Mechanical properties of solid oxide fuel cell glass-ceramic seal material. G18, are studied at high temperatures. Samples of G18 are aged for either 4h or 100 h, resulting in samples with different crystallinity. Reduced modulus, hardness, and time-dependent behavior are measured by nanoindentation. The nanoindentation is performed at room temperature, 550, 650, and 750 degrees C, using loading rates of 5 mN s(-1) and 25 mN s(-1). Results show a decrease in reduced modulus with increasing temperature, with significant decrease above the glass transition temperature. Hardness generally decreases with increasing temperature, with a slight increase before Tg for the 4 h-aged sample. Dwell tests show that creep increases with increasing temperature, but decrease with further aging. (C) 2011 Elsevier B.V. All rights reserved.