1 wherein, said Cu is milled into mechanically alloyed Cr-Nb in an end cycle.