The degradation mechanism of MoxW1-xSi2 ultrahigh-temperature heating elements fabricated by selfpropagating high-temperature synthesiswas investigated. The MoxW1-xSi2 specimens (with and without post-annealing) were subjected to ADTs (accelerated degradation tests) at temperatures up to 1,700℃ at heating rates of 3, 4, 5, 7, and 14℃/min. The surface loads of all the specimen heaters were increased with the increase in the target temperature. For the MoxW1-xSi2 specimens without annealing, many pores and secondary-phase particles were observed in the microstructure; the surface load increased to 23.9 W/㎠ at 1,700℃, while the bending strength drastically reduced to 242 MPa. In contrast, the MoxW1-xSi2 specimens after post-annealing retained single- MoxW1-xSi2 phases and showed superior durability after the ADT. Consequently, it is thought that the formation of microcracks and coarse secondary phases during the ADT are the main causes for the degraded performance of the MoxW1-xSi2 heating elements without post-annealing.
