一种含硼第三代镍基单晶高温合金的初熔及固溶处理

Incipient Melting and Solution Heat Treatment of a Boron-Bearing Third Generation Single Crystal Nickel Base Superalloy

采用电子探针测试结合Thermo-Calc软件计算,研究了一种含0.001%(质量分数)硼第三代单晶高温合金枝晶间区域的初熔过程。结果表明,初熔相为M_2B,初熔温度为1265℃,远低于用差示扫描量热仪测得的共晶熔化温度1352℃。采用扫描电镜分析固溶处理过程中合金组织的演化过程,发现共晶组织中马赛克状共晶和扇状共晶率先溶解,粗大γ′最后溶解。初熔区域空冷可发生均质形核,重新凝固后的共晶组织呈圆形,初熔组织中粗大γ′组织较初始凝固的粗大γ′组织更细,而相比残余共晶组织,初熔组织中含有马赛克状共晶和扇状共晶。在通用分步固溶处理制度的基础上,通过低于硼化物初熔的首步处理和适当提高最终固溶温度(ST2),可以有效避免初熔并完全消除共晶。

The incipient melting process of a B bearing third generation single crystal superalloy was investigated by Thermol-Calc software. The simulation data was obtained by EPMA. The results show that the incipient melting phase is M_2B and the incipient melting temperature is 1265 °C, which is significantly lower than the melting temperature of eutectic（1352℃） obtained by DSC. The dissolution of γ/γ′ eutectics was studied by SEM. It is indicated that more time and higher temperature are necessary to dissolve the coarse γ′ in eutectics than mosaic-like eutectics and fan-like eutectics. The eutectics shape of the incipient melting region is round. Homogenous nucleation could be found in incipient melting region due to the fast cooling rate of air cooling. The resolidification structure owns mosaic-like eutectics and fan-like eutectics which are dissolved in the early stage of solution heat treatment.