Secondary phases formation in lanthanum-doped titanium-zirconium-molybdenum alloy

Lanthanum-doped titanium-zirconium-molybdenum (La-TZM) alloys have good mechanical properties, including high strength and toughness due to complex secondary phases. Herein, the formation process of the secondary phases in the La-TZM alloy was revealed by thermodynamics calculations. The Delta G values of possible reactions during sintering were obtained. Results show that the formation process of the secondary phases was controlled by different reactions at different stages. At the first stage (0-500 degrees C), the main reactions are listed as follows: TiH2+O2(()g)-> TiO2+H-2 up arrow(g), ZrH2+O-2(g)-> ZrO2+H-2 up arrow(g), C6H12O6 ->[C]+ H2O up arrow, [C]+ O-2(g)-> CO2(g)up arrow, [C]+Mo -> MoC, La(NO3)(3)center dot 6H(2)O -> La2O3+NO2 up arrow+ NO up arrow+O-2 up arrow+H2O; [C]+TiH2 -> TiC + H-2(g)up arrow, [C]+ZrH2 -> ZrC + H-2(g)up arrow. At the secondary stage (680-960 degrees C), the dominant reactions include: TiH2 -> Ti + H-2(g)up arrow, ZrH2 -> Zr + H-2(g)up arrow. At the last stage (>= 1200 degrees C), the primary reaction is Ti + Zr+[O]-> ZrTiO4. The secondary phases in the La-TZM alloy include TiO2, ZrO2, ZrC, TiC, MoC, ZrTiO4, La2O3 and the solid Ti and Zr phases. These results can guide the design of new ingredients for Mo alloys. (C) 2018 Elsevier B.V. All rights reserved.