钻基钎料钎焊DD5单晶高温合金的接头微观组织演变与力学性能研究

MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF DD5 SINGLE CRYSTAL SUPERALLOY JOINT BRAZED BY Co-BASED FILLER ALLOY

利用SEM,EPMA和TEM,观察了在1453 K Co-Ni-Si-B钎料钎焊的DD5镍基单晶高温合金接头的显微组织,分析保温时间变化对接头显微组织和力学性能的影响,并深入讨论接头的形成机制.结果表明:接头主要由钎料合金区、界面连接区和元家扩散区3个区域组成.钎料合金区位于焊缝中央,由Ni-Co固溶体、M_3B_2型硼化物、CrB和Ni-Si化合物构成;与之相邻为界面连接区,主要为等温凝固形成的Ni-Co固溶体组织;元素扩散区位于界面连接区与母材之间,由γ相、γ′相和元素互扩散形成的颗粒状M_3B_2构成.随着保温时间的延长,焊接缺陷减少,界面连接区厚度增加,钎料合金区中球形Ni-Co固溶体尺寸增大,脆性化合物相数量减少,接头在1143 K的抗拉强度由198.5 MPa提高至580 MPa.高温拉伸试样的断口观察表明:断裂发生在焊缝处,为混合断裂模式,保温时间延长可提高焊缝与母材的界面结合强度,控制脆性化合物相的形成,改善接头的高温力学性能.综合考虑接头的组织和性能,最佳保温时间约为180 min.

The single crystal supperalloy DD5 was brazed using Co Ni Si-B filler alloy at 1453 K. The microstructure of joint and effect of brazing time on the microstructure and mechanical properties were investigated by SEM, EPMA and TEM. The formation mechanism of joint was dis- cussed deeply. The result indicates that three distinct regions can be identified in a joint： the filler alloy zone, interracial bonding zone, element diffusion zone. The filler alloy zone in the center of joint consists of Ni-Co solid solution, M3B2 type boride, CrB and Ni-Si compounds. The interracial bonding zone adjacent to the filler alloy zone is composed of Ni-Co solid solution formed isothermally at brazing temperature. The element diffusion zone between the interracial bonding zone and substrate consists of V phase, γ phase and granular M3B2 phase which was formed in element diffusion. With extending brazing time, the brazing defects reduce, the thickness of bonding layer and the size of spherical Ni-Co solid solution in the filler alloy zone increase, and the brittle compounds reduce. The tensile strength at 1143 K increases from 198.5 MPa to 580 MPa. The investigation on fracture of high temperature tensile specimens exhibits that the fracture occurred in the seam and the fractural model is a mixed fracture. Through extending brazing time the bonding strength between seam and substrate can be improved, the brittle compounds can be controlled and the mechanical properties of joint are improved. The analysis results of microstructure and properties also imply that the optimum holding time would be 180 min.