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İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Anabilim Dalı

Aluminyum matrisli B4C takviyeli kompozit kaplamanın soğuk gaz dinamik püskürtme yöntemiyle üretilmesi ve mekanik özelliklerinin incelenmesi

Production and mechanical properties of aluminum matrixed B4C reinforced composite coating by cold gas dynamic spraying method

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Özet:

Alüminyum malzemeler yüksek korozyon dirençleri, termal iletkenlik özellikleri ve yüksek spesifik mukavemetleri ile günümüzde birçok alanda tercih edilmektedir. Özellikle yüksek spesifik mukavemetleri (mukavemet/ağırlık) ile günümüzde otomativ ve havacılık sektöründe demir esaslı malzemelerin yerini almaktadır. Bu üstün özelliklerinin yanında düşük sertlik ve düşük aşınma direnci gibi özelliklerinden dolayı , sürtünme ve aşınmanın yoğun olduğu tribolojik uygulamalarda alüminyum kullanımı istenilen düzeyde olamamaktadır. SGDP yöntemi, 1980'li yıllarda Rus bilim adamı Prof. Anatolii Papyrin ve arkadaşları tarafından keşfedilmiştir. SGDP yöntemi prensip olarak, toz partiküllerinin taşıyıcı bir gaz yardımıyla yüksek hızlarda bir altlık üzerine püskürtülmesi prosesidir. Bu yöntemde tozlar, ultrasonik hızlarda ve düşük sıcaklıkta hedef altlık üzerine püskürtülmek suretiyle biriktirilir. Aşınma ve sürtünmenin yoğun olduğu ortamlarda yüksek sertlik ve aşınma direnci gösteren malzemelerin kullanımı gerekmektedir. Bu tip uygulamalarda en yaygın kullanılan malzemelerden birisi de bor karbür (B4C)'dür. Yüksek sertliği, yüksek korozyon direnci ve yüksek sıcaklıklarda bile kullanılabilir olması ile B4C, hem mekanik hem de tribolojik performans beklenen uygulamalarda beklentileri karşılamaktadır. Bu nedenle genellikle farklı malzemeler ile birlikte destek malzemesi olarak kullanılmaktadır. Özellikle metal matrisli kompozit malzemelerde en sık kullanılan destek malzemelerinden birisidir. Bu çalışmanın amacı, Soğuk Gaz Dinamik Püskürtme (SGDP) yöntemi ile aşınma direnci yüksek alüminyum matrisli B4C takviyeli kompozit kaplamaların üretilmesidir. Bu amaç doğrultusunda, alüminyum ve bor karbür tozları farklı hacim oranlarında karıştırılarak, 6061 kalite alüminyum altlık üzerine kaplanmıştır. Kaplanan numuneler daha sonra mikroyapı incelemeleri ve faz analizleri ile incelenmiş, sertlik ve aşınma testlerine tabii tutulmuştur. Böylece SGDP yöntemiyle oluşturulan alüminyum matrisli B4C takviyeli kaplamaların farklı aşınma koşullarındaki aşınma davranışları incelenerek, B4C katkısının ve aşınma ortamının bu kaplamaların aşınma özellikleri üzerindeki etkisi araştırılmıştır. Yapılan çalışmalar ve analizler göstermiştir ki, SGDP yöntemi ile alüminyum ve B4C takviyeli alüminyum kompozit kaplamalar başarılı bir şekilde yapılabilmektedir. Yapılan kaplamalara uygulanan aşınma testleri sonucunda B4C katkısının alüminyum kaplamalarda sürtünme katsayısını düşürdüğü ve aşınma direncini arttırdığı görülmüştür. Kuru ve ıslak ortamda yapılan testler sonucunda kaplamaların, ıslak ortamda daha az aşındığı görülmüştür. Suda yapılan aşınma testleri sonucunda, B4C takviyesinin alüminyum kaplamaların aşınma direncini 26 kata kadar arttırdığı görülmüştür. Ayrıca numunelere 45℃ sıcak suda aşınma testleri yapılarak sıcaklığın ıslak ortam aşınma performansına etkisi incelenmiştir. Kaplamaların sıcak suda normal suya göre daha az aşındıkları tespit edilmiştir.

