IMS: Verification of Hornbogen's Hypothesis on Discontinuous Precipitation

Past studies have shown it is undesirable to have small quantities of discontinuous precipitation (DP) in structural alloys as detrimental effects on mechanical properties are observed. In 1972, however, Erhard Hornbogen hypothesized that owing to the similarities between pearlite formation in steels and discontinuous precipitation transformations in some alloys, the use of the resulting lamellar structure from a complete DP transformation would improve the mechanical properties of these alloys.

Even though previous work has provided some support to Hornbogen’s claim, a direct comparison of the microstructure and mechanical properties between a completely DP transformed and a CP transformed alloy has never been conducted. Therefore, this investigation serves as a pioneering effort to verify Hornbogen’s hypothesis.

In this work, a ternary Ni-base alloy, with a composition of Ni-48.0Co-13.5Al, was aged under different conditions for DP and CP, where the resulting microstructures from both transformations were observed and the corresponding mechanical properties were determined.

Results indicated that a complete DP transformation was achieved after aging at 450°C for 4 hours, while CP aging conditions produced a limited amount of DP at the grain boundaries. Tensile tests determined that fully DP transformed sample demonstrated superior strength compared to the CP transformed sample. This finding verified Hornbogen’s hypothesis for the first time and has contributed the necessary information to promote further investigation of this work.