Scale effect in mechanical characterization of WC-Co composites

Abstract

© 2017 Elsevier LtdThe study of mechanical response of materials at small length scales has gained importance due to the recent advances in micro- and nano-fabrication as well as testing systems. However, most of the reported work has been dedicated to investigate single-crystals or boundary-containing metallic systems, while much less attention has been paid to composite materials, and in particular those combining soft and hard phases. In this work, a systematic procedure is followed for machining micropillars of diameters ranging from 1 to 4 µm in a WC-Co composite with a WC mean grain size around 1 µm, by means of focused ion beam milling. In-situ uniaxial compression of the micropillars and subsequent field emission scanning electron microscopy inspection were conducted. Clear size effects are evidenced. Smaller test specimens (probe size approaching the mean WC size) exhibit deformation/failure mechanisms observed for WC crystals; while for bigger sample sizes, the mechanical response involves several mechanisms directly linked with the microstructural characteristics of the bulk-like cemented carbide material. On the other hand, independent of micropillar size, carbide-carbide or carbide-binder interfaces are found to be preferential sites for nucleation of critical damage events.Peer ReviewedPostprint (author's final draft

Small-Scale Mechanical Testing of Cemented Carbides from the Micro- to the Nano-Level: A Review

“…In most cases, the fracture was preceded by a controlled plastic deformation with work hardening and occasionally a sudden strain burst was observed. This stress value is very close to the stress value reported by Sandoval et al [106] for the micropillar tests when the micropillar was prepared from one WC grain. prepared using the FIB process [108].…”

“…A systematic procedure for using FIB milling to produce micropillars of 1 to 4 µm diameter in a WC-Co composite with a small WC grain size was recently reported [106]. As expected, the micropillar with the smallest diameter contained only WC, while micropillars with larger diameters contained WC grains and Co ligaments, with a distribution characteristic of the investigated system.…”

Study on Strain Rate–Dependent Deformation Mechanism of WC–10 wt% Ni3Al Cemented Carbide by Micropillar Compression

“…The compressive strength of the pillars at 5 × 10 −2 , 1 × 10 −2 , 5 × 10 −3 , and 5 × 10 −4 s −1 are 8.19, 8.15, 7.69, and 7.32 GPa, respectively. These values are all higher than 4.5 GPa, the compressive strength value for WC–11 wt% Co with the same micropillar size, which demonstrates that Ni 3 Al can accommodate deformation better than Co in WC cermets. Notably, the compression tests at a low strain rate result in more stress bursts as opposed to the smooth response at a higher strain rate.…”

“…The nominal stress–strain curves were calculated from the load‐displacement data by using the diameter of the pillar at 1 μm below the surface. And the compliance for both the indenter and the bulk material was taken into account by Sneddon's approachwhere x Sneddon is the displacement corrected by Sneddon's approach, F meas is the measured force, d t and d b are the diameters of the micropillar at the top and bottom, respectively, and the Young's modulus and Poisson's ratio of the diamond tip are E i and ν i , and were taken to be 1140 GPa and 0.07, respectively . The Young's modulus and Poisson's ratio of the WC–10 wt% Ni 3 Al were measured by an ultrasonic pulse reflecting method, and they were 581 GPa and 0.24, respectively.…”

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.…”