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CrN ve TiN kaplamaların galvanik korozyon davranışı

Galvanic corrosion behaviour of TiN and CrN coatings

  1. Tez No: 101211
  2. Yazar: SELİM TAŞÇI
  3. Danışmanlar: PROF.DR. MUSTAFA ÜRGEN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Metalurji Mühendisliği, Metallurgical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2000
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 74

Özet

ÖZET İnce seramik kaplamaların galvanik korozyon özellikleri hakkında literatürde geniş kapsamlı bir çalışmaya rastlanmamıştır. Bu çalışmada iletken özelliği olmayan alümina numuneler kullanılarak TİN ve CrN kaplama malzemesinin korozyon davranışları incelenmiştir. % 3.5 NaCl çözeltisinde TiN-Karbon çeliği, CrN-Karbon çeliği, TiN-Yüksek hız çeliği ve CrN- Yüksek hız çeliği kullanılarak gerçekleştirilen galvanik korozyon deneyleri ve Evans diyagramları değerlendirildiğinde; galvanik korozyon deneylerinin ve Evans diyagramlarının birbirleri ile uyum içerisinde olduğu görülmüştür. TİN kaplama ile eşleştirme yapılan karbon çeliği ve yüksek hız çeliğinden geçen akım miktarının, CrN kaplama ile eşleştirme yapılan karbon çeliği ve yüksek hız çeliğinden geçen akım miktarından daha fazla olduğu görülmektedir. TİN ve CrN kaplamaların başlangıç potansiyellerindeki farklılık ve TİN kaplamalar üzerindeki oksijenin redüksiyon reaksiyonunun CrN kaplamalar üzerindeki oksijenin redüksiyon reaksiyonundan daha fazla olması geçen korozyon akımının fazla olmasına etki etmektedir. Havaya doyurulmuş % 3.5 NaCl çözeltisinde gerçekleştirilen galvanik korozyon deneylerinden elde edilen sonuçlardan TİN ve CrN kaplamaların karbon çeliğine ve yüksek hız çeliğine karşı galvanik bir etki oluşturduğu görülmüştür. TİN ve CrN kaplamalar %3.5 NaCl çözeltisinde 304 paslanmaz çelik ile galvanik bir etki oluşturmamaktadır. %3.5 NaCl çözeltisinde, TİN kaplamalar CrN kaplamalara göre daha fazla galvanik etki oluşturmaktadır. %3.5 NaCl çözeltisinde yüksek hız çeliği karbon çeliğine göre daha fazla galvanik etki oluşturmaktadır. TİN ve CrN kaplamalar İN H2SO4+O.5M NaCl çözeltisinde 304 paslanmaz çelik ile galvanik etki oluşturmaktadır. İN H2SO4+O.5M NaCl çözeltisinde nötral çözeltide olduğu gibi TİN kaplamalar CrN kaplamara göre daha fazla galvanik etki oluşturmaktadır. rx

Özet (Çeviri)

CORROSION BEHAVIOUR OF CHROMIUM NITRIDE AND TTTANnJM NITRTOE COATING SUMMARY Over the past 10 years there has been a worldwide upsurge in interest in new coatings and surface treatment methods. Numerous research have been carried out over the past 20 years to develop new coatings and films. In addition to the theoretical wear resistance or hardness, a good coating must also exhibit other properties. Their relative importance may vary in different applications. Although a number of papers have been published on this subject, corrosion of the coated surfaces still remains a problem that is often encountered in industry. Hard coatings are commonly used in many tribological applications, such as cutting and forming tools, bearings, and machine parts. They also exhibit other superior properties, making them a class of outstanding materials, such as decorative applications, corrosion protective coatings, superconductive components, or diffusion barriers. While numerous investigations deal with the physical properties and tribological performance of the hard coatings as a function of deposition process and parameters, relatively limited number of publications cover corrosion studies. Accelarated-test are widely accepted and commonly employed method for testing the performance of the corrosion resistance of the coatings, (along with electrochemical measurements). The results, however, are comparable because different corrosion solutions and testing parameters are used and coating properties (chemical composition, structure, porosity) as well as coating-substrate properties affect the results. Additionally, the surface quality of the substrates strongly influences layer properties and, hence, corrosion behaviour. In order to improve lifetime of tools and machine parts it is important to reduce damage caused by wear and corrosion. As both are surface effects it seems Xlikely that surface treatment of the tool can lead to positive results without changing the bulk material. It was realized from early on that thin coatings deposited at low temperatures may not offer good corrosion resistance, and care must be taken not to expose them to aggressive environments. However, since there was considerable interest in studying new applications, attempts to apply the coatings also in rather aggressive environments were made. It was also observed that by controlling the deposition parameters, the quality of the coatings could be improved. Although not all the mechanisms that might be responsible for the failure of the coating are well understood, the basic mechanism responsible for the corrosion of coated substrates has been known for some time. Many investigations have been made to change surface characteristics by plasma nitriding, electrolytically deposited coatings or deposition of PVD-, CVD- coatings. One of the most recent PVD-techniques is ion beam assisted deposition (IBAD). Evaporated or sputtered material is recondensed under bombardment with energetic ions, that strongly influence the film formation and hereby the film properties. By altering certain parameters of deposition process, such as ion and atom flux, ion type, ion energy and incident angle, physical and crytallographic characteristics, like composition, microstructure, texture and intrinsic stress can also manipulated in the desired way. Surfaces form an important part of almost any engineering component since they interact with the surroundings and thus determine largely the behaviour of the component. Coatings are used in order to modify the physical and the chemical properties of the surfaces without affecting the bulk properties of an engineering component. The purpose of the coatings from the electrochemical point of view is to isolate the base material from the aggressive environment. PVD processes can be divided into two groups according to the generation of vapour: evaporation and sputtering. XIEvaporation is the oldest and the simplest PVD method. Material to be deposited is placed in a boat or crucible then heated resistively or by the high current electron beam or laser beam or arc. In all methods, the material evaporates and form a vapour flux in the vacuum chamber. Condensation of this vapour onto the substrate produces the desired film. When the surface of a material is bombarded with high energetic particles, generally ions, physical erosion occurs on the surface of the material. This effect is known as sputtering. Sputtering is widely used as a source of vapour for thin film deposition. In all sputtering PVD processes the ions for sputtering is produced by glow discharge plasma. Alloys of the transition metals and elements of group HI to V are often used as hard coatings with low friction to resist wear attack. The corrosion behaviour of the coated system is usually determined by the defects, that reach through the coating and thus enable the formation of a galvanic couple between the substrate and the coating. Various methods are used in the electrochemical characterization of the coatings and in the porosity determination. However, there are problems concerning the interpretation of the experimental results. TiN and CrN layers, because they are ceramic materials and almost inert, are therefore very resistant to corrosion in various environments. Hence a very important potential area of their application may be as corrosion-resistant coatings. Corrosion resistance of these coatings is also very important in their tribological and decorative applications because, if their corrosion resistance can be improved, the environments in which they can be safely used could be extended. For this reason the corrosion behaviour of nitride-coated materials has been the subject of several investigations. The aim of this work is to study the galvanic corrosion behaviour of chromium nitride and titanium nitride coating. Galvanic corrosion tests were conducted on TiN-Carbon steel, CrN-Carbon steel, TiN-HSS and CrN-HSS couples in the solution of 3.5% NaCl. Evaluation of xnEvans diagrams revealed that galvanic corrosion tests accord with related Evans diagrams. According to the results obtained from the couples of TiN-Carbon steel and TiN-HSS, measured current density was higher than those of CrN-Carbon steel and TiN-HSS pairs. Differences in corrosion rate of TiN and CrN coatings could be explained with the differences in half cell potentials of these coatings. Moreover, relatively high reduction reaction of oxygen on TiN coatings compared to that of CrN coatings might influence the corrosion current density. Another conclusion from the result of experiments carried out on TiN and CrN coatings on 304 SS in the solution of İN H2SO4+O.5M NaCl appeared that, change in current density in Evans diagram occurred in active region of polarization curve of 304 SS. Polarization curves of these couples exhibited similar behaviour in IN H2SO4+O.5M NaCl solution; first a decreasing trend then a continuous increase in polarization curve. This observation could be explained with the formation of passive film on the surface of 304 S S at the initial stage. Passive film formation results in above mentioned drop in polarization curve. In the following stage of corrosion, passive film detoriate and causes continuous increase in corrosion current density. Cathodic coatings posses more stable corrosion characteristics compared to substrate material. However, any defects interrupting continuity of the coating that might be introduced during coating process, cause initiation of galvanic corrosion. In this study, TiN and CrN (cathode) were coated on a non-conductive substrate material (anode), namely AI2O3, and by applying 1 : 1 ratio of current area between anode and cathode, current was measured. Due to some coating defects on TiN and CrN applied on carbon steel and HSS, substrate material behaves as anode and accordingly coated material behaves as cathode and generated high current between two material. In the present study, that covers galvanic behaviour of TiN and CrN coatings, alumina substrate were coated with TiN and CrN by employing PVD technique. The results of galvanic corrosion tests obtained from TiN-carbon steel, CrN-Carbon steel, TiN-HSS and CrN-HSS pairs can be summarised as follows; TiN and CrN coatings created a galvanic interaction with carbon steel and HSS. TiN and CrN coatings did not form a galvanic pair with 304SS in the solution of 3.5% NaCl. In the same solution, galvanic interaction of TiN with 304 SS more pronounced compared to CrN- xm304 SS pair. Tendency of HSS to galvanic corrosion was higher than that of carbon steel. TiN and CrN coatings crated galvanic corrosion with 304SS in İN H2SO4+05M NaCl solution. Similar to the galvanic corrosion in neutral solution, TiN coatings created higher galvanic interaction than CrN in İN H2SO4+O.5M NaCl. XTV

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