高性能MgB_2长线材制备及性能表征

Fabrication and characteristics of long MgB_2 wire with high superconducting properties

采用原位粉末装管工艺,分别以Mg粉(99.5%),无定形B粉(99.9%)为原料,以纳米SiC(10—30nm)作为掺杂材料制备铁基MgB2线.首先将已混合的原料在丙酮介质中球磨,真空干燥后,将粉末填入铁管内,然后通过孔型轧制、旋锻和拉拔等冷加工工艺得到11m长外径Ф1.75mm铁基MgB2超导线.用扫描电镜,电子能谱,X射线衍射仪和超导量子干涉仪测试发现,样品微观结构整齐,晶粒大小均匀,内部仅含微量MgO,TC(onset)=35.1K,ΔTC=5.3K.纳米SiC掺杂后,其中C造成MgB2晶格畸变,形成有效磁通钉扎中心,C元素在MgB2中分布均匀.标准四引线测试结果表明,11m线均分10段后,各点的Jc(4.2K,10T)均超过1.0×104A/cm2,最高值达到1.2×104A/cm2.在10—18T范围各点临界电流值分布均匀,变化率小于10%.

Appling the in situ powder-in-tube method,11 meter long Fe-sheath MgB2 superconducting wires with outer diameter 1.75mm were fabricated,using 99.5% Mg powder and 99.9% amorphous boron powder doped with 30 nm SiC powder as starting materials.This procedure begins with ball-milling of the mixture powder immersed in acetone solution in a jar and subsequently drying in vacuum.Then the iron tube loaded with the powder mixture was grooved,swaged and drawn to the final wire size.The transition temperature,microstructure,lattice constant and chemical element distribution were evaluated by SQUID,XRD,SEM and EDS,respectively.It was found that T C（onset）and ΔTC are 35.1K and 5.3K,respectively.All samples containing a small amount of MgO,exhibit rather uniform microstructure.Besides,by nano-SiC doping,the MgB2 lattice distortion due to substitution of boron by carbon,results in forming effective flux pining centers,which significantly improves the critical current,and the C element was uniformly distributed in the MgB2 matrix.The standard four-probe measurement shows that all the 10 sample points,which were evenly cut at 1 meter intervals of the 11 meter length wire,have good superconducting homogeneity with critical current values fluctuating within 10% under the applied fields vavying from 10 to 18 Tesla,and all Jc values are above 10^4 A/cm^2,with the highest value reaching 1.2×10^4 A/cm^2 at 4.2K and 10T.