Strengthening and plastic flow of Ni₃Al alloy microcrystals

Abstract

Ni₃Al alloys exhibit remarkable deformation characteristics at small scales that are tied to their unique dislocation core structures. The present work examines microcrystal strengthening and flow for a binary Ni₃Al alloy and two alloys containing −0.25% Hf and −1.0% Ta, and evaluates their response relative to known dislocation mechanisms for this material and sample size effects in other materials. The work includes analysis of the flow-stress anomaly mechanisms, dislocation velocity, the single-arm source model, exhaustion strengthening and dislocation multiplication for describing the response of Ni₃Al alloy microcrystals. Primary remaining needs are to understand the nature of double cross slip and dislocation sources that trigger the onset of flow and limit size-dependent strengthening.

Keywords:

• strengthening mechanisms
• dislocations
• defect structures
• Ni₃Al
• size effects
• microcrystals
• plasticity
• experimental
• TEM

Acknowledgements

The authors are indebted to S.L. Kim and Dr P. Sarosi for assisting in developing the methods for TEM sample preparation. We thank Dr T.A. Parthasarathy and Dr Y-S. Choi for helpful technical discussions. We also acknowledge the Air Force Office of Scientific Research, the Defense Advanced Research Projects Agency and the Air Force Research Laboratory, Materials and Manufacturing Directorate for financial support. Finally, DMD offers a debt of gratitude to the late Dr P. Veyssière, who provided a countless number of comprehensive discussions and insights over more than two decades regarding the myriad details of dislocation micromechanistic behaviour in Ni₃Al alloys, as well as the −0.25% Hf-containing crystals used for this study. His professional presence in the community elevated the standard of performance for most in the field (including my own), while his personal friendship offered welcoming interactions on many occasions. He is sorely missed.