| Summary: | 碩士 === 國立臺灣大學 === 機械工程學系研究所 === 86 === A Study on the Composite Carbide，Nitride and Carbonitride Coating of Die
Steels in a Fluidized Bed
Abstract
The implementation of a fluidized bed CVD process for the formation of hard
wear-resistant , corrosion-resistant , oxidation-resistant , dense and
strong adhesion coatings of carbides , nitrides and carbonitrides of die
steels is feasible since it can lead to a flexible surface modification
technology combining adaptability with reducing capital and operational
costs . In this paper , FBCVD is coupled with conventional CVD and
TRD(Thermo-Reactive Diffusion & Depostion Process) for the production of
coatings . The method developed has the advantages of being simple , clean
and environmentally friendly compared with conventional coatings .
Die Steels(SKD11 & SKD61) were used for the substrates . For different
coating species , this research involved a treating agent consisting of a
powder mixture of Al2O3 with titanium powder , chromium powder or V-Fe
powder . HCl was used as activator of the process . During the coating
process , the bed can be fluidized by inert gas or gas mixtures like Ar ,
Ar+H2 , Ar+N2 etc . The present study reports on the characteristics of
formation of TiC/TiN composite coating , CrC/VC composite carbide , CrCN ,
CrN on die steels . The experimental parameters such as temperature ,
time , gas composition ratio , powder content ratio , HCl concentration
and prenitrided condition were investigated to appraise their effects on
the growth rate of the coating species . The optimal processing condition
was obtained from the evaluation of the experimental parameters .
The growth rate and the microstructure of the coatings were investigated by
measuring the weight change , the thickness and the hardness . EPMA was
carried out to analyze the chemical composition of the coatings . XRD was
also performed to examine the structure and compounds of the coatings .
Coating investigations of corrosion resistance , oxidation resistance ,
adhesion strength and wear test reveal the coating effects in a fluidized
bed .
According to the results , TiC/TiN composite coating behaved better in
adhesion strength and wear protection compared with TiC and TiN coating .
Deposition of TiC/TiN composite coating can effectively retard the
oxidation at temperature below 650℃ . The mechanical properties of CrC/VC
composite carbide coating just lie between CrC and VC . The hardness and
the tribological potential of CrC/VC composite carbide coating have been
enhanced through the presentation of vanadium carbide . Coatings of CrCN
or CrN were observed to have excellent adhesion strength and pronounced
corrosion resistance to nitric acid(69%) and sulfuric acid(96%) . Both of
CrCN and CrN were shown to have the highest oxidation resistance and proved
to be oxidation resistant to at least 700℃ . Among the Ti-based coatings
and the Cr-based coatings , CrCN had particularly high wear-resistance
potential and CrN had the lowest oxidation rate .
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