Kalay katkısı ile modifiye edilmiş Cu-Cr-Zr alaşımının fiziksel özelliklerinin incelenmesi
Investigation of physical properties of tin modified Cu-Cr-Zr alloy
Yazar: MUSTAFA KIZILBAY
Danışman: YRD. DOÇ. DR. NURİ SOLAK ; YRD. DOÇ. DR. ŞABAN HAKAN ATAPEK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Metalurji Mühendisliği = Metallurgical Engineering ; Mühendislik Bilimleri = Engineering Sciences

Özet:
Çökelti sertleşebilen sert bakır alaşımlarının, elektriksel ve termal iletkenliklerinin yüksek olmalarının yanı sıra korozyona ve aşınmaya karşı dayanıklı olmaları, geniş kullanım alanı bulmalarını sağlamaktadır. Bakır alaşımlarının bu üstün özellikleri alaşım elementi eklentileri, uygulanan mekanik ve ısıl işlemler sayesinde alaşımlara kazandırılmaktadır. Yaşlandırma ısıl işlemi, azalan sıcaklık ile birlikte matriks içerisinde alaşım elementi çözünürlüğünün azaldığı bazı bakır alaşımlarında mukavemet artışı sağlamaktadır. Bakır berilyum alaşımları tipik yaşlandırılabilir bakır alaşımlarından biridir. Sert bakır berilyum alaşımları çökelti sertleşmesi sayesinde bakır alaşımları içerisindeki en yüksek sertliğe sahip alaşımlardan biri olma özelliği kazanmaktadır. Fakat berilyum metalurjisinin toksik olması sebebiyle, berilyum içerikli bakır alaşımlarına benzer fiziksel özelliklere sahip alternatif bakır alaşımları geliştirilmesi gereksinimi doğmuştur. Bu sayede toksik berilyum içeren bakır alaşımlarının üretim ve kullanım miktarları azaltılmaya çalışılmaktadır.
Yüksek sıcaklıkta yüksek mekanik özelliklerin yanı sıra ısıl ve elektriksel iletkenliğin de birlikte istendiği durumlarda CuCrZr alaşımının kullanımı önem kazanmaktadır. Kullanım alanlarına her geçen gün bir yenisi daha eklenen ve özellikleri sürekli geliştirilmekte olan bu alaşımların en yaygın uygulama alanları kontak malzemeleri ve elektrik direnç kaynağı elektrotlarıdır. CuCrZr üçlü alaşımı, konvansiyonel CuCr ve CuZr alaşımları ile karşılaştırıldığında daha yüksek elektriksel iletkenlik, tokluk ve iki kat daha fazla kullanım ömrüne sahip olması sayesinde tercih edilmektedir. CuCrZr alaşımları çökelti sertleşebilmesi sayesinde hem üstün elektriksel iletkenlik ve mukavemet özellikleri sağlamakta hem de toksik içerik bulundurmamaktadır. Dolayısı ile berilyum içerikli alaşımlara alternatif alaşım olarak geliştirilmeye açıktır.
Çalışma kapsamında üretilen CuCrZr alaşımı ağırlıkça %5 ve %10 kalay eklentisi ile iki farklı kompozisyonda modifiye edilmiştir. Elde edilen CuCrZr, CuCrZr-5Sn ve CuCrZr-10Sn alaşımları 950°C'de 1 saat çözeltiye alınıp suda su verilmiş ve ardından 400°C'de 2-48 saat yaşlandırma işlemine tabi tutulmuştur. Üretilen alaşımların döküm konumundaki, çözeltiye alınmış konumdaki ve yaşlandırılmış konumdaki sertlik ve elektriksel iletkenlik değerleri ölçülüp, tedarik edilen CuSn10, CuBe ve CuCoNiBe alaşımlarının sertlik ve elektriksel iletkenlik değerleri ile kullanılabilirlik açısından karşılaştırılmıştır. Daha sonra üretilen ve tedarik edilen alaşımlar 5N ve 10N yüklemelerde, 0.05 m/s ve 0,15 m/s kayma hızlarında ball – on – disc kuru sürtünme testlerine tabi tutularak tribolojik özellikleri karşılaştırılmıştır. Aşınma yüzeyleri ışık mikroskobu (IM), elektron mikroskobu (SEM) ve 3D profilometrik analiz cihazı ile karakterize edilmiştir. Üretilen alaşımlardan 10 saat yaşlandırılmış CuCrZr-10Sn alaşımının CuBe alaşımına benzer fiziksel özellikler gösterebildiği ortaya koyulmuştur.

Abstract:
Copper is mankind's oldest metal, dating back some 10,000 years. All of the great civilizations of the past, including the Sumerian, Egyptian, Greek, Roman, and Chinese, used copper and copper alloys (principally bronze and later brass) for both decorative and utilitarian purposes. From antiquity through the Middle Ages and the Renaissance, copper was used for military purposes, artistic applications such as church bells and statuary, tools, and numerous other functional objects. However, it was the Industrial Revolution that brought about a tremendous change in the production and consumption of copper and copper alloys. Electrical engineering in the modern industrial sense followed from many discoveries in the history of copper. To this day, copper remains the key to modern power generation.
