INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

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1 INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 ISSN (Print) ISSN (Online) Volume 4, Issue 2 March April 2013, pp IAEME: Journal Impact Factor (2013): (Calculated by GISI) IJARET I A E M E SLURRY EROSION COMPARISON OF D-GUN SPRAYED STELLITE- 6, Cr 3 C 2-25NiCr COATINGS AND SUBSTRATE 13Cr4Ni UNDER HYDRO ACCELERATED CONDITION Gurpreet Singh 1 and Sanjeev Bhandari 2 1 M.Tech, Department of Mechanical Engineering, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, Punjab , India 2 Assistant Professor, Department of Mechanical Engineering, Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib, Punjab , India ABSTRACT Degradation of under water parts in hydro turbines is serious issue mainly in the North India. So it s a challenge to develop new more erosion resistant materials. In the present study, slurry erosion performance of detonation gun (D-gun) spray ceramic coatings (Stellite-6 and Cr 3 C 2-25NiCr) on 13Cr4Ni stainless steel has been investigated. Attempt has been made to study the comparison between coatings and substrate steel under a particular set of parameters (concentration, average particle size and rotational speed) in hydro accelerated condition. Commercially available silica sand is used as an abrasive media. All experimentation is done in High Speed Erosion Test rig. Comparison is made on two different angles i.e. 30 and 90. At 30, Stellite-6 coating performed better in comparison with Cr 3 C 2-25NiCr coating and substrate steel specimen. On the other hand substrate steel specimen performed better at 90 than the coatings. Index Terms - Slurry erosion, High speed erosion tester, D-gun Spraying, Ceramic coatings. 1. INTRODUCTION Hydro power plants which are located on the Himalayan Rivers have had to face high silt content in the water passing through the turbines causing the large amount of damage to various under water components of turbines like runner, guide vanes, needles and seats of Pelton-type turbines. Water contains Quartz, Tourmaline, Garnet, Zircon, etc of Hardness 7 on mho scale [1]. These sediments are formed due to the fragmentation of rocks, erosion of land and land sliding because of heavy rains during the monsoon period in the 210

2 Himalayan region of India [2]. Because of this kind of environment erosion of turbine components occurs [3]. Erosion due to the impact of hard particles is common phenomenon of underwater parts in turbines [4]. A lot of investigations have been done by the researchers to identify the factors responsible for the slurry erosion behavior of turbine materials due to the water containing silt. It has been shown that slurry erosion at oblique angle can generate a rougher surface when compared with that at normal incident. Also at oblique angles it can render a greater susceptibility to pitting during erosion than at normal incident. Thus Individual erosion events at oblique angles are thus expected to be more destructive than those at normal incident [5]. Ductile materials during erosion are considered to loose material through a cutting and ploughing mechanism at a low impact angle [6]. On the other hand, cracking, fragmentation and removal of flakes is common phenomenon of erosion in brittle materials [7]. 1.1 Detonation Spray Coating To improve the surface performance and durability of engineering components which expose to different forms of wear such as abrasion, erosion and corrosion Thermal Spray techniques are a versatile means of developing a large variety of coatings/protective layers [8 10]. Detonation gun (D-gun) spray process is a thermal spray coating process, which provides an extremely low porosity, good adhesive strength, coating surface with compressive residual stresses, low oxide contents and high intersplat strength [11, 12]. The D-gun spray process involves the impingement of powdered materials with the supersonic speed through a water-cooled barrel on the surface of substrate. The two phase mixture of coating are heated to plasticity and impinges against a target substrate, where the high temperature, high velocity coating particles bond into the surface of substrate and a mechanical interlocking and microscopic welding may take place [13]. Ceramic materials are now commonly employed in the form of coatings to resist wear. Due to high melting point of the ceramic powders which require a high temperature jet to get deformed during coating formation, these coatings are usually deposited by atmospheric plasma spraying [14]. However, plasma sprayed coatings are possess more porous and brittle nature than high velocity thermal-sprayed coatings [15, 16]. On the other hand, due to close interlamellar contacts and small porosity, the high-velocity combustion spraying techniques provides greater hardness [17, 18]. This is why several efforts have been undertaken to use these highvelocity spray techniques like to spray oxides D-gun spraying is mainly used [18]. 2. EXPERIMENTATION 2.1 Material CA6NM steel containing 13% Cr and 4% Ni (also known as 13/4) is being used in fabrication of hydro turbine underwater parts. Chemical composition of 13/4 stainless steel is given in table 1. Rectangular specimens of 10 mm x 10 mm were prepared. Table 1. Chemical composition of 13/4 stainless steel (wt %) Steel C Si Mn Cr Ni N S Cu Co P Mo Fe 13/ Bal. 211

