Carbide

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

Reaction-formed silicon carbide

Abstract: The reaction bonding of silicon carbide (SiC) typifies liquid-solid reaction processes for the synthesis of refractory ceramic composites. These processes have particular advantages over conventional sintering and hot-pressing techniques in their lower processing temperatures, shorter times and near-net shape fabrication capabilities. Two particular modifications that we have employed in order to improve the mechanical properties and the ultimate use temperature of reaction-bonded SiC are the use of microporous carbon pre-forms derived from polyfurfural alcohol for refinement of microstructure, and the use of alloyed melts in order to replace detrimental residual silicon with a refractory silicide. The control of reaction rate is always a key issue in reaction processing. We have studied the kinetics and mechanisms of the liquid SiC reaction. Experiments on carbon fibers and plates show that the principle mechanism is one of solution-reprecipitation. There is an increased solubility of carbon at very fine SiC particles formed by the spallation of the misfitting carbide from the carbon interface, leading to reprecipitation of SiC at defective seed crystals. Molybdenum and boron at low concentrations (3.2 mol.%) have little effect on reaction kinetics, whereas aluminum is able to impede the reaction through the formation of an interfacial carbide layer.

s-Process Zirconium in Presolar Silicon Carbide Grains

Abstract: The isotopic composition of zirconium in silicon carbide grains from the Murchison meteorite was measured by resonant ionization mass spectrometry of laser-ablated neutral atoms. These grains are condensates from the atmospheres of red giant stars that existed before the formation of our sun and solar system, and they contain records of nucleosynthesis in these stars. The r-process–dominated isotope zirconium-96 was depleted by more than a factor of 2 compared with the s-process–dominated isotopes zirconium-90, zirconium-91, zirconium-92, and zirconium-94, in agreement with expectations for neutron capture nucleosynthesis in asymptotic giant branch stars.

Structural Relaxation of Amorphous Silicon Carbide

Abstract: We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions.

Microstructure and Mechanical Properties of an Ultrahigh-Strength 40SiMnNiCr Steel during the One-Step Quenching and Partitioning Process

Abstract: The quenching and partitioning (Q&P) process is a novel heat treatment for the enhancement of the strength level of steels without a significant deterioration of ductility. In this work, a study of 40SiMnNiCr steel subjected to the one-step Q&P process is presented. The study results suggest that the strength level of the steel subject to one-step Q&P increases at first and subsequently decreases with the partitioning time because of the synergistic effect of the increase in the retained austenite fraction, the decrease in carbon supersaturation in martensite, the change in the dislocation density in martensite, and the formation of transition carbide. The presence of the transition carbide markedly increases the strength level of the one-step quenched and partitioned steel, with the ultimate tensile strength (UTS) over 2400 MPa and the ductility more than 10 pct during partitioning at 453 K (180 °C) for 180 seconds. Isothermal martensite transformation possibly occurred in this medium-carbon ferrous alloy during the one-step Q&P processing. Meanwhile, in the early stages of the low-temperature partitioning process, carbon partitioning from martensite to austenite plays a dominant role in the carbon redistribution competitions. In addition, the relationship between the microstructure and mechanical properties of the one-step quenched and partitioned steel is discussed.

Application of fine grained tungsten carbide based cemented carbides

Abstract: Fine grained submicron cemented carbides with a market share of 10–15% of total carbide consumption are characterized by an almost optimal combination of hardness and toughness. They are mainly used in machining wood and wood based materials, plastics, composites, ferrous and non-ferrous metals as well as in chipless operations such as in can tooling, high pressure punches and for wear parts. Tailored submicron cemented carbide has widened the application range of carbide and has led to a multifold improvement in abrasive wear life.