Abstract
This research was devoted to studying the influence of the taper angle on the micro-compression of micro-pillars fabricated from near-amorphous and nanocrystalline Mo-B-C coatings. A series of micro-pillars with a taper angle between 4–14° was fabricated by focused ion beam technique. The deformation mechanism was found to be dependent on the taper and, also, on the crystallinity of the coating. In order to obtain correct values of yield strength and Young’s modulus, three empirical models of stress correction were experimentally tested, and the results were compared with nanoindentation measurements. It was shown that the average stress correction model provided comparable results with nanoindentation for the yield strength for taper angles up to ~10°. On the other hand, the average radius or area model gave the most precise results for Young’s modulus if the taper angle was <10°.
Highlights
The stress–strain behavior is one of the key factors determining the mechanical properties of solids.When the nanoindentation technique is used, it is very complicated to obtain the stress–strain relations due to the constrained flow of material under pressure, leading to a very complex stress field under the indenter depending on its geometry
The corrected yield strength exhibited similar results as in the crystalline case, i.e., the σ3 average stress correction showed results comparable with the 350 nanoindentation data, whereas the other two models showed underestimation in the calculated yield strength, which increased with the taper angle
A series of pillars with different taper angles in the range between 4° and 14° was fabricated from the surface of the near-amorphous and nanocrystalline Mo-B-C coatings, which were afterward subjected to micro-compression testing with the flat punch indenter
Summary
The stress–strain behavior is one of the key factors determining the mechanical properties of solids.When the nanoindentation technique is used, it is very complicated to obtain the stress–strain relations due to the constrained flow of material under pressure, leading to a very complex stress field under the indenter depending on its geometry. The micro-pillars are usually fabricated by focused ion beam (FIB) techniques, and their diameters are typically ranging from ~100 nm up to several μm This technique has already been used to analyze a wide range of materials in either a bulk form or as a thin film [1,2,3,4,5,6,7,8]. It is very convenient to fix as most of them as possible to avoid any over or under-estimations of calculated mechanical properties While it is very time-consuming to prepare a large number of micro-pillars to study any possible drawbacks of this technique, the finite element modeling (FEM) [9,10] proves to be very useful for finding general rules how to obtain reliable results from the micro-compression
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