Increase In Carbide Content Research Articles

On the microstructure-dependency of mechanical properties and failure of low-pressure cold-sprayed tungsten carbide-nickel metal matrix composite coatings

This study improves upon understanding of the effects of reinforcing particle content and microstructure on the mechanical properties and failure of low-pressure cold spray fabricated tungsten carbide-nickel (WC-Ni) metal matrix composite (MMC) coatings. Image analyses were performed on scanning electron microscope (SEM) micrographs of the coatings to characterize the microstructure and measure the total interfacial area between the reinforcing WC particles and the Ni metal matrix, the mean free path between the particles, the average particle size, and the porosity of the coating. Uni-axial quasi-static tensile testing was conducted on the as-sprayed coatings. The tensile stresses that were measured were coupled with the evolving strains that were calculated by using the digital image correlation (DIC) technique. The results showed that mechanical properties, namely tensile strength and Young's modulus, of the composite coatings increased with increasing WC content in the coatings. The increases were due to the refined microstructural features that occurred with the decrease in the porosity of the coating that was caused by significant consolidation of the Ni metal matrix. Furthermore, this increase in strength and Young's modulus was also related to the increase in the interfacial area between the reinforcing carbide particles and the metal matrix that was caused by the increase in carbide content in the coating, a decrease in the average size of the carbides in the coating, and a reduction of the mean free path between the carbide particles. A framework was presented to elicit the micro-macro relationships between the microstructure and the tensile strength of the cold-sprayed composite coatings. Based on the developed framework, two distinct coating mechanical strength regimes were observed, indicating a significant increase in the tensile strength of the coatings that were comprised of more than 30 wt% WC due to the refined microstructure of the coatings. The higher value tensile strength regime was also confirmed by the larger average mechanical energy absorbed to failure under tensile loading and lower damage accumulation. This collection of data of mechanical properties and the microstructures presented in this study are important to validate numerical-based failure models for cold-sprayed composite coatings. Altogether, the results of this study will enhance understanding of the sensitivity of mechanical response of a composite coating to microstructural changes.

Three-body abrasive wear of cermets

Abstract The present paper is focused on three-body abrasive wear of cermets on the base of tungsten, titanium and chromium carbides with different contents of binder phase. A series of samples of different cermets was tested using a block-on-ring test machine by the method of ASTM B611 using normal loads of 40 and 200 N. Silica sand was used as the abrasive. The wear resistance of TiC–NiMo and Cr3C2–Ni cermets was compared with WC–Co based hardmetals. The volume wear of the cermets decreases with the increase of carbide content in the composites, which corresponds to an increase in the bulk hardness. The volume abrasive wear of the cermets increases approximately linearly with the sliding distance. The wear tracks of the worn compositions blocks abraded at low-load and high-load conditions were analyzed by scanning electron microscopy (SEM). Abrasive wear mechanisms are similar for different cermets, depending mainly on the material/abrasive relative hardness and loading value.

Two-body dry abrasive wear of cermets

The present paper concerns the two-body dry abrasive wear phenomenon of a series of cermets on the base of titanium and chromium carbides with different composition, using a “block on abrasive grinding wheel” test machine. WC–Co hardmetals were used as reference material. Abrasive wear resistance of WC-base hardmetals is superior to that of TiC- and Cr 3C 2-base cermets. The wear coefficient of the cermets reduces with the increase of carbide content in the composites. The volume wear decreases with the increase in bulk hardness. At the first period volume wear of cermets increases linearly with the sliding distance up to the first 100 m; after that the alumina grits become blunt. Scanning electron microscopy examination of the wear tracks in the worn blocks suggests that abrasive wear mechanisms of different cermets are similar and occur through surface elastic-plastic and plastic deformation (grooving). The fracturing of bigger carbide grains and carbide framework the formation of sub-surface cracks by a fatigue process under repeated abrasion is followed by loss of small volumes of the material.

Ejection force in the pressing of two-component metal powder materials

1. A study was made of the effects of compaction pressure and carbide content on the ejection force for the systems Fe-ZrC, Fe-NbC, Fe-Mo2C, Co-ZrC, Co-NbC, Co-Mo2C, Ni-ZrC, Ni-NbC, and Ni-Mo2C. It is demonstrated that the Pe/Pc ratio nonlinearly increases with rise in compaction pressure. With increase in carbide content, the value of Pe/Pc diminishes. 2. The dependence, established earlier, of the Pe/Pc ratio on compaction pressure and on the amount of a second component has been confirmed.