Carbide

About: Carbide is a research topic. Over the lifetime, 36331 publications have been published within this topic receiving 503586 citations.

Surface phonon dispersion in graphite and in a lanthanum graphite intercalation compound

Abstract: Using high-resolution electron energy-loss spectroscopy the surface-phonon dispersion of graphite has been determined in the \ensuremath{\Gamma}K direction over the whole energy range and the whole Brillouin zone. Born\char21{}von Karman model calculations are used to describe the dispersion relations. An unexpected result is the splitting of the ZA and ZO mode at the K point. Following a previously introduced procedure to form in situ rare-earth graphite intercalation compounds (GIC), which for lanthanum results in an intermediate carbide phase, we prepared this carbidic phase and the final GIC-like phase. The carbide shows five dispersionless features that may be attributed to Einstein modes of graphite islands. The phonon dispersion of the final phase shows the same modes as graphite shifted in energy: softening of the optical and stiffening of the acoustical phonons occurs. This is described within a Born\char21{}von Karman model by weakening the nearest-neighbor interaction and strengthening the second-nearest-neighbor interaction. The evolution of the phonon dispersion gives a first hint that the GIC-like phase may develop in two stages: first a monolayer graphene on top of the carbide and then the very thin GIC layer.

Investigation on the formation of tungsten carbide in tungsten-containing diamond like carbon coatings

Abstract: A series of tungsten-containing diamond-like carbon (Me-DLC) coatings have been produced by unbalanced magnetron sputtering using a Hauzer HTC-1000 production PVD system. Sputtering from WC targets has been used to form W-C:H coatings. The metal to carbon ratio has been varied to study changes in the metal carbide formation and distribution within the amorphous hydrocarbons (a-C:H) matrix. The difference in the formation of the metal carbide is then linked to changes in the mechanical and tribological properties of the coatings. Detailed high-resolution cross-section TEM has been carried out to analyze the microstructure of the coatings. By changing the amount of a-C:H in the W-C:H coatings, the coefficient of friction could be varied between 0.129 and 0.312. The hardness was found to vary between 8 and 27.5 GPa by using different acetylene gas flows. It was observed that all coatings did have a pronounced multilayered structure.

Influence of silicon content on the precipitation of secondary carbides and fatigue properties of a 5%Cr tempered martensitic steel

Abstract: In comparison with the conventional AISI H11 tool steel, which contains approximately 1 wt.% silicon, the modified steel AISI H11 (∼0.35 wt.% silicon) exhibits improved tensile and fatigue properties at 550 °C – the estimated tool surface temperature during the high-pressure injection of aluminium alloys. The effect of silicon on the stability of secondary carbides was studied using transmission electron microscopy and small-angle neutron scattering. Silicon has a considerable influence on the precipitation of secondary carbides. A higher volume fraction and density of small particles were observed in the low-silicon-grade steel, both after heat treatment and after fatigue testing. The final discussion focuses on the influence of silicon in the precipitation sequence. It is concluded that silicon has a detrimental effect as it shifts the secondary hardening peak towards lower tempering temperatures.

Phase Equilibria in Fe-Mn-Al-C Alloys

Abstract: Phase constitutions of Fe-(20-30)wt%Mn-(0-10)wt%Al-C alloys have been investigated by electron probe microanalysis and transmission electron microscopy. The phase relations between austenite and perovskite carbide, (Fe, Mn)3AlC in the temperature range of 900-1 200°C have been carefully examined. An L12-type ordered structure, which was reported to be formed in rapidly solidified alloys as a metastable phase has not been detected in specimens aged at temperatures above 600°C.

Pick for disintegrating natural and man-made materials

Abstract: An attack tool for working natural and man-made materials that is made up of one or more segments, including a steel alloy base segment, an intermediate carbide wear protector segment, and a penetrator segment comprising a carbide substrate that is coated with a superhard material. The segments are joined at continuously curved interfacial surfaces that may be interrupted by grooves, ridges, protrusions, and posts. At least a portion of the curved surfaces vary from one another at about their apex in order to accommodate ease of manufacturing and to concentrate the bonding material in the region of greatest variance. The carbide used for the penetrator and the wear protector may have a cobalt binder, or it may be binderless. It may also be produced by the rapid omnidirectional compaction method as a means of controlling grain growth of the fine cobalt particles. The parts are brazed together in such a manner that the grain size of the carbide is not substantially altered. The superhard coating may consist of diamond, polycrystalline diamond, cubic boron nitride, binderless carbide, or combinations thereof.