Modern aerospace engineering requires using titanium-based alloys with enhanced high-temperature strength properties and heat resistance. These requirements can be fulfilled by modifying alloys’ structure employing rare earth metal doping. Gadolinium is particularly suitable doping element but direct addition of metallic gadolinium to titanium is complicated due to high chemical activity of gadolinium and significant vapor pressure at elevated temperatures. To overcome these complications gadolinium-containing master alloys with relatively low Gd content can be employed, and Gd-Al master-alloy is particularly attractive since aluminum is also one of major components of titanium alloys for aerospace applications. There are several approaches to fabrication of gadolinium-aluminum master alloys including electrolysis, alumothermic reduction, exchange reactions, etc. Most of them require specific equipment. The easiest and reliable method for Al-Gd master-alloy synthesis is direct fusion of aluminum with gadolinium at temperatures exceeding melting point of aluminum and under specific conditions allowing to avoid the formation of Al-Gd intermetallic compounds with high melting points (i.e. Al3Gd and Al2Gd) and minimize gadolinium oxidation. The presented study was aimed at determining optimal conditions for Al-Gd alloy fabrication and characterization of the obtained material. A number of parameters were varied to achieve uniformity of synthesized master-alloy, such as gadolinium-to-aluminum mass ratio, temperature, process time, etc. It was found that gadolinium content in the starting mixture should be below 15 wt. % to achieve the maximum working temperature of less than 850 oC. This agrees with the Al-Gd binary phase diagram. Increasing fusing time is necessary for homogenization of the alloy; various types of segregation in the alloy samples were noticed when the duration of the process was insufficient. To decrease oxygen contamination, fusing was performed under a layer of molten alkali halide (chloride) flux in the atmosphere of high-purity argon. It was found that addition of sodium fluoride allowed to decrease oxygen content in the final master-alloy due to dissolution of surface oxides in the fluoride containing flux. Mechanical and thermophysical properties of the obtained master-alloys depend on their homogeneity and oxygen content. The work was supported by Government of the Russian Federation (Contract 14.581.21.0002)

Aluminum-gadolinium master-alloy for aerospace application: Synthesis and properties

251st National Meeting (2016)

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