研究了硼含量对凝固过程的影响,讨论了疏松的形成过程.硼在γ固溶体中的溶解度很小,凝固时富集于凝固固体前沿液体中.高硼合金凝固时,凝固固体周围包了一层极高硼含量的低熔点液体,形成蜘蛛网似的补缩通道,从而扩大了可补缩的温度区间,减少了不能补缩的剩余液体量.因此,这种合金不仅疏松少,而且工艺宽容度大.正常硼含量(0.01wt-%)合金,硼富集程度不足以形成液体网,凝固枝晶很快相互连接,形成一些较大的孤立的液体池.这种不能补缩的液体池,形成了较严重的疏松.
The influence of B content on the solidification and on the porosity forma-tion of cast Ni-base superalloys has been examined.Because of the solubility ofB in γ-solid solution is quite limited,the B may be enriched in melt at the frontof frozen solid during solidification.For superalloys containing more B,say 0.1%,the solidified grain may be surrounded by a much low melting point liquid coatingenriched with extreme B as high as 1%.It was found under metallographic obser-vation that their microstructure reveals as the interconnected continuous“web-likefilling channels”which expand the temperature range in molten state and reducethe residual amount of liquid unable to fill the pores.Thus,an improvement ofthe cast superalloys over both porosity elimination and technologic allowance hasbeen noticed.The liquid pools in alloys are small and isolated,and the micropo-rosities are finely distributed.For superalloys of normal B content,say about0.01%,the B did not be enriched to such extent that the liquid web was not yetformed.The solidified dentritic grains may be interconnected rather promptly alongcertain fastly growing directions,and the residual liquids isolated each other intolarge pools.In this case,the unsolidified liquid pools may be up to 30% in vol-ume of the alloys.Therefore,the more serious porosities will be resulted.
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