Solid-state processing of oxidation-resistant molybdenum borosilicide composites for ultra-high-temperature applications

The high-temperature capabilities of multi-phase composites based on Mo5Si3Bx are examined after solid-state processing and pulsed laser deposition (PLD) coating fabrication approaches. These composites are prepared by mechanical alloying of elemental powders and densified by vacuum hot pressing, which is a scalable processing approach. Chemical analyses of the hot-pressed compacts reveal a consistent 15-22 percent loss of boron, which is primarily due to the high-temperature hot-pressing step. Composites possessing sufficient amounts of boron are evaluated by thermogravimetric studies in temperatures up to 1650 A degrees C in air. One composition demonstrates oxidative stability after long-term (100 h) isothermal conditions, as well as thermal cycling to simulate solar-thermal operation. Hot-pressed samples of composites consisting of Mo5Si3Bx + MoSi2 + MoB are also employed as deposition targets for PLD trials. X-ray diffraction analysis of the resulting films indicates the absence of long-range crystallographic order.