Xie Miaoxia, Shang Xiangtao, Li Yanxin, Zhang Zehui, Zhu Minghui, Xiong Jiangtao
School of Mechanical and Electrical Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, China.
Materials (Basel). 2020 Apr 22;13(8):1957. doi: 10.3390/ma13081957.
A large instantaneous axial forging load is required to be applied for the final stage of rotary friction welding (RFW), which is usually conducive to obtaining clean, compact, and high-quality joints. However, for slender fuel claddings made of molybdenum (Mo) with low stiffness, the instantaneous axial forging load cannot be applied at the final stage of welding. This study carried out RFW tests without upset forging on Mo in the atmospheric environment and investigated the effects of welding time on joint morphology, axial shortening, microstructures, microhardness, tensile strength, and tensile fracture morphology. It found that the excessive and abrupt burning and a lot of smoke were generated around the weld zone during welding and spiral flashes were observed after welding. Under welding pressure of 80 MPa and spindle speed of 2000 r/min, the minimum average grain size and maximum tensile strength can be obtained in 4 s when the welding time is between 2-5 s. Scanning electron microscope (SEM) results show that there were morphologies of a large number of intergranular fractures and a small number of transgranular fractures in the fracture. The above results demonstrated that it is feasible to use RFW without upset forging to seal the last weld spot on upper end plugs of fuel claddings made of Mo in high-pressure inert gas, which would not only obtain reliable welding quality but also seal high-pressure inert gas in cladding tubes. The research results have a practical guiding significance of manufacturing accident-tolerant Mo nuclear fuel cladding.
旋转摩擦焊接（RFW）的最后阶段需要施加较大的瞬时轴向锻造载荷，这通常有利于获得清洁、致密和高质量的接头。然而，对于由低刚度钼（Mo）制成的细长燃料包壳，在焊接的最后阶段无法施加瞬时轴向锻造载荷。本研究在大气环境中对钼进行了无镦锻的旋转摩擦焊接试验，并研究了焊接时间对接头形貌、轴向缩短、微观组织、显微硬度、抗拉强度和拉伸断裂形貌的影响。研究发现，焊接过程中焊缝区周围会产生过度且突然的燃烧以及大量烟雾，焊接后观察到螺旋状飞边。在80 MPa的焊接压力和2000 r/min的主轴转速下，当焊接时间在2 - 5 s之间时，4 s时可获得最小平均晶粒尺寸和最大抗拉强度。扫描电子显微镜（SEM）结果表明，断口中存在大量沿晶断裂和少量穿晶断裂的形貌。上述结果表明，在高压惰性气体中，采用无镦锻的旋转摩擦焊接来密封钼制燃料包壳上端塞的最后一个焊点是可行的，这不仅能获得可靠的焊接质量，还能将高压惰性气体密封在包壳管中。该研究结果对制造耐事故钼核燃料包壳具有实际指导意义。
