Strengthening mechanisms of Mo-La2O3 alloys processed by solid-solid doping and vacuum hot-pressing sintering

The molybdenum alloys doped with different contents (0.3, 0.6, 0.9, 1.5 and 2.5 wt %) La2O3 were prepared via solid-solid doping method followed by vacuum hot-pressing sintering. SEM observation and laser diffraction particle size analyzer demonstrated that the presence of La2O3 particles could availably refine the Mo powders after high energy ball milling for 15 h. For the sinters, the grain size of Mo-La2O3 alloys was greatly decreased and the minimum was 83% less compared with pure Mo. TEM analysis revealed that submicro- and nano-scale La2O3 particles were distributed in Mo matrix. Especially, most of the nano-scale La2O3 particles were located within the grains. Meanwhile, Mo-La2O3 alloys with high relative density were obtained. The uniaxial compression tests results showed that the addition of La2O3 particles also improved the yield strength of Mo alloys. Due to the optimized distribution of La2O3 particles, a yield strength peak that is 78% higher compared with pure Mo is exhibited in Mo-0.9 wt % La2O3 alloy. The quantitative relationships between the yield strength and the size, as well as the volume fraction of La2O3 particles and Mo grain size were presented. Calculation results showed that refinement strengthening contributed more compared with Orowan strengthening.