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

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 from 164.5HV0.3 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 0.193 μm on the initial relative smooth surface to 2.298μm on the surface of the CEBSP modified layer.