Nikel bor master alaşımlarının üretimi ve geliştirilmesi
Production and development of nickel boron master alloys
Yazar: KEREM CAN TAŞYÜREK
Danışman: PROF. DR. ONURALP YÜCEL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Metalurji Mühendisliği = Metallurgical Engineering
Dizin: Malzeme üretimi = Material production ; Metal döküm = Metal casting ; Sert lehimleme = Brazing

Özet:
Nikel esaslı alaşımların oldukça geniş bir yelpazede kullanım alanları vardır. Bunların başında üretim metalürjisinde, yüksek sıcaklık, korozyon, basınç ve aşınma uygulamaları gelmekle beraber havacılıkta türbin kanatlarında, enerji sektöründe kullanılan birçok parçada, çelik kalitesini arttırıcı ilaveler gibi temel uygulamalarda, ferro manyetik hafızalı alaşımlarda ve termal kaplama tozu olarak kullanımı gelmektedir.
Nikel bor alaşımlarının üretimleri konusunda çeşitli yöntemler geliştirilmiştir. Bu yöntemlerden en avantajlı olanı karbotermik redüksiyon metodu ile derin daldırmalı ark ocağında üretimidir. Bu yöntemle odun kömürü, odun talaşı, borik asit ve nikel oksit ark ocağında doğrudan indirgenmektedir. Odun talaşı fırın içinde gaz geçirgenliği sağlayabilen bir şarj sütunu oluşturmaktadır ve odun kömürü redüksiyon için karbon kaynağı olarak kullanılmaktadır.
Çalışma konusu kapsamında, ergitme işleminde daldırmalı tip doğru akım elektrik ark fırını kullanımının avantajı ise küçük tane boyutuna sahip cevher ya da konsantrelerin kolaylıkla işlenebilmesi ve metalin yüksek oranda kazanılabilmesidir. Daldırmalı tip fırınlarda yükseklik arttırılarak ark bölgesinde oluşan ısı ve redükleyici gazların şarj sütunu içinde kalması sağlamaktadır.
Tek fazlı elektrik ark fırınlarına, doğru akım (DC) trafolarından güç beslenmeye başlanması önemli bir gelişme olarak kabul edilmektedir. DC ark fırınlarının, üç elektrotlu AC (alternatif akım) fırınlarına göre avantajları elektrot tüketiminin %40-50 oranında daha az olması elektrik enerjisinin ve refrakter aşınmasının daha az olması, şarj içinde ısı dağılımının daha homojen olması ve ergimiş fazın daha hareketli olması nedeniyle homojen ürün elde edilmesi şeklinde sıralanabilir. 
Bu çalışmada bor kaynağı olarak borik asit, nikel kaynağı olarak nikel oksit, redükleyici madde olarak odun kömürü, şarj yoğunluğunu azaltıcı ve sinter yapıcı olarak odun talaşı kullanılmıştır. Farklı oranlarda şarj harmanları hazırlanarak nikel bor master alaşımı üretmek amacı ile 270 kVa?lık daldırmalı tip, tek fazlı ve doğru akım elektrik ark fırını kullanılarak ergitilmiştir. 
Deneysel çalışmalar sonucunda şarj bileşimi, enerji-elektrot tüketimleri, fırının elektriksel karakteristikleri ve ayrıca fırın içinde gelişen olaylar nikel bor master alaşımlarının oluşum mekanizmasını açıklamak üzere incelenmiştir. Karakterizasyon çalışmaları kapsamında elde edilen ürünlere AAS/ICP ve XRD teknikleri uygulanmıştır.
Deneylerde farklı oranlardaki başlangıç karışımı ve sabit karbon oranları denenmiştir. Yapılan bu çalışmalar sonucunda endüstriyel uygulamalarda kullanılmak üzere standart kalitede lehim malzemesi üretilmiş olup içeriğinde ağırlıkca % 84,12 Ni, % 15,08 B, % 0,11 Al, % 0,005 S, % 0,15 Si, % 0,40 Fe, % 0,18 C bulunmaktadır, nikel verimi % 88 ve bor verimi % 84 olarak hesaplanmıştır.

