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 ΔG 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 °C), the main reactions are listed as follows: TiH2+O2(g)→TiO2+H2↑(g), ZrH2+O2(g)→ZrO2+H2↑(g), C6H12O6→[C]+ H2O↑, [C]+ O2(g)→CO2(g)↑, [C]+Mo→MoC, La(NO3)3·6H2O→ La2O3+NO2↑+ NO↑+O2↑+H2O; [C]+TiH2→TiC + H2(g)↑, [C]+ZrH2→ZrC + H2(g)↑. At the secondary stage (680–960 °C), the dominant reactions include: TiH2→Ti + H2(g)↑, ZrH2→Zr + H2(g)↑. At the last stage (≥1200 °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.