Effect of Mo Addition on Phase Stability and High-Temperature Strength of NbSi₂/Nb₅Si₃ Composites

Abstract

Directionally solidified NbSi 2 /Nb 5 Si 3 in-situ composites have been prepared. Scanning Electron Microscopes (SEM) and X-ray diffraction (XRD) have been used to investigate phase constitution and microstructure. It was found that microstructure and phase stability of directionally solidified alloys depended on growth rate, heat-treatment and alloying element. Compression strength was tested in the temperature range from 1473 to 1773 K and compression axes parallel to growth direction was chosen. High-temperature strength of NbSi 2 /Nb 5 Si 3 composites increased from 222.9 to 593.77 MPa at 1773 K due to Mo addition.

Effect of Mo addition on the phase stability of β-Nb5Si3 phase

“…Moreover, our previous work [6] shows that the addition of 2 at.% Mo results in the decrease of Si content in b-Nb 5 Si 3 from 39.5 to 37.5 at.%. Therefore, it is possible that there is a certain relationship between Mo atoms and Si Nb atoms.…”

“…It had been assumed [6] that excess Si atoms in the b-Nb 5 Si 3 phase of Nb-57Si alloy are due to Si Nb substituting for Nb, where Si Nb denotes Si atoms which occupy the Nb position. Moreover, our previous work [6] shows that the addition of 2 at.% Mo results in the decrease of Si content in b-Nb 5 Si 3 from 39.5 to 37.5 at.%.…”

“…As high temperature structural materials, it is important to obtain stable Nb 5 Si 3 phase in the high temperature range over 1473 K. The study by Kim et al indicated that Mo addition stabilized b-Nb 5 Si 3 in Nb/Nb 5 Si 3 composites [5]. In our previous works [6], b-Nb 5 Si 3 was also stabilized at 1473 K by Mo addition in NbSi 2 /Nb 5 Si 3 composites. Nb 5 Si 3 displays a complex tetragonal structure with 32 atoms per cell in both of its allotropic forms.…”