Anil Kumar, Vivek Srivastava, N.K. Mishra
Keywords: Detonation-Gun, High temperature, Oxidation and Hot-corrosion, SEM & EDS morphology
In current scenario, the demands of electricity are increase due to increasing the population. To fulfill such requirement, we must need to improve the efficiency of boiler, gas turbine for industrial applications. The development of boiler and gas turbine strongly demands not only design of good boiler and gas turbine system, but also the development of materials, which can abruptly use at high temperatures. Iron- based materials used in boiler and gas turbine, where the surfaces are in contact with air as well as salty environment, detorate abruptly at high temperature. Detoration of material occurs due to use of low quality fuels like sulfur, sodium, chloride require special observations to the event of oxidation and hot corrosion. To improve the corrosion resistance at high temperatures, detonation gun sprayed 75%Cr3C2-25%NiCr coating has been tested on Silicon Wire tune furnace. The specimens were examined by Scanning Electron Microscopy &Energy Dispersive Spectrometry (SEM&EDS) techniques to analyze the corrosion products. The result of uncoated SA213 suffered major weight loss 26 mg/cm2 in case of air, but high weight gain 18 mg/cm2 in case of salty environment. The 75% Cr3C2-25% NiCr sprayed coating showed composite structure of Ni in presence of air and granules structure of iron in presence of salty environment.
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If you wish to view the human-readable version of the preprint, then please Register (if you have not already done so) and Login. Registration is completely free.High temperature corrosion behavior of bare and detonation gun sprayed Cr3C2-25NiCr coating on SA-213 boiler steel in air and salt environments at 8000C 1 3 Anil Kumar, 2Vivek Srivastava, 3N.K. Mishra 1 School of engineering, Babu Banarasi Das University, Lucknow, India-226028 2 School of engineering, Babu Banarasi Das University, Lucknow, India-226028 Babu Banarasi Das Northern India Institute of Technology, Lucknow, India-226028 Email: email@example.com Abstract In current scenario, the demands of electricity are increase due to increasing the population. To fulfill such requirement, we must need to improve the efficiency of boiler, gas turbine for industrial applications. The development of boiler and gas turbine strongly demands not only design of good boiler and gas turbine system, but also the development of materials, which can abruptly use at high temperatures. Iron- based materials used in boiler and gas turbine, where the surfaces are in contact with air as well as salty environment, detorate abruptly at high temperature. Detoration of material occurs due to use of low quality fuels like sulfur, sodium, chloride require special observations to the event of oxidation and hot corrosion. To improve the corrosion resistance at high temperatures, detonation gun sprayed 75%Cr3C225%NiCr coating has been tested on Silicon Wire tune furnace. The specimens were examined by Scanning Electron Microscopy &Energy Dispersive Spectrometry (SEM&EDS) techniques to analyze the corrosion products. The result of uncoated SA213 suffered major weight loss 26 mg/cm2 in case of air, but high weight gain 18 mg/cm2 in case of salty environment. The 75% Cr3C2-25% NiCr sprayed coating showed composite structure of Ni in presence of air and granules structure of iron in presence of salty environment. Keywords: Detonation-Gun, High temperature, Oxidation and Hot-corrosion, SEM & EDS morphology 1. INTRODUCTION The growing population requires enhancing the amounts of electricity from sources that will have reduced environmental impact. The demand of worldwide energy will increase by around 40% by 2030, and coal combustion is supposed to account for 30% of the future worldwide energy production .Oxidation & hot-corrosion have been located as a significant problem like boiler, internal combustion engine, and gas turbine etc. on metals and alloys [2-3].The use of low-quality fuels, like sulfur, sodium, chlorine & vanadium require special observations to the event of oxidation and hot-corrosion. These events, which are the major failure methodology of roasting section parts used in gas turbine. Metal and alloy have been insufficient to reduce the effect of oxidation and hot-corrosion problem at high temperature. For preventing oil and ash corrosion on metals and alloys, Fuel additives and inhibitors have been used. Caused by its productiveness and cheap in cost, the common fuel additives MgO is used [4-5]. The MgO, CaO and SnO2 based inhibitors are mostly used to salty environment for iron, nickel & cobalt based superalloys to reduce the effect of corrosion . Due to high temperatures, inhibitors were not able to sustain the total effect of elevated temperature corrosion, such that protective coatings have been found the excellent techinique to save the metals against corrosion [7-8]. Detonation gun is the most efficient coating techinique, which is capable of