Nanoindentation studies on Ti–Zr–Ni bulk quasicrystalline intermetallics

Abstract

Polycrystalline Ti₄₀Zr₄₀Ni₂₀ bulk quasicrystals are used for microindentation and nanoindentation studies. The microindentation test gives the Meyer's hardness as 6.22 ± 0.16 GPa, but it does not exhibit any indentation size effect (ISE) nor any cracking, even at a higher 200g load. From nanoindentation tests, the reduced Young's modulus (E_r) was found to vary from 115 to 124 GPa. Assuming suitable elastic constants of the indenter, the average Young's modulus (E) was determined to be 127 ± 6 GPa. Nanohardness appears to vary from 8.5 to 11.2 GPa over a wide range of load, indicating an indentation size effect at a nanoscale. The discontinuities in the plot (known as pop-ins or strain bursts) of P–h data, obtained from nanoindentation tests, are observed frequently and these are correlated with shear bands, which are observed under atomic force microscopy (AFM). The first pop-ins, observed in the load range 50–100 µN, led to the estimation of maximum shear stress as ∼8 GPa, close to the theoretical shear strength (∼E/25), and estimation of the energy as 0.67 eV/atom, which is required for elastic–plastic transition of this type of material. Thus, the pop-ins has been attributed to elastic–plastic transition during nanoindentation tests.

Acknowledgements

The authors thank Professor P. Paufler, Professor G.V.S. Sastry and Dr R.K. Mandal for useful discussions. The support of Department of Science and Technology, New Delhi, India is acknowledged.