Preparation of Low Activity Fe-Al Coating on 316L Steel Surface
The Fe-Al coatings were prepared on the surface of 316L stainless steel plate and the in-ner surface of 316L tubes by pack cementation method.The effect of aluminizing agent ratio,tempera-ture and time on the microstructure and phase composition of the Fe-Al coatings were investigated by Scanning electron microscopy(SEM),energy spectrum analysis(EDS)and X-ray diffractometer(XRD).The growth rate of coatings was measured for the planar samples and the inner wall of the tubes.The re-sults showed that uniform Fe-Al coatings with good coherence to the substrate were obtained after alumi-nizing at 700～800℃ for 6 h.The higher growth rate of coating was achieved in the aluminizing agent with Fe-Al powder content of 75％.The aluminizing temperature has little effect on the phase compositions of the coatings obtained in the range of 700～800℃.The prepared Fe-Al coating show double-layered struc-ture,with the outer Al-rich layer mainly composed of FeAl toughness phase,and the inner elemental diffu-sion layer mainly composed of Fe3Al phase.With the increasing time,the element diffusion is enhanced in the coating,which leads to dense and smooth coating surface.On the other hand,due to the en-hanced element diffusion,some pores with 1-2μm diameter appears in the region near the interface be-tween Al-rich layer and diffusion layer and the number of pores is increasing with time.The Fe-Al coating without pores at the interface of the 316L substrate was prepared on inner surface of 316L stainless steel tubes in the temperature range of 700～800℃.After the same aluminizing process,the thickness of the coating grown on the inner tube surface is about 1.1～2.1 times of that on the plate surface.It can be ex-plained by the smaller nuclei volume of coating nucleated on a curved surface than that on a flat surface,which result in the higher nucleation efficiency and faster growth rate of coating on the inner surface of tubes.
surface and interface in the materialsFe-Al coatingpack cementation method316L steelnucleation efficiencypipe wall coating
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