GGG 40 sınıfı küresel grafitli dökme demirlerin yorulma davranışına tin kaplamanın etkisi
Başlık çevirisi mevcut değil.
- Tez No: 75553
- Danışmanlar: DOÇ. DR. M. KELAMİ ŞEŞEN
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Malzeme Bilim Dalı
- Sayfa Sayısı: 201
Özet
ÖZET Endüstride kullanılan makina parçaları ve yapı elemanlarından çoğu tekrarlı değişken yüklere ve titreşimlere maruz kaldıkları için yorulma hasarına uğramaktadırlar. Yorulmada çatlak oluşumu genellikle yüzeyde başlar. Bu yüzden malzemenin yorulma dayanımı, yüzey özelliklerinin arttırılmasıyla geliştirilir. Son yıllarda yapılan araştırmalarda, malzeme yüzeylerinin ince sert seramik filmlerle kaplanması sonucunda, kaplanmamış malzemelere kıyasla yorulma dayanımında önemli oranda artış sağlandığı görülmektedir. İnce sert seramik filmlerle kaplamanın malzeme yüzeylerine başarı ile yapılabildiği yöntemlerden bir tanesi Fiziksel Buhar Biriktirme (PVD) yöntemidir. Bu yöntem, vakum altında bulundurulan malzemelerin buharlaştırılarak veya sıçratılarak atomların yüzeyden kopartılması ve kaplanacak malzeme yüzeyine atomsal veya iyonsal olarak biriktirilmesi esasına dayanır. Bu çalışmada, otomotiv sektöründe bol miktarda kullanılmakta olan GGG 40 sınıfı küresel grafitli dökme demir malzemelerin bir kısmının Katodik Ark PVD yöntemiyle TİN ince sert seramik filmlerle kaplanmış ve diğer kısmı ise kaplanmamış olarak yorulma deneylerine tabi tutulmuşlardır. Yorulma deneyleri, R=-l gerilme oranında çift yönlü eğmeli yorulma yapılarak gerçekleştirilmiştir. Yorulma deneyleri sonucunda kaplanmış ve kaplanmamış numunelerin yorulma kırık yüzeyleri Taramalı Elektron Mikroskobunda incelenmiştir. Bunun yanında TİN kaplamaların kalınlıklarının, yüzey pürüzlülüklerinin, taban malzemesine yapışmalarının belirlenmesi için karakterizasyon deneyleri yapılmıştır. Ayrıca sertlik ölçümü ve çekme deneyi gibi mekanik deneyler de yapılmıştır. Çalışmalar sonucunda, Katodik Ark PVD yöntemiyle TİN kaplanmış GGG 40 sınıfı küresel grafitli dökme demir numunelerinin yorulma dayanımları kaplanmamış malzemelere kıyasla tüm gerilme genliklerinde artmıştır. TİN kaplanmış numunelerin yorulma dayanım sınırı kaplanmamış numunelere kıyasla yaklaşık %T lik bir artış sergilemiştir. XVU1
Özet (Çeviri)
SUMMARY THE EFFECT OF TiN COATING ON FATIGUE BEHAVIOR OF GGG 40 GRADE NODULAR CAST TRON The production of thin layer of ceramics on the surface of various engineering components by a variety of techniques has received considerable attention in the past few years. A number of superior properties of ceramic thin films produced by physical vapor deposition, such as high hardness, good wear resistance and chemical stability, corrosion resistance may attribute to surface improvement of metals. Coating technology on materials will be utilized more widely for various kinds of machine components and structures which require high wear resistance, high corrosion resistance and cavitation-erosion resistance. Most of the machine components and structural elements are subjected to fatigue failure due to cycling loading and vibrations. Generally crack initiation in fatigue damage begins at the surface. Therefore fatigue strength of materials are improved by improving surface properties. In the researches done, it has been found that surface properties of the material surface coated with thin hard ceramic film by PVD technique are improved, but so far there is very little information available about the effect of a coating film on the fatigue behavior of metals. PVD techniques which is a kind of thin film deposition processes performed in vacuum and in which material is derived from a source by physical means the deposited on a substrate. PVD technology consists of the techniques of evaporation, ion plating and sputtering. Each technique finds application in areas where given technique meets specific performance and commercial requirements. Evaporating, materials to be deposited, is melt in a either resistively heated boat or by the heating action of a high current electron beam. In either case, the material evaporates and forms a cloud of vapor which fills the deposition chamber. Condensation of this vapor onto the substrate produces the desired thin film. The atoms of the source materials in the vapor phase have very low energy, 0.2 to 2.6 eV, and as a result, do not produce high adherent or dense films when condensed on to the substrate. Despite this and other short comings of the process, evaporation probably continues to be the most widely used PVD technique. XIXSputtering. When the surface of a material is bombarded with energetic particles, normally ions, one consequence is the physical erosion of the material from the surface. In vacuum chamber, back filled with a sputtering gas to a pressure in the mtorr range, a potential is applied between two electrodes. Given a sufficiently high voltage, a gas discharge plasma is composed of equal number of gas ions and electrons. The gas ions, which carry the positive charge attracted to the negative electrode, or cathode. When these energetic ions arrive at the cathode surface making