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采用电磁场近液相线熔体保温工艺对Ni-20Cr-18W(质量分数,%)高温合金进行处理,获得了平均晶粒尺寸d=127μm,凝固组织为球状晶粒的60 kg铸锭.借助于OM,SEM和EBSD等手段,针对所获得的电磁场对原子团簇、界面稳定化以及树枝晶向球状晶转变的研究结果,从形核热力学方面对近液相线处理后高温合金铸锭晶粒细化机制进行了研究.结果表明:该工艺能够细化凝固组织;其细化机制为原子团簇与球晶分别作为后续凝固过程中的形核核心,促进凝固过程中晶粒形核,细化组织.此外,在改善熔体宏观温度场均匀性的基础上,电磁场促进了球晶稳定化以及树枝晶向球状晶的转变,并提高其形核率.
The Ni-20Cr-18W (mass fraction,%) superalloy was treated by electromagnetic field near liquidus melt-holding process, and the 60 kg ingot with the average grain size d = 127μm and the solidified structure was spheroidal grains was obtained. In the fields of OM, SEM and EBSD, aiming at the research results of atomic clusters, interfacial stabilization and dendrite-to-spherulitic transformation in the electromagnetic field, the effects of nucleation and thermodynamics on the microstructure of ingot grains The results show that this process can refine the solidified structure. The refinement mechanism is that the atomic clusters and spherulites respectively act as nucleation centers during subsequent solidification and promote the nucleation and refinement of the grains in the solidification process In addition, on the basis of improving the uniformity of the macro-temperature field of the melt, the electromagnetic field promotes the stabilization of spherulites and the dendrite to spherulitic transformation, and improves the nucleation rate.