A Study on the Deposition of Chromium Carbide by Modified TRD
| Autor: | Jui-Wen Liu, 劉瑞文 |
|---|---|
| Rok vydání: | 2001 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 89 Some special tooling have been designed and fabricated to match the mass production of electronics parts in last few decades. The major requirements for these tooling are reduces the surface residual stress of the tool which is especially needed to improve the adhesion between the coated layer and substrate, promotes the hardness of tool surface, as well as increases the wear resistance and chemistry stability of the tool, all for the purpose of extending the tool life. TRD (Thermal Reactive Deposition / Diffusion) was a thermal-chemical process in which an adherent halides was formed on specimen surface, first by the reaction of C.F.E. or N.F.E. (e.g. V, Cr, Ti, Nb, W) with activator (e.g. NH4Cl, KBF4) at high temperature. Next, produce a dense and very hard carbide, nitride or carbonitride layer (~Hv2000) by the reaction of adherent halides with the carbon or nitrogen atoms diffused outward from the steel substrate. TRD process can be conducted in a pack, salt bath and fluidized bed. It is hard to find which one is the best because of their different advantages. The modified TRD process developed by this work was reformed from the V.F.B. TRD (Vacuum Fluidized Bed TRD) process, which is initiated by our lab. The V.F.B. TRD is a more economical way over the conventional fluidized bed TRD because it tremendously reduces the gas consumption. Meanwhile, the surface quality of the specimen treated by the V.F.B. TRD can be improved as well. However, a huge amount of chromium powder is still necessary for generating the reactive gas. This drove us to the question how to generate the sufficient reactive gas for the coating reaction purpose with minimum amount of the chromium powder it comsumed. Finally, a new trial has been proven to be effective by filling the premixed chromium powder and activator into a heated-evacuated empty retort. The process seems that it combines the mechanism of TRD and CVD. And the results indicated that the thickness, hardness, and the surface quality are equivalent to that of the existed TRD processes. The high carbon tool steel JIS SK3 and DC53 (a modified JIS SKD11 produced by Daido Steel company, Japan) were used as the specimens in this research. The experimental parameters included the influence of amount of activator addition, the carbide forming element contained in the treating powders were investigated to discuss their effects on the thickness, hardness, microstructure, crystal structure and properties of the coated layers. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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