Protective Coatings on Superalloys and C/SIC Composites for Efficient Gas Turbine Components /

Abstract

Energy is one of basic need of any human entity. Pakistan is 6th largest state in the world on the basis of population. It requires huge amount of energy to fulfill their demands. Pakistan producing approximately 65% of the total electricity from thermal power plants. Gas turbines are the essential part of thermal power sources. Objective of this research is to make turbine components more durable and sustainable under severe environmental conditions. There are two ways to meet the required energy demand, either to improve the process efficiency or to develop renewable energy source. Gas turbines used at thermal power plants are operated at temperature i-e normally 700-1000 ºC in a CHP loop while gas turbines used in aerospace application operated at very high temperature i-e 1400-1500 ºC. At this elevated temperature, the components of gas turbines are corroded and we must protect turbine components like Inlet section, Compressor, Blades and combustion chamber from heat, corrosion and wear. Under this research project, we used YSZ coating to protect superalloy from wear and silicon slurry optimization for C/SiC substrate. Firstly, we select the substrates, one is Monel-400 from superalloy category while other is C/SiC from ceramic matrix composites. The salient reasons behind the selection of these substrates are (i) Super alloys are used for the manufacturing of hot sections of gas turbines. (ii) C/SiC having high strength to weight ratio used in jet engine. (iii) Both having excellent mechanical and thermal properties. Silicon slurry was optimized by varying the concentration of silicon powder, solvent and dispersant, coating process deposit this slurry via dip coater on C/SiC substrate. On Monel-400 we used bilayer concept and deposit aluminum as a bond coat and 7YSZ as top coat via thermal spray process. After deposition of bond layer, we performed thermal annealing at 500 ºC to form nickel-aluminum bonding. This thing strengthens the bond layer and provide excellent surface for top coat. Then characterized the coated coupon with different tools like XRD, SEM, EDX and especially via tribometer to check the wear rate and compare it with non-coated sample. It was observed that coated sample having much less wear rate i-e 1.38% than non-coated sample under 5N load condition and this coating definitely enhance the efficiency of turbine components against wear and tear.