Mechanical Properties of Transparent Polycrystalline Alumina Ceramics Processed Using an Environmentally Benign Thermal Gel Casting Process
- 760 Downloads
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.
KeywordsSubmicron alumina Hot isostatic pressing Microstructure Hardness Fracture toughness Fracture energy
One of the authors (NEP) is grateful to Dr. K Tamilmani, Distinguished Scientist and CE (Airworthiness), CEMILAC for his encouragement and support.
- 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
- 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.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
- 8.Krell A, Strassburger E (2002) High-purity submicron Al2O3 armor ceramics: design, manufacture, and ballistic performance. Ceram Trans 134:463–471Google Scholar
- 10.Agrawal D, Cheng J, Roy R (2002) Microwave reactive sintering to fully transparent aluminum oxynitride (AlON) ceramics. Ceram Trans 134:587–593Google Scholar
- 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.Pascucci M. Aerodynamic infrared dome. CeraNova Corporation. Website-www.ceranova.com
- 20.Lange FF (1974) Fracture mechanics of ceramics I. Bradt RC, Hasselman DPH, Lange FF (ed) Plenum, New York, pp 3Google Scholar