The industrial importance of copper in the 20th and 21st centuries has been extended by which it combines with other metals. Tin and zinc have been the principal alloying elements, but many other (aluminum, nickel, beryllium, chromium, cadmium, manganese, etc.) alloys with combinations of mechanical and physical properties and excellent corrosion and wear resistance. Copper and its alloys being the material of choice for building construction (e.g., plumbing, wiring, and roofing), in many demanding engineering applications in the marine, automotive, chemical, and electronics industries. Continuing developments in superconductors, electric vehicles and solar heating should ensure that copper remains an essential material in the future.
Copper-base metals are commonly used in plugs, jacks, sockets, connectors, and sliding contacts. Yellow brass (C27000) is preferred for plugs and terminals because of its machinability. Phosphor bronze (C50500 or C51000) is preferred for thin socket and connector springs and for wiper-switch blades because of its strength and wear resistance. Nickel silver is sometimes preferred over yellow brass for relay and jack springs because of its high modulus of elasticity and strength, resistance to tarnishing, and better appearance. Sometimes, copper alloy parts are nickel plated to improve surface hardness, reduce corrosion, and improve appearance. Copper and copper alloys constitute one of the major groups of commercial metals. They are widely used because of their excellent electrical and thermal conductivities, outstanding resistance to corrosion, ease of fabrication, and good strength and fatigue resistance. They are generally nonmagnetic. They can be readily soldered and brazed, and many coppers and copper alloys can be welded by various gas, arc, and resistance methods. For decorative parts, standard alloys having specific colors are readily available. Copper alloys can be polished and buffed to almost any desired texture and luster. They can be plated, coated with organic substances, or chemically colored to further extend the variety of available finishes. Pure copper is used extensively for cables and wires, electrical contacts, and a wide variety of other parts that are required to pass electrical current. Coppers and certain brasses, bronzes, and cupronickels are used extensively for automobile radiators, heat exchangers, home heating systems, panels for absorbing solar energy, and various other applications requiring rapid conduction of heat across or along a metal section. Because of their outstanding ability to resist corrosion, coppers, brasses, some bronzes, and cupronickels are used for pipes, valves, and fittings in systems carrying potable water, process water, or other aqueous fluids. Copper-base alloys offer a wide range of properties for sleeve-type and other types of sliding bearings. The most commonly employed copper bearing alloys are commercial bronze, copper-lead alloys, and leaded and unleaded tin bronzes. Cast copper is soft and low in strength. Increased strength and hardness and good conductivity can be obtained with heat treated alloys containing silicon, cobalt, chromium, nickel, and beryllium in various combinations. 
The precipitation-hardened CuCrZr alloy has attracted considerable interest recently because of its superior combination of high mechanical strength and high thermal/electrical conductivity. Aging is a common heat treatment for many copper alloys, with the aim of raising their strength and hardness. Previous results were reported from transmission electron microscopy (TEM) investigations, which found that the high strength of the aged CuCr and CuCrZr alloy was brought about by very small coherent chromium rich particles which precipitate in a dispersive manner from a supersaturated copper matrix and then become coarse and loose coherency on overaging. The strengthening mechanism usually proposed in this case was that of dislocation pinning by the stress fields around the coherent precipitates. Therefore, the precipitation-hardened CuCrZr alloy has attracted considerable interest recently because of its superior combination of high mechanical strength and high thermal/electrical conductivity.
CuBe and CuCoNiBe alloys are precipitation hardenable copper alloys and they are widely used in several applications in which excellent corrosion resistance, high strength, adequate electrical/thermal conductivity and high resistance to softening at elevated temperature are required. As similar to the lead metallurgy, the melting process of alloys containing beryllium is highly toxic and recent trends focus on producing non-toxic and hard copper alloys replacing to CuBe and CuCoNiBe alloys.
In this present work, the microstructure and physical properties of 0-5-10 wt% Sn alloyed CuCrZr were investigated. To prepare CuCrZr, CuCrZr-5Sn and CuCrZr-10Sn (Cu–0.89%Cr–0.01%Zr-10.2%Sn) alloy of the desired composition, small pieces of CuCrZr master alloy and tin weighed in an appropriate ratio, were melted together in an induction furnace in a graphite crucible. The ingot, cylindrical shaped with 20 mm radii and approximately 500 g, was cut to pieces of 5 mm thickness.
The pieces were solutionized at 950 °C for 1 h and then water quenched and aged at 400 °C for 2-48 h. For revealing the microstructure of alloy in solutionized and aged condition, pieces were metallographically polished to 1 µm diamond finish and then etched chemically in Kroll solution. Microstructural examinations were carried out by an Olympus BX41M-LED light microscope and physical property examinations were carried out by a Future Tech FV-700 Macro Hardness Meter and GE Auto Sigma 3000 Inspection Technologies Electrical Conductivity Meter by means of Vickers and MS/m, respectively. Microphotonics Inc. Nanovea Series Microtest SMT/A ball on disc tribometer were used to examine the tribological behavior of all tested copper alloys and results were investigated by light microscope, electron microscope and Nanovea 3D Profilometer. Although modified CuCrZr-10Sn alloy aged at 400 °C for 10 h had a lower electrical conductivity value (7.7 MS/m) than those of CuBe (14.1 MS/m) and CuCoNiBe (21.2 MS/m) cast alloys, its hardness value (166,1 HV) was measured as close to that of CuBe cast alloy (165,9 HV) and was higher that of CuCoNiBe cast alloy (107,5 HV). According to those results, 10h aged CuCrZr-10Sn alloy has better mechanical properties from which could be alternative to beryllium containing copper alloys in applications that needs wear resistance.