obtaining the high velocity of gas and metal particles tends to higher than sounds speed. This technique imparts the chance of generating with outstanding coating strength and good hardness [9-10]. Detonation gun coating which is able to high velocity of gas and particles approaching 4-5 times of sound speed. This coating provides the supreme hardness and sufficient strength [1-112].The D-gun method offers highest velocity (600-1200 m/s) for sprayed powders that are not obtained by plasma (400 m/s) and highvelocity oxy-fuel (500 m/s) coatings .The main objective of our tests are to examine the elevated temperature oxidation and hot corrosion conduct of detonation gun covered Cr3C225NiCr coatings in presence of air and salt environments at 800°C temperature. The experiments were done total 50 cycles and each cycle heating the sample one hour and after that cooling 20 minutes under cyclic process. 2. Experimental 2.1 Material and coating formulation SA-213 boiler steel material has been utilized as substrate materials as they are employed in boiler & gas turbine component because of their high strength & creep resistance at towering temperatures. Specimen each measuring 20 mm x 15 mm x 5 mm approximately were cut, polished by using emery papers of 220,400,600 mesh sizes and subsequently grit-blasted with the alumina particles of mesh size 40 after that the action of deposing of Cr3C2-25NiCr covering was done by detonation gun spraying technique. Chemical composition report in table1. Table-1 SA-213 (347H) C Chemical composition 0.04 2.0 (mass %) Mn P S Si Cr 0.04 0.03 0.75 17-19 max max Ni Fe 9.0-13.0 65.08 2.2 Development of coating Commercially accessible Cr3C2-25NiCr powders having particles size 30-60 µm size (M/S H.C. Stars Company, Germany) were deposited on the substrate by Detonation gun method at XVX Powder M Surface Engineering Pvt.Ltd, Noida (India).All the process specifications were remained constant at the time of coating process. Table.2. Thermal spray parameter used for detonation gun coating Oxygen Flow rate 2800 SLPH C2H2 600 SLPH N2 2400 SLPH Spray distance 165 mm Frequency of slots 3 SLPH: standard Liters per Hour 2.3. Characterization of as-sprayed Coating The Cr3C2-25NiCr layering has been characterized with the help SEM and EDS analysis. This morphology was employed to calculate the permeability of deposited coating. SEM and EDS were utilized to characterize surface morphology & formation of oxide scales at the particular surface area of the sample material with the Cr3C2-25NiCr sprayed coating. 2.4 Oxidation and hot corrosion ExperimentsThe experiments were done at 800°C using silicon tube furnace inbuilt with PID temperature controller. The samples were finished, which will provide consistency of reaction while high temperature corrosion occurs. Then dimensions computed by digital vernier calipers to find the surface area which give the relation between weight change per unit area versus the number of cycles. Finally, samples were polished with ethanol then put on alumina boat. This alumina boat before starting experiment was kept in the tube furnace for 4- 5 hours at 240°C and then kept in the furnace at 800°C for 2-3 hours so that moisture has been totally removed. Before inserting the sample inside the tube weight was taken and then placed in the tube furnace. Oxidation and hot corrosion behaviors of bare and coated steel SA213 have been investigated in oxidizing and salty environments under cyclic conditions at 800°C for 50 cycles. Each cycle sample heating one hour at 800°C in tube furnace followed by 25 minutes cooling at ambient temperature and their weight were taken by electronic balance having the sensitivity of 0.001gms.Small parts scales were also taken into account which falls into the boat i.e. the total weight was measure along with the boat. 3. Result and Discussion 3.1 Kinetics of Air and Salt environment at Elevated Temperature - The oxidation and hot corrosion of samples which occurred in air and salt at a temperature of 800°C is shown by plotting a graph. Fig 1. Shows, number of cycles on x-axis and on y-axis weight gain/area (mg/cm2) was taken. Both bare SA213 specimen in oxidation and hot corrosion environment were attributed weight gain up to 10 cycles followed by maximum weight loss 26 mg/cm2 at the end of exposure in air and maximum weight gain 18 mg/cm2 in presence of aggressive environment. The mass loss of this case may be attributed to the formation of some volatile phases or large spalling, during the oxidation studies and weight gain showed the higher oxidation rate. The behavior of bare boiler steel SA213 was not protective non-parabolic. In coated specimen SA213, oxidation and hot corrosion alloy steels have been attributed continuous weight gain, which may be due to higher oxidation rate of the coated specimen. The air is interrupted during the deposition of detonation gun coating and sheltered in the pores, science cooling of the coating was rapid, and there is shortage of time for the residual air to react with the surrounding coating alloy. Fig.2. shows the square graph of weight change/area against number of cycle which gradient, denotes the parabolic rate constant (Kp).The values of Kp based upon the parabolic rate equation, y2 = (Kp. t) + constant, where y is the weight change per unit surface area, t is the time of exposure, and Kp is the parabolic rate constant. The value Kp have been found for bare and coated specimen in presence of excess air, 665.64 x 10-10 g2 /cm4 s-1& 5.43 x 10-10 g2 /cm4 s-1 respectively. The value of Kp for both bare and coated specimen in presence of salty environment were observed to be 324 x 10-10 g2 /cm4 s-1& 37.21x 10-10 g2 /cm4 s-1 respectively. 