Effect of post annealing on the microstructure, mechanical properties, and failure of MoxW1-xSi2 heaters produced by self-propagating high-temperature synthesis

Abstract

High-performance tungsten molybdenum disilicide (MoxW1-xSi2) heating elements were prepared using a self-propagating high temperature synthesis process. The effect of post annealing on the degradation behavior of the alloy was experimentally investigated. Increasing the attrition milling time up to 20 min during powder preparation resulted in MoxW1-xSi2 heaters with the highest density, which increased the fracture strength compared to samples with shorter attrition times. Such samples were annealed and evaluated as heating elements using accelerated degradation tests and failure analysis in order to compare their structural characteristics and flexural strength with as-fabricated samples. The annealed MoxW1-xSi2 heater showed a relatively dense structure with few pores and no secondary phases, apart from a SiO2 layer. This favorable structure prevented bubble formation, which can result in fracturing of the heater, as revealed by evaluation at high temperatures with various heating rates. The flexural strength of the annealed specimen was 2.5-times higher than that of the as-fabricated specimen, which was attributed to removal of secondary phases during annealing. Failure time and surface load analyses were used to investigate the fracture mechanism of the MoxW1-xSi2 heaters in detail at 1790 °C by quantifying bubble formation and the presence of secondary phases.