Abstract:
Nickel based alloys have a wide range of areas. The primary usage areas of nickel based alloys are production metallurgy, high temperature, corrosion, pressure and wear applications in aviation turbine wings coming together, many track used in the energy sector, such as steel additions to improve the quality of basic applications, is the use of ferromagnetic memory alloys and thermal coating powder.
In nickel boron metal alloys, boron is an essential alloying element in numerous nickel alloys used in thermal spraying for hardfacing purposes. It provides significant reduction of the melting point of pure nickel and allows production of dense, hard coatings. An additional feature of technical importance in ternary alloys is its tendency to form complex borides having a high hardness. 
Various methods have been developed in the production of nickel-boron alloys. The most advantageous method for the carbothermic reduction of these methods arc furnace production of deep immersion. 
In this method, charcoal, wood flour, boric acid and nickel oxide is reduced directly to the arc furnace. A charging column in the oven can provide gas permeability of wood shavings and wood charcoal is used as a carbon source for the reduction.
It is known to carbothermally reduce oxidic boron raw materials in a low shaft electric arc furnace whose electrodes reaches toward the furnace bottom from aboce and are of adjuctable height so that close to the furnace bottom, upon which melt of the alloy is formed, a reducing zone is constituted into which the electrode extend. 
The burden or charge above this zone consists of fine grained boron containing raw material, fine grained oxides of the basic metal and small pieces of the basic metal as well as carbon carriers. Above the reducing zone, this charge or burden is constituted as a gas permeable burden layer. 
In general, the electrodes are raised and lowered in accordence with the conductivity of the burden, usually with an automatic control system.  
The scope of the study, dipped type direct current electric arc furnace smelting process, the advantage of the use of the small grain size and metal ores or concentrates can be processed easily gained a high rate. Dip type furnaces in height by increasing the arc column to remain in charge of providing heat and reductant gases.
DC arc furnace, the three-electrode AC (alternating current) electrode advantages over furnaces of electric power consumption is less than % 40-50 and is less refractory wear, a more uniform heat distribution to be charged and melted in phase due to a more homogeneous product from moving be listed as.
Single-phase electric arc furnaces, direct current (DC) power transformers feeding initiation is considered to be an important development. 
Nickel boron master alloys can be produced with three main process; aluminothermic, silicothermic and carbothermic methods. Production of nickel boron with either aluminothermic method or silicothermic method, concentration of Al or Si impurities exceed limits for manufacture of metal alloys.
The carbothermic method of nickel boron production yields a better product, which satisfies the impurity limits set by the metal alloys industry.
High temperature brazing with nickel based filler metal, which has been widely used as a cost effective means in high technology industries, has been demonstrated to be able to produce high performans joints with excellent static and dynamic load resistance as well as high corrosion resistance. 
In brazing, the fusing dissolution of solid base metal in the molten liquid brazing filler metal is inevitable, in particular for high temperature brazing. The main beneficial aspect of the dissolution of base metal is that it can enhance the alloying process of the brazed welds, thus improving the mechanical properties of the brazed joints. When using nickelbased brazing filler metals to join stainless steels and high temperature alloys, at high brazing temperatures (usually from 900 to 1200 ?C).
Joints made with nickel based filler metals tend to be more brittle than joints made with other filler metals. Care must be taken when using nickel filler metals containing boron on thin sections due to the erosive nature of the molten filler metal and the ability of this material to alloy with the base metal. Time and temperature must be monitored very carefully to prevent the molten filler metal from perforating the base metal. 
Thermodynamic consideration of the reduction of NiO and B2O3 in the presence of carbon shows that reduction sequence with solid carbon includes NiO, B2O3(g) and B2O3(l). Nickel is reduced prior the boron, and the reduction of gaseous boron starts at 1650 K. Reduction of the liquid phase starts at 1900 K. 
Nickel is an element that can be alloyed with a variety of elements such as: iron, chromium and cobalt having a high solubility. Ni-based alloys are used in several industrial applications gas turbine parts,medical applications and nuclear systems, whichmainly solve wear resistance, corrosion and thermal fatigue problems. These features lead the development of new Ni-based alloys with mechanical properties that prolong the lifespan.
Nickel based filler metals are used to braze ferrous and nonferrous high temperature base metals. These braