• Selection of TBCs based on some basic requirements 1.High melting point2.No phase transformation between room temperature and operation temperature3.Low thermal conductivity4.Chemical inertness5.Thermal expansion match with the metallic substrate6.Good adherence to the metallic substrate and 7.Low sintering rate of the porous microstructure

•Four layers - Metal substrate, metallic bond coat, TGO and ceramic topcoat

• Ceramic layer - thermal gradient

• Produced mainly by EBPVD and APS

• YSZ - superior cycling life and established processability by EBPVD and APS

• YSZ- two degradation mechanisms operate

• LZ - Low thermal conductivity, Low sintering activity and High temperature phase stability

• Cubic pyrochlore structure with corner shared ZrO6 octahedra forming the back bone of the network and La(3+) ions fill the holes which are formed by 6 ZrO6 octahedra

• Stable up to approx. 2400 degree Celsius

Fig. 1 Phase diagram of La2O3-ZrO2 system

• Thermally sprayed coatings can provide wide variety of functional properties

• Depending on the type of spraying system i.e. spraying instrument and sprayed material, the desired properties can be achieved

• Oxide systems are used as thermal barrier coatings

• Focus of present work is to develop a new thermal barrier material and its characterization

• Objective of my work is to synthesize and characterize a thermal barrier coating material which has a reportedly higher temperature resistance than the existing commercial coating materials.

• Synthesis of powders

1.Co- precipitation technique – hydrated lanthanum nitrate and zirconium oxychloride with diluted ammonia 2.Solid state mixing technique – mixing of lanthanum oxide and zirconium oxide powders in 1:2 proportion

• Compaction technique

• Sintering technique and determination of sintered density

• XRD analysis of both the sintered pellets

• Microhardness and Weibull analysis (co-precipitated pellet)

• Porosity determination by image analysis

Fig. 2 Pellets obtained after compaction

Fig. 3 Pellets obtained after sintering

Average radius, r = 21.739/2 mm = 10.869 mmAverage thickness, h = 4.431 mm

Volume = ᴨr2h = 1643.806 mm3 = 1.643 cc

To account for the loss of the powder due to cracking of the edges during sintering and compaction, the volume is taken as 90% of this

volume.

Actual volume = 0.9 * 1.643 cc = 1.4787 ccWeight taken after sintering = 7.264g

Thus, sintered density = weight/ actual volume = 4.911 cc

Theoretical density of LZ powder = 5.963cc

Thus, sintered density = (4.911/5.963)*100 = ~82%

Microhardness ReadingsMicrohardness ReadingsFor the cross section of the co-precipitated sintered pellet,

Hardness = 7.335 GPaDeviation = 14.56%

For the surface of the co-precipitated sintered pellet,

Hardness = 8.783 GPa Deviation = 9.63 %

Fig. 8 Input and Output images for the cross section of the pellet

Fig. 9 Input and Output images for the surface of the pellet

I acknowledge my sincere gratitude; offer my cordial thanks to my respected sir Prof. N. Bandyopadhyay (Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur) for his kind co-operation, thankful assistance, grateful counsel and constant encouragement for initiating me into the field of “Synthesis and Characterization of a Novel Material for High Temperature Resistant Coating”.  I shall be failing my duty if I do not express my indebtness for Dr. Monojit Dutta (Head, Coated Product, Research Group, R&D TATA Steel), Abhisekh Pathak (Researcher, R&D TATA Steel), Anirban Chowdhury (Researcher, R&D TATA Steel) for their resourceful and lofty guidance in my project. I also acknowledge in debtness for the invaluable help of the books, journals, reports etc. mentioned in the reference. I owe gratefulness to many other laboratory assistants, research associates, supervisors, many other members in the Coated Product Group (R&D Division, TATA Steel) for their sympathetic help to complete this paper.

1. X.Q. Cao. , R. Vassen. , D. Stoever. , Ceramic materials for thermal barrier coatings. Journal of the European Ceramic Society 24 (2004) 1–10, Received 30 June 2002; received in revised form 20 February 2003; accepted 7 March 2003.

2. Carlos G. Levi. , Emerging materials and processes for thermal barrier systems. Current Opinion in Solid State and Materials Science 8 (2004) 77–91, Accepted 23 March 2004.

3. Qiang Xu., Wei Pan., Jingdong Wang., Chunlei Wan., Longhao Qi., Hezhuo Miao., Kazutaka Mori., Taiji Torigoe., Rare-Earth Zirconate Ceramics with Fluorite Structure for Thermal Barrier Coatings. J. Am. Ceram. Soc., 89 [1] 340–342 (2006) DOI: 10.1111/j.1551- 2916.2005.00667.

4. Robert Vassen., Xueqiang Cao., Frank Tietz., Debabrata Basu., Detlev Stover., Zirconates as New Materials for Thermal Barrier Coatings. J. Am. Ceram. Soc., 83 [8] 2023–28 (2000).