Optical investigation of anomalous slip-line patterns in high purity niobium and tantalum single crystals after tensile deformation at 77 K

High-purity niobium and tantalum single crystals with an interstitial impurity content of less than 4 at.ppm (C + N + O) have been deformed at liquid nitrogen temperature (77 K). The nature of the slip lines and the slip activity were studied by optical microscopy using Nomarski interference contrast. The deformation was dominated by slip on the anomalous (01-bar1) plane. Most of the shear strain took place on the (01-bar1)[111] and (01-bar1)[1-bar11] slip systems whereby the higher stressed direction [1-bar11] also produced the greater strain. (Auth.)