PREPARATION AND PROPERTIES OF CR-C-P HARD COATINGS ANNEALED AT HIGH TEMPERATURE FOR HIGH TEMPERATURE APPLICATIONS

摘要

Chromium plating from the trivalent state is relatively environmentally friendly as compared to a hexavalent chromium bath. Incorporation of non-metallic and metalloid elements into the coating should lead to enhanced properties. The relationship between composition, structure, and properties o annealed Cr-C-P layers electrodeposited from chromium-based trivalent baths is discussed. These coatings are amorphous in the as-deposited state, but upon thermal treatments, chromium nanosrystallization, as well as precipitation of carbides and phosphides occurs. Incorporation of phosphorous strongly influences the structural evolution and mechanical properties. Electroplated Cr-C alloy coatings exhibit significant increases in hardness and strength, when exposed to temperatures up to about 600⁰C, owing to the evolution of their nanostructure. This evolution can be shifted to higher temperatures (approaching 850⁰C), through a ternary addition of phosphorous. The resulting Cr-C-P coatings may be suitabl for applications at higher service temperatures, where more conventional Cr-based coatings soften rapidly.