FORM 2
THE PATENTS ACT, 1970
(39 of 1970) As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
METHOD TO DETERMINE QUALITY OF SINTERING
APPLICANTS
Crompton Greaves Limited, CG House, 6th House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Nemade Janamejay Bhaichandra of Crompton Greaves Limited, Advanced Materials and Process Technology Centre, CG Global R&D Centre, Kanjur Marg (E), Mumbai, Maharashtra, India, an Indian National
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:
The invention relates to the field of sintering.
The present invention relates to an improved method for determining the quality of sintered materials.
BACKGROUND OF THE INVENTION:
Sintering is a method for making objects from powder, by heating the material in a sintering furnace below its melting point until its particles adhere to each other. The sintering process causes the particles in contact to form metallurgical bonds, alloys by diffusion, and improves the mechanical and physical properties by creating a coherent compact. In general, the bonding occurs through two means of material transport: 1) at the particle areas, the boundaries are lost and bonds are formed through mass transport; 2) along the pore edges, the surfaces become smoother through vapor phase transport.
Visually, the effectiveness of sintering is characterized by changes in the appearance of the microstructure as a disappearance of particle boundaries, smoothening of sharp features along pore edges, and a lessening in the pore perimeters.
Various microscopy techniques are used for the qualitative and quantitative analysis of the microstructure of the sintered materials to study various parameters such as grain and pore sizes, distribution, morphology, etc. The conventional method of observing microstructure involves grinding and

polishing the specimen surface to mirror finish. Further, if required, the finished specimen may be etched with a suitable etchant in order to distinguish between the various phases, precipitates, grain boundaries and other micro-structure constituents. Etching is typically done in order to remove the highly deformed thin layer during earlier stages and create visual differences by selectively dissolving the surface.
The present invention relates to a method of determining the quality of the sintered materials by an improved method by eliminating the need for grinding and polishing the specimen.
SUMMARY OF THE INVENTION:
According to this invention, there is provided an improved method for determining the quality of sintered materials, said method comprisesthe steps of:
a. etching a specimen of said sintered materials for a predetermined amount
of time in order to completely dissolve all the phases or constituents in
said specimen, except the at least pre-defined phase or constituent of
interest;
b. dissolving said sintered material to a pre-defined depth such that the
visible regions satisfy the needs of the intended purpose for determining
quality; and

c observing said visible regions under a high resolution microscope for analyzing pre-defined patterns, thereby determining the goodness of quality of said sintered materials.
Preferably, the method includes the step of etching said specimen for a time period between 5 seconds to 10 minutes.
Typically, the step of etching includes the step of selecting one or more etchants for the etching step.
Typically, the step of etching includes the step of selecting an etchant depending upon the nature of the constituents to be dissolved.
Typically, the step of etching includes the step of selecting an etchant depending upon the nature of the constituent to be analyzed
Typically, the step of etching includes the step of selecting multiple etchants adapted to dissolve different constituents occurring in said specimen, selectively in stages.

Typically, the step of etching includes the step of selecting at least an etchant such that it has minimal effect on the constituent of interest to be analyzed,
Typically, said method includes the step of determining one of the parameters from a group of parameters for determining the quality, said group of parameters consisting of parameter relating to more number of rounded particles, parameter relating to single modal and narrow peak of the particle size distribution, parameter relating to smooth and clean surface area with little or no sharp corners, parameter relating to joint with good 'necking', parameter relating to reduced overall particle size, parameter relating to extent of increased roundness, parameter relating to extent of the shift to lower particles size of the mode(s), parameter relating to reduced surface roughness and reduced presence of sharp corners.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Table 1 describes parameters of particles before sintering;
Table 2 describes parameters of particles after a bad sintering process;
Table 3 illustrates describes parameters of particles after a good sintering process;

Figure 1 illustrates observed sintered particles at a magnification of 1000X after the process of etching;
Figure 2 illustrates observed sintered particles at a magnification of 500X after the process of etching;
Figure 3 illustrates observed sintered particles at a magnification of 1000X after the process of etching; and
Figure 4 illustrates observed sintered particles at magnification of 1000X after the process of etching.
DEATILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to the present invention, the method of determining the quality of sintered materials comprises the step of etching the specimen for a predetermined amount of time to completely dissolve all the phases or constituents in the specimen, except the one of interest. The depth of material dissolved is enough such that the visible regions satisfy the needs of the intended purpose. The specimen maybe etched between a time period of 5 seconds to 10 minutes. According to the method of the present invention, it is not essential that the specimen be ground and polished to a mirror finish before the etching is done.

According to the invention, one or more etchants may be used for the etching step. The choices of etchants depend upon the nature of the materials to be dissolved and the nature of the material to be analyzed. For example, 10% nitric acid can be used to dissolve copper, etc. Further, multiple etchants may be used to dissolve different constituents occurring in the specimen selectively in stages.
Further, the selection of the etchant is made such that it has no or minimal effect on the constituent(s) of interest to be analyzed. This deeper etching leaves skeleton of the phases or constituents of interest.
According to the present invention, the specimen thus etched is observed under a high resolution and/or a high depth of field microscope e.g. scanning electron microscope. Further, the images of the specimen are analyzed for the following parameters:
1. Shape of the particles, P1
2. Size distribution of the particles, P2
3. Nature of the surface of the particles, P3
4. Type of joint between the particles, P4
In case of powder metallurgical components the initial size, size distribution, shape, nature of the surface of the particles etc. may also be compared with the similar observed parameters to determine the following :
1. Change in the size of the particles, P5
2. Change in the shape of the particles, P6
3. Change in the size distribution of the particles, P7

4. Change in the nature of the surface of the particles, P8
Based on this data gathered the quality of the sintered material obtained by the sintering process is determined to be better if the following is observed:
1. Parameter P9: More number of rounded particles.
2. Parameter P10: Singal modal and narrow peak of the particle size distribution
3. Parameter P11: Smooth and clean surface area with little or no sharp corners
4. Parameter P12: Joint with good 'necking'.
5. Parameter P13: Reduced overall particle size.
6. Parameter P14 : Extent of increased roundness
7. Parameter P15: Extent of the shift to lower particles size of the mode(s)
8. Parameter P16: Reduced surface roughness and reduced presence of sharp corners
Table 1 describes parameters of particles before sintering;
Table 1

Grain No Dl D2 Mean Roundness Surface roughness Sharp corners Necking
1 U4 57.68 L5 50.78 54.23 3.00 1.00 10.00 0.00
2 L6 30.28 L7 19.43 24.86 2.00 2.00 9.00 0.00
3 L9 62.18 L10 25.03 43.61 2.00 1.00 8.00 0.00
4 Lll 50.60 L12 29.41 40.00 3.00 1.00 9.00 0.00
5 L13 24.73 L14 13.16 18.95 3.00 2.00 9.00 0.00
6 LIS 33.37 LI6 22.62 28.00 3.00 1.00 9.00 0.00
7 L17 29.43 L18 14.36 21.69 3.00 1.00 8.00 0.00
8 LI 9 67.04 L20 25.32 45.18 2.00 2.00 9.00 0.00
9 L2I 40.72 L22 17.82 29.27 3.00 1.00 9.00 0.00
10 L25 25.01 L26 10.27 17.64 2.00 ZOO 8.00 0.00
11 L27 20.32 L28 If.40 15.86 2.00 1.00 10.00 0.00
12 L29 33.79 L30 37.17 37.98 2.00 1.00 9.00 0.00
13 L31 43.49 L32 17.45 30.47 3.00 2.00 9.00 0.00
14 L33 52.54 L34 12.74 32.64 2.00 1.00 9.00 000
Average 31.54 2.50 8.93
RelTig 1

