摘要
Refractory molybdenum (Mo) alloys exhibit great potential for service in extreme environments. However, their poor room-temperature plasticity and strong tendency toward brittle fracture severely limit further engineering applications. As a representative engineering Mo alloy, the toughness of TZM still requires substantial improvement. In this study, spark plasma sintering (1900 °C) was employed to systematically investigate the effects of La 2 O 3 additions (0, 0.5, and 1.0 wt%) on the microstructural evolution and mechanical properties of TZM alloy, with an emphasis on elucidating the underlying strengthening-toughening mechanisms. The results reveal that an appropriate La 2 O 3 addition (0.5 wt%) markedly refines grains through the Zener pinning effect and promotes sintering densification, while simultaneously inducing the formation of second-phase particles composed of La 2 O 3 cores surrounded by La-Ti-O composite structures. The TZM-0.5 wt% La 2 O 3 alloy exhibits the most desirable strength-ductility synergy, characterized by an ultimate tensile strength of 642.5 MPa, an elongation of 28.9%, and a strength-ductility product of 18.6 GPa·%. Fractographic analysis shows a typical ductile fracture mode dominated by microvoid coalescence. In contrast, excessive La 2 O 3 addition leads to particle coarsening and significantly deteriorated plasticity. Quantitative analysis indicates that grain refinement provides a strength increment of approximately 6.4 MPa estimated using the Hall Petch relationship, whereas Orowan strengthening contributes a strength increment of approximately 19 MPa. Together, these effects establish a coupled strengthening-toughening pathway based on grain refinement and intragranular dispersion strengthening. Within the investigated range, this work identifies 0.5 wt% La 2 O 3 as the optimal doping level for TZM alloys and theoretical basis for achieving a synergistic enhancement of strength and ductility in Mo alloys.
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