b3 ioana csaki
TRANSCRIPT
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Composite Plasma Coating Steel to Use in Geothermal Condition
1 Metav- R&D, Bucharest, 31 C.A.Rosetti St, 020011, Romania 2“Politehnica” University Bucharest, 313, Splaiul Independentei, 60042, Romania.3 Tehnoid Com Ltd.,48 Baritiu St, 011295, Romania.4 Innovation Center Iceland-ICI, Arleyinir 2-8 Reykjavik , Iceland.5Orka Náttúrunnar,110 Baejarhals , Iceland.6 Vélvík ehf, 110 Hofðabakka, Reykjavik, Iceland.
Aurelian Buzăianu1, Ioana Csáki2, Petra Moţoiu3, Kolbrun Ragna Ragnarstottir4, Kristjan Leosson4, Adalsteinn Arnbjornsson4, Saemundur Guðlaugsson5, Daniel
Guðmundsson6
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Acknowledgements This work is supported by the Romanian Grant EEA Financial Mechanism Committee 2009-2014 and Iceland as Donor Stat. Bilateral Agreement Program Iceland – Romania: „Research within priority sectors”- Contract 16 SEE /30.06.2014 – GEOTUR Project.
Geothermal Iceland areas with temperature exceeding 2500C
at 3 km depth.
Geothermal Romania areas with temperature exceeding 1400C
at 3 km depth.
Iceland Romania
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University POLITEHNICA of Bucharest Materials Science &
Engineering Faculty
TEHNOID – Romanian SME Partner
METAV R&D – Project Coordinator
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Innovation Centre Iceland (ICI)Keldnaholt facility, Reykjavik
Our Nature (ON) power plant
VÉLVÍK EHF -Precision machining
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Turbine MHI rotor at Iceland Hellisheiði power plant
Main problem:
Defects in the coating surface allow turbulent eddies to form
Undercutting of the protective film
Damaging of the protective film
Beginning the undercut of the protective film
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Fig.1 Rotor erosion from water trapped in interstage area.
Fig.4. Water erosion damage on exhaus side on first stage nozze inner port wall.
Fig.2 Rotor eroded from scale deposition
Fig.3.Abrasive erosion of trailing edge of diaphragm vane caused by debris in steam.
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preventing corrosion
SOLUTIONS:
providing good reliability
ceramic materialsmetallo-ceramic
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Plasma spray process and schematic representation of METCO-4MP plasma jet metalizing device
Plasma spray process
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The specific experiments are related to the synthesis of new complex powder mixtures with different addition of Ni-Cr components and powder elements such as: Si-B-Al and 3.5 %WC to obtain complex-ceramic protective layers.
Commercial base metal powders• Cr (7-12 μm-99.5% pure); • Ni (4-8μm-99.5% pure); • Al (4.5μm-97.5% pure); • B (2-4μm-99.5% pure).
Plasma process (ASP&HVOF)
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Powders analysis
Elements Ni Cr Si B Al Fe OComposition (wt
%)65.78 20.09 5.50 2.04 0.52 4.47 1.60
Chemical composition of the base complex powders.
Characteristics of powder Apparent density Flow rate SizingNi20Cr5Si2B0.5Al
and 3.5W4.2g/cm3 3.3s/50g -43/+20µm
(mesh -330//+20µm)
Feature of the characteristics of complex powders
Powders flowing rate under atmospheric conditions
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SEM image of the cross-section morphology of the powder particles. The image shows the nano-size
elemental powder distributed in the atomized particle
SEM of complex powders Ni-Cr-B-Si-Al base. Gas atomized, rounded to spherical in shape
particles with relative smooth surfaces.
Powder microstructure analysis
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Presence of boron depresses the melting temperature and contributes to the formation of hard phases. Silicon is added to increases the self-fluxing properties, and NiCrSiBAl alloys are widely used because of the good resistance of boride, carbide and silicide solid phase to wear and steam corrosion.
EDX spectrum analysis of complex Ni-Cr-B-Si-Al powder particles.
Plasma HVOF parameters and EDX analysis
Gas Volume flow [SLPM]* Operating pressure [MPa]
Oxygen 250-350 1.0Propane 40-80 0.05
Air 450-600 0.07
* SLPM = Standard Liters per Minute Gas consumption.
Characteristics of experimental HVOF samples deposition
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The coating HVOF spray samples on substrate stainless steel 4307 (304L) to test the complex matrix composites
deposition in different geometrical shapes.
SEM image of multi-composite protection surface coating 65Ni20Cr5Si2B0.5Al
X 500
Plasma HVOF coating analysis
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Optimization of spraying parameters and stress relaxation processes will be as important as fixed thickness of steel deposition and properties cermets composite.
Oxygen [l/sec]
Propane [l/sec]
Air[l/sec]
Carrier gas pressure
Series 1 [atm]
Carrier gas pressure Series 2
[atm]
Carrier gas pressure Series 3
[atm]4.5 1.2 8 8.8 10.2 11.5
The experimental powder deposition and main specification of HVOF process
HVOF coating analysis
The Series 3 sprayed from at distance of 150 mm have the highest values of micro-hardness followed by the sample Series 3, that was sprayed at 200 mm.
Microstruture of the deposition layerNi-Cr-B-Si-Al
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The micro hardness of multi-composite coating 65Ni20Cr5Si2B0.5Al obtained in variables spray distances and operating pressures conditions
Microhardness results
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XRD analysis
Were observed the major cubic Cr6Ni16Si7 and tetragonal phases Cr0.7Ni0.3, - with the effects in carburizing and chlorination resistance.
Were observed to the minor orthorhombic phase Ni3B similar cemented structure and similar properties of silicides - chemically stable and inert.
The increase of Si content up to 5.50%, results in the presence of chromic silicides Cr5Si3.
A higher content of Si and B significantly lowers the plastic properties of the composite layers.
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The SEM analysis confirming the crystalline and fine size;The Cr0.7Ni0.3 improves adherence increase resistance of oxide layer, and hence improves oxidation, sulfidation and carburization resistance.
Scanning electron micrograph of a tipical coating composites plasma deposition powders used for thick-film (2) Ni-Cr-Si-B-Al and Ni-Co-Cr as a sub-layer (1)
2
1
HVOF coating results
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Formation of the protective coating oxide layer with plasma HVOF deposition is a practical way to decrease their oxidation and the corrosion rate of the geothermal turbines components. Thermal plasma deposition of Ni, Cr, B, Si or Al coatings form the stable oxides with low diffusion coefficients for oxygen.
The complex matrix composites greater corrosion and oxidation resistance and maintain hard hardness, strength and wear resistance up to operating geothermal steam conditions.
The spray distance is an important parameter to be considered for tuning the processing conditions and thus to maintain or even improve the adhesion of the coatings.
Conclusions
