Solid-Solution Strengthening by Oxygen in Nb-Ta and Nb-Mo Single Crystals

We have investigated the high-temperature solid-solution strengthening by oxygen in Nb, Nb–Ta and Nb–Mo single crystals by compression tests with constant strain rate. Nb, Nb–20Ta, Nb–40Ta, Nb–20Mo, and Nb–40Mo single crystals with various O content were grown by use of the electron-beam floating zone melting method. It is found that Nb and Nb–Ta single crystals are strengthened by oxygen at temperatures below 1100 K, while Nb–20Mo single crystals are strengthened even at 1473 K. The critical resolved shear stress (c.r.s.s.) of Nb–Ta single crystals at 298 K increases linearly with increasing O content, irrespective of Ta content. Furthermore, the increment of c.r.s.s. of Nb–Ta single crystals is larger than that of Nb. The c.r.s.s. of Nb-Mo single crystals is higher than that of Nb for all temperatures tested, and the c.r.s.s. of Nb–20Mo single crystals also increases with increasing O content. These results indicate that the interstitial–substitutional (i–s) interaction between O and Ta or Mo affects the mechanical properties in the Nb-based alloys at high temperature.