Study On Preparation Technology And Structure And Properties Of Liquid - Liquid RE Doped Molybdenum Alloys

RE doped molybdenum alloys have excellent properties and wide range of applications, however, the existing solid-solid doped method and liquid-solid doped method can not ensure RE distributes uniformly. In this study, using liquid - liquid doped method to prepare doped precursor, then using Sol-gel technology to get dry gel, roasting the dry gel to get RE doped MoO₃,RE doped Mo powder is prepared by using the two restore technology, RE doped Mo blank is prepared through profiling, pre-sintering and vertical melting sintering. In this paper, the preparation process of liquid-liquid RE doped molybdenum alloys are studied, using SEM, XRD, TEM, metallographic, average-particle-size analyzer, micro hardness tester, DTA and so on to test the morphology, phase, particle size and hardness of the doped alloys prepared in individual process. This study is mainly supported by the following conclusions:When the initial solution pH≤2.5 and the adding volume of citric acid is slightly larger than 1.19 times of sec-ammonium molybdenum can get the best dry gel; using restore sintering method can not remove the gel, but using the direct sintering method at 560℃can remove the gel very excellently.The doped Mo powder with average particle size of 0.8nm, particles are spherical and very uniform can be prepared under the initial solution pH=1 condition; the doped molybdenum billet prepared under pH=1 condition, RE particles and Molybdenum substrate particles distribute alternately; with the reduce of the initial solution pH value, the distribution of RE particles tend to homogenization and shift from inter-die to grain boundary gradually in the doped molybdenum blanks, the dispersion strengthening effect is more obvious; the density of the doped molybdenum billet is minimum but the average hardness is maximum when the initial solution pH=1.In the Mo-La binary alloy, the initial presence of lanthanum is La₂ (MoO₄)₃, transform into a crystal after heat treatment at 600℃; lanthanum exists in the form of La₂O₃ or La-Mo complex oxide in the doped MoO₃, RE particles adhere to the surface of the MoO₃ particles; lanthanum exists in the form of La2O3 in the doped Mo power, the La-Mo complex oxide decomposes in the reduction process; in the doped molybdenum billet ,the RE particle size gets to nano-scaling , disperses evenly in the molybdenum matrix.The doping elements and doping contents impact very little about the morphology, size in the Mo-La-Y ternary alloys; however, in the doped molybdenum blanks, the matrix particles generally become thinner with the doping content increasing, and gradually regularization, In the same doping levels, dual-doping compared to unit-doping, the refinement effect is more obvious; increasing the doping content and the Co-doping can improve the hardness of the doped molybdenum blanks.