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Bakır-bor alaşımlarının üretimi ve ısıl sistemi

Production and heat treatment of copper-boron microalloys

  1. Tez No: 39535
  2. Yazar: TUNCAY YETER
  3. Danışmanlar: PROF.DR. ADNAN TEKİN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Metalurji Mühendisliği, Metallurgical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1994
  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: 53

Özet

ÖZET: Bu çalışmada bakırın mekanik ve fiziksel özelliklerine kalsiyumhegzabor (CaB6) ile yapılan deoksidasyonun etkisi incelenmiştir. Deoksidasy ondan sonra yapıda alaşım elementi olarak kalan borun özellikle elektrik iletkenliğine olan etkisine bakılmış ve çeşitli oranlarda bor içeren bakır-bor alaşımlarının 200°C ile 300°C'de 0-6000 dakika arasında değişen sürelerde yaşlanma işlemleriyle sertlik ve çekme mukavemeti değerleri irdelenmiştir. Yapılan incelemeler sonucunda bakır içindeki bor miktarının bakırın elektrik iletkenliğini önemli ölçüde etkilemediği ve elektrik iletkenliğindeki düşüşlerin bakırın elektrik endüstrisinde kullanımını engellemediği görülmüştür. Elde edilen sonuçlara göre, bakır-bor alaşımlarında meydana gelen sertlik artışlarının borun yaptığı öotektik fazın tane sınırlarına çökelmesi sonucu ortaya meydana geldiği saptanmıştır. Aynı şekilde CaB6 ile deoksidasyonun diğer elementlerle yapılan deoksidasyon işlemlerine oranla çok daha başarılı sonuçlar verdiği ve döküm yapısındaki borun bakırın mekanik özelliklerine katkıda bulunduğu ve oksijenin %0.75 CaB6 ilavesiyle 20 ppm'e kadar indirilebileceği sonucuna varılmıştır. -m-

Özet (Çeviri)

