Hf对一种镍基高硼铸造高温合金凝固行为及疏松情况的影响

Effects of Hf on Solidification Behavior and Porosity of Nickel-Based High-Boron Cast Superalloys

研究了Hf的添加对一种镍基高硼铸造高温合金显微组织、凝固行为、疏松情况的影响。显微组织分析、差热分析(DSC)、等温凝固淬火试验结果显示,Hf在合金的凝固过程中强烈偏析于枝晶间区域,并在凝固末期以Ni_(5)Hf相的形式从残余液相中析出;Hf的加入降低了合金的液/固相线温度、γ/γ′共晶相和硼化物析出温度,延缓了合金的凝固过程,加宽了凝固温度范围,显著增大了γ/γ′共晶相的含量。自主设计并浇铸一种薄壁管铸件,渗透检验结果显示Hf的加入使得薄壁管的疏松明显减少,合金的疏松倾向性显著降低。

The effects of Hf addition on the microstructure,solidification behavior and porosity of a nickel-based high-boron cast superalloy were studied.The results of microstructure analysis,differential thermal analysis(DSC)and isothermal solidification quenching test show that Hf segregates in interdendritic regions during the solidification process of the alloy,and precipitates from the residual liquid phase in the form of Ni_(5)Hf phase at the end of the solidification process.The addition of Hf reduces the precipitation temperature of liquid/solidus,γ/γ′eutectic phase and boride,delays the solidification process of the alloy,widens the solidification temperature range from 166.3℃to 200.5℃,and significantly increases the content ofγ/γ′eutectic phases.A thin-walled tube cast is independently designed by the authors.Penetration test results show that the addition of Hf remarkably reduces the porosity of the thin-walled tube,and the tendency of porosity forming of the alloy is obviously reduced.