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Experimental Mechanics

, Volume 53, Issue 1, pp 123–129 | Cite as

Mechanical Properties of Transparent Polycrystalline Alumina Ceramics Processed Using an Environmentally Benign Thermal Gel Casting Process

  • G. SundararajanEmail author
  • P. Biswas
  • N. Eswara Prasad
Article

Abstract

Technological advancements in ceramic powder synthesis, shaping and sintering have made it possible to tailor the microstructural, mechanical and optical property relationships in the case of advanced transparent ceramic materials. Transparent polycrystalline alumina (TPCA) is the hardest known transparent ceramic and one of the emerging candidate materials for transparent armour applications. The prerequisites for obtaining transparency with the high hardness, is to achieve the sintered average grain sizes <1 μm in combination with density close to the theoretical value. This paper outlines the processing of TPCA by an environmentally benign methyl cellulose based thermal gel casting (MCTG) process, which is employed for the first time in shaping of the TPCA. The green specimens shaped through this technique were pressureless sintered (PLS) to >96 % density at an optimum temperature of 1350 °C. The post sintering by Hot Isostatic Pressing (HIP) at an optimum temperature of 1350 °C and a pressure of 195 MPa resulted in >99.5 % of the theoretical density and a grain size of 0.7 μm. For the sake of comparison, conventional polycrystalline alumina samples (non-transparent) were also processed by sintering at 1550 °C under PLS condition with nearly the same densities (designated as PCA). The TPCA thus developed exhibit a combination of high hardness of 21 GPa, flexural strength of 550 MPa and excellent fracture resistance properties as compared to conventional PCA samples.

Keywords

Submicron alumina Hot isostatic pressing Microstructure Hardness Fracture toughness Fracture energy 

Notes

Acknowledgements

One of the authors (NEP) is grateful to Dr. K Tamilmani, Distinguished Scientist and CE (Airworthiness), CEMILAC for his encouragement and support.

References

  1. 1.
    Krell A, Blank P, Ma H, Hutzler T, Van Bruggen MPB, Apetz R (2003) Transparent sintered corundum with high hardness and strength. J Am Ceram Soc 86(1):12–18CrossRefGoogle Scholar
  2. 2.
    O YT, Koo J, Hong KJ, Park JS, Shin DC (2004) Effect of grain size on transmittance and mechanical strength of sintered alumina. Mater Sci Eng A374:191–195Google Scholar
  3. 3.
    Gentilman R, McGuire P (2003) Large-area sapphire windows. Proc SPIE 5078:54–60CrossRefGoogle Scholar
  4. 4.
    Tatartchenko VA (2005) Sapphire crystal growth and applications. In: Capper P (ed) Bulk crystal growth in electronic, optical and optoelectronicmaterials. John Wiley & Sons, Ltd, New York, pp 299–338Google Scholar
  5. 5.
    Krell A, Baur G, Dähne C (2003) Transparent sintered sub-μm Al2O3 with IR transmissivity equal to sapphire. In: Tustison RW (ed) Window and dome technologies VIII, Proceedings of SPIE conference (Orlando, FL/USA, April 22–23, 2003), Vol. 5078, Washington, pp 100–207Google Scholar
  6. 6.
    Wei GC, Hecker A, Goodman DA (2001) Translucent polycrystalline alumina with improved resistance to sodium attack. J Am Ceram Soc 84(12):2853–2862CrossRefGoogle Scholar
  7. 7.
    Krell A, Blank P, Ma H-W, Hutzler T, Nebelung M (2003) Processing of high- density submicrometer Al2O3 for new applications. J Am Ceram Soc 86(4):546–553CrossRefGoogle Scholar
  8. 8.
    Krell A, Strassburger E (2002) High-purity submicron Al2O3 armor ceramics: design, manufacture, and ballistic performance. Ceram Trans 134:463–471Google Scholar
  9. 9.
    Krell A, Klimke J, Hutzler T (2009) Advanced spinel and sub-μm Al2O3 for transparent armour applications. J Eur Ceram Soc 29:275–281CrossRefGoogle Scholar
  10. 10.
    Agrawal D, Cheng J, Roy R (2002) Microwave reactive sintering to fully transparent aluminum oxynitride (AlON) ceramics. Ceram Trans 134:587–593Google Scholar
  11. 11.
    Shimada M, Endo T, Saito T, Sato T (1996) Fabrication of transparent spinel polycrystalline materials. Mater Lett 28(4–6):413–415CrossRefGoogle Scholar
  12. 12.
    Krell A, Hutzler T, Klimke J. Physics and Technology of Transparent Ceramic Armor: Sintered Al2O3 vs Cubic Materials. RTO-MP-AVT-122Google Scholar
  13. 13.
    Pascucci M. Aerodynamic infrared dome. CeraNova Corporation. Website-www.ceranova.com
  14. 14.
    Medvedovski E (2010) Ballistic performance of armour ceramics Part-I. Ceram Int 39:2103–2115CrossRefGoogle Scholar
  15. 15.
    Li J, Ye Y (2006) Densification and grain growth of Al2O3 nanoceramics during pressureless sintering. J Am Ceram Soc 89:139–143CrossRefGoogle Scholar
  16. 16.
    Usmatsu K, Sekiguchi M, Kim JY, Saito K, Mutoh Y, Inoue M, Fujino Y, Miyamoto A (1993) Effect of processing conditions on the characteristics of pores in hot isostatically pressed alumina. J Mater Sci 28:1788–1792CrossRefGoogle Scholar
  17. 17.
    Mizuta H, Oda K, Shibasaki Y, Maeda M, Machida M, Ohshima K (1992) Preparation of high-strength and translucent alumina by hot isostatic pressing. J Am Ceram Soc 75(2):469–473CrossRefGoogle Scholar
  18. 18.
    Godlinski D, Kuntz M, Grathwohl G (2002) Transparent alumina with submicrometer grains by float packing and sintering. J Am Ceram Soc 85(10):2449–2456CrossRefGoogle Scholar
  19. 19.
    Krell A, Blank P, Ma H-W, Hutzler T, Nebelung M (2003) Processing of high-density submicrometer Al2O3 for new applications. J Am Ceram Soc 86(4):546–553CrossRefGoogle Scholar
  20. 20.
    Lange FF (1974) Fracture mechanics of ceramics I. Bradt RC, Hasselman DPH, Lange FF (ed) Plenum, New York, pp 3Google Scholar
  21. 21.
    Eswara Prasad N, Kumari S, Kamat SV, Vijayakumar M, Malakondaiah G (2004) Fracture behaviour of 2D-weaved silica-silica continuous fibre-reinforced, ceramic-matrix composites (CFCCs). Eng Fract Mech 71:2589–2605CrossRefGoogle Scholar
  22. 22.
    Armstrong RW, Cazacu O (2006) Indentation fracture mechanics toughness dependence on grain size and crack size. Application to alumina and WC-Co. Int J Refractory Metals & Hard Mater 24:129–134CrossRefGoogle Scholar
  23. 23.
    Krell A, Hutzler T, Klimke J (2008) Transmission physics and consequences for materials selection, manufacturing, and applications. J Eur Ceram Soc 29(2):207–221CrossRefGoogle Scholar

Copyright information

© Society for Experimental Mechanics 2012

Authors and Affiliations

  1. 1.International Advanced Research Centre for Powder Metallurgy and New MaterialsHyderabadIndia
  2. 2.Regional Centre for Military Airworthiness (Materials), CEMILACHyderabadIndia

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