3 2.1 Deposition of Coatings Commercially available powder of Stellite-6 and Cr 3 C 2-25NiCr are coated on 13Cr4Ni stainless steel using D-Gun process available with SVX Powder M Surface Engineering Pvt. Ltd., Noida, India. 2.2 Slurry Erosion Testing A high speed erosion tester (DUCOM TR401, Bangalore make) was used to study the slurry erosion behavior of 13Cr4Ni stainless steel specimens. The tester shown in Figure 1 consists of various components such as slurry abrasion chamber, slurry tank, rotor, control panel, 3 phase induction motor. Figure 1 Experimental setup of High Speed Erosion Tester (DUCOM TR401) In slurry abrasion chamber test specimens and slurry is enclosed and specimens are rotated. Slurry tank is a cylindrical vessel made up of stainless steel, in which the slurry is prepared to the required concentration. There are three inlet and three outlet pipes between slurry abrasion chamber and slurry tank for re-circulation of slurry. Due to rotation of rotor vacuum is created in the slurry abrasion chamber and therefore slurry from cylindrical vessel through inlet pipes to chamber and used slurry leaves the chamber and enters the tank from bottom side through outlet pipes, thus ensuring continuous re-circulation of slurry. This high speed erosion tester is capable of creating accelerated hydro conditions to simulate the erosion of standard test specimens with water containing abrasive particles of controlled size and composition (slurry). Main advantages of this rig is that at a time, 12 specimens may be tested, thus ensuring zero tolerance to change of experimental conditions during comparison of slurry erosion testing of different specimens under similar experimental conditions. Only cylindrical samples can be tested in this tester. 212

4 For placing rectangular specimen in this tester we needed to design a specimen holder in which we can accommodate rectangular specimen. After two different designs we design the specimen holder shown in Fig 2. Figure 2 Specimen holders for rectangular specimens T 304 Stainless Steel Square bar was selected for the fabrication of specimen holders as it is ideal for all applications where greater strength and superior corrosion resistance is required. 304 Stainless Square has a durable dull, mill finish that is widely used for all types of fabrication projects that are exposed to the elements - chemical, acidic, fresh water, and salt water environments. Specifications, application and Mechanical Properties of T304 stainless steel are mention in table 2. Table 2 Specifications, application and Mechanical Properties of T304 stainless steel Specifications of T304 ASTM A276, QQS-763, T304/304L, non-polished finish. Applications Frame work, braces, supports, shafts, axels, marine, etc. Workability Easy to Weld, Moderate Cutting, Forming and Machining. Mechanical Properties Brinell = 170, Tensile Strength = 505 MPa, Yield Strength = 215 MPa, Nonmagnetic Effect of average particle size, concentration (ppm) and velocity has been studied by several researchers and showed that these are significant factors, which can affect the erosion phenomenon. To study this, commercially used silica sand is used as slurry medium as silica is found to be main constituent of slurry as is evident from the literature; the slurry is found to be consisting of SiO 2, Al 2 O 3, CaO, and MgO in hydro power plant in northern India [4,19]. Slurry concentrations having average particle sizes of 300 µm were prepared to simulate the test in more accelerated conditions. Tests were carried under concentration of ppm, with erodent particle size 300 µm and rotation speed of 3800 rpm to study the slurry erosion performance of Stellite-6 and Cr 3 C 2-25NiCr coated 13Cr4Ni and 13Cr4Ni stainless steel which were placed at 2 different angles i.e 30 and 90. These two angles were 213

5 select to analyze the performance of specimen when sand particles strike the surface tangentially and normally. The interaction of slurry particles with rectangular specimen in slurry chamber is shown in Figure 3. A typical erosion test cycle began with mounting of specimen holder at the proper place at correct angle. Then specimen was placed in the holders in the slurry chamber. After fixing the specimens in holders every time chamber was made air tight by tightening the nuts at four places so that proper vacuum can be created. The water was filled in stainless steel water tank and silica sand of appropriate particle size was added to the water for preparing required concentration. Then rotational speed was set and test was started. After completing the slurry erosion testing cycle of 1 h, specimens were removed from the rotor assembly, brushed gently and cleaned with acetone to remove attached sand particles if any. The specimens were weighed before and after each slurry erosion cycle. The loss in mass of each specimen was recorded with the help of precision micro weighing scale having an accuracy of 0.1 mg. As erosion is a surface phenomenon so the peripheral surface area of each specimen was calculated by measuring the length and width at two places, taking their mean for getting average length and width of specimen with the help of digital vernier caliper of least count 0.01 mm. Figure 3 Interaction of slurry particles with rectangular specimen in slurry chamber 214

6 Specific mass loss was calculated using Specific mass loss = mass loss (g) X 10 6 / Exposed surface area (m 2 ) The slurry erosion process was repeated for six cycles for each of the samples The results have been plotted as cumulative mass loss per unit area in (g/m 2 ) versus time of exposure (h) to ascertain the kinetics of slurry erosion behavior of coatings and substrate. 3. RESULTS AND DISCUSSION Figure 4 shows cumulative weight loss per unit area (g/m 2 ) versus time (h) graph of bared 13Cr4Ni stainless steel and Stellite-6 coated 13Cr4Ni at 30 under a set of parameters of concentration of ppm, erodent particle size 300 µ and rotation speed of 3800 rpm. From graph it can be observed that as the time increases the cumulative weight loss per unit area increases for both materials. Also it can be seen that after a run of 6 hours overall specific weight loss for 13Cr4Ni is g/m 2 and for Stellite-6 coating it is g/m 2. It means specific weight loss for 13Cr4Ni is 5.5 times the specific weight loss of Stellite-6. Figure 4 Comparision between cumulative mass loss per unit area of 13Cr4Ni and Stellite-6 at 30 Figure 5 shows cumulative weight loss per unit area (g/m 2 ) versus time (h) graph of bared 13Cr4Ni stainless steel and Stellite-6 coated 13Cr4Ni at 90 under same set of parameters. It can be observed that as time progresses cumulative weight loss per unit area also increases. After a run of 6 hours overall specific weight loss for 13Cr4Ni is g/m 2 and for Stellite-6 coating it is g/m 2. It means specific weight loss for Stellite-6 is 2.43 times the 13Cr4Ni. 215

7 In Figure 6 there is a comparison between 13Cr4Ni and Cr 3 C 2-25NiCr at 30 on cumulative mass loss per unit area versus time graph. With the increase in time weight loss per unit area increases for both. After 6 hour run overall specific weight loss for 13Cr4Ni is g/m 2 and for Stellite-6 coating it is g/m 2. Specific weight loss for 13Cr4Ni is 1.35 times specific weight loss for Stellite-6. Figure 5 Comparision between cumulative mass loss per unit area of 13Cr4Ni and Stellite-6 at 90 Figure 6 Comparision between cumulative mass loss per unit area of 13Cr4Ni and Cr 3 C 2-25NiCr at

