Thermomechanical behavior of mullite
- INCAR CSIC, Oviedo (Spain)
- GEMPPM INSA de Lyon, Villeurbanne (France)
- ICV CSIC, Madrid (Spain)
- ICMM-CSIC, Madrid (Spain)
In the present work a complete analysis of the mechanical properties of dense mullite compacts and their relationship with microstructural features is made. The flexural strength curve shows three different regions corresponding to a low temperature region (20--600 C) with a transgranular fracture of mullite grains, a medium temperature region (600--1,200 C) where an increase in {sigma}{sub f} is observed due to a lower stress intensity factor value at the tip of the critical defects due to a poor load transmission across the sample, and a high temperature range (T > 1,200 C) were fracture appears at lower stress, first by non-catastrophic intergranular propagation up to a critical size where transgranular fracture takes place. Fracture toughness was found to be highly dependent on the deformation rate. The low value of the stress exponent in the creep law (n = 1 at 1,200 C) is associated with diffusion assisted by a sliding process. The diffusional shape changes of the mullite grains are accommodated by grain boundary sliding assisted by viscous flow of the glassy phase. Due to the high sintering temperature (> 1,600 C) required to obtain dense mullite compacts, a silica rich glassy phase is present at grain boundaries leading to plastic deformation under load at high temperatures. The thermomechanical behavior of mullite is controlled by the viscosity of such a grain boundary amorphous phase and has been determined by using the internal friction technique.
- Sponsoring Organization:
- European Union EU, Brussels (Belgium)
- OSTI ID:
- 483608
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 3 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
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