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Chromium and Chromium Alloys
Various alloying additions have been discovered which render unalloyed chromium much less susceptible to low-temperature embrittlement as well as to nitridation in air at elevated temperatures. These include additions of the Group IIIA metals, magnesia, and carbides based on the Groups IVA and VA metals. Of these additions, only the carbides contribute significantly to the hot strengthening of chromium. The combination of selected carbides and solid-solution-strengthening elements such as tungsten, molybdenum, and/or tantalum, has resulted in experimental alloys which retain useful strengths at temperatures through 1316 C (2400 F). These high strengths are achieved at some sacrifice in the low-temperature ductility of chromium. Also, despite the improvements afforded in the oxidation and nitridation resistance of chromium through alloying, no alloys are available which are capable of service in long-time exposures in air above 982 C (1800 F) without suffering some property degradation.
Chromium Alloys
Chromium containing alloys such as ferritic or austenitic steels and nickel-base alloys generally show good oxidation and corrosion resistance as well as high strength, and have been widely used for components in chemical plant, power plant or aircrafts. However, it seems to be necessary to introduce a new technology for further application of these alloys. Nano-structured materials have recently drawn considerable attention, because these materials sometimes show very high strength without serious loss of ductility compared to the materials with deformed microstructure formed by usual processing, and also have large internal friction. This book discusses the composition, properties, electrodeposition, and the applications of chromium alloys. It also provides information on the production of nano-structured chromium-containing alloys.
Friction and Wear of Cobalt-molybdenum and Cobalt-molybdenum-chromium Alloys for Prosthetics
Studies were conducted in heptane with cobalt alloys on a disk-and-conforming-shoe apparatus simulating the single motion of a human hip joint. The results showed that cobalt-molybdenumchromium alloys were brittle; that the surface finished by grinding fragmented locally; and that, subsequently, abrasion of sliding surfaces occurred. When the ground surfaces were altered by glass-bead blasting, fragmentation during the wear process was minimized. Particles loosened by the grinding.process were removed, and the bead-blasted surface provided pockets to entrap debris. Friction and wear for the bead-blasted cobalt-molybdenum-chromium alloy were significantly lower than for vitallium.