8 The cumulative specific mass loss curves of the 13Cr4Ni and Cr 3 C 2-25NiCr coated 13Cr4Ni steel at 90 for a total duration of 6-h slurry erosion testing are shown in Figure 7 for same set of parameters. It can be observed from the graph that the overall specific mass losses are remarkably different. The maximum specific weight loss at the end of 6 hour of slurry erosion testing for the bared 13Cr4Ni and Cr 3 C 2-25NiCr coating is and g/m 2, respectively. So it can be observed coating is eroded 5.6 times than bared steel. Figure 7 Comparision between cumulative mass loss per unit area of 13Cr4Ni and Cr 3 C 2-25NiCr at 90 Figure 8 depicts the comparision chart between cumulative mass loss per unit area of Stellite-6 and Cr 3 C 2-25NiCr at 30 and in Figure 9 Stellite-6 and Cr 3 C 2-25NiCr at 90 for a total duration of 6-h slurry erosion testing with same set of parametes. At 30 the maximum specific mass loss at the end of 6 hour run is and g/m 2 for Stellite-6 and Cr 3 C 2-25NiCr respectively. At 90 the maximum specific mass loss at the end of 6 hour run is and g/m 2 for Stellite-6 and Cr 3 C 2-25NiCr respectively. It can be observed that from Figure 8 and 9 that maximum specific weight loss for Stellite-6 is less than that of Cr 3 C 2-25NiCr. Maximum specific weight loss after 6 hour for Cr 3 C 2-25NiCr is 4.05 times than Stellite-6 at 30 while at 90 maximum specific weight loss for Cr 3 C 2-25NiCr is 2.3 times than Stellite

9 Figure 8 Comparision between cumulative mass loss per unit area of Stellite-6 and Cr 3 C 2-25NiCr at 30 Figure 9 Comparision between cumulative mass loss per unit area of Stellite-6 and Cr 3 C 2-25NiCr at

10 Figure 10 shows cumulative weight loss per unit area (g/m 2 ) versus time (h) graph of bared 13Cr4Ni stainless steel 30 and 90 under same set of parameters. It can be seen from the graph that that 13Cr4Ni get more eroded at 30 than at 90 approximately 11 times. As the maximum weight loss for 13Cr4Ni at 30 is g/m 2 and at 90 it is g/m 2 after 6 hour run in erosion tester. Figure 10 Comparision between cumulative mass loss per unit area of 13Cr4Ni at 30 and 90 Cumulative mass loss per unit area of Stellite-6 at 30 and 90 is shown in Figure 11. From the graph it can be seen that Stellite-6 performed better at 30 as the maximum weight loss for Stellite-6 at 30 is less than the Stellite-6 at 90. The maximum weight loss for Stellite-6 at 30 is g/m 2 and at 90 it is g/m 2. In Figure 12 there is a comparison between cumulative mass loss per unit area of Cr 3 C 2-25NiCr at 30 and 90. More erosion of Cr 3 C 2-25NiCr takes place at 30. The maximum weight loss for Cr 3 C 2-25NiCr is and g/m 2 at 30 and 90 respectively after a 6 hour run in slury erosion chamber of high speed tester. The ratio of maximum weight loss at 30 to 90 comes out

11 Figure 11 Comparision between cumulative mass loss per unit area of Stellite-6 at 30 and 90 Figure 12 Comparision between cumulative mass loss per unit area of Cr 3 C 2-25NiCr at 30 and