Summary:

With the development of technology, traditional materials have become unable to meet their needs and have led scientists to search for materials with superior properties.Particularly in today's technology, which has changed in as little as 10 years, material technologies are developing at the same speed. One of the materials to meet today's needs is composite materials. Composite materials are macroscopic combination of two or more materials with a compatible interface between each other. Composite materials are preferred not only because of their structural properties but also because of their electrical, thermal, and tribological properties. Composite materials consisting of a combination matrix and an additional phase in the supporting phase are generally classified according to the matrix material. Another classification method of composite materials is the form of the material used as support material. In general, composites can be collected in four classes. Fiber reinforced composites are a form of two-phase weave structure that envelops each other throughout the structure. In layered composites, the matrix and support materials support each other in the form of laminates, not in the form of braids. Mixed type composites using different types of composite mechanisms can also be created. Particle reinforced composite formation is the most commonly used method for metal matrix composites. In this method, a matrix with a high softness and adhesion property is used together with a support material which is hard, brittle but has mechanical properties. Aluminum and magnesium are the most frequently used metal matrix materials today. Ceramic particles are generally used as reinforcing material. B4C, SiC, Al2O3, hBN, Si3N4 are frequently used ceramic reinforcement particles. Aluminum materials with high corrosion resistance, thermal conductivity properties and high specific strength are preferred today. Especially with its high specific strengths (strength / weight), iron-based materials are now in the automotive and aerospace sector. Because of their superior properties and low hardness and low abrasion resistance, the use of aluminum in tribological applications where abrasion and abrasion is intense can not be desired. Today, ceramic particulate reinforced metal matrix composites have a special place in the field of aluminum. It is the most preferred matrix material for metal matrix composites due to its high specific strength, high plastic deformation ability and its ability to form a mesh around ceramic particles. The most important advantages of aluminum as matrix material are; High specific strength, low density, developable high temperature properties, high oxidation resistance, high damping ability and low thermal expansion coefficient. These deficiencies of aluminum, which have disadvantages such as low mechanical properties as well as their advantages, can be improved by forming composite with high mechanical properties of particulate reinforcements. For example, when the elastic modulus of pure aluminum is 70 GPa, it can be increased up to 240 GPa with 60% Al2O3 reinforcement. In the same way, the abrasion resistance of aluminum composites reinforced with 20% SiC particles may be better than gray cast iron. Many properties of aluminum can be improved in this way depending on the type of particle used as reinforcement material and the volume ratio. Aluminum matrix, on the other hand, also increases the total mechanical properties of the structure by forming a net structure and covering hard and brittle ceramic particles. The SGDP method was discovered in the 1980s by the Russian scientist Anatolii Papyrin and his colleagues. The SGDP method is in principle the process of spraying powder particles onto a substrate at high speed with the aid of a carrier gas. In this method, dusts are deposited at the ultrasonic speeds and at low temperatures by spraying onto the target substrate. In order to coat with Cold Spray method, it is necessary to use suitable base and plastic deformation ability high powders. B4C can be coated by forming ceramic composite with low plastic deformation ability, high hardness ceramic particles, soft and plastic deformable materials such as aluminum. One of the most important advantages of the Cold Spray method is that the coating process takes place at very low temperatures. In the cold spray method, the gas sprayed at room temperature reaches a temperature of about 100 ° C at the outlet of the nozzle because it is sprayed at very high speeds. However, this is a relatively low temperature for the formation of a corrosive effect. This is one of the most important features of the Cold Spray method in terms of preventing the formation of unwanted oxide phases during coating. In addition, spraying with ultrasound speeds can be performed in a very short time. In environments where abrasion and abrasion are intensive, the use of materials with high hardness and abrasion resistance is required. One of the most commonly used materials in such applications is boron carbide (B4C). With high hardness, high corrosion resistance and even high temperatures, the B4C meets expectations for both mechanical and tribological performance applications. For this reason, it is often used as a support material with various materials. It is one of the most frequently used support materials especially in metal matrix composite materials. The purpose of this work is to produce composite coatings with B4C reinforced aluminum matrix with high wear resistance by the Cold Gas Dynamic Spray (SGDP) method. For this purpose, aluminum and boron carbide powders are mixed with different volume ratios and coated on 6061 quality aluminum base. The coated specimens were then examined by microstructure and phase analyzes and subjected to hardness and abrasion tests. Thus, by investigating the wear behaviors of aluminum matrix B4C reinforced coatings formed by SGDP method under different wear conditions, the effect of B4C admixture and wear environment on the wear properties of these coatings was investigated. The studies and analyzes show that aluminum composite and B4C reinforced aluminum composite coatings can be successfully achieved with the SGDP method. As a result of the abrasion tests carried out on the coated coatings, it has been found that the B4C addition decreases the friction coefficient in the aluminum coatings and increases the abrasion resistance. Tests in dry and wet conditions indicated that the coatings were less abraded in the wet environment. As a result of water abrasion tests, it was found that B4C reinforcement increased the abrasion resistance of aluminum coatings by 26 times. In addition, samples were subjected to 45 ° C hot water wear tests and the effect of temperature on wet environment wear performance was investigated.Coatings were found to be less abraded in hot water than normal water.