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Bu çalışmada çelik malzemenin yüzeyi, akımsız kaplama yöntemi ile Ni-B/Ni-B-W ile kaplanmış, kaplamaların içyapı ve korozyon direnci incelenmiştir. Ni-B/Ni-B-W kaplaması asidik hipofosfit ve alkalin borohidrid indirgeyici banyolarla akımsız olarak kaplanmıştır. Kimyasal bileşim analizi için EDS yöntemi kullanılmıştır. Tarayıcı Elektron Mikroskobu (SEM) ile kaplamanın kesit ve yüzey morfolojisi incelenmiştir. SEM analizi sonucu kaplamaların üniform olduğu, yüzeye çok iyi bir adezif bağ ile gözeneksiz bir şekilde bağlandığı ve kaplamaların birbirleriyle uyumlu olduğu gözlemlenmiştir. XRD analizleri sonucu her iki kaplamanın da amorf yapıda olduğu, 450 ºC’de bir saat uygulanan ısıl işlem ile kaplamanın kristalleştiği ve nikel borit (Ni2B ve Ni3B) çökeltilerinin oluştuğu tespit edilmiştir. Çelik, ısıl işlem görmemiş ve görmüş Ni-B ve Ni-B/Ni-B-W kaplamaların korozif karakterini incelemek için 5% H2SO4 çözeltide daldırma ve Potansiyometrik Polarizasyon deneyleri (%3,5 NaCl sulu çözeltide) gerçekleştirilmiştir. Deneyler sonucu her iki tür kaplamanın korozyon direncinin kaplanan malzeme olan çelikten daha yüksek olduğu görülmüştür. Isıl işlem görmemiş Ni-B/Ni-B-W kaplamasının korozyon direncinin Ni-B kaplamaya göre daha iyi olduğu gözlemlenmiştir. Isıl işlemin uygulanması sonucu her iki kaplamanın da korozyon direnci artmıştır. Ancak Ni-B/Ni-B-W dubleks kaplamasında artış Ni-B kaplamaya göre daha fazladır. Kaplamaya tungstenin eklenmesi ile ısıl işlem sonrası yüzeyde oluşan koruyucu tungsten oksit tabakasından dolayı, kaplamanın korozyon direnci artırmıştır.
In this study, the surface of the steel material, covered with Ni-B/Ni-B-W with the wireless coating method, studied the interior structure of the coating and corrosion resistance. Ni-B/Ni-B-W coating is covered with acidic hypofosphate and alkaline borohydride decreasing baths. The EDS method is used for chemical composition analysis. The scanner electron microscope (SEM) has studied the cutting and surface morphology of the cover. The results of the SEM analysis have been observed that the coatings are uniform, that the surface is connected with a very good adhesive bond and that the coatings are compatible with each other. The XRD analysis found that both coatings were in amorphic structure, that the coatings were crystallized with a heat process applied for a hour at 450 oC and that the nicel borite (Ni2B and Ni3B) was formed. For the study of the corrosive character of steel, thermal unprocessed and seen Ni-B and Ni-B/Ni-B-W coatings, 5 % H2SO4 solution immersion and potential polarisation experiments (3.5 % NaCl water solution) were carried out. Experiments have shown that both types of coating have a higher corrosion resistance than the coated material of steel. It has been observed that the non-heating Ni-B/Ni-B-W coating has a better corrosion resistance than the Ni-B coating. As a result of the application of the heating process, the corrosion resistance of both coatings has increased. However, the increase in Ni-B/Ni-B-W double cover is greater than Ni-B cover. Due to the protective layer of tungsten oxide formed on the surface after thermal processing with the addition of tungsten to the coating, the coating has increased corrosion resistance.
The present work deals with the formation of Ni-B/Ni-B-W duplex coatings on steel by electroless plating process and evaluation of their microstructure and corrosion resistance. The Ni-B/Ni-B-W duplex coatings were prepared using dual baths (alkaline borohydride- reduced electroless nickel baths) with Ni-B as inner layer. EDS analyses were carried out for chemical composition analyses. Scanning electron microscopy (SEM) of the cross-sectional view of the electroless nickel duplex coatings reveal that the coatings are uniform and the compatibility between the layers is good. Also the surface morphology was analysed to characterize the surface properties. Coatings were characterized using XRD. The study reveals that the Ni-B and Ni-B-W coatings are amorphous in their as-plated condition and upon heat treatment at 450 ºC for 1 h, both Ni-B and Ni-B-W coatings crystallize and produce nickel and nickel borides (Ni2B ve Ni3B) in the respective coatings. Polarization tests (in 3,5% NaCl aqueous solution) and immersion tests (in 5% H2SO4 solutions) were carried out to analyse the corrosion properties. The tests were applied on substrate steel, as-plated and heat treated Ni-B and Ni-B/Ni-B-W coatings and were compared with each other. According to the results, all coatings performed better corrosion resistance (CR) than the substrate steel. As-plated Ni-B/Ni-B-W coatings demonstrated better CR than Ni-B coatings. By applying heat treatment, corrosion characteristics improved in both Ni-B and Ni-B/Ni-B-W coatings but much more improvement was observed by Ni-B/Ni-B-W coatings. Adding tungsten to the coating improved additionally the CR due to the formation of protective tungsten oxide layer.
Alan : Fen Bilimleri ve Matematik; Mühendislik
Dergi Türü : Ulusal
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