TECHNICAL FIELD
1. The present disclosure relates to a novel way of improving erosion resistance and abrasion resistance of WC-Co based HVOF coatings by controlled heat treatment under inert atmosphere.
2. The present disclosure relates to establish a unique heat treatment process to improve HVOF coating properties by improving hardness and porosity for under water Hydro turbine components like pelton needle, pelton bucket, guide vanes, top cover, lower rings, labyrinth etc.
BACKGROUND
3. Hydro Turbine power stations situated in Uttarakhand and Himalayan Regions are facing severe erosion problem due to presence of high silt content in the flowing water. In general silt consist of hard quartz particle size ranging from 10 to 200 microns. During monsoon season, excessive land slide causes increase in silt content of the river water. When this silt and water mixer strikes the surface of hydro turbine components, severe erosion can be observed. Major affected parts of Hydro Turbine are pelton needle, pelton bucket, guide vanes, top cover, lower rings, labyrinth etc. Erosion of these parts leads to decrease in efficiency of power generation and operation life as well as increases maintenance cost and down time.
4. HVOF coatings are being used for erosion and corrosion resistance application however these coatings were not undergoing any heat treatment process. With increase in silt content in flowing water these HVOF coatings are eroding slowly and there after affecting the base material. As a result, the spare parts of hydro turbine components are being replaced frequently. Sometimes these parts are failing that leads to shut down of power station resulting in huge revenue losses.
5. WC-Co based HVOF (High Velocity Oxy Fuel) coatings are being widely used on hydro turbine components to protect from silt erosion because of their high erosion and corrosion resistance. Generally, these coating thickness varies between 250-350 microns. With these hard

coatings the erosion rate can be decreased to a large extent but erosion still exist and causing frequent repair/replace of Hydro Turbine parts.
6. W.r.t Indian patent reference No: 235/KOL/2005, HVOF coatings are applied to improve erosion and corrosion resistance. W.r.t. Indian patent reference No: 1732/KOL/2007, HVOF coatings properties were improved by diamond surface grinding method.
7. But these coatings often fails to provide the desired efficiency in erosion resistance and accordingly, the present invention has been designed to improve the life of WC-Co based HVOF coatings further by heat treating them under controlled atmosphere.
OBJECTS OF THE DISCLOSURE
00008. Some of the objects of the present disclosure, which at least one embodiment herein
satisfy, are listed hereinbelow.
00009. A general object of the present disclosure is to provide a process for improving the WC-
Co HVOF coating properties.
10. Another object of the present disclosure is to provide a process for enhancing the erosion and abrasion resistance of the WC- Co HVOF coating properties by improving hardness and porosity.
11. Yet another object of the present disclosure is to provide a process for improving the WC- Co HVOF coating properties under controlled heat treatment.
12. Further of the present disclosure is to provide a process for improving the WC- Co HVOF coating for under water Hydro turbine components like pelton needle, pelton bucket, guide vanes, top cover, lower rings, labyrinth etc.
13. Another object of the present disclosure is to provide a process for improving the WC- Co HVOF coating, which is environment friendly and rapid yet effective.

000014. These and other objects and advantages of the present invention will be apparent to
those skilled in the art after a consideration of the following detailed description taken in
conjunction with the accompanying drawings in which a preferred form of the present invention
is illustrated.
SUMMARY
000015. The present invention discloses a process for improving the WC- Co HVOF coating
properties for under water Hydro turbine components, said process comprises the steps:
placing the HVOF Coated samples under heating furnace and creating vacuum;
an inert atmosphere was created by purging argon gas and maintained the pressure at atmospheric pressure ,
initiation of heat treatment by using PID controller at a temperature of 400 -8000C for a duration of 2 hour followed by cooling ,
cutting of sample after the heat treatment and placed in a hot mounting machine and grinded followed by cloth polishing subjected to different characterization.
16. Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
17. It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
18. The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS
19. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:
20. Figure 1 illustrates the Hardness measurement with an embodiment of the present disclosure.
21. Figure 2(a-f) illustrate the details of the microstructure at 200X with an embodiment of the present disclosure.
22. Figure 3 illustrates the graphical presentation of Slurry Erosion Test results with an embodiment of the present disclosure.
23. Figure 4 illustrates the graphical representation of abrasion Test results with an embodiment of the present disclosure.
24. Figure 5 illustrates the graphical representation of XRD Analysis with an embodiment of the present disclosure.
DETAILED DESCRIPTION
25. In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
26. While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be

