Investigation Of The Microstucture And Mechanical Properties Of Mo-La₂O₃ Alloys Prepared By Hot Pressing

In this paper,the Mo-La₂O₃ alloys with different content(0.3,0.6,0.9,1.5,2.5 wt.%)of La₂O₃ were fabricated by high-energy ball mill and hot pressing sintering(HP)technique.The microstructure change of powders before and after the high-energy ball mill process was investigated.It was also studied that the La₂O₃ content effected the microstructure and mechanical properties.The strengthening mechanisms of the La₂O₃ doped Mo-La₂O₃ alloys were discussed as well.Alloys were heat treated at different temperatures(1600?,1700?,1800?)with analyzing microstructure and mechanical properties of the alloys before and after heat treatment.It is found that the high-energy ball mill process can refine the particles,which is conducive to sinter.The microstructure of sintered alloys indicates that the grain size of alloys decreases and then increases with La₂O₃ content.The grain size of the Mo-0.6wt%La₂O₃ alloy which is minimum is about 2.68 ?m.There are two-scale lanthanum oxide particles in Mo-La₂O₃ alloys.The fine Lanthanum oxide particles which are submicron mainly diffuse within the grain,and a small amount of distribution on the grain boundary.While the micron grade of lanthanum oxide particles are mainly distributed on the grain boundary.Mo-La₂O₃ alloy has a higher density after hot pressing sintering.The hardness of alloys increases with lanthanum oxide doping.The hardness value of Mo-1.5wt%La₂O₃ alloy is the maximum,which increases by 64.6%relative to the Mo-La₂O₃ alloy.The result of compression experiments at room temperature shows that the yield strength of the alloys increases and then decreased with the La₂O₃ content increasing.The yield strength value of Mo-0.9wt%La₂O₃ alloy reaches the maximum and is 78%higher than that of pure molybdenum.The result of three-point bending test shows that the bending strength value of the alloy increases and then decreases with lanthanum oxide increasing.The bending strength value of Mo-0.9wt%La₂O₃ alloy reaches the maximum,which is 14%higher than pure molybdenum.The lanthanum oxide doped molybdenum have not improved toughness at room temperature.The result of fracture toughness test shows that:the greater the amount of lanthanum oxide doped,the greater fracture toughness value of alloys at the room temperature.But the brittle fracture mode of molybdenum remains unchanged,which is mainly caused by the coarse particles of lanthanum oxide.Fracture morphology of pure molybdenum is transgranular cleavage fracture and Mo-La₂O₃ alloy show intergranular fracture morphology like sugar lump.There are sectional secondary cracks,prominent lanthanum oxide particles and the pits which is left after particles removing on the fracture surface.Compared with sintered Mo-La₂O₃ alloy,the grain grow after heat treatment at 1600? for 3h,the average grain size of Mo-0.9wt%La₂O₃ alloy which is 9.8 ?m is the smallest.The hardness,yield strength values of the alloys are dropped significantly.The hardness and compression yield strength value of Mo-0.3wt%La₂O₃ alloys is the largest,which are 199 HV and 475.7 MPa respectively.Mo-La₂O₃ alloy show intergranular fracture morphology after three point bending.