Growth kinetics of a silicon-modified aluminide coating on a TiNM-B1 intermetallic alloy

TiAl-based intermetallic alloys are used as a structural material in high-temperature applications such as aircraft and turbine engines. To improve the mechanical properties of TiAl, it is often modified by adding other elements such as niobium or chromium. The one of disadvantages of TiAl alloys is not sufficient oxidation resistance. The pack cementation process is one well-known method of modifying TiAl, which involves coating the surface of the alloy with a special mixture containing silicon, to enrich it with this element. As a result of this process, Si-modified aluminide coating is formed, which exhibits improved resistance to high temperatures, making it ideal for use in the aerospace and turbine industries. The study was conducted on a substrate of one of the latest generation of TiAl alloys which we have not yet analyzed. The powder used in the pack cementation process consisted of 20 wt.% Si, 20 wt.% Al, 2 wt.% NH4Cl activator, and the rest Al2O3, as well as 40 wt.% Si, 40 wt.% Al, 1-2% NH4Cl activator, and the rest Al2O3 calculated for 100 g of powder. The process was carried out at a temperature of 950°C for 2, 4, and 6 hours. The following analyses were performed after the pack cementation process: scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) attachment for microanalysis, as well as X-ray diffraction (XRD). Test results indicated a coating structure typical of silicon-modified coatings including the presence of titanium silicides. It was found that increasing the silicon content causes a significant increase in coating thickness.