AN ATOM-PROBE CHARACTERIZATION OF CARBON-DOPED NIAL

The atom probe field ion microscope has been used to characterize stoi chiometric NiAl doped with 300 ppm (0.1 at%) carbon. Field ion images of grain boundaries showed no decoration indicative of segregation. Th is observation was consistent with atom probe analyses which did not d etect carbon at the grain boundaries. Matrix analyses revealed that on ly a small percentage (3-6%) of the carbon was in solid solution the r emainder being in the form of ultrafine MC precipitates ranging from l ess than 1 nm to approximately 20 nm in diameter. Atom probe compositi on measurements revealed that the metallic component of the precipitat es consisted of Ti, V, W and Cr which are present as trace impurities in the alloy. The enormous increase in the yield stress of carbon-dope d over the undoped alloy is predominantly due to precipitation hardeni ng from the carbide precipitates.