PREPARATION, DOPANT DISTRIBUTION, AND MECHANICAL-PROPERTIES OF FE MICROALLOYED HIGH-PURITY NIAL SINGLE-CRYSTALS

The paper investigates microalloying effects of Fe in NiAl crystals. H igh-purity NiAl-0.2 at% Fe single crystals were prepared by a modified Bridgman method. The impurity content was less than 20 wt ppm metalli c impurities, 50 wt ppm oxygen and 5 w;t ppm nitrogen. The alloy compo sition was analyzed by different wet chemical methods, which give evid ence to stoichiometry deviations smaller than 0.2 at%. The residual re sistivity ratio of the as-grown crystals was near R-295K/R(4.2K)approx imate to 4 The secondary ion mass spectrometry investigations revealed segregation effects of Fe. These could be reduced by increasing the g rowth rate. For soft orientated [123] Fe microalloyed NiAl samples roo m-temperature compressive deformations to failure of more than 40% hav e been achieved, which exceed the level of approximate to 20% for bina ry NiAl crystals. There was a significant reduction of the critical re solved shear stress at room temperature from 104 MPa for as grown bina ry crystals to 54 MPa for Fe microalloyed crystals. This value is comp arable with 45 to 55 MPa of annealed binary high-purity NiAl crystals. A dopant/point defect interaction mechanism is supposed to be respons ible for the improvement of the mechanical properties due to microallo ying.