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Wear behavior of a fine‐grained dual‐phase high‐entropy carbide/boride ceramics was investigated using ball‐on‐flat dry sliding methods in air, applying rotational and linear reciprocation motion with SiC counterpart. The investigated system showed very high nanohardness of the carbide and boride grains with mean values of 37.4 ± 2.3 and 43.0 ± 2.9 GPa, respectively, with the microhardness of dual system HV1 29.4 ± 2.0 GPa. The stabilized friction coefficient values during the circular tests changing from.62 to.77. During the reciprocal test, the frictional coefficient values are very similar with an average value of.53. The specific wear rates during the circular motion were similar in the range from 4.65 × 10−7 to 1.68 × 10−7 mm3/N m. During the reciprocal test, the wear rates at 5 and 25 N were similar as in the case of circular motion, but at 50 N load, the wear rate increased significantly to the value of 9.11 × 10−6 mm3/N m. The dominant wear mechanisms in all cases were oxidation driven tribochemical reaction and tribolayer formation in boride grains and mechanical wear in carbide grains. During the linear reciprocation test, the loading mode created conditions resulted in relatively low coefficient of friction and very high specific wear rate. [ABSTRACT FROM AUTHOR]

Abstract: Silicon nitride+1wt% graphene platelet composites were prepared using various graphene platelets (GPL) and two processing routes; hot isostatic pressing (HIP) and gas pressure sintering (GPS). The influence of the processing route and graphene platelets’ addition on the fracture toughness has been investigated. The matrix of the composites prepared by GPS consists of Si3N4 grains with smaller diameter in comparison to the composites prepared by HIP. The indentation fracture toughness of the composites was in the range 6.1–9.9MPam0.5, which is significantly higher compared to the monolithic silicon nitride 6.5 and 6.3MPam0.5. The highest value of K IC was 9.9MPam0.5 in the case of composite reinforced by the smallest multilayer graphene nanosheets, prepared by HIP. The composites prepared by GPS exhibit lower fracture toughness, from 6.1 to 8.5MPam0.5. The toughening mechanisms were similar in all composites in the form of crack deflection, crack branching and crack bridging. [Copyright &y& Elsevier]

Silicon nitride+1wt.% graphene platelet composites were prepared using various graphene platelets with the aim to improve the fracture toughness of Si3N4. The fracture toughness was significantly higher for all composites in comparison to the monolithic Si3N4, with the highest value of 9.92MPam0.5. The main toughening mechanisms originated from the presence of graphene platelets, and the increase in the fracture toughness values was attributable to crack deflection, crack branching and crack bridging. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Silicon nitride+1wt% graphene platelet composites were prepared using various graphene platelets (GPLs) as filler. The influence of the addition of GPLs on the microstructure development and on the fracture toughness of Si3N4 +GPLs composites was investigated. The GPLs with thickness from 5nm to 50nm are relatively homogeneously distributed in the matrix of all composites, however overlapping/bundle formation of GPLs was found, containing 2–4 platelets as well. The single GPLs and overlapped GPLs are located at the boundaries of Si3N4, and hinder the grain growth and change the shape of the grains. The fracture toughness was significantly higher for all composites in comparison to the monolithic Si3N4 with the highest value of 9.9MPam0.5 for the composite containing the GPLs with smallest dimension. The main toughening mechanisms originated from the presence of graphene platelets, and responsible for the increase in the fracture toughness values are crack deflection, crack branching and crack bridging. [Copyright &y& Elsevier]