Abstract
Molybdenum-silicon-boron-titanium-iron (Mo-Si-B-Ti-Fe) alloys are of interest for high temperature applications primarily due to their superior creep resistance. However, these alloys have high corrosion rates in high temperature environments, thereby necessitating the need for protecting the surface of these alloys against oxidative attack. Aluminizing is one approach that could be effective. A Mo–12.5Si–8.5B–25Ti–2Fe (atom %) alloy was aluminized using halide activated pack cementation (HAPC). The process was carried out at 750°C, for times ranging from 1 to 25 hours in an argon environment. The aluminized specimens were characterized using X-ray diffractometry (XRD), optical microscopy and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Coating thickness, structure, phase identification and elemental compositions were obtained using these techniques. The morphologies for different coating times in the 1–25 h range demonstrate a single layer coating that increases in thickness with processing time. Cyclic oxidation tests of both aluminized and as-received Mo-Si-B-Ti-Fe were conducted for several cycles with each cycle consisting of a 1-hour hold at 800°C followed by room temperature exposure for 10 minutes. Aluminized coupons exhibited superior oxidation resistance relative to the as-received alloys of Mo-Si-B-Ti-Fe.
