Probe geometry and surface roughness effects in microscale impact testing of WC-Co

Abstract

Depth-sensing repetitive micro-impact tests have been performed on cemented carbide cutting tool inserts with spheroconical diamond probes with end radii of 8, 20 and 100 µm. Results were strongly dependent on probe radius and applied load. At higher load there was a transition to a faster damage rate marking the onset of more variability in rate and in the residual depth of the impact crater when using 8 and 20 µm probes. SEM images show break-up of the WC skeleton at the periphery of the contact zone. Lower surface roughness slowed the initial damage rate at higher load but did not significantly influence the final crater depth. The loaddependent fatigue mechanism displayed by the cemented carbide also has implications for the study and optimisation of coatings when these are deposited.

Nano- and Micro-Scale Impact Testing of Hard Coatings: A Review

“…The accelerating distance is typically set at 40 μm so that differences in impact energy are obtained by altering the applied load (0.5-5 N). Sphero-conical diamond test probes with end radii of 8-100 μm have been most commonly used [36,49,59]. The impact energy is given by the product of the impulse force and accelerating distance.…”

“…The power of the test as a reliable simulation tool is that in many cases, this is more representative of actual contact conditions in applications; i.e., wear resistance is controlled by a combination of load support and resistance to fracture rather than by coating hardness or toughness alone. To improve our understanding of coating system behaviour under repetitive impact, it has proved beneficial to also (i) develop analysis methods for quantifying deformation in single impacts [40,41], (ii) perform repetitive impacts on uncoated substrates [49], (iii) develop test metrics from single impacts, which can be used to detect the onset of fracture [50,52], and (iv) support conclusions with multi-sensing approaches such as acoustic emission monitoring [53,54].…”

Influence of probe geometry in micro-scale impact testing of nano-multilayered TiAlCrN/NbN coatings deposited on WC-Co

“…Micro-impact tests were performed with a NanoTest Vantage with a loading head modified for impact testing as described in references [32][33][34][35][36]. The loading head was actuated with a large electromagnet capable of pulling the probe >50 µm away from the sample surface.…”

“…To fill the gap between the nano-and macro-scale, a micro-impact test has been developed which uses impact loads in the micro-range (~0.5-5 N) together with spheroconical diamond probes with end radii of ~20 µm [32][33][34][35][36]. The maximum energy that can be supplied per micro-impact is x100 greater than in nano-impact.…”

“…The micro-impact test has been used to study the impact resistance of monolayer AlTiN and TiAlCrN coatings on cemented carbide [32], mono-and multilayer TiAlSiN coatings on cemented carbide [33], graded DLC coatings on hardened steel [34] and uncoated cemented carbides [35][36]. A strong sensitivity of the damage tolerance on the applied load was reported in all these studies, which used diamond indenters of end radius ~20 m as the impact probe.…”