Table 2 describes parameters of particles after a bad sintering process;
Table 2

Grain No Dl D2 Mean Roundness Surface roughness Sharp corners Necking
1 L5 45.55 L6 35.57 40.56 6.00 3.00 9.00 0.00
2 L7 43.29 L8 15.31 29.30 6.00 4,00 8.00 0.00
3 L9 31,83 L10 20.74 26.28 4.00 3.00 8.00 0.00
4 LI! 73.71 L12 36.31 55.01 5.00 3.00 7.00 0.00
5 L13 25.89 LI4 14.24 20.07 5.00 3.00 9.00 0.00
6 L18 72.68 L19 41.22 56.95 4.00 2.00 8.00 0.00
7 L20 29.29 L21 22.50 25.89 4.00 3.00 9.00 0.00
8 L27 23.80 L28 12.06 17.93 3.00 4.00 8.00 0.00
9 L29 29.37 L30 18.59 23.98 5.00 3.00 8.00 0.00
10 L31 30.62 L-32 23.87 27.24 3.00 2.00 7.00 0.00
11 L33 26.08 L34 20.69 23,39 4.00 2.00 8.00 0.00
12 L35 61.05 L36 28.68 44.87 3.00 2.00 8.00 0.00
13 L37 45.26 L38 21.50 33.38 4.00 3.00 9.00 0.00
14 L40 20.40 L4! 20.16 20.28 4.00 3.00 6.00 0.00
Avera.ee
31.80 4.29 8.00
RefFig 2
and Table 3 illustrates describes parameters of particles after a good sintering process.
Table 3

Grain
No Dl D2 Mean Roundness Surface roughness Necking
1 LI 14.35 L2 14.10 14.22 10,00 9.00 0.71*
2 L3 24.19 L4 24.73 24.46 9.00 9.00 0.8814*
3 L5 21.58 L6 19.44 20.51 9.00 9.00 0.51*
4 L7 27.98 L8 26.29 27.13 8.00 9.00 0.63*
5 L9 22.52 L10 19.50 21.01 6.00 10.00 0.91*
6 Lll 23.88 LI2 18.90 21.39 6.00 8.00
7 L14 38.82 L15 22.11 30.46 7.00 10.00
8 L16 43.45 L17 43.23 43.34 9.00 9.00
9 L18 29.35 L20 30.49 29.92 8.00 8.00
10 L21 20.08 L22 18.38 19.23 9.00 9.00
11 L23 26.87 L24 20.67 23.77 8.00 9.00
J2 L27 J8.71 L28 19.60 19.16 9.00 9.00
13 L29 17.85 L30 14.44 16.14 7.00 9.00
14 L31 31.86 L32 25.58 28.72 8.00 9.00
Average 24.25 8.07
RcfFig3 Rcffig4
Figure 1 illustrates observed sintered particles at a magnification of 1000X after the process of etching; Figure 2 illustrates observed sintered particles at a

magnification of 500X after the process of etching; Figure 3 illustrates observed sintered particles at a magnification of 1000X after the process of etching; and Figure 4 illustrates observed sintered particles at a magnification of 1000X after the process of etching.

We claim,
1. An improved method for determining the quality of sintered materials, said method comprising the steps of:
a. etching a specimen of said sintered materials for a predetermined amount
of time in order to completely dissolve all the phases or constituents in
said specimen, except the at least pre-defined phase or constituent of
interest;
b. dissolving said sintered material to a pre-defined depth such that the
visible regions satisfy the needs of the intended purpose for determining
quality; and
c. observing said visible regions under a high resolution microscope for
analyzing pre-defined patterns, thereby determining the goodness of
quality of said sintered materials.
2. A method as claimed in claim 1 wherein, the method includes the step of
etching said specimen for a time period between 5 seconds to 10 minutes.
3. A method as claimed in claim 1 wherein, the step of etching includes the step
of selecting one or more etchants for the etching step.

4. A method as claimed in claim 1 wherein, the step of etching includes the step of selecting an etchants depending upon the nature of the constituents to be dissolved.
5. A method as claimed in claim 1 wherein, the step of etching includes the step of selecting an etchants depending upon the nature of the constituent to be analyzed
6. A method as claimed in claim 1 wherein, the step of etching includes the step of selecting multiple etchants adapted to dissolve different constituents occurring in said specimen, selectively in stages.
7. A method as claimed in claim 1 wherein, the step of etching includes the step of selecting at least an etchant such that it has minimal effect on the constituent of interest to be analyzed.
8. A method as claimed in claim 1 wherein, said method includes the step of determining one of the parameters from a group of parameters for determining the quality, said group of parameters consisting of parameter relating to more number of rounded particles, parameter relating to single modal and narrow peak of the particle size distribution, parameter relating to smooth and clean surface area with little or no sharp corners, parameter

relating to joint with good 'necking', parameter relating to reduced overall particle size, parameter relating to extent of increased roundness, parameter relating to extent of the shift to lower particles size of the mode(s), parameter relating to reduced surface roughness and reduced presence of sharp corners.