Creep of MgO-Y2O3 nanocomposite optical ceramic

Creep rates were measured on MgO-Y2O3 nanocomposite optical ceramic (NCOC) samples in compression at 1200 degrees C, 1300 degrees C, 1400 degrees C, and 1500 degrees C and at stress from 5 to 150 MPa. The NCOC samples had log-average grain-size distributions of -0.39 +/- 0.19 (Log mu m) for MgO and -0.49 +/- 0.10 (Log mu m) for Y2O3. At 1500 degrees C, there was significant grain growth during creep, with MgO grain-size doubling in 34 h. Some samples were deformed to over 20% strain; strain of 38% at 100 MPa in 36 min at 1400 degrees C was the largest observed. Strain rates at 1% strain fit an Arhennius power-law expression with a flow stress exponent of 2.6 and an activation energy of 488 kJ/mol. There was significant strain hardening that increased with decreasing stress and increasing temperature. Transmission electron microscopy and scanning electron microscopy characterizations show narrow deformation bands with fracture, microfracture, cavitation, and MgO grains with dense dislocation forests, interspersed with large regions without visible evidence of deformation. Grain shape did not change during creep. Deformation mechanisms and applications of the results are discussed.