Mechanical behavior of metallic glass / HCP nanolayered coatings

Date

2019-09-01

Author

Özerinç, Sezer
Abboud, Mohammad
Motallebzadeh, Amir

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Introduction/Purpose High hardness, large elastic limits and grain-boundary free structure of metallic glasses (MG) make them promising materials for wear resistant, corrosion resistant and biocompatible coatings [1]. However, the brittle nature of MGs in monolithic form is a major disadvantage. MG/crystalline nanolayered composites can overcome this problem by impeding the catastrophic propagation of shear bands [2]. Most studies so far on these nanocomposites have focused on MG/FCC crystalline structures [3] and little is known about nanolayers with different crystal structures. In this work, we investigate metallic glass/HCP nanolayers, to gain insight into the effect of crystal structure on their mechanical behavior. Methods 1 um-thick nanolayered MG/HCP coatings of CuZr/Zr and CuTi/Ti were deposited on silicon substrates with layer thicknesses in the range 10–100 nm. XRD, TEM, nanoindentation, and nanoscratch measurements characterized the samples. Wear tracks were further analyzed by FIB cross- sectioning and AFM scans. Results Hardness values of nanolayered CuZr/Zr and CuTi/Ti are very close to their MG counterparts; CuZr, and CuTi, respectively; and are independent of layer thickness. This behavior is quite different than MG/FCC layers, where hardness increases with decreasing layer thickness due to the strengthening effects in the crystalline phase [3]. The results can be interpreted by the confined layer slip model [4], which suggests that the size- independent strength of the softer MG layers mediate the initiation of plastic behavior in the nanolayers. When it comes to scratch measurements, CuZr/Zr nanolayers exhibit decreasing scratch resistance with decreasing layer thickness, which can be attributed to the low shear strength of the amorphous/crystalline interface. The nanolayered coatings are highly damage tolerant, and can maintain their integrity at compressive strains exceeding 80%. Conclusions MG/HCP nanolayers exhibit a unique behavior of size-independent strength combined with good fracture resistance under sliding loads, making them a promising model system for the design of new protective coatings.

URI

https://hdl.handle.net/11511/86902
https://drive.google.com/file/d/1wcxLmmu_jtbxwOHWiP6XyC3X_88ImCYx/view

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Department of Mechanical Engineering, Conference / Seminar