Future steam turbines will use hollow structures so that the turbine inlet temperature can be increased to improve the thermal efficiency. These hollow structures are made of the nickel-base alloy Nicrofer 6025 HT and...Future steam turbines will use hollow structures so that the turbine inlet temperature can be increased to improve the thermal efficiency. These hollow structures are made of the nickel-base alloy Nicrofer 6025 HT and consist of a wire mesh between two cover sheets. The cover sheets can be joined to the wire mesh by capacitor discharge welding due to its extremely short welding duration. The goal of this research is to investigate suitable welding parameters so that the weld spots form in an optimum way to increase the tensile shear strength and reduce spattering. Tensile shear tests, three-point bending tests, and micrographs were used to judge the joint quality of structures made with various welding parameters. The results show that the best welds are obtained with a transmission ratio of 1：200, welding energy of 70% to 95%, and electrode force of 7 to 9 MPa.展开更多
Based on the network theory, the discharge circuit model of capacitor discharge percussion welding machine is established. The discharge current waveform is calculated by means of simulation method. A thorough inquir...Based on the network theory, the discharge circuit model of capacitor discharge percussion welding machine is established. The discharge current waveform is calculated by means of simulation method. A thorough inquiry into the factors affecting the discharge current waveform is made by using orthogonal design method. Results show that the calculation results of the calculation program proposed well coincide with the actual experiment data.展开更多
Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means...Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means of scanning electron microscope （ SEM）. Microstructures of the joint were examined by means of optical microscope and SEM. The results showed that the teusile strength of the inhomogeneous joint （ TiNi-SS joint） was low and the joint was brittle. Because TiNi SMA and SS melted, a brittle as-cast structure and compound were formed in the weld. The tensile strength and the shape memory effect （SME） of TiNi-SS joint were strongly influenced by the changes of composition and structure of the weld. Measures should be taken to prevent defects from forming and extruding excessive molten metal in the weld for improving the properties of TiNi-SS joint.展开更多
基金Supported by the DAAD (German Academic Exchange Service) CSC (China Scholarship Council) on Tsinghua University/ RWTH Aachen Joint Master Program
文摘Future steam turbines will use hollow structures so that the turbine inlet temperature can be increased to improve the thermal efficiency. These hollow structures are made of the nickel-base alloy Nicrofer 6025 HT and consist of a wire mesh between two cover sheets. The cover sheets can be joined to the wire mesh by capacitor discharge welding due to its extremely short welding duration. The goal of this research is to investigate suitable welding parameters so that the weld spots form in an optimum way to increase the tensile shear strength and reduce spattering. Tensile shear tests, three-point bending tests, and micrographs were used to judge the joint quality of structures made with various welding parameters. The results show that the best welds are obtained with a transmission ratio of 1：200, welding energy of 70% to 95%, and electrode force of 7 to 9 MPa.
文摘Based on the network theory, the discharge circuit model of capacitor discharge percussion welding machine is established. The discharge current waveform is calculated by means of simulation method. A thorough inquiry into the factors affecting the discharge current waveform is made by using orthogonal design method. Results show that the calculation results of the calculation program proposed well coincide with the actual experiment data.
文摘Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means of scanning electron microscope （ SEM）. Microstructures of the joint were examined by means of optical microscope and SEM. The results showed that the teusile strength of the inhomogeneous joint （ TiNi-SS joint） was low and the joint was brittle. Because TiNi SMA and SS melted, a brittle as-cast structure and compound were formed in the weld. The tensile strength and the shape memory effect （SME） of TiNi-SS joint were strongly influenced by the changes of composition and structure of the weld. Measures should be taken to prevent defects from forming and extruding excessive molten metal in the weld for improving the properties of TiNi-SS joint.
