Study On Doping And Properties Of IMD Single Core Wire

Internal magnesium diffusion(IMD)technology is one of the main research directions of MgB2 wire preparation at present,and it has attracted much attention in the research field.Compared with powder-in-tube(PIT)technology,the wire produced by IMD technology has higher current carrying performance.Therefore,studying IMD wire is of great significance to the practicality of MgB2 wire.However,there are several problems that need to be solved in IMD wire at present.The first is the introduction of effective magnetic flux pinning center;the second is the problem of residual hole after the diffusion of magnesium rod in the center of the wire during the phase sintering,and a large number of unreacted boron-rich phases are caused by insufficient diffusion reaction;The third is the development of IMD long wires.In this paper,we will systematically improve the IMD process from the perspectives of carbon doping method optimization and IMD production process optimization in view of the above-mentioned problems in the preparation process of IMD wire,so as to obtain the performance improvement of IMD wire.The main research contents are as follows:The MgB2 bulks were prepared by the in-situ method,and doped respectivetly with carbon-coated boron powder,amorphous carbon powder,and graphene powder.Comparing the effects of the three doping methods on the phase composition,microstructure and superconducting properties of MgB2 bulks,it was found that the effect of lattice distortion caused by the doping of carbon-coated boron powder was the best,the microstructure was more dense,and the agglomerating phenomenon of C atoms is the least.The superconducting transition test at zero field was performed on the doped samples.It was found that the Tc of the sample prepared by carbon-coated boron powder was the most obvious and the diamagnetic resistance was the strongest,therefore it is the best precursor powder for preparing IMD wire.The carbon-coated boron powder is used to prepare the precursor powder of the IMD wire.By adjusting the sintering temperature,the diffusion and phase transformation of the Mg-B system in IMD wire under the conditions of solid-solid and liquid-solid reaction changes with heat treatment time are analyzed,and it is finally determined that the Mg-B liquid-solid reaction is more suitable for the preparation of IMD single core wireUnder the condition of Mg-B liquid-solid reaction,IMD single core wire with larger thickness of MgB2 were prepared,and adding a certain amount of magnesium powder to the precursor powder is for the preparation of IMD-Mg wire,which eliminates the boron-rich phase in the wire during sintering.By testing the critical current characteristics and tensile properties of these two wires,the Jc,Je and n values are systematically compared,and the results show that the addition of magnesium enhances the superconducting related parameters in different degrees,and the strength of the wire is also enhanced,but the plasticity decreases.Therefore,this process is suitable for the subsequent preparation of MgB2 long wires.