镍基高温合金GH4738的凝固偏析和碳化物析出行为

Solidification segregation and carbide precipitation behavior of nickel-based superalloy GH4738

高温合金铸锭凝固过程内部各区域散热条件不同,冷却速率存在明显差异。采用差示扫描量热分析(DSC)、高温共聚焦显微镜(HT-CLSM)原位观察和定向凝固(DS)的方法,研究了宽冷速范围下GH4738合金的凝固偏析和碳化物析出行为。结果表明,GH4738合金的凝固顺序为L→γ+L,L→γ+L+MC,L→γ+MC+η+(γ+γ′),其中MC型碳化物、η相和(γ+γ′)共晶相为合金凝固过程中的主要偏析产物;Ti、Mo元素是合金的主要枝晶间偏析元素;提高冷却速率能有效降低凝固前沿残余液相中的溶质富集程度;铸态组织中的的碳化物主要为富Ti的MC型碳化物(TiC、Ti(N)C)和以TiN或Al_(2)O_(3)为核心的MC型复合碳化物(Al_(2)O_(3)-TiC、TiN-TiC);随着冷却速率降低,碳化物平均尺寸增大,体积分数减小,形貌由小块状向长条状、汉字状和大块状演变。

Internal cooling rate of superalloy ingot is obviously different due to the variation of heat dissipation condi-tions.The solidification segregation and carbide precipitation behavior of nickel-based superalloy GH4738at a wide range of cooling rate were investigated by differential scanning calorimeter(DSC),high temperature confocal laser scanning microscopy(HT-CLSM)and directional solidification(DS)experiments.The results indicated that the so-lidification sequence of GH4738superalloy was L→γ+L,L→γ+L+MC,L→γ+MC+η+(γ+γ′),among which MC,ηand(γ+γ′)eutectic phase were the main segregation products during the solidification process.Ti and Mo were the main solute elements segregated to the interdendritic regions,and increasing the cooling rate could effec-tively reduce the concentration of solute in the residual liquid phase at solidification front.The carbides in the as-cast alloy were mainly divided into titanium-rich carbide,like TiC,Ti(N)C,and MC type composite carbides with TiN or Al_(2)O_(3)as the core(Al_(2)O_(3)-TiC,TiN-TiC).With the decrease of cooling rate,the average size of carbide in-creased,but the volume fraction decreased,and the morphology evolved from small block to long strip,Chinese character and large block.