Zr对一种高Al+Ti镍基高温合金铸态和均匀化态组织的影响

Effect of Zr on As-cast and As-homogenized Microstructures of High Al+Ti Containing Ni-Based Superalloy

采用真空感应炉制备了一种高Al+Ti含量镍基变形高温合金铸锭,然后将其重熔成3种Zr含量的铸锭。观察了这些铸锭的显微组织并对其进行了均匀化处理,重点研究了Zr对这类合金均匀化后显微组织演变的影响。结果表明,Zr对铸锭原始晶粒的尺寸和形貌没有明显影响。添加Zr显著促进了非平衡(γ+γ′)共晶和富Zr相在枝晶间析出,并且增加了枝晶间区域显微孔洞的形成。经均匀化处理后,3种Zr含量铸锭中的非平衡相完全溶解,枝晶偏析明显减轻,晶粒发生了明显长大,且Zr含量越高晶粒长大的越显著。3种Zr含量铸锭中显微孔洞的尺寸和面积分数均较原始铸态的明显增加,且Zr含量越高孔洞形成越多。Zr增加铸态合金中孔洞形成主要与Zr向剩余液相中的富集阻碍合金凝固有关。Zr促进均匀化过程中晶粒长大和孔洞形成的主要原因是,较多(γ+γ′)共晶和富Zr相的析出加剧了溶质元素间的相互扩散。

A high Al+Ti containing Ni-based wrought superalloy ingot was prepared by a vacuum induction furnace.Then the ingot was remelted into three with different Zr contents in the same furnace.After as-cast microstructures observation,these ingots were homogenized.The effect of Zr on microstructures evolution during the homogenization process was emphatically studied.The results show that the Zr addition has no obvious influence on the initial grain size of the ingots,but significantly promotes the non-equilibrium solidification eutectic(γ+γ′) and Zr rich phase precipitation,especially at the grain boundary.Besides,Zr significantly promotes the formation of micropores in the interdendritic region.After homogenization,the non-equilibrium phases completely dissolve,the dendrite segregation obviously reduces and the original grains grow obviously.Interestingly,the higher the Zr content is,the more obvious the grain growth is.Besides,the size and area fraction of micropores increase markedly compared with those in the as-cast microstructure,and the micropores formation in the as-homogenized microstructure also increases significantly with the increase of Zr content.Zr increases the micropores formation in the as-cast alloy is mainly related to the enrichment of Zr in residual liquids which retards the alloy solidification.The principal reason why Zr promotes the grain growth and micropores formation during homogenization is that more eutectic(γ+γ′) and Zr-rich phase formation aggravates the interdiffusion between solute elements.