Brazing Oxide Dispersion-Strengthened Fe-Based Steels with a Cu-Based Filler Metal
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JMEPEG https://doi.org/10.1007/s11665-019-04015-0
Brazing Oxide Dispersion-Strengthened Fe-Based Steels with a Cu-Based Filler Metal Xiaoqiang Li, Jingmao Li, Xiuhui Diao, Zhun Cheng, Zhongli Dong, Jingpei Ao, and Dezhi Zhu (Submitted October 7, 2016; in revised form January 23, 2019) In a search for a high-performance joint, a Cu-based filler was developed to braze MGH956 alloy (Fe-20Cr5Al-0.5Ti-0.5Y2O3, wt.%), and a reliable joint was obtained by assembly and welding under a high-purity argon atmosphere. The optimal joint was obtained by brazing at 1050 °C for 20 min. The microstructure, microhardness and tensile strength were investigated. The microhardness distribution across the joint was evaluated. The tensile strength of the joint mainly decreased linearly with an increase in test temperature in the range of room temperature (RT) to 700 °C. An interesting phenomenon was found: The joint strength at RT was 557.8 MPa and reached approximately 75% of the value of the base material. However, at 500 °C, the joint (428.7 MPa) achieved 95% of the strength of the base material (450.7 MPa). The fractography of a specimen tensile-tested at 500 °C indicates a higher percentage of intergranular fracture than that at RT. Keywords
brazing, Cu-based filler, MGH956 alloy, oxide dispersion-strengthened alloy
1. Introduction Due to their excellent corrosion resistance, high-temperature strength and oxidation resistance, oxide dispersion-strengthened (ODS) steels are considered a promising candidate as a structural material (Ref 1, 2). To date, ODS steels have achieved widespread applications in the aerospace, energy source and nuclear industries. To further extend the application of ODS steels, many researchers have attempted to develop feasible joining technology for it, including tungsten inert gas (TIG) welding (Ref 3), electron beam welding (Ref 4), friction stir welding (FSW) (Ref 5-8), brazing (Ref 9-11) and transient liquid-phase (TLP) bonding (Ref 12-14). Nevertheless, ODS steels are difficult to bond because of their unusual microstructure and unique mechanical properties. In ODS steels, the strengthening phase oxides, such as nanoscale Y2O3 particles, are insoluble in the matrix metal even at high temperature. The particle strengthening effect may subsist below the melting point of the matrix, which equips ODS steels with excellent strength and wear resistance at high temperature while also becoming an obstacle to bonding them. For instance, dispersed oxides are prone to segregate and coarsen in the center of a welded seam during fusion welding, which will weaken the joint strength. The FSW technique, as a solid-state joining method, can avoid the segregation of oxides and preserve the advantageous microstructure of ODS steels, leading to an ideal Xiaoqiang Li, Jingmao Li, Xiuhui Diao, Zhun Cheng, Jingpei Ao, and Dezhi Zhu, National Engineering Research Center of Near-NetShape Forming for Metallic Materials, South China University of Technology, Guangzhou 510641, China; and Zhongli Dong, Electric Power Research Inst
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