Molecular dynamics study on compressive yield strength in Ni₃Al micro-pillars

Abstract

Recent nanoindentation experiments on bulk samples as well as compression tests on micro-pillars indicate that the micron-sized material volumes exhibit a first yield point that strongly depends on the sample size. In this work, molecular dynamics (MD) simulations are carried out to investigate the onset of yielding in Ni₃Al nano-sized pillars. The MD results show that dislocation generation is from the free surfaces of the micro-pillars, when thermal vibration induces too large a local interatomic displacement. The statistical distributions of the near-surface thermal atomic displacements gathered from the MD simulations are used in conjunction with a survival probability model to predict the yield conditions of real-sized micro-pillars in real time scales. The predicted results agree fairly well with experimental results in the literature.

Acknowledgements

This research was supported by grants from the Research Grants Council, Hong Kong Special Administrative Region of China (No. HKU 7201/03E), and the University Research Committee of the University of Hong Kong (No. 10206180.16180.14500.301.01).