25 SA213(UC-OXIDATION) 20 SA 213(C-OXIDATION) SA213(UC-HOT CORROSION) 15 SA213(C-HOT CORROSION) Weight Change mg/cm2 10 5 0 1 8 15 22 29 36 43 50 -5 -10 -15 -20 -25 -30 Number of cycles Fig.1.Weight gain against number of cycles plots for the bare and coated with Cr3C2- 25NiCr coating on SA213 subjected to air and salty environment (Na2SO4+50%NaCl) at 800°C for 50 cycles. 800 SA213(UC-OXIDATION) SA 213(C-OXIDATION) SA213(UC-HOT CORROSION) SA213(C-HOT CORROSION) Linear (SA213(UC-OXIDATION)) Linear (SA 213(C-OXIDATION)) Linear (SA213(UC-HOT CORROSION)) Linear (SA213(C-HOT CORROSION)) 700 (Weight change/Area)2 (mg/cm2)2 600 500 400 300 200 100 0 1 8 15 22 29 36 43 50 -100 -200 Number of cycles Fig.2. shows [weight change/area]2 against number of cycles, for bare and coated with Cr3C2-25NiCr coating on SA213 in air and salty environment(Na2SO4+50%NaCl) at 800°C for 50 cycles. 3.2 EDS: The surface morphologies with EDS spectrum for bare and 75%Cr3C2-25%NiCr sprayed coating on SA213, in presence of excess air and salty environment at 800°C for 50 cycles are shown in fig. 3(a), fig. 3(b), fig.3(c), fig. 3(d) respectively. The EDS spectrum of the bare and coated samples in presence of air [fig. 3(a) & fig. 3(b)] have shown peaks of Fe, Cr, Si & Ni, Cr, Si respectively, but in cases of salty environment bare and coated samples [fig.3(c) & fig. 3(d)] have shown peaks Fe, Cr in both cases. In coated sample the percentage of Cr is more and less Fe, as compared to bare sample. So that coated sample in presence of air, Ni, Cr and in presence of salt, Cr, have been found to be in dominance mode. Hence the probability to formation of anti-corrosive Cr2O3 oxides is maximum in presence of air because Ni works as catalyst on the material surfaces. Si-1.25% Cr-16.39% Fe-50.51% Si-2.24% Cr-19.66% Ni-78.10% (a) (b) Si-0.95% Cr-0.87% Fe-88.43% Cl-1.1% Cr-5.33% Fe-72.03% (c) (d) Fig.3 Surface scale morphology and EDS analysis (wt.%) for bare and coated SA213 boiler steel sample shown in fig.3(a)&(b) in presence of air and fig.3(c)&(d) in presence of salty environment, subjected to the cyclic oxidation at 800°C for 50 cycles. 3.3 SEM (Scanning Electron Microscopy) (a) (b) (c) (d) Fig.4. SEM micrographs of (a) SAE-213 bare & (b) SAE-213 coated in presence of air (c) SAE-213 bare & (d) SAE-213 coated in presence of salty environment (Na2SO4 -50% NaCl) at 8000C for 50 cycles. Figure4. (a) & (b) Shows the surface morphology of bare SA213 and coated sample in presence of air. In bare sample shows large spalling in the form of chips but the surface morphology of Cr3C2-25%NiCr coating on SA213 alloy oxidized at 8000C reveals that small spallations has taken place and pits can also be seen on the surface. EDS analysis, presence of large quantity of Fe, Cr in bare sample and Ni, Cr in coated sample. Ni works as catalyst in presence of Cr, hence probability to formation of Cr2O3 oxide is maximum, which find more protective in presence of air. Figure4. (c) & (d) Shows the surface morphology of bare SA213 and coated sample in presence of salty environment. Among bare and coated samples, in salty environment, bare sample showed huge spallation as compared to the coated sample. Due to presence of higher amount Fe, probability of formation of Fe2O3 dominated which revealed by EDS plots, which were also reported by M. Kaur et.all  & Manpreet Kaur et.all. 4. Conclusions The cyclic oxidation and hot corrosion of SA213 boiler steel in air & salty environment follows parabolic law but in SA213 boiler steel after 10th cycle it showed maximum weight loss ( 26 mg/cm2) upto 50 cycles in presence of airy environment but in presence of salt, both bare and coated samples showed weight gain upto 50 cycles. The value of Kp for bare and coated specimen in presence of air and salt environment have been found 665.64 x 10-10 g2 /cm4 s-1& 5.43 x 10-10 g2 /cm4 s-1and 324 x 10-10 g2 /cm4 s-1& 37.21x 10-10 g2 /cm4 s-1 respectively. The Cr3C2-25%NiCr sprayed coating was found to have composite structure of Ni in presence of air and granules structure in presence of salty environment. Bare SAE-213 steel, suffered intense spalling of the scale during the oxidation (weight loss) while hot corrosion suffered with a significant overall weight gain. The Detonation gun sprayed Cr3C225NiCr coating found to be best adherence on the boiler steel in both envoirement. 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