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Nano-mechanical and wear characteristics of ZrB2 + Al2O3:Cr3+,Nd3+ (Al2O3 co-doped with Cr3+ and Nd3+ ions) luminescent ceramic composites have been investigated using nanoindentation and tribological tests. Nanoindentation was carried out using a Berkovich diamond tip applying continuous stiffness measuring (CSM) mode with a maximum depth of 200 nm. The wear behaviour was studied during dry sliding in the air with a SiC counter body at applied loads of 5 and 50 N, and sliding speed of 0.1 m/s. The nanohardness of the ZrB2 and Al2O3 are very similar with mean values of 34.2 GPa and 32.6 GPa, respectively The Young modulus for ZrB2 is higher with a mean value of 555.6 GPa in comparison to the Young modulus of alumina with mean value of 473.8 GPa. Pop – in effect was found during the indentation of ZrB2 grains at indentation loads from 0.2–8.0 mN. The lowest coefficient of friction was measured for ZrB2 + 8%Al2O3:Cr3+,Nd3+ at 5 N load with value of approximately 0.5. The wear rate of the system ZrB2 + 32 % Al2O3:Cr3+,Nd3+ at 5 N is significantly lower in comparison to the wear rate of ZrB2 + 8% Al2O3:Cr3+,Nd3+ but at a load of 50 N the wear of the systems is very similar approximately 1. 10−5 mm3/N.m. Tribolayer formation connected with debris origin, oxidation and tribochemical reactions were characteristic for both composites with similar chemical composition but different size and thickness of tribolayers.

The effect of the addition of Cr3+/Nd3+ doped Al2O3 nanoparticles (Al2O3 co-doped with 1% Cr3+ and 1% Nd3+ ions) on the mechanical and luminescent properties of ZrB2 ceramic composites was investigated. ZrB2 based composites with addition of 8, 16 and 32wt.% of alumina nanoparticles were prepared by spark plasma sintering (SPS). Microstructure characteristics were studied by scanning electron microscopy (SEM), elastic modulus by ultrasonic wave transition method, hardness and fracture toughness by the Vickers indentation methods. The addition of alumina nanoparticles had positive effect on the mechanical properties of the composites. Thus, the hardness increased from 14.5 to 16.2GPa and the fracture toughness from 3.91 to 5.89MPa•m1/2 in comparison to the values of the monolithic ZrB2 system. The composite with the highest additive content showed evident luminescent character and the increase of the temperature caused a reduction of luminescent intensity. This is the first report which shows luminescent properties of ZrB2 composites. Moreover, for the first time, luminescent properties of Cr3+ ions were used to develop ZrB2 matrix composites with Cr3+/Nd3+ doped Al2O3 particles with the self-temperature readout functionality via luminescent thermometry.

The wear resistance and tribological characteristics of spark plasma sintered ZrB2 + B4C, ZrB2 + SiC and ZrB2 + ZrC composites were investigated under dry sliding conditions at applied loads of 5 N and 50 N in air. The microstructure, deformation and damage characteristics were studied using scanning electron microscopy, confocal electron microscopy, a focused ion beam and atomic force microscopy. The friction coefficient values were very similar for all composites with values ranging from 0.63 to 0.72 and with the lowest value recorded for the ZrB2 + SiC composite at a 5 N applied load. The ZrB2 + ZrC composite was the most wear resistant, with wear rates at a 5 N load of 6.15 × 10−6 mm3/(N·m) and at a 50 N of 7.3 × 10−6 mm3/(N·m). None, or a very limited number of grain pull-outs and/or lateral fractures of grains were found during the wear tests. At the 5 N load, abrasive grooves connected with deformations and Hertzian crack formations were the main wear mechanisms in all systems, with limited crack formations in the ZrB2 + ZrC composite. Tribofilm formations connected with debris origin, oxidation and tribochemical reactions were dominant in all composites, with similar chemical compositions but different sizes and thicknesses at the 50 N load.

Anisotropic dislocation nucleation of differently oriented zirconium diboride (ZrB2) grains in a polycrystalline ZrB2-based ceramic composite was investigated during nanoindentation with a Berkovich tip. Based on the Hertzian stress analysis of the measured strain bursts, the critical resolved shear stresses for slip systems of 10 1 ¯ 0 11 2 ¯ 0 , 10 1 ¯ 0 0001 and 10 1 ¯ 0 11 2 ¯ 3 types were determined. Homogeneous dislocation nucleation was revealed with near theoretical critical resolved shear stress (~35 GPa) for each slip system. The analysis of the orientation dependence of the calculated maximal resolved shear stress values inferred anisotropic dislocation nucleation in ZrB2 grains with single and simultaneous activation of the investigated slip systems.

Deformation, damage and wear characteristics of spark plasma sintered VC, NbC and ZrC refractory carbides have been investigated using nanoindentation, tribology and micro/macro − indentation tests. Fractography, using SEM, AFM and confocal microscopy, was used for the characterization of deformation and damage mechanisms. Considerable indentation load − size effect was found in all systems with hardness values from 30 to 36 GPa to 13–17 GPa corresponding to the applied loads of 1 mN and 100 N, respectively. During nanoindentation, characteristic stress-drops were observed on hardness-displacement profiles of NbC and ZrC at depth region of 15–30 nm while this was not typical in VC. The highest coefficient of friction was measured for NbC with a value of 0.45 and the lowest for ZrC with an average value of 0.3. The wear rate of the NbC, and VC was similar, approximately 3 × 10−6 mm3/Nm only the wear rate of ZrC was larger, approximately 2 × 10−5 mm3/Nm.

In this overview, we summarize the results published to date concerning the small-scale mechanical testing of WC−Co cemented carbides and similar hardmetals, describing the clear trend in the research towards ever-smaller scales (currently at the nano-level). The load-size effect during micro/nanohardness testing of hardmetals and their constituents and the influence of the WC grain orientation on their deformation, hardness, indentation modulus, fracture toughness, and fatigue characteristics are discussed. The effect of the WC grain size/orientation, cobalt content, and testing environment on damage accumulation, wear mechanisms, and wear parameters are summarized. The deformation and fracture characteristics and mechanical properties, such as the yield and compression strength, of WC−Co composites and their individual WC grains at different orientations during micropillar compression tests are described. The mechanical and fracture properties of micro-cantilevers milled from WC−Co hardmetals, single WC grains, and cantilevers containing WC/WC boundaries with differently-oriented WC grains are discussed. The physical background of the deformation and damage mechanisms in cemented carbides at the micro/nano-levels is descri and potential directions for future research in this field are outlined.

The influence of the crystal orientation of WC grains on their nanoscratch resistance in WC–Co system was investigated. Instrumented nanoindentation with Berkovich tip was used for nanoscratch measurement. Electron backscatter diffraction (EBSD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) investigations were performed to determine the orientation of WC grains and to study the surface morphology after the scratch test. The scratch resistance of the WC grains exhibits significant angle dependence with higher resistance of grains close to the basal orientation in comparison to the grains close to prismatic orientation.