described in detail below. It should be understood, however that it is not intended to limit the disclosure to the forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.
27. The terms “comprises”, “comprising”, “includes” or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that includes a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
28. In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.
29. Hereinafter, the present disclosure relates to a novel process for improving the erosion and abrasion resistance of the WC- Co HVOF coating by controlled heat treatment under inert atmosphere by improving hardness and porosity.
Sample preparation
30. SS 410 base plates of dimension 200mm x 200mm X 6mm were coated with WC-Co based HVOF coatings. Thickness of above coatings was measured by using Elco-meter and found between 250-300 microns. From these coated plates a set of erosion and abrasion samples were prepared with dimensions 50mm X 50mm X 6mm and 75mm X 25mm X 6mm respectively.
31. The process mainly has below steps:

i. HVOF coating of samples includes tungsten carbide powders and the thickness is
between from 280 to 300 microns.
ii. Loading of samples in a furnace and creating fine vacuum level up to 10-5 bar using
high vacuum arrangement.
iii. Purging of argon gas and maintaining pressure in the furnace to atmospheric
pressure.
iv. Programming on digital PID (Proportional, Integral, Derivative) controller to
desired heating rate, cooling rate and holding time.
v. Starting the furnace heating cycle, always and the pressure inside tube should be
atmospheric pressure by regulating argon gas flow.
vi. Furnace cooling of samples.
Example:
000032. HVOF Coated samples were heat treated at temperature ranging from 400oc –
800oC under controlled atmosphere (argon) in a Tubular Furnace. Before start of experiment samples were loaded at the center of the tubular furnace which is having constant heating zone length of 200mm. Both the ends are seal tightened and vacuum was taken up to 10-5 bar. Later argon gas was purged with flow rate of 30ml/s-50ml/s and pressure inside tube was brought to atmosphere pressure. Heat treatment program was set by using PID controller with heating rate of 10/min, holding time for 2hr followed by 10/min cooling rate.
000033. After the heat treatment from one of erosion sample a piece was cut under diamond
wheel slow cutting machine. This piece was mounted in hot mounting machine for better sample
handling. This mounted sample was grinded with emery papers ranging from 150 to 1000 followed
by cloth polishing. This sample was observed under microscope for porosity, thickness, hardness
etc and various charcaterisation tests are performed as given below:
Hardness measurement:
000034. Hardness was measured using Vickers Hardness tester at 300gms load, in distance
intervals of 500 microns and minimum of 6 readings. Figure 1 illustrates the maximum and
minimum hardness. It can be observed that hardness values improved for the samples heat treated

at temperature ranging 4000C – 7000C and later it decreased at 8000C. Hardness was measured for without heat treatment sample (as coated) is 1050Hv-1186Hv whereas after heat treatment at 4000C – 8000C is 1353Hv– 1706Hv.
Microstructure analysis:
000035. Optical microscopic images were taken using Leica DM4000 at 200X
magnification as shown in Figure 2(a -f). From Figure 2 it can be observed that coting heat treated
at 4000C has become denser in comparison with as coted and coatings heat treated at temperature
ranging from 5000C – 8000C. Porosity of as coated HVOF sample is in the range of 0.7-0.9 after
het treatment at 4000C porosity decreased to 0.25-0.35.
Slurry erosion test:
000036. Slurry jet erosion test was conducted on the samples (50mm X 50mm X 6mm)
as per ASTM STP 1199. In this process, water slurry jet was directed on sample surface. Before
the test heat treated samples were subjected to diamond grindings for making surface smooth.
Samples weighed before and after the test weight loss was calculated and converted into volume
loss (density of WC-Co HVOF coating 14.5) as shown in Fig 3. It can be observed from Fig 3,
that volume loss of sample heat treated at 4000C decreased against as coated and the samples heat
treated at 5000C, 6000C, 7000C and 8000C the volume loss increased. This indicates that heat
treatment above 5000C is not favorable so far erosion resistance is concerned. Improvement in
erosion resistance against as coated samples is around 28% - 30% WC-Co HVOF coatings heat
treated at 4000C temperature.
Abrasion test:
000037. Abrasion test was conducted on the samples as per ASTM G-65 standard. In this
test sample was subjected to sliding wear test. Before the abrasion test heat treated samples were
subjected to diamond grindings for making the surface smooth. Samples weighed before and after
the test, weight loss was calculated and converted into volume loss (density of WC-Co HVOF
coating 14.5) as shown in Fig 4. It can be seen from Fig4, that volume loss of the sample heat
treated at 4000C is lowest in comparison to as coated and samples heat treated at 5000C, 6000C,
7000C and 8000C. Similar trend is also noticed in the slurry jet erosion test. Improvement in

abrasion resistance against as coated is around 28%-30% WC-Co HVOF coatings heat treated at 4000C temperature.
X-Ray diffraction:
38. X-Ray diffraction patterns was generated using Empyrean XRD, PAnalytical make using Voltage 45KV and Current 40mA, 2 Theta ranging from 200 to 800. These patterns were analyzed using Xpert High Score plus software and the comparison of XRD patterns as shown in Fig 5. Fig 5 shows that formation of W2C compound in samples heat treated from 4000C - 6000C, which is causing increase in hardness of the coating and samples heat treated above 6000C presence of oxides (CoO, CoWo4, WO3) can be seen which are leading to lower hardness.
39. Conclusion:

• Heat treatment of HVOF coatings under inert atmosphere of WC-Co based HVOF coatings are beneficial.
• Micro hardness value of the sample heat treated at 4000C increased substantially to 1353Hv - 1438Hv in comparison to the as coated sample, which are ranging from 1050Hv - 1186 Hv.
• Coating became dense and less porous after heat treatment of coating at 4000C temperature.
• Around 30% improvement in erosion and abrasions resistance has been observed in the sample heat treated at 4000C.
• Even though Hardness values for the samples heat treated at 6000C, 7000C and 8000C is on the higher side but erosion and abrasion resistance were not favorable.
• Hence it is recommended to heat treat under argon atmosphere at a temperature 4000C for better performance of HVOF Coatings.
000040. TECHNICAL ADVANTAGES
i. The present disclosure provides a process as claimed hereinafter improves porosity of
HVOF coating to a level of 0.4% from as coated HVOF coating 1%.

ii. The present disclosure provides a process improves hardness of HVOF coating from
1050Hv - 1186Hv to 1350HV – 1450HV at 4000C temperature.
iii. The present disclosure provides a process improves erosion resistance of HVOF
coatings about 28%-30% at 4000C temperature.
iv. The process improves abrasion resistance of HVOF about 28%-30% at 4000C
temperature
Equivalents:
41. The specification has described a process for improving the WC- Co HVOF coating properties.
42. The illustrated steps are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the manner in which particular functions are performed. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope and spirit of the disclosed embodiments. Also, the words "comprising," "having," "containing," and "including," and other similar forms are intended to be equivalent in meaning and be open-ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.
000043. Finally, the language used in the specification has been principally selected for
readability and instructional purposes, and it may not have been selected to delineate or
circumscribe the inventive subject matter. It is therefore intended that the scope of the invention

be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the embodiments of the present invention are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

We claim:
1. A process for improving the WC- Co HVOF coating properties for under water Hydro turbine
components, said process comprises the steps:
placing the HVOF Coated samples under heating furnace and creating vacuum;
an inert atmosphere was created by purging argon gas and maintained the pressure at atmospheric pressure;
initiation of heat treatment by using PID controller at a suitable temperature for a suitable duration followed by cooling;
cutting of sample after the heat treatment and placed in a hot mounting machine and grinded followed by cloth polishing subjected to different characterization.
2. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein
the sample is loaded and the furnace is vacuumed up to 10-5 bar.
3. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein the flow rate of argon gas is 30ml/s-50ml/s so that the pressure in the furnace to be maintained at atmospheric pressure always.
4. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein said heating occurs for a duration of 2 hours at a heating rate of 10/min.

5. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein the said heating occurs at a temperature of 4000C to 8000C.
6. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein most preferred temperature of heating is 4000C.
7. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein the cooling occurs at a rate of 10/min.
8. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein the thickness of the WC- Co based HVOF coated samples is 250-300micron.

9. The process for improving the WC- Co HVOF coating properties as claimed in claim 1, wherein
the hardness of HVOF coating improves from 1050Hv - 1186Hv to 1350HV – 1450HV at 4000C
temperature.
10. The process for improving the WC- Co HVOF coating properties as claimed in claim 1,
wherein erosion resistance and abrasion resistance of HVOF coatings improves at 28%-30% at
4000C temperature.