以一种新型高Cr镍基单晶高温合金为基础,调整Ru的添加量,通过对3种不同Ru含量合金铸态组织的观察,研究了Ru对合金相析出特征与元素分布规律的影响。结果表明,随着Ru含量(0、1.5%、3%,质量分数)的增加,合金一次枝晶间距与二次枝晶间距逐渐减小,(γ+γ′)共晶含量先增后降,γ′相尺寸逐渐变小;3%的Ru添加使合金凝固组织中析出β-NiAl相,该相除Ni、Al基本组成元素外,还包含一定量的Cr、Co和Ru;Ru对合金中其它元素具有典型的“逆分配”作用,β-NiAl相的析出降低了Ru对其它元素“逆分配”的影响程度;Ru提高了正偏析元素Ta、Al和负偏析元素Re的偏析程度,降低了正偏析元素Mo、Cr的偏析程度。
Ni-based single crystal superalloys have been widely used in manufacturing the critical components of aero-engines, such as turbine blades and vanes. Improvements in phase stability on the addition of Ru are well known in the field of Ni-based superalloy development. Cr is beneficial to hot co-rrosion resistance of Ni-based superalloys. Generally, superalloys which used under easy corrosion conditions should contain high levels of Cr. Early researches about the influence of Ru on solidification microstructures in Ni-based single crystal alloys are mostly focused on low-Cr systerms (<6%). Since Cr has complex interactions with Ru, it is meanful to study the effects of Ru on solidification microstructures in high-Cr (>10%) Ni-based single crystal superalloy systems. The materials used in this work are Ni-based single crystal superalloy with high Cr content. Three superalloys by changing Ru addition (0, 1.5%, 3%, mass fraction) were designed. By observing the as-cast structure, the effect of Ru on the elements distribution and the precipitation characters of different phases in these alloys were studied. It is found that as the Ru content increases, the primary and secondary dendrite arm spacings decrease gradually; the volume fraction of (γ+γ′) eutectic increases firstly and then decreases; the γ′ size is reduced progressively. The addition of 3%Ru leads to the formation of β-NiAl phase, which contain a certain amount of Cr, Co and Ru except the basic elements Ni and Al. The typical "reverse partitioning" of other alloying elements is exhibited with the addition of Ru, while the formation of β-NiAl phase can reduce the "reverse partitioning" of other alloying elements. The addition of Ru could enhance the segregation of positive segregation elements Ta, Al and negative segregation element Re while reduce the segregation of positive segregation elements Mo and Cr.
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