Coupling effect of intergranular and intragranular particles on ductile fracture of Mo-La₂O₃ alloys

Mo-xLa₂O₃ (x=0, 0.5, 1.0, 1.5, and 2.0wt%) alloys were prepared by using the solid-solid mixing/doping method. Addition of La₂O₃ particles effectively refines the grains and significantly elevates the recrystallization temperature of the Mo alloys. Both intragranular and intergranular La₂O₃ particles are formed in the alloys, with size and volume fraction increasing with La₂O₃ additions. Room temperature (RT) tensile testing results show that the Mo-La₂O₃ alloys with 0.5-1.0wt% La₂O₃ additions have high strength (100MPa above the pure Mo) and simultaneously great elongation (2 times of the pure Mo). Elongation will be reduced when La₂O₃ addition beyond 1.5wt%. The strengthening mechanisms of the Mo-La₂O₃ alloys are mainly intragranular particle strengthening and grain boundary strengthening. The ductile fracture is predominantly controlled by the microcrack nucleation at intergranular particles. However, high temperature (HT) tensile testing results show that the Mo-La₂O₃ alloys with 1.0-1.5wt% La₂O₃ additions have the superior strength-elongation combination. Microvoids (dimples) are formed after intragranular particle debonded. The HT deformation mechanisms involve the microvoid coalescence in the grain interior and the intergranular microcrack propagation. The ductile fracture depends on a competition between the intergranular and intragranular damage development. The present experimental results provide in-depth insight into the coupling effect of intergranular and intragranualr particles on the ductile fracture of Mo-La₂O₃ alloys at RT and HT, respectively.