Elevated temperature micro-impact testing of TiAlSiN coatings produced by physical vapour deposition

Abstract

A high temperature micro-impact test has been developed to assess the fracture resistance of hard coatings under repetitive dynamic high strain rate loading at elevated temperatures. The test was used to study the temperature dependence of the resistance to micro-scale impact fatigue of TiAlSiN coatings on cemented carbide at 25-600 C. Nanoindentation and microscratch tests were also performed over the same temperature range. The results of the microimpact tests were dependent on the impact load, coating microstructure, coating and substrate mechanical properties, and their temperature dependence. At higher temperatures there was a change in failure mechanism from fracture-dominated to plasticity-dominated behaviour under the cyclic loading conditions. This was attributed to coating and substrate softening.

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

“…Previous micro-impact tests with this instrumentation have used spheroconical diamond probes with end radii in the range 17-20 m. [17,18,23] The smallest radius probe produced qualitatively similar impact behaviour to the 20 m probe but more rapidly and at a lower load. Higher plasticity in the tests with this probe result in pile-up under repetitive contact and cracking extending further outside the contact circle at higher load.…”

“…For the micro-impact tests the 30 N high load head of the NanoTest Vantage was modified for impact testing as described previously. [17,18] The loading head was actuated with a large electromagnet capable of pulling the probe >50 µm away from the sample surface. Three different test probe geometries were used as impact probes in this study: (i) a spheroconical diamond indenter with 90 cone angle and calibrated end radius of 20 µm (ii) a spheroconical diamond indenter with 90 cone angle and calibrated end radius of 8 µm and (iii) a diamond test probe with approximately 100 m end radius.…”

“…The response of the uncoated cemented carbide substrate can then be compared to previous data on coated systems with the same substrate to determine whether the substrate or coating fails first. [17,18] Some impact tests with a 20 m end radius probe were performed under the same experimental conditions as in ref. [16] , allowing the results to be compared to those obtained on the grades tested in that study.…”

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

“…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.…”