PRODUCTION AND HEAT TREATMENT OP COPPER-BORON MICROALLOYS SUMMARY Copper is a very important metal which is widely used in the electronic and electro-technical industries. The quality of its products strongly depends on their electrical conductivity and mechanical properties such as ductility and toughness. These properties are influenced by the internal porosity. Copper has several forms that are produced by various methods. One of the these forms is the ETP (electrolitic tough pitch) copper type. It has a minimum of 99.99% copper and a nominal 0.04% oxygen contents. The mean limits of oxygen in ETP copper are between 200 and 500 ppm. The oxygen has some advantages and disadvantages in copper: Advantages of the oxygen; 1- At room temperature, solubility of oxygen in copper is 20 ppm. If the oxygen exceeds this value, it forms cuprous oxide (Cu20). In the presence of hydrogen, it leads to formation of porosities. Because of the changes in the hydrogen solubility from liquid to solid state, porosities are formed in copper. Oxygen which enters the melt from the atmosphere reacts with hydrogen. According to equilibrium between oxygen and hydrogen, when concentration of oxygen is reduced to a certain level, concentration of hydrogen increases. 2- The oxygen also reacts with the impurities in copper. As a result of these reactions, the impurity elements are converted by oxygen to their oxide state. This would increase the electrical conductivity of ETP copper, as the impurities are removed. -iv-Disadvantages of oxygen; 1- The oxygen in ETP copper exists mainly at the grain boundaries in the form of finely divided Cu20 particles. This causes a slight impairment of the mechanical properties at room temperature. At high temperatures such as 400 °C, the effect of the oxygen on mechanical properties is very significant in the presence of hydrogen or hydrogen-containing gases. Hydrogen diffuses into ETP copper and reacts with the cuprous oxide to form vapour at the grain boundaries by the following reaction: H2 + CU20 -+ Cu + H20 Since the hydrogen atoms are very small, they are able to diffuse into the solid copper. Therefore, they react with dispersed Cu20 to form steam as per the reaction above. The steam formed leads to high pressures causing the grain boundaries of the material to rupture. This phenomenon is called hydrogen embrittlement. Therefore, the oxygen must be removed by a deoxidant. 2- When the oxygen content in copper is reduced to its minimum level, the best ductility and toughness are obtained. Hence, the copper must be deoxidized by the elements such as lithium, phosphorus, aluminium, magnesium, boron, calcium and zinc etc. These elements also help in removing the hydrogen from the copper. Since the impurities are partially dissolved in copper, the mechanical and physical properties of copper change negatively, especially electrical conductivity which is very important property for its use in electronic industry. Copper has good electrical conductivity. But in addition to excellent conductivity, copper and its alloys should have good mechanical properties as well. But, increase in mechanical properties leads to decrease in electrical conductivity because of its inherent characteristics. Deoxidation of copper by phosphorus (P) is common in industry. But this method of deoxidation leaves more than 0.01%P, which reduces the electrical conductivity drastically. Deoxidation of copper by lithium (Li) in industry is uncommon because of high cost. But it is possible to completely deoxidize the copper using calcium bor ide (CaB6). After copper deoxidation using CaB6, boronremains in the copper as an alloying element. In this study, the influence of copper-deoxidation by CaB6 on the electrical conductivity and mechanical properties of copper was investigated. First, the ETP copper containing oxygen between 200 and 500 ppm was melted in graphite crucible in a furnace under soot black protection. During the melting operation, the surface of the melt was covered by a layer of 30 mm of soot black in air. Then, the melt was held for 7 minutes at 1150°C. Specimens obtained by melting process were firstly subjected to the solution process for 60 minutes at 980 °C. After quenching in ice water, they were cold-worked in the range of 35% and 70%. Alloys containing the various contents of boron were held at two temperatures such as 200°C and 300°C for various times. The properties of the copper such as hardness and strength were improved by means of adequate heat treatments. During the experiments, the analyses of the oxygen and boron and the electrical conductivity of the specimens were determined. The hardness and tensile properties were also measured. It was observed that during copper deoxidation using CaB6, some boron remains in the copper as an alloying element. According to the results obtained by the experiments, boron remains in the copper within the range of microalloys contents. The hardness values of alloys produced, in cast condition, increase with increasing the boron contents in copper. These values for three alloys produced were determined 43 HV, 50 HV and 53 HV, respectively. The amounts of the remaining boron were measured as 0.045%, 0.07% and 0.1% for these alloys. The correspondent oxygen concentrations were lOOppm, 75ppm and 20ppm, respectively. The electrical conductivity was not affected by the remaining boron. It has been found that these values varied between 50 and 55 m/mm n, depending on the remaining boron in copper. Oxygen presents in copper as Cu20 which practically remains at the grain boundaries. According to literatures, after the deoxidation treatment with CaB6, the boron was distributed in the matrix as well as in the grain boundaries. This indicates that the removed oxygen has been replaced by boron at the grain boundaries. Therefore, light reflecting areas in the Scanning Electron Microscopy (SEM) micrographs were thought to be rich in free boron. -vi-It was observed that deoxidation with CaB6 does not appreciably affect the electrical conductivity. Copper has minimum value of 56 m/mm n of electric conductivity for use in electronic and electro-technical industries. After deoxidation with CaB6 and thermomechanical treatments, it was found to be the electrical conductivity of copper had more than 56 m/mm fi, indicating that boron does not have any appreciable effect on the electrical conductivity of copper. However, if copper is deoxidized with phosphorus, the electrical conductivity of copper is negatively affected by P-resiudal and reduces to 46 m/mmf2. Hence, copper deoxidized by phosphorus is used in the applications where the electrical conductivity is not important. The higher values of the hardness and tensile strength can be obtained by performing the thermomechanical treatments such as solution treatment, cold working and ageing. A tensile strength about three times that of pure copper can be attained by means of these treatments. The correspondent strength is 350 to 450 N/mm. The hardness also can be enhanced its higher values, 120 to 140 HV, depending on boron contents and thermomechanical treatments. The electrical conductivity is negligibly lower than that of pure copper. The increase of the strength is caused by a boron- rich phase which, in cast condition, can be mainly found at the grain boundaries, but also, after thermomechanical treatments, in very fine precipitations in the matrix. The ageing curves indicates that the increases in hardness and tensile properties were due to boron-enriching phase which exists in the grain boundaries during recrystallization. Small particles in the recrystallization were observed Transmission Electron Microscopy (TEM) investigations. Remaining boron in copper does not appreciably influence the recrystallization temperature of copper. The recrystallization temperature of copper having the various contents of boron is the almost same as pure copper. The results obtained in this study are briefly given as follows: - Deoxidation with CaB6 was found to be more effective than other deoxidants in producing better electrical conductivity. - Remaining boron did not have a measurable effect on the electrical conductivity of copper. -vii-- The mechanical properties of copper-boron microalloys are better than those of pure copper. - Remaining boron does not appreciably affect the recrystallization temperature of copper. - Boron-enriching phase was existed in the grain boundaries, which causes increases in mechanical properties. These properties were negatively influenced overageing. -Vlll-

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