Hall-Petch strengthening of the constrained metallic binder in WC-Co cemented carbides: Experimental assessment by means of massive nanoindentation and statistical analysis

WC–Co cemented carbides are geometrically complex composites constituted for two interpenetrating networks of the constitutive ceramic and metal phases. Accordingly, assessment of microstructural effects on the local mechanical properties of each phase is a challenging task, especially for the metallic binder. In this work, it is attempted by combining massive nanoindentation, statistical analysis, and implementation of a thin film model for deconvolution of the intrinsic hardness and flow stress of the metallic phase. Plotting of yield stress values as a function of the binder mean free path results in a Hall-Petch strengthening relationship with a slope (ky) of 0.98 MPa m1/2. This value points out the effectiveness of WC–Co phase boundaries as strong obstacles to slip propagation; and thus, for toughening of the brittle phase (WC) by means of crack-bridging ductile (Co) reinforcement.Peer ReviewedPostprint (author's final draft

Focused ion beam tomography of WC-Co cemented carbides

The microstructure of three different grades of WC-Co cemented carbides (hardmetals) has been reconstructed in three dimensions after sequential images obtained by focused ion beam. The three dimensional microstructual parameters are compared against the well-known two dimensional parameters of grain size, phase percentages and mean free path. Results show good agreement with the exception of individual grain recognition, which could not be univocally segmented. In the case of mean free path, the three-dimensional image depicts a more realistic description of the metal interconnections in the composite. Aiming for a simple example of direct application of these FIB tomography outcomes, reconstructed real microstructure for the coarser hardmetal grade studied was translated in a finite element modelling mesh, and elastic residual stresses were estimated from sintering to room temperature. Calculated thermal stresses agree with experimental results and show significant local variations in their value due to the complex microstructure of cemented carbides.Postprint (author's final draft

Real-time motion analytics during brain MRI improve data quality and reduce costs

Head motion systematically distorts clinical and research MRI data. Motion artifacts have biased findings from many structural and functional brain MRI studies. An effective way to remove motion artifacts is to exclude MRI data frames affected by head motion. However, such post-hoc frame censoring can lead to data loss rates of 50% or more in our pediatric patient cohorts. Hence, many scanner operators collect additional 'buffer data', an expensive practice that, by itself, does not guarantee sufficient high-quality MRI data for a given participant. Therefore, we developed an easy-to-setup, easy-to-use Framewise Integrated Real-time MRI Monitoring (FIRMM) software suite that provides scanner operators with head motion analytics in real-time, allowing them to scan each subject until the desired amount of low-movement data has been collected. Our analyses show that using FIRMM to identify the ideal scan time for each person can reduce total brain MRI scan times and associated costs by 50% or more

Intrinsic hardness of constitutive phases in WC–Co composites:Nanoindentation testing, statistical analysis, WC crystal orientation effectsand flow stress for the constrained metallic binder

The intrinsic hardness of the constitutive phases in WC–Co composites is investigated by combining experimental and statistical analysis nanoindentation techniques. It is done on the basis of considering the cemented carbide material as effectively heterogeneous at the microstructure scale, i.e. consisting of three phases defined by either different chemical nature (carbides and binder) or distinct carbide crystal orientation (i.e. with surface normal perpendicular to either basal or prismatic planes). As main outcome, experimentally measured and statistically significant intrinsic hardness values for the defined phases (WC and constrained metallic binder) are analyzed and determined. Besides the evidence of crystal anisotropy for the WC phase, they permit to identify and account the expected strengthening of the plastic-constrained metallic binder, a critical input parameter for hardness and toughness modelling as well as for microstructural design optimization of ceramic composites reinforced by ductile metallic ligamentsPeer ReviewedPostprint (author's final draft

Intrinsic hardness of constitutive phases in WC-Co composites: Nanoindentation testing, statistical analysis, WC crystal orientation effects and flow stress for the constrained metallic binder

The intrinsic hardness of the constitutive phases in WC-Co composites is investigated by combining experimental and statistical analysis nanoindentation techniques. It is done on the basis of considering the cemented carbide material as effectively heterogeneous at the microstructure scale, i.e. consisting of three phases defined by either different chemical nature (carbides and binder) or distinct carbide crystal orientation (i.e. with surface normal perpendicular to either basal or prismatic planes). As main outcome, experimentally measured and statistically significant intrinsic hardness values for the defined phases (WC and constrained metallic binder) are analyzed and determined. Besides the evidence of crystal anisotropy for the WC phase, they permit to identify and account the expected strengthening of the plastic-constrained metallic binder, a critical input parameter for hardness and toughness modelling as well as for microstructural design optimization of ceramic composites reinforced by ductile metallic ligaments. (C) 2015 Elsevier Ltd. All rights reserved.Postprint (published version

Corrosion damage in WC-Co cemented carbides: Residual strength assessment and 3D FIB-FESEM tomography characterization

The effect of corrosion damage on cemented carbides was investigated. The study included residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterization. Experimental results point out a strong strength decrease associated with localized corrosion damage, i.e. corrosion pits acting as stress raisers, concentrated in the binder phase. These pits exhibit a variable and partial interconnectivity, as a function of depth from the surface, and are the result of heterogeneous dissolution of the metallic phase, specifically at the corrosion front. However, as corrosion advances the ratio between pit depth and thickness of damaged layer decreases. Thus, stress concentration effect ascribed to corrosion pits gets geometrically lessened, damage becomes effectively homogenized and relatively changes in residual strength as exposure time gets longer are found to be less pronounced.Postprint (published version

Mechanical deformation of WC–Co composite micropillars under uniaxial compression

In thiswork,WC–Co micropillars machined by focused ion beamhave been tested under uniaxial compression to investigate the stress–strain behavior and associated deformation mechanisms. The results indicate that yielding phenomena is evidenced by multiple strain bursts. Experimental data is found to fall within the bounds defined by the mechanical responses expected for an unconstrained Co-binder like model alloy and a bulk-like constrained binder region in WC–Co composites; capturing then local phase assemblage and crystal orientation effects.Peer ReviewedPostprint (author's final draft

Correction of respiratory artifacts in MRI head motion estimates

Head motion represents one of the greatest technical obstacles in magnetic resonance imaging (MRI) of the human brain. Accurate detection of artifacts induced by head motion requires precise estimation of movement. However, head motion estimates may be corrupted by artifacts due to magnetic main field fluctuations generated by body motion. In the current report, we examine head motion estimation in multiband resting state functional connectivity MRI (rs-fcMRI) data from the Adolescent Brain and Cognitive Development (ABCD) Study and comparison \u27single-shot\u27 datasets. We show that respirations contaminate movement estimates in functional MRI and that respiration generates apparent head motion not associated with functional MRI quality reductions. We have developed a novel approach using a band-stop filter that accurately removes these respiratory effects from motion estimates. Subsequently, we demonstrate that utilizing a band-stop filter improves post-processing fMRI data quality. Lastly, we demonstrate the real-time implementation of motion estimate filtering in our FIRMM (Framewise Integrated Real-Time MRI Monitoring) software package