热加工纯钴及电阻焊组织性能研究
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摘要
纯钴在大于600℃热加工成丝材,采用电阻焊方法制得焊接丝材端头。利用光学显微镜、万能试验机和扫描电子显微镜对热加工丝材和不同焊接电流对焊丝材接头的微观组织、力学性能和断裂机制进行研究。结果表明:热加工丝材为具有孪晶和细小亚晶的再结晶组织,局部存在残余的FCC结构,断裂机制为微孔聚集型断裂。随着焊接电流增大,接头组织的缺陷逐渐降低,电流为16.1 A时,接头组织发生再结晶长大,接头强度最高。焊接电流增至18.4 A后,接头组织出现孔洞,强度降低。随着焊接电流逐渐增大,接头由沿晶断裂转变为准解理断裂,电流为16.1 A时,为微孔聚集和解理混合断裂,断裂位置在粗晶与细晶交界的热影响区。
Pure cobalt was hot processed into wire at temperatures above 600 ℃.The wire ends were welded by resistance welding method.The microstructure,mechanical properties and fracture mechanism of hot-processed wire and welded wire joints with different welding currents were investigated by optical microscope,universal testing machine and scanning electron microscope.The results show that the hot-processed wire has a recrystallized structure with twins and fine subgrains,and there is a residual FCC structure,locally.The fracture mechanism is micro-void coalescence.As the welding current increasing,the defect of the joint structure gradually decreases.When the current is 16.1 A,the joint structure recrystallizes and the joint strength is the highest.After the welding current is increased to 18.4 A,the joint structure has holes and the strength is reduced.The joint changes from crystal fracture to quasi-cleavage fracture with the welding current gradually increasing.When the current is 16.1 A,the fracture mechanism is micro-void coalescence and cleavage mixed fracture.The location of the fracture is in the heat affected zone at the boundary between coarse and fine grains.
Pure cobalt was hot processed into wire at temperatures above 600 ℃.The wire ends were welded by resistance welding method.The microstructure,mechanical properties and fracture mechanism of hot-processed wire and welded wire joints with different welding currents were investigated by optical microscope,universal testing machine and scanning electron microscope.The results show that the hot-processed wire has a recrystallized structure with twins and fine subgrains,and there is a residual FCC structure,locally.The fracture mechanism is micro-void coalescence.As the welding current increasing,the defect of the joint structure gradually decreases.When the current is 16.1 A,the joint structure recrystallizes and the joint strength is the highest.After the welding current is increased to 18.4 A,the joint structure has holes and the strength is reduced.The joint changes from crystal fracture to quasi-cleavage fracture with the welding current gradually increasing.When the current is 16.1 A,the fracture mechanism is micro-void coalescence and cleavage mixed fracture.The location of the fracture is in the heat affected zone at the boundary between coarse and fine grains.
引文
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[4] ZHANG X,JIA C.The microstructural characteristics of the deformed nanocrystalline cobalt[J].Materials Science & Engineering A,2006,418(1):77-80.
[5] PAUL B,SARKAR A,CHAKRAVARTTY J K,et al.Dynamic recrystallization in sintered cobalt during high-temperature deformation[J].Metallurgical & Materials Transactions A,2010,41(6):1 474-1 482.
[6] 朱玉涛.多晶纯钴在动态塑性变形后的退火组织及变形孪晶研究[D].重庆:重庆大学,2012.
[7] 晋家兵,张喜燕,陈建华,等.多晶纯钴退火组织中的孪晶转变规律研究[J].稀有金属材料与工程,2016,45(2):353-357.
[8] PAUL B,KAPOOR R,CHAKRAVARTTY J K,et al.Hot working characteristics of cobalt in the temperature range 600～950 ℃[J].Scripta Materialia,2009,60(2):104-107.
[9] 范亮,尚再艳,黄志勇,等.钴再结晶退火的研究[J].热加工工艺,2013,42(4):182-183.