Effect of Grain Boundaries and Indentation Load on the Electrical Properties of Nickel Base Super-alloys

Abstract

AbstractWe have used impedance spectroscopy to evaluate the effect of the presence of grain boundaries and plastic deformation, as caused by hardness indentation, on the electrical response of several commercial nickel base super-alloys at room temperature. These alloys consist of a mostly nickel matrix that contains small precipitates of intermetallic phases such as Ni3Al or Ni3Ti(often referred to as gamma prime) as a reinforcing phase. Measurements were made as point contacts so that data could be tracked from point to point. Results indicate that the grain boundaries tend to have higher conductivities than the individual grains in most cases. It is speculated that this is due to the boundary regions having a different compositional profile than the center of the grains(as determined by gamma prime size, shape and distribution). Hardness indentation, on the other hand, had a more dramatic effect, by causing the magnitude of the imaginary impedance to change in size as well as position. Complementary microscopy results are included as supporting evidence for the effects discussed.