12 4. CONCLUSIONS Due to higher hardness, Stellite-6 coating performed better at 30 than uncoated 13Cr4Ni while substrate13cr4ni steel (due to high toughness) showed better slurry resistance than Stellite-6 coating at 90. Cr 3 C 2-25NiCr coating was found to be more erosion resistant at 30 than bared 13Cr4Ni but not at 90. At 90 substrate 13Cr4Ni steel showed far much better perforamnce than Cr 3 C 2-25NiCr coating. While comparing both coatings it was found that Stellite-6 coating ( due to higher toughness) is more resistant to slurry erosion than Cr 3 C 2-25NiCr coating at 30 as well as at 90. Uncoated 13Cr4Ni steel and Cr 3 C 2-25NiCr coating showed a better performance to slurry erosion at 90 than at 30 while Stelite-6 coating was better at 90 when compraing their performances separately at two different angles. 5. REFERENCES 1. R.P.Singh, Silt damage control measures for underwater parts-nathpa Jhakri Hydro Power Station, Case study of a success story, Vol. 66, No. 1, January-March, 2009, p B.S.K. Naidu, Renovation and Modernization of Silt Prone Hydropower Stations in India, Workshop on Silting Problems in Hydroelectric Power Stations, June 25-26, 1987 (New Delhi), p V-13-V B.S. Mann, High-Energy Particle Impact Wear Resistance of Hard Coatings and Their Application in Hydro Turbines, Wear, 2000, 237, p A. K. Chauhan, D. B. Goel and S. Prakash, Erosion behaviour of hydro turbine steels, Bull. Material Science, Vol. 31, No. 2, April 2008, pp G.T. Burstein, K. Sasaki, Effect of impact angle on the slurry erosion corrosion of 304L stainless steel, Wear, 2000, 240, p G.I. Sheldon, A. Kanhere, An investigation of impingement erosion using single particles, Wear 21, 1972, p I. Finnie, Erosion of surfaces by solid particles, Wear 3, 1960, p S.V. Joshi, R. Sivakumar, Protective coatings by plasma spraying, Trans. Indian Ceram. Soc. 50, 1999, p K.G. Budinski, Surface engineering for wear resistance, Prentice Hall, Englewood Cliffs, F. Rastegar, D.E. Richardson, Alternative to chrome: HVOF cermet coatings for high horse power diesel engines, Surf. Coat. Technol. 90, 1997, p B. Rajasekaran, S.G.S. Raman, S. Joshi, G. Sundararajan, Influence of detonation gun sprayed alumina coating on AA 6063 samples under cyclic loading with and without fretting, Tribol. Int. 41(4), 2008, p P.M.J. Vuoristo, K. Niemi, T. Mantyala, On the properties of detonation gun sprayed and plasma sprayed ceramic coatings, Berndt, C. (ed.) Thermal Spray: International Advances in Coatings Technology, pp ASM International, Metals Park, OH, W. Wolentarski, Material coating by the Detonation Gun process, Proceedings of the eleventh turbomachinery symposium, Newyork. 221

13 14. Y. Liu, T.E. Fischer, A. Dent, Comparison of HVOF and plasma-sprayed alumina/ titania coatings microstructure, mechanical properties and abrasion behavior, Surf. Coat. Technol. 167, 2003, p P.P. Psyllaki, M. Jeandin, D.I. Pantelis, Microstructure and wear mechanisms of thermal-sprayed alumina, Coat. Mater. Lett. 47, 2001, p J. Voyer, B.R. Marple, Sliding wear behavior of high velocity oxy-fuel and high power plasma spray-processed tungsten carbide- based cermet coatings, Wear , 1999, p Y. Wang, Friction and wear performances of detonation-gun and plasma-sprayed ceramic and cermet hard coatings under dry friction, Wear 161, 1993, p L. Pawlowski, The Science and Engineering of Thermal Spray Coatings, Wiley, West Susseex P109 IUD, S. Bhandari, H. Singh, H. K. Kansal, V. Rastogi, Slurry Erosion Behaviour of Detonation Gun Spray Al2O3 and Al2O3 13TiO2-Coated CF8M Steel Under Hydro Accelerated Conditions, Tribol Lett 45, 2012, p Prof. Mohammed Yunus, Dr. J. Fazlur Rahman and S.Ferozkhan, A Genetic Programming Approach for the Prediction of Thermal Characteristics of Ceramic Coatings, International Journal of Industrial Engineering Research and Development (IJIERD), Volume 2, Issue 1, 2011, pp , ISSN Online: , ISSN Print: Mohammed Yunus, Dr. J. Fazlur Rahman and S.Ferozkhan, Prediction of Mechanical and Tribological Characteristics of Industrial Ceramic Coatings using a Genetic Programming Approach, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 1, 2012, pp , ISSN Print: , ISSN Online: Mohammed Yunus, Dr. J. Fazlur Rahman and S.Ferozkhan, Evaluation of Machinability Characteristics of Industrial Ceramic Coatings using Genetic Programming Based Approach, International Journal of Mechanical Engineering & Technology (IJMET), Volume 2, Issue 2, 2011, pp , ISSN Print: , ISSN Online: