http://www.metallurgie.rwth-aachen.de/old/images/pages/publikationen/comp_maet_scien_id_5675.pdf

Predicting thermodynamic stability of crucible oxides in molten titanium and titanium alloys

Interactions between TiAl alloys and yttria refractory material in casting process

http://www.metallurgie.rwth-aachen.de/new/images/pages/publikationen/rec_of_gaemmae_id_2176.pdf

Recycling of gamma titanium aluminide scrap from investment casting operations

The solubility of yttrium and oxygen in molten Ti, Ti3Al, and TiAl equilibrated with solid Y2O3 has been measured from 1793 to 2093 K. The equilibrium constant of reaction Y2O3 (s)=2
 
$$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{Y} $$

 (mass pct)+3
 
$$\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{O} $$

 (mass pct) and the interaction parameter between yttrium and oxygen in molten metals were determined. The standard Gibbs energy of reaction was also obtained as a function of temperature. The deoxidation of Ti, Ti3Al, and TiAl by using yttrium-based fluxes is discussed and the deoxidation ability of yttrium is compared with that of calcium.

Thermodynamics of yttrium and oxygen in molten Ti, Ti3Al, and TiAl

Salt-fluxing treatment is an effective technique to improve the glass-forming ability (GFA) of bulk metallic glass (BMG)-forming melts, as demonstrated before in Pd- and Fe-based systems. However, it has been challenging to develop similar fluxing protocol for more reactive melts, such as Al-rich BMG-forming systems. Here we design new fluxing agents, from a thermodynamics perspective that takes into account combined effects of physical absorption and chemical absorption (reaction) between the fluxing agents and oxide inclusions. MgCl2-CaCl2 composite salts were selected, and their fluxing effects were systematically studied on an Al86Ni6.75Co2.25Y3.25La1.75 alloy, the best BMG-forming composition reported thus far for Al-rich alloy systems. The oxygen content was found to continuously decrease in the master alloy with increasing cycles of salt-fluxing treatment, with chlorate products on the surface suggesting concurrent physical absorption and chemical reaction. The fluxing treatment developed has enabled a record critical size (diameter) of 2.5 mm for Al-based BMGs. Our finding is thus an advance in developing highly desirable Al-based BMGs, and also provides guidance for designing processing protocol to produce larger-sized BMGs in other reactive systems.

Melt fluxing to elevate the forming ability of Al-based bulk metallic glasses.

The deoxidation equilibrium of molten titanium and titanium-aluminum alloys saturated with solid CaO has been measured in the temperature range from 1823 to 2023 K. The equilibrium constant of reaction CaO (s)=Ca (mass pct in Ti,Ti-Al)+O (mass pct in Ti,Ti-Al) and the interaction parameter between calcium and oxygen were determined for Ti, TiAl, and TiAl3. The standard Gibbs energy of reaction for TiAl was obtained as follows: 
$$\Delta G^\circ = 279,000 - 103TJ/mol$$

 The possibilities for the deoxidation of titanium and titanium-aluminum alloys by using calcium-based fluxes are discussed.

Toshiyuki Hatta

Papers

Thermodynamics of calcium and oxygen in molten titanium and titanium-aluminum alloy