Comparison of the high-temperature deformation of alumina-zirconia and alumina-zirconia-mullite composites
- PDF / 308,728 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 240 Views
An alumina-based ceramic codispersed with 15 vol% zirconia and 15 vol% mullite (AZM) was synthesized by reactive processing, and the creep behavior was compared to alumina with 30 vol% zirconia (AZ). Constant stress compressive creep behavior for AZM exhibited a stress exponent of 2 and an activation energy of 770 KJ/mol, while a similar stress exponent but lower activation energy of 660 KJ/mol was found for AZ. The strain rate of AZM, however, was more than twice that of the AZ under the same deformation conditions, indicating a better potential for superplastic shape forming.
High-temperature deformation in fine-grained pure alumina is limited in both tension and compression.1–4 The elongation to failure of pure alumina is reported to be less than 20%1 due to extensive dynamic grain growth during high-temperature deformation. Grain growth during deformation causes strain hardening and cavitation, resulting in fracture. Therefore, grain size stability is considered to be one of the most important factors to be controlled to achieve superplastic deformation in finegrain alumina-based ceramics. Several different methods have been used to limit grain growth in alumina during high-temperature deformation. Doping Al2O3 with MgO lowers the grain boundary mobility through a solute drag effect.5 A second phase dispersion of zirconia in Al2O3 is even more effective in impeding the static and dynamic grain growth through second phase pinning. It has been shown that the alumina grain growth at 1650 ºC in a 50/50 alumina/cubic zirconia composite is 100 times slower than that of pure alumina.6 The slow grain growth is attributed to limited solid solubility and the extended diffusion paths due to reduced interconnection of similar phases. Taking this concept a step further, a fine-grain three-phase zirconia-alumina-spinel ceramic composite was demonstrated to exhibit high strain rate superplasticity with a strain of more than 1050% in tension and a strain rate of 0.4 s−1 at 1650 ºC.7 The high strain rate and high strain to failure was attributed to a combination of limited grain growth in the tri-phase structure and dislocation-induced plasticity in the zirconia particles.7 The three phase microstructure more effectively increases the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0029 J. Mater. Res., Vol. 20, No. 1, Jan 2005
http://journals.cambridge.org
Downloaded: 24 Mar 2015
separation distance between the same phases and increases the cation diffusion path length, inhibiting grain growth. Since limited high-temperature deformation studies have been performed in three-phase material systems other than zirconia-alumina-spinel, this paper examines the effect of a three-phase microstructure on the creep behavior of alumina with zirconia, and alumina with zirconia and mullite. These two-phase and three-phase alumina-based ceramic composites were synthesized with the same volume fraction of alumina. The effect of the codispersion of zirconia and mullite on the hightemperature def
Data Loading...
