Effect of Si content on microstructural evolution of Nb-Si binary alloys fabricated by laser rapid forming

The high purity Nb powder and Si powder were used as raw powder and four kinds of Nb-Si binary alloys with different Si content were fabricated by laser rapid forming with double coaxial powder feeding. The microstructural evolution and the micro-hardness of these alloys were investigated by scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction spectrometer (XRD). The results showed that with the content of Si increasing from 7% to 25%, the microstructure of Nb-Si binary alloys was changed from NbSS+Nb3Si to primary NbSS+ (NbSS/Nb3Si) eutectic structure. When the content of Si was 18%, the fabricated alloy is almost 100% NbSS/Nb3Si eutectic structure. With the Si content reaching 25%, the primary β-Nb5Si3 phase appears and the NbSS/Nb3Si eutectic structure still existed. Moreover, under the high energy of laser beam, the in situ reaction between Nb and Si powder would occur and the microstructure of Nb-Si alloys could be refined significantly. With the content of Si increasing, the volume fraction of silicide increased gradually and the micro-hardness of the alloys increased from 746 HV to 1 342 HV.