Effects of oxygen (O) on orientation dependence of critical resolved shear stress (c.r.s.s.) and of active slip plane in Nb, Nb-20Ta and Nb-20Mo single crystals were investigated by compression tests at 298 and 973 K. c.r.s.s. is remarkably increased by O addition. At 298 K, coarse wavy slip lines evidencing macroscopic cross slip are observed in the low O content alloy, while fine straight slip lines are observed in the high O content alloy. Observed slip planes of O-doped Nb and Nb alloys correspond nearly to maximum resolved shear stress planes (m.r.s.s.p.). Orientation dependence of c.r.s.s. is emphasized by O addition in Nb-20Ta at 298 K and in Nb-20Mo at 973 K. From these results, interaction between O atoms and screw dislocations is discussed.
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