高压涡轮导向叶片裂纹分析

采用Co-Cr-Ni-W-Al-Ti系钎料对K644钴基高温合金进行了真空钎焊工艺研究，通过扫描电镜及能谱分析对不同保温时间下获得的钎焊接头的微观组织及物相组成进行了观察与分析，测试了接头的高温持久寿命。结果表明，在1 220 ℃下，钴基钎料可实现K644合金的良好连接，钎缝主要由灰色的Ni-Co固溶体、浅灰色的CrB型骨架状硼化物相、白色的(Cr,Co,W)₃B₂型骨架状硼化物相，白色的富Ti，Ta和W的不规则状和弥散分布颗粒状的MC型碳化物相组成。随着保温时间的延长，钎缝变宽，化合物相的总量减少，骨架变细，化合物相的成分趋于一致。固溶体初晶内和化合物相骨架间的γ′相含量明显升高，尺寸轻微增大，形状与分布更加均匀。接头的高温持久寿命轻微减少后持续增加，在保温120 min条件下获得的接头性能最佳，平均持久寿命达到487 h 21 min。

Effects of welding defects on reducing lifetimes of first stage nozzles of a 123 MW gas turbine made of FSX-414 alloy

Vacuum brazing technology of K644 cobalt-based superalloy was studied with Co-Cr-Ni-W-Al-Ti brazing filler metal. Microstructure and phase composition of brazed joints obtained at different holding times were observed and analyzed by scanning electron microscopy and energy spectrum analysis, and rupture life of brazed joints at high temperature was tested. The results showed that K644 alloy could be well joined with cobalt-base brazing filler metal at 1 220 ℃. Brazing seam was mainly composed of gray Ni-Co solid solution, light gray CrB type skeleton boride phase, white (Cr,Co,W)₃B₂ type skeleton boride phase, white Ti, Ta and W rich irregular and dispersed granular MC type carbide phase. With the extension of holding time, brazing seam became wider, the total amount of compound phase decreased, skeleton became thinner, and composition of compound phase tended to be consistent. The content of γ' phase in the primary crystal of solid solution and between skeleton of compound phase increased obviously, size increased slightly, and shape and distribution became more uniform. Rupture life of brazed joints at high temperature decreased slightly and then increased continuously. The best performance of brazed joints was obtained under the condition of holding time for 120 min, and the average rupture life of brazed joints reached 487 h 21 min.