镍基高温合金定向凝固用陶瓷型壳粘砂反应

Sand-burning Reaction of Ceramic Shell for Directional Solidification of Nickel-based Superalloy

以合金表面粘砂比例和粗糙度为优化指标,采用多指标正交实验设计方法,通过极差分析研究了定向凝固用陶瓷型壳面层粒度配比和Cr_(2)O_(3)添加剂对铸件表面质量的影响。结果表明,铸件表面粘砂层的主要成分为Al_(2)O_(3)以及少量Cr、Ni等合金元素;调整陶瓷型壳面层的粒度级配能降低陶瓷型壳面层的孔隙率,使型壳面层形成致密的结构,从而减少在定向凝固过程中合金液向陶瓷型壳面层的渗入、减少铸件表面的物理粘砂;Cr_(2)O_(3)添加剂与型壳中的Al_(2)O_(3)反应生成的二元化合物Al_(2)O_(3)-Cr_(2)O_(3)或Al_(2)O_(3)-Si O2-Cr_(2)O_(3)三元系产物,抑制了合金中的活性元素(Ni、Ti、Al等)与型壳中游离的Si O2反应,从而减少铸件表面的化学粘砂、提高铸件的表面质量。

The influence of the particle size ratio of the ceramic shell for directional solidification of superalloy and the Cr_(2)O_(3)additive on the surface quality of castings was investigated by means of multi-index orthogonal experiment and the range analysis while taking the sand-burning on the surface quality and roughness of the resulted castings as the calibration.The results show that the main components of the sand-burning layer on the casting surface includes Al_(2)O_(3)and elements Cr,Ni of the alloy.Adjusting the particle size gradation can reduce the porosity of the ceramic shell surface layer and then yield a dense shell surface layer,thereby reducing the penetration of the molten alloy into the ceramic shell surface layer during the directional solidification process and reducing the physical adhering sand on the surface of the casting.The addition of Cr_(2)O_(3)additive can induce the reaction of Cr_(2)O_(3)with Al_(2)O_(3)in the shell resulting in the formation of the binary compound Al_(2)O_(3)-Cr_(2)O_(3)or ternary compound Al_(2)O_(3)-Si O2-Cr_(2)O_(3),which can inhibit the active elements(Ni,Ti,Al,etc.)in the casting react with free Si O2in the ceramic shell to reduce the formation of Al_(2)O_(3)on the casting surface,thereby reducing the chemical adhering sand on the casting surface and improving the casting surface quality.