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Surface Engineering of Metals - Principles, Equipment and Technologies Part 16

Tham khảo tài liệu 'surface engineering of metals - principles, equipment and technologies part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 5.32 Schematic of furnace for CARBO-JONIMP glow discharge carbonitriding and carburizing 1 - resistance glow-discharge heating chamber 2 - lock 3 - quench vestibule. From Kowalski S. et al. 54 . With permission. in the main stream chemical reactions take place which have a significant effect on the rate of formation and properties of surface layers. For that reason selection of the chemical composition of the atmosphere its homogenization and supply to direct contact with the treated load surface is one of the fundamental problems of PACVD methods. Special mention should be made of the chamber design for processes such as glow discharge carburizing and carbonitriding developed by the Institute of Precision Mechanics in Warsaw 54 . It comprises two chambers separated by a vacuum-tight baffle. The first chamber is used for carrying out the process of nitrocarburizing atmosphere composed of H2 N2 CH4 or carburizing H2 CH4 under glow discharge while the second is for cooling of load Fig. 5.32 . The cooling chamber is equipped with a transport mechanism and a quench tank. 5.4 Glow discharge applications 5.4.1 Glow discharge nitriding Glow discharge nitriding is a method used in thermo-chemical treatment yielding diffusion cases of varied structure featuring high hardness very good fatigue properties good wear resistance and resistance to corrosion in some environments. In the conventional gas nitriding method nitrogen available for diffusion is obtained as a result of dissociation of ammonia which flows continuously over the load surface heated to process temperature. In glow discharge nitriding active nitrogen particles are obtained by ionization of the reactive gas nitrogen or a mixture of nitrogen and hydrogen brought about by the effect of glow discharge. During the flow of current around treated 1999 by CRC Press LLC elements of the load a strongly ionized zone is formed known as the cathodic glow see Fig. 5.2 . Ions formed in this zone as well as high energy