Carbide

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

In Situ Toughened Silicon Carbide with Al‐B‐C Additions

Abstract: “In situ toughened” silicon carbides, containing Al, B, and C additives, were prepared by hot pressing. Densification, phase transformations, and microstructural development were described. The microstructures, secondary phases, and grain boundaries were characterized using a range of analytical techniques including TEM, SEM, AES, and XRD. The modulus of rupture was determined from fourpoint bend tests, while the fracture toughness was derived either from bend tests of beam-shaped samples with a controlled surface flaw, or from standard disk-shaped compact-tension specimens precracked in cyclic fatigue. The R-curve behavior of an in situ toughened SiC was also examined. A steady-state toughness over 9 MPa·m1/2 was recorded for the silicon carbide prepared with minimal additives under optimum processing conditions. This increase in fracture toughness, more than a factor of three compared to that of a commercial SiC, was achieved while maintaining a bend strength of 650 MPa. The mechanical properties were found to be related to a microstructure in which platelike grain development had been promoted and where crack bridging by intact grains was a principal source of toughening.

Effect of carbon concentration on precipitation behavior of M23C6 carbides and MX carbonitrides in martensitic 9Cr steel during heat treatment

Abstract: The distributions and precipitated amounts of M23C6 carbides and MX-type carbonitrides with decreasing carbon content from 0.16 to 0.002 mass pct in 9Cr-3W steel, which is used as a heat-resistant steel, has been investigated. The microstructures of the steels are observed to be martensite. Distributions of precipitates differ greatly among the steels depending on carbon concentration. In the steels containing carbon at levels above 0.05 pct, M23C6 carbides precipitate along boundaries and fine MX carbonitrides precipitate mainly in the matrix after tempering. In 0.002 pct C steel, there are no M23C6 carbide precipitates, and instead, fine MX with sizes of 2 to 20 nm precipitate densely along boundaries. In 0.02 pct C steel, a small amount of M23C6 carbides precipitate, but the sizes are quite large and the main precipitates along boundaries are MX, as with 0.002 pct C steel. A combination of the removal of any carbide whose size is much larger than that of MX-type nitrides, and the fine distributions of MX-type nitrides along boundaries, is significantly effective for the stabilization of a variety of boundaries in the martensitic 9Cr steel.

Effects of carbide size and Co content on the microstructure and mechanical properties of HVOF-sprayed WC–Co coatings

Abstract: Twelve commercially available WC–Co powders with different average WC grain sizes (0.2, 2, and 6 μm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process. Hardness, Young's modulus, and fracture toughness of the coatings were measured. While the hardness and Young's modulus decreased with increasing cobalt content from 1600 to 1100 Hv and from 400 to 300 GPa respectively, the fracture toughness remained in the range from 4 to 6 MPam 1/2 . The coatings with 2 μm carbide showed lower hardness than those deposited from 0.2 and 6 μm carbide. These measured mechanical properties were discussed with the help of microstructures of the coatings investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. Finally, the hardness of the binder phase in these coatings was estimated to range from 1000 to 1300 Hv by applying the mixture rule for composites to the experimental data, demonstrating that such hardening of the binder phase is a key factor affecting the mechanical properties of the coatings.

ε -Iron carbide as a low-temperature Fischer–Tropsch synthesis catalyst

Abstract: e-Iron carbide is a promising catalyst for low-temperature Fischer–Tropsch synthesis but is difficult to synthesize. Here, the authors report a rapid-quenching process for the synthesis of nanocrystalline e-iron carbide, and evaluate the catalytic activity and selectivity of the material.

Ionic Liquid Monomers and Polymers as Precursors of Highly Conductive, Mesoporous, Graphitic Carbon Nanostructures

Abstract: In this contribution a template-free preparation of mesoporous graphitic carbon nanostructures with high electric conductivity is presented, using ionic liquid monomers or poly(ionic liquid) polymers as carbon precursors. The carbonization was performed in the presence of FeCl2 at temperatures between 900 and 1000 °C. It was found that FeCl2 plays a key role in controlling both the chemical structure and the texture morphology of the graphitization process. A detailed investigation on the carbonization process demonstrated that 900 °C is a threshold temperature where a synergistic formation process enables the development of the superior physical properties, such as large surface area and low resistance. The as-synthesized carbon products are graphitic, mesoporous, and highly conductive, as proven by XRD and TEM characterizations and conductivity measurements. Via an acid etching process, iron and iron carbide nanoparticles, the remainder of the primary catalyst, can be removed, leaving pure mesoporous ca...