The deformation of Nb–N single crystals at low temperatures

Abstract

Abstract Previous work by Bowen and Taylor in 1977 on the mechanical properties of Nb–N single crystals tested in compression in the temperature range 50–300 K has be supplemented by new experiments on similar alloys in tension in the range 4.2–77 K. The characteristics studied include the temperature dependence of the yield and flow stresses, the strain rate dependence of the flow stress, and the slipline morphology. Measured yield stresses at 77 K were generally compatible with those of Bowen and Taylor in compression, but the spread in values with nitrogen content was appreciably smaller. Alloys with up to 70at.p.p.m. N behaved like pure niobium and exhibited a loss of temperature dependence of the yield stress in the range 77–50 K where anomalous slip often occurs, followed by a steep rise with decreasing temperature at lower temperatures. Alloys with 200 and 320 at.p.p.m. N did not show the low-temperature plateau, anomalous slip was suppressed and the yield stress at low temperatures was significant...