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La Doping Methods Affected La-TZM Alloy’s Properties

Doped with a certain amount of La₂O₃ during powder metallurgy process can obtain La-TZM alloy which has higher strength than TZM alloy. Different doping methods have different effect on La-TZM alloy. Separately doped lanthanum by solid-solid doping method and solid-liquid doping  method, then after sintering, hot rolling, warm rolling, cold rolling and other processing procedures to obtain La-TZM alloy. Using solid-solid alloy doping method obtained alloy were labeled as 1# and solid - liquid were labeled as 2#.

Observed La-TZM alloy powder morphology and particle size distribution found that 2 # doping is more uniform more than 1# and there exists a local reunion phenomenon in 1#, form this we can see solid-liquid can obtain uniformly mixed material. After mechanical properties tensile testing found that La-TZM alloy tensile property is better than TZM alloy. Besides, 2# tensile property is superior to 1#, increased 10.9%. From this we will know solid-liquid is more conducive to improving the mechanical properties of the alloy. Analyzed La-TZM alloy SEM micrographs found the second phase in alloy not only distributes in the grain boundary, also distributes in the grain. And the average grain size of 2 # is less than 1 #. It is mainly because the powder which obtained by solid-liquid method is finer than solid-solid method and the finer powder, the smaller grain size is after sintering. In addition, there are a series of reactions of La2 (NO3) 3 at the beginning of sintering, so La₂O₃ mix more evenly. (La₂ (NO₃) ₃ • 6H₂O → La (NO₃) ₃ • 5H₂O → La (NO₃) ₃ • 3H2O → La (NO₃) ₃ → LaONO₃ → La2O₃ • LaONO₃ → La₂O₃).

The fracture morphology of solid-solid doped alloy plate and solid-liquid doped alloy plate is similar, but solid - liquid doped alloy plate fracture will be more careful and distributes fine and uniform second phase. The second phase is mainly distributed in the grain boundary and it can hinder the propagation of intergranular crack. Besides it has smaller crack and cleavage plane and it mainly shows intergranular fracture characteristics. Solid-liquid doping method second phase distribution is uniformly, and solid-solid doping method second phase has stratification phenomenon, so using solid-liquid can produce high quality and good properties alloy.

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