Microstructure and high-temperature internal friction of unidirectionally solidified Al2O3/YAG eutectic composite

High-temperature internal friction of unidirectionally solidified Al2O3/YAG eutectics and sintered Al2O3/YAG composites were examined up to 1400 degre esC in an ambient atmosphere, in comparison with Al2O3 single-crystal, The internal friction for all samples slightly increases with increasing temper ature at above 1000 degreesC, The internal friction of the sintered spcimen at 1400 degreesC was about seven times higher than that of the unidirectio nally solidified one. The internal friction of unidirectionally solidified composite was slightly higher than that of Al2O3 single-crystal, The differ ence in internal friction values among these samples strongly depends on th e Al2O3/YAG interfacial area per unit volume and may also be related to the characteristic of the grain boundary, The apparent activation energy calcu lated from the slope of Arrhenius plots was 180, 110, and 110 kJ/mol for th e sintered composite, the unidirectionally solidified Al2O3/YAG eutectic co mposite, and the Al2O3 single-crystal, respectively. The internal friction values at each temperature and/or the apparent activation energy for unidir ectionally solidified Al2O3/YAG eutectic composite and Al2O3 single-crystal are almost the same, which implies composite behaving as a material having no-interface. The shear modulus for all the tested samples gradually decre ased with increasing temperature.