Microstructure and fracture morphology of Mo-Cu/Cr18-Ni8 brazed joint in vacuum

Mo-Cu composite and Cr18-Ni8 stainless steel were brazed with Ni-Cr-P filler metal in a vacuum of 10-4 Pa and a Mo-Cu/Cr18-Ni8 joint was obtained. Microstructure in Mo-Cu/Cr18-Ni8 joint was investigated by field-emission scanning electron microscope( FE-SEM) with energy dispersive spectrometer( EDS). Shear strength of Mo-Cu/Cr18-Ni8 lap joint was measured by electromechanical universal testing machine. An excellent Mo-Cu/Cr18-Ni8 joint with a shear strength of 155 MPa was achieved at 980 ℃ for 20 min. Brazed joint was mainly comprised of eutectic structure in the center of brazing seam,matrix structure and lump structure. Ni-Cu( Mo) and Ni-Fe solid solution were at the interface beside Mo-Cu composite and Cr18-Ni8 stainless steel,respectively. Shear fracture exhibited mixed ductile-brittle fracture feature with trans-granular fracture,ductile dimples and tearing edges. Fracture originated from the interface between brazing seam and Mo-Cu composite.

Al_2O_3-TiC/Cr18-Ni8扩散焊界面附近元素分布及析出相

采用Ti/Cu/Ti复合中间层实现Al2O3-TiC陶瓷基复合材料和Cr18-Ni8不锈钢的扩散焊接。采用光学显微镜(OM)、电子探针(EPMA)、X-射线衍射(XRD)等分析手段,对Al2O3-TiC/Cr18-Ni8扩散焊接头的显微组织、元素分布及析出相进行分析。结果表明:Al2O3-TiC/Cr18-Ni8界面结合紧密,界面过渡区与两侧基体间界面平直。Ti与Al2O3间的反应主要发生在陶瓷表面附近;在Cu层内,Ti和Cu浓度轮廓互补;Ti向不锈钢侧扩散较大的距离,Fe、Cr表现为相似的扩散趋势;Ni呈现"上坡"扩散的特点。Al2O3-TiC/Cr18-Ni8接头的界面结构为Al2O3+TiC,NiAl2O4,TiC,CuTi+Cu(Ni),FeTi+Cr2Ti+TiC和Fe。