LOGIN TO YOUR ACCOUNT

Username
Password
Remember Me
Or use your Academic/Social account:

CREATE AN ACCOUNT

Or use your Academic/Social account:

Congratulations!

You have just completed your registration at OpenAire.

Before you can login to the site, you will need to activate your account. An e-mail will be sent to you with the proper instructions.

Important!

Please note that this site is currently undergoing Beta testing.
Any new content you create is not guaranteed to be present to the final version of the site upon release.

Thank you for your patience,
OpenAire Dev Team.

Close This Message

CREATE AN ACCOUNT

Name:
Username:
Password:
Verify Password:
E-mail:
Verify E-mail:
*All Fields Are Required.
Please Verify You Are Human:
fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Cain, M. G. (Markys G.)
Languages: English
Types: Doctoral thesis
Subjects: QC
The objectives for the thesis were to generate tough ceramics utiising the toughening\ud mechanisms inherent to zirconia materials. The aims have been realised with the\ud successful fabrication of hot pressed silicon nitride / zirconia composite ceramics.\ud The zirconia was prestabilised with two different types of dopant additives, yttria\ud and ceria, with the intention of understanding the chemical compatibility with the\ud silicon nitride matrix and the overall effect on the subsequent mechanical properties.\ud The volume fraction of added zirconia was also varied. The increased toughness over\ud silicon nitride materials alone was attributed to the toughening agents inherent to\ud zirconia which existed either in the form of the tetragonal polymorph or the monoclinic\ud variant. The toughening modes were dependent on initial chemistry of the\ud composite system. When the zirconia was prestabilised with yttria the tetragonal\ud polymorph was retained within the composite. The enhanced toughness was attributed\ud to a transformation toughening mechanism. However, when the zirconia\ud was prestabiised with ceria the depletion of Ce from solid solution with the zirconia\ud during processing resulted in the formation of the unstabiised monoclinic variant.\ud The enhanced toughness was attributed, in this case, to a microcrack type energy\ud absorption mechanism, similar to several ZTA composite ceramics.\ud Additionally, an experiment using ultrasound non-destructive testing, indicated\ud that Tetragonal Zirconia Polycrystals (TZP) is ferroelastic and, as such, can provide\ud a significant contribution to enhanced levels of fracture toughness in these materials\ud or composites containing the same. Further work has been conducted to actually\ud observe, as a function of applied unia.xial stress, the crystallographic changes occurring\ud within the bulk of a 3Y-TZP ceramic via neutron elastic scattering at the ILL,\ud Grenoble, France. This experiment has provided clear direct proof of the ferroelastic\ud nature of zirconia. A similar experiment will be carried out at the Rutherford\ud Laboratory, though with significantly improved statistics.\ud An approach to improve the high temperature properties of TZP via the chemical\ud alteration of the grain boundary phase was also considered. As a preliminary step\ud the grain boundary volume was increased through controlled additions of the grain\ud boundary composition in the form of both a premilled and a premelted glass. Poor\ud fired densities were attained, however, due to the solute additive partitioning from\ud the generation of an enhanced grain boundary phase to overstabilisation of the\ud zirconia resulting in the formation of cubic stabilised zirconia. Furthermore, the\ud incorporation of nitrogen within the grain boundary phase, via sintering TZP with\ud sole additions of A1N, resulted in the attainment of poor fired densities and hence\ud was not considered a suitable method for grain boundary modification.
  • The results below are discovered through our pilot algorithms. Let us know how we are doing!

    • Lewis M H 'Nitride Ceramics for Gas Turbine Applications', in First Parsons International Turbine Conference, Parsons Press, Trinity College Dublin, Institution of Mechanical Engineers London, 181-189 (1984).
    • Cer., p 2473 (1987).
    • Fisher G, Bull. Am. Cer. Soc., , [2], 249-252 (1984).
    • Mechoisky J J, Bull. Am. Cer. Soc., , [2], 367 (1989).
    • Mechoisky J J, ibid, p.367-368.
    • Lewis M H, 'Ceramics, Applications and Limitations', in Materials at their Limits, Proc. Inst. Metals, Inst. Metals, 1-20 (1986).
    • Stevens R, 'An Introduction to Zirconia', Written for Magnesium Elektron Publication No.113.
    • Garvie R C, Nature, , 703 (1975).
    • Jack K, J. Mat. Sci., II, 1135 (1976).
  • No related research data.
  • No similar publications.

Share - Bookmark

Cite this article