Analysis on time sequence characteristics of occurrence status of lanthanum in Mo alloy wires

The sensitivity of the microstructure and mechanical properties of as-worked Mo-La alloy wires to the La content was studied. The results showed that with the increase of La content, the microstructure and mechanical properties of as-worked Mo-La alloy wires were scarcely improved, which was entirely different from the phenomenon that the toughening effect of annealed Mo-La alloy wires changed with the different La content. The fact was due to the occurrence status of La element in Mo alloy wires and the timing sequence characteristics during its transformation process. The grain refinement and dislocation pinning effects of Mo-La alloy wire depended greatly on the quantity of La₂O₃ particles and their dispersity in molybdenum substrate. XRD patterns showed that Mo-La alloy powders, which were obtained by the reduction of the solid-liquid doped MoO₂, were composed of Mo atoms and La₂Mo₂O₇. In the subsequent thermomechanical processing of as-worked Mo-La alloy wires, La₂O₃ particles were gradually generated by the combination between La³⁺ ions and free oxygen atoms or the decomposition of La₂Mo₂O₇. The thermomechanical processing was unable to make all of La³⁺ ions became La₂O₃, resulting in that the generation of La₂O₃ particles lagged largely behind the termination of the whole process, so the microstructure and mechanical properties of the alloy wires were not obviously sensitive to the La addition level.