Abstract
A new method of forming dispersion-hardening oxide inclusions in the process of thermoreactive synthesis from aluminum nanoparticles introduced into WC-Co powder mixture is proposed. Such multiphase and fragmentarily nanostructured composite is characterized by additional heterogeneity, which is determined by the difference in sizes and elastic properties of the phases. In the structure of WC-Al2O3-Co composites a “barrier” effect is provided, the length of the carbide grains contacts is reduced. Carbide grains are separated by a thin cobalt layer with increased strength. In accordance with the results of numerical estimates using finite element analysis (FEA) method, the maximum stress intensity in tungsten carbide is 9.1 GPa (occurring at an external tension of 3 GPa), which is 30% less than the maximum stress intensity in the basic material. The strength improvement predicted by the FEA method in fragmented nanostructured hardmetal composite correlates with experimental results of measurements of fracture toughness according to Palmqvist data. In case of the optimal amount of additives, the increase in crack resistance is equal to 50% compared with the basic material.
Highlights
A new method of forming dispersion-hardening oxide inclusions in the process of thermoreactive synthesis from aluminum nanoparticles introduced into WС-Co powder mixture is proposed
In the course of experimental studies, two methods of introducing aluminum oxides modifying additives into the structure of a hardmetal composite were compared: at the stage of mechanical mixing WC-Co powders with nanoparticles of oxides, carbides, as well as a new method of forming dispersion-strengthening oxide inclusions in the process of thermoreactive synthesis from aluminum nanoparticles of W-Co powders introduced into the mixture
Due to the size difference and specific surface area of the particles of the basic mixture and additional phase, it is possible to estimate the volume content of the nanophase in the composite - from 6 to 10% of vol Changes in the structural-phase state of compacts and sintered samples obtained from the powder mixtures of tungsten carbide, cobalt and aluminum nanopowders were monitored by thermogravimetric method (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) using Jupiter STA449C derivatographs («Netzsch», Germany) and SDT Q600 V20.5 («Netzsch», Germany) in combination with X-ray phase analysis on D8 ADVANCE diffractometer (Germany) – figure 1
Summary
A new method of forming dispersion-hardening oxide inclusions in the process of thermoreactive synthesis from aluminum nanoparticles introduced into WС-Co powder mixture is proposed. Methods and equipment For obtaining hard metals with adjustable graininess, structure and improved properties, the modifying additives of nanoparticles are introduced into bimodal powder mixture.
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