连续电子束扫描处理的U-5.5Nb合金的表面层微结构和性能

The Microstructure and Properties of the Surface Layer of Continuous-Electron-Beam-Scanning Processed U-5.5Nb Alloy

采用连续电子束扫描处理技术(CEBSP)首次在U-5.5Nb合金表面制备了重熔改性层,通过OM、SEM/EDS、便携式表面粗糙度测量仪及维氏硬度计等分析方法对重熔改性层的微观结构与物性特征进行了表征、分析。研究结果表明:由于快速熔凝会形成含有大量细小夹杂且具有枝晶组织的重熔改性层(厚度为毫米级),使其表面微观硬度从基体的164.5HV0.3升高至重熔改性层的211.5HV0.3。利用Kou模型计算了重熔改性层在快速凝固过程中裂纹敏感性因子-固相分数关系曲线,分析认为凝固裂纹是高Nb含量U-Nb合金在快速熔凝过程中难以避免的一类表面缺陷,也是表面粗糙度Ra从初始相对光滑表面0.193μm升高至重熔改性层表面2.298μm的主要原因。

A remelting modified layer on U-5.5%Nb(U-5.5Nb)was firstly prepared by the continuous electron beam scanning process(CEBSP).The microstructure and properties of the modified layer were characterized by optical microscope(OM),scanning electron microscope,energy dispersive spectrometer(EDS),surface roughness tester,and microhardness tester.The results show that the CEBSP modified layer with the thickness of millimeter level contains numerous small inclusions and dendrite structures,increasing the microhardness from164.5HV0.3 on the base metal to 211.5HV0.3 on the CEBSP modified layer.Based on the Kou model,the crack susceptibility index during the rapid solidification process is evaluated,and the calculation results indicate that the solidification cracking is an inevitable kind of surface defect for the U-Nb alloy with a high Nb concentration.As a result,the surface roughness of U-5.5Nb increases from 0.193μm on the initial relative smooth surface to 2.298μm on the surface of the CEBSP modified layer.