Influence of specimen size and microstructure on uniaxial compression of WC-Co micropillars

Abstract

The current interest on the development of components on the micrometer size regime demands the evaluation of the mechanical behavior at such small length scales. Regarding cemented carbides, evaluation of mechanical properties at the micrometer scale is a relatively unexplored subject. In the present work we propose and validate a testing protocol based on uniaxial compression of micropillars milled by focused ion beam, to evaluate the elastic and plastic response of WC-Co alloys. In doing so, we studied three WC-Co alloys: fine, medium and coarse grained. First, we determined an appropriate Representative Elementary Volume (REV) to consider the tested sample as a bulk. Then, we performed uniaxial compression on the micropillars that met that REV. Based on the stiffness recorded for each micropillar, we found that the estimated elastic modulus for the fine and medium grained alloys is within the range expected for WC-Co alloys with a similar volume fraction of constitutive phases as those studied here. Finally, we stablished a correlation among stress-strain response, microstructure and yielding within constitutive phases by linking strain bursts taken place at different stress levels to plastic deformation/damage features observed in the micropillars after uniaxial compression.

In-Depth Understanding of Fatigue Micromechanisms in Cemented Carbides: Implications for Optimal Microstructural Tailoring

“…Such a condition is referred to as "typical" for defining the FCG threshold, as it is commonly found when the transition from the near-threshold regime to the intermediate stage is observed [33]. Inserting relatively high effective yield stress values (between 1 and 4 GPa [34][35][36][37][38]) in the above r c equation, together with those measured for ∆K I (between 4 and 15 MPa•m 1/2 ), a sub-micrometric size for the plastic region ahead of the crack tip, i.e., close to length scale of the binder mean free path of the studied cemented carbides, is attained. Third, both surface and subsurface inspection clearly highlights that, different from other extrinsically-toughened brittle materials, the strength lessening under cyclic loads of cemented carbides must be rationalized via the suppression of toughening mechanisms (developed under monotonic loading) rather than the degradation of them.…”

Development of manufacturing technology on WC–Co hardmetals

“…Roa et al [90] also assessed local hardness and the elastic modulus through high-speed massive nanoindentation and subsequent statistical analyses, reporting the strong correlation between mechanical properties and compositional phases. The test results of micropillars testing [91][92][93] and micro-cantilever testing [94,95] were scattered and more micromechanical testing still needs researches in the future.…”

WC-base cemented carbides with partial and total substitution of Co as binder: Evaluation of mechanical response by means of uniaxial compression of micropillars

“…Maximum displacement was fixed at 300 nm and 400 nm for WC-Co and WC-NiMo micropillars and was varied between 300 and 600 nm for WC-CoNi ones. Details of the experimental protocol followed are described elsewhere [19,20]. After uniaxial compression, deformation and/or damage features at the surface of micropillars were inspected by FESEM.…”