Paslanmaz çelik yüzeylerin mekanik özelliklerinin geliştirilmesi = Improvement of the mechanical properties of stainless steel surfaces

Abstract

Bu tez çalışmasında, Diamalloy 2002 (Tungsten Karbür, krom bazlı) ve Sulzer Metco 7202 ( Karbür, Krom bazlı) tozlar, farklı konsantrelerde hazırlanmış olup, endüstri ve sanayide sıkça kullanılan 316 paslanmaz çelik yüzeylerine High Velocity Oxygen Fuel (HVOF) yöntemiyle yapılan kaplamaların yüzey özelliklerinin iyileştirilmesi hedeflenmiştir. Bu çalışmada iki tip toz kullanılmıştır. Bu tozlar Diamalloy 2002 ve Sulzer Metco 7202 tozlarıdır. %50 Diamalloy ve %50 Sulzer Metco 7202 toz karışımından oluşan M grubu numuneleri , %100 Sulzer Metco 7202 tozundan oluşan G grubu numuneleri hazırlanmıştır. Bu tozların çeşitli kombinasyonlarda HVOF metodu ile kaplama özelliklerine etkileri analiz edilmiştir. M ve G numuneleri için aşınma testleri yapılmıştır. Bu testlerde Alümina bilya (Al2O3) kullanılmış olup farklı hız, yük, yol mesafesi ve paso sayısı ile testler gerçekleştirilmiştir. Aşınma testleri sonrası numunelerin SEM görüntülerine bakılmış, XRD analizleri gerçekleştirilmiş, pürüzlülük testleri yapılmış ve kaplama sonrası detaylı olarak incelenmiştir. HVOF yöntemi, endüstri ve sanayide yaygın olarak kullanılan maliyeti az bir teknolojik prosestir. HVOF yöntemi ile çok yüksek yoğunlukta kaplama kalınlıkları elde edilir. Yüksek püskürtme sayesinde elde edilen yüksek yapışma sonuçları metodun en iyi özellikleridir. Aynı zamanda HVOF ile elde edilen kaplama sonuçları incelendiğinde parçacık hızlarının fazla olması nedeniyle az sayıda porozite içermektedir. Porozite değerleri %1'in altında kalabilmektedir. HVOF metodu çok yüksek yapışma sağlamakta ve kaplama ömrü uzun olmaktadır. Bütün malzemeler bu metot ile kaplanabilmektedir [4]. Endüstrideki paslanmaz çelikler düşük maliyet ve yüksek korozyon dayanımı ile gerekli uygulamalarda sanayi ve endüstrinin ihtiyacını karşılamaktadır [5]. Paslanmaz çelikler iyi özelliklerinin yanında, yüksek maliyetlere çıkabilen ve zorlu bozunma süreçlerine sebep olabilecek uygulamalarda da çalışılabilmektedir. Bu durum paslanmaz çelik kaplamalarının geliştirilmesi için önem arz etmiştir. Yüzeye yapılan kaplamalar ile aşınma özelliklerinin geliştirilmesi, numunelere farklı hız, yol, yük ve paso sayısı ile aşınma deneyleri uygulanmış ve kaplama üzerindeki etkileri incelenmiştir. Kaplama kalınlıkları ölçülerek sertlik ve aşınma üzerine etkileri irdelenmiştir. Kaplama yüzeylerinde aşınma deneyi öncesi ve sonrası görüntüler alınmıştır. Makro ve mikro incelenen görüntüler ile kaplama hataları araştırılmıştır. X ışınları analizleri yapılmış olup yapıda ki fazların tayini yapılmıştır. Yüzey pürüzlülüklerine bakılmış, aşınma deneyinden sonra iz genişliği ölçümleri yapılarak aşınma oranları tespit edilmiştir. Aşınma yüzeylerinin SEM görüntülerine ve EDS analizlerine göre yüzeylerde meydana gelen değişimler yorumlanmıştır.

In this thesis, Diamalloy 2002 (Tungsten Carbide, chrome based) and Sulzer Metco 7202 (Carbide, chrome based) powders have been prepared in different consantration and their surfaces have been coated by the method of HVOF on 316 stainless steel which is frequently used in industry, in order to improve surface characteristics. Powder of Diamalloy 2002 and Sulzer Metco 7202 have been used in this study. Sample M is the mixture of 50% Diamalloy 2002 and 50% Sulzer Metco where as Sample G is 100% Sulzer Metco 7202. Different combination of these two samples have been coated by HVOF process, thus coated properties have been analyzed. Corrosion tests have been conducted for the sample of M and G by exposuring them to different velocity, pressure, distance and number of passes. In these experiments Alumina ball (Al203) has been used. Thereafter the corrosion tests, SEM images and XRD results have been analyzed, roughness measurements have been made and evaluated in detail after coating. Surface coating methods have become very popular and application areas have increased in recent years thanks to the financial, theoretical and technological benefits they provide [1,2]. Coating is done to change the chemistry and physical properties of a material. The surface coating process aims to improve the surface of the material, improve its appearance, and make it resistant to the conditions in its environment as a result of precipitation of an element suitable for the material on the surface of the material. In surface technology, in some cases, obtaining the desired material is only possible thanks to coating technologies [5,6]. It is a surface engineering method that aims to improve the surface of the coating material by examining its wear, corrosion and fatigue strength, to increase its advantages and to repair the materials in need of repair [7-13]. The high velocity oxy-fuel (HVOF) process can be used to achieve relatively low particle temperature and high speed (900 m/s). Thus, dense coatings with low porosity and less prone to oxidation can be obtained [10]. High velocity oxy-fuel (HVOF) improve the wear resistance and decrease the friction coefficient between various sliding components in automotive, aeronautical and space. The HVOF sprayed WC-based cermet hard coatings such as WC–Co, WC–CoCr and others are applied in different engineering applications due to wear resistance and good corrosion resistance. Cobalt acts as a tough binder, which deforms plastically on impact onto the substrate and accommodates the wear-resistant WC particles [14]. In this work, coatings were made on the surface of 316 stainless steel by using various powders by HVOF method. Coating thicknesses were measured and their effects on hardness and wear were examined. Before the wear test on the coating surfaces and optic images were taken. Coating structure was investigated with macro and micro-examined images. X-ray analyzes were made and the phases in the structure were determined. Surface roughness was checked, trace width after wear test the wear rates were determined by measuring the wear surfaces. Changes in surfaces according to images and EDS analyzes interpreted. Improving the wear properties with the coatings applied to the surface, wear tests were applied to the samples with different speeds, paths, loads and number of passes. The effects on the coating were investigated. Level-2 In this experimental study, AISI 304 L stainless steel was used as the substrate and HVOF coating method was applied on the selected steel samples. The changes in the surface properties as a result of the coating were investigated. Two different powders were used in this study. The first powder is Diamalloy 2002 powder and the other powder is Sulzer Metco 7202 powder. These powders were taken in different percentages and it was aimed to observe how they affect the surface properties. From the powders applied to the samples called A and B groups, 50% Diamalloy 2002 powder and 50% Sulzer Metco 7202 powder were mixed into the first sample (A), and the other sample (B) was coated with the HVOF method by using 100% Sulzer Metco 7202 powder. In order to examine the effect of the number of passes in the experiments, different pass numbers were used. 1.5 bar pressure was applied to sample A and sample B. Diamalloy 2002 (Tungsten carbide-Nickel Chromium powder), one of the coating powders used in the experiment, is a powder with wear resistance. This is because it creates very hard surfaces. The properties of Diamalloy 2002 powder consisting of tungsten carbide and Nickel chromium are given in Table 2 [25]. Our other powder used in coatings is Sulzer Metco 7202 (Chromium carbide- 25% Nickel Chromium powder). This powder provides high oxidation and corrosion resistance. It shows high wear behavior especially in acidic and alkaline environments. Sulzer Metco 7202 material is a high hardness and high wear resistant phase, coating material containing 75% chromium-carbide, agglomerated and sintered powders for thermal spray process. Properties of Sulzer Metco 7202(Chromium carbide- 25% Nickel Chromium powder) powder are shown in Table 2. In the HVOF coating process, 316L stainless steel with dimensions of 100 x 100 x 4 mm was used as the substrate in this parameter (Table 3). AISI 316 stainless steel has been sandblasted for this is to increase the efficiency of the coating to be made on the steel material. Percentages of powders to be coated are given in Table 4. The number of passes applied to these samples varies. The sample with 15 passes is marked as A1, the sample with 10 passes is marked as A2, and the sample with 6 passes is marked as A3. The parameters of the samples obtained with B group 100% Sulzer Metco powder are 1.5 bar nitrogen pressure, 2 cm length and 10 seconds' time. The number of passes applied to these samples varies. Experimental studies were carried out after coating with HVOF and their findings were evaluated. Mixing 50% Diamalloy 2002 and 50% Sulzer Metco 7202 powders to A group samples, and 100% Sulzer Metco 7202 powder to B group samples using 316 stainless steel HVOF was applied to the steel base material and the coating images of the samples, on which metallographic applications were performed, were examined with an optical microscope and the coating thicknesses were examined. The different powders are used for HVOF coating such as the 50% Diamalloy 2002 and 50% Sulzer Metco 7202 powder. The process parameters were changed in coating process. The coating thickness of A powder was measured as 213 μm. The layer thickness of B is 232 μm. The fact that the samples coated with the same parameters have different coating thicknesses can be associated with powder composition ratios. This is due to the difference in the structure and dimensions of the mixture powders and the homogeneous non-melting situation. In some cases, it may also occur due to the device used in the experiment phase. WC, W2C, Cr7C3, Cr23C6 phases were found in the X-ray analyzes of the samples after coating. Cr23C6 phase was also formed in 100% 7202 powder mixture. In both samples, the hard phase WC and W2C phases emerged. These hard phases improved the mechanical properties (wear and hardness) of the coating surface. The wear resistance of AISI 316 stainless steels, which were coated with the HVOF spraying method, was increased and their mechanical properties were improved. In a short time, the surfaces of the steels coated with the HVOF spraying method can be improved and used advantageously in industrial and economic pain. it was found that the number of passes and the wear rates were generally inversely proportional. Wear properties of B group samples better than A samples. The powders content is important for mechanical properties. The coating parameters are very important all surface properties