| Fe-Al intermetallic has high specific strength and excelente corrosion resistance. However, due to the drawbacks of poor tenacity, being difficult to process and poor high-temperature integrated performance, its industrial application has been seriously restricted.Recent studies have shown that Nb is an important alloying element which improves the stability of Fe-Al alloy microstructure, strength and corrosion resistance of high-temperature. Therefore, preparing the Fe-Al-Nb alloy coating with excellent comprehensive performance to solve the problem of cracks and peels off under the complex working conditions will provide a new technical way of Fe-Al intermetallic practical applications.In this paper, hot-dipping process was used to prepare Fe-Al alloy coating on the surface of 45 steel substrate, and then double glow plasma surface modification technology alloying Nb was exploited to prepare the Fe-Al-Nb alloy coating. The optimal process parameters were explored as follows: source electrode voltage 800V~900V; substrate electrode voltage 350V~450V; testing temperature 900℃~1000℃; operating atmospheric pressure 40Pa; inter-electrode distance 20mm; and soaking time 4h. The microstructure, composition distribution and organization structure were characterized through SEM, EDS and XRD. And microhardness test, scratch test, finite element analysis of the nano indentation process and isothermal oxidation test were carried out to further investigate and analyze the mechanical properties and high temperature oxidation resistance of the alloyed layer prepared under optimal conditions. The results showed that: Fe-Al-Nb alloyed coating was dense and uniform with cystiform patterns, which was well bonded with the substrate. The elements in the alloyed layer exhibited gradient distribution from the surface to the inner. The main phases include Nb, Al Nb2, Fe7Nb6, Fe2Al5 and Fe3 Al. The surface microhardness of the alloyed layer was about 900HV0.1, which was higher than the Fe-Al coating and was 4.5 times higher than the substrate. The elasticity modulus of the alloyed layer was 316.2GPa, implying a stronger ability to resist plastic deformation. Simulating by using the displacement control method, the stress distribution, the strain distribution and the load-displacement curve were got, which was relatively similar with the result of nanoindentation test. Simulating by using the force loading control method, analyzing the results we can qualitative judge the bonding strength between the layer and the substrate, which conformed to scratch test. The high-temperature oxidation mechanism of the alloyed coating was: the outer Nb mainly formed Nb2O5 and Fe Nb O4. With the increase of oxidation temperature and oxidation time, Nb2O5 gradually cracking and spalling, whose oxidation resistance reduced, while Fe Nb O4 gradually increased with certain antioxitant activity. At the same time, Fe Al2O4 and Al2O3 oxides formed between the alloyed layer and the outer oxide film, which could effectively prevent the spread of the oxygen with stable structure and coutinous density. This multilayer structure of oxide film had a higher oxidation resistance. |
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