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Mo-12Si-8.5B alloys with different La2O3 contents were fabricated by mechanical alloying and then hot pressing.The effects of La2O3 on microstructure,room and elevated temperature mechanical properties of Mo-12Si-8.5B alloys were studied.The microstructure of Mo-12Si-8.5B alloy with La2O3 additions exhibits a continuous α-Mo matrix,where the spherical Mo3Si and MosSiB2 intermetallic phases are distributed inside the grains and along the grain boundaries.The detailed microstructure shows that some nanoscale La2O3 particles are dispersed mainly in the α-Mo grains and partially in the intermetallics.These La2O3 particles can refine the grain sizes of α-Mo matrix and intermetallic,but the refining effect is limited with the La2O3 addition further increasing.The mechanical testing results show that the La2O3 addition simultaneously improves the compression strength and fracture toughness of Mo-12Si-8.5B alloy,due to that the α-Mo matrix is strengthened and toughened at ambient temperature and intermetallics are strengthened at elevated temperatures.The enhancing effect is sensitive to the amount of La2O3 additions,and the Mo-12Si-8.5B alloy can obtain a better combination of strength and toughness when the content of La2O3 is 0.9 wt％.