Development of Oxidation Resistive Coating for High Temperature Applications

Abstract

Titanium and its alloys are commercially used in airplanes, missiles, and rockets owing to high mechanical strength, low weight, and prone to oxidation resistance at high temperatures. Aluminide coatings were developed on titanium alloy (Ti-6Al-4V) substrate to protect them from oxidation at high temperature. Coatings were deposited by solid-state diffusion reaction through, chemical vapor deposition (CVD) by adopting halide activated pack cementation (HAPC) technique. The pack consisted of 20 wt% source materials (Al), 10 wt% activator (NH₄Cl) and 70 wt % Al₂O₃ used as a filler. The aluminide coating was carried out for 3 hours at 1000°C. The coated and bare (Ti-6Al-4V) substrates were characterized for structural, microstructural, elemental analysis and thermal stability using X-ray diffraction (XRD), optical microscope (OM) and thermal gravimetric analysis (TGA) respectively. XRD spectra confirm the high concentration of Ti-phase in the Ti-6Al-4V substrate. Aluminum rich phase (Al₃Ti) identified in aluminide coated substrate. Optical micrographs revealed that 60μm aluminide thick coating was developed. TGA results concluded that the (Ti-6Al-4V) bare substrate was not stable and oxidized beyond 600°C in air. The substrate coated with aluminide coating showed good thermal stability up to 1000°C.