High temperature oxidation of LaB6-ZrB2 eutectic in situ composite

LaB6-ZrB2 eutectic in situ composites are interesting candidates for manufa cture of turbine blades because of their excellent mechanical properties. T he oxidation behavior of LaB6-ZrB2 eutectic in situ composites prepared by electric are melting was studied in a temperature range of 916-1223 degrees C and in a pressure range of 1.5x10(4)-7.2x10(4) Pa. The specific weight c hange of the LaB6-ZrB2 eutectic obeys the Arrhenius equation below the oxid ation temperature of 1094 degrees C and appears to obey a paralinear equati on above this temperature. The rate of weight change is described by k(p) = 9.71 x 10(-3) exp(-31000/RT) mg(2)/cm(4) min in the range 916-1094 degrees C. Above 1094 degrees C, rapid oxidation kinetics were observed, La2O3. B2 O3 and La2O3. 3B(2)O(3) being the primary scale constituent with ZrO2 defic iency in the outer scale. The oxidation increases with P-O2 up to 3.9 x 10( 4) Pa, above which the trend is reversed due to the active oxidation of ZrB 2. The oxidation appears to be controlled by oxygen diffusion through the s cale and the oxidized layers consist mainly of La2O . B2O3, La2O3. 3B(2)O(3 ) and trace of ZrO2. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.