no contribution to the sputtering process. The ions may enter the surface when momentum transfer from the atom to be ejected from the surface. Concurrent with these events is the emission of secondary electrons from the target. These secondary electrons are important in that they produce further ionization of the sputtering gas energy process, depositing atoms having energies in the range of 4.0 to 10.0 eV. Ion plating, The properties of coating, particularly adhesion, may be enhanced by increasing the temperature of the substrate. There are occasions, however, when upper temperature limitation imposed by the substrate itself preclude the possibility of operating at high enough temperature to obtain the desired coating property. One answer to this problem is to bombard the substrate with the energetic particles both before and during deposition. This has an effect similar to elevated temperature, therefore it is not necessary to heat the substrate to high temperatures. The process that employ ion bombardment to enhance the film are the highest energy deposition methods currently available. Particle arrival energies at the substrate can be on the order of several hundred eV. This process is called ion implating. In this process, a negative voltage is applied to the substrate and cause the ions to be accelerated and arrive at the substrate with significant energies. Arrival energies are normally sufficient to cause some sputtering. In this manner, good adhesion is achieved. Fatigue is the progressive localized permanent structural damage that occurs in material subjected to repeated or fluctuating strains at stresses having a maximum value less than the tensile strength of the material. Fatigue may culminate in cracks or fracture after a sufficient number of fluctuations. Fatigue fractures are caused by the simultaneous action of cyclic stress, tensile stress and plastic strain. If any one of these three is not present fatigue cracking will not initiate or propagate. The cyclic stress starts the crack; the tensile stress produces crack growth. Although compressive stress will not cause fatigue, compression loads may do so. In early literature, failure fractures were attributed two“ crystallization”because of their crystallite fracture appearance. But metals are crystalline solids, and therefore the use of term crystallization in connection with fatigue is confusing and should be avoided. XXThe process of fatigue may be considered as consisting of three stages: 1. Initial fatigue damage leading to crack initiation. 2. Crack propagation until the remaining uncracked cross section of a part becomes too weak to carry the load imposed. 3. Final, sudden fracture of the remaining cross section. The purpose of this thesis is to clarify the fatigue behavior of spherical graphite cast iron coated with ceramics in order to apply ceramic coatings to automotive components. The material substrate used in this investigation was the GGG40 grade nodular cast iron produced according to DIN 1693. The chemical composition of this material is given in Table 1. Table 1. Chemical composition of material to be tested. The experimental materials were produced in the form of Y-Block in Ferro Döküm A. Ş. (GEBZE). The Specimens were machined to a minimum diameter of 4.8 for fatigue tests in air. Surface of specimens was polished with emery paper up to grade #1200 before coating deposition. Mechanical tests are performed on uncoated and coated samples to determine the effect of TiN coating on mechanical behavior. Mechanical tests result of uncoated and TiN coated materials is given in Table 2. Ceramic coating was deposited onto the specimen surfaces by use of PVD processes. In PVD coating of TiN, arc PVD was employed in two steps; cleaning and coating deposition. The deposition parameters are given in Table 3. Table 2 Mechanical Properties of uncoated and TiN coated materials to be tested XXITable 3 TiN deposition parameters V Cleaning > Coating After coating the specimens characterization of the coating is done. The following tests are performed as characterization tests. 1. CaloTest ( for coating thickness) 2. Scratch Test ( for adhesion measurements) 3. Surface Roughness Measurements The characterization data of the TiN coating is summarized in Table 3. Table 3 Characterization data of the TİN coating xxuFatigue tests with coated and uncoated specimens was conducted in air at room temperature using cantilever type bending fatigue machine under a testing frequency of 23 Hz and at the stress amplitudes ranges of 350-250 MPa. The stress ratio in fatigue tests was -1. S-N curves are formed using the data observed in fatigue tests at different stress amplitudes. It is clearly observed from the S-N curves of uncoated, TiN coated specimens, that the endurance limit (and fatigue strength) of TiN coated specimens are higher than uncoated ones. From this result we can conclude that TiN thin films deposited by arc PVD process improves the fatigue strength and endurance limit 7% in GGG 40 grade nodular cast iron. XX1H
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