In this study 99.9% aluminium was thermal sprayed on the specimens of 0.25%C (S25C) and 0.55%C (S55C) steels by the wire arc spraying method. Armco iron specimens were also coated with aluminium to examine the effect of carbon on the diffusion process. These specimens were heat treated at temperatures from 923 to 1123 K for 3.6 and 10.8 ks in the atmosphere using a muffle furnace. The microstructure and Vickers hardness of the heat treated specimens were examined. Identification of the formed phases was carried out by X-ray diffraction patterns and EPMA.
Results obtained were as follows:
(1) Diffusion of aluminium into the substrates occurred and diffusion of iron from the substrate also occurred. Intermetallic compounds of Fe-Al were formed and the total thickness of the alloy phases formed by the heat treatment at 923 K for 10.8 ks was about 250 μm.
(2) Several intermetallic compounds formed in the alloy layer were identified by the X-ray diffraction method. The compounds were arranged in order of stoichiometric atomic ratio in the interface zone between the coated aluminium layer and the substrate, and the Fe
2Al
5 phase was predominant over other phases. The maximum value of the Vickers hardness of the diffused layer attained about 1000.
(3) In the case of armco iron, the growth of the alloy phases was not uniform. However, in the case of carbon steels, it was comparatively uniform. This may be attributed to the diffusion of aluminium in carbon steels was suppressed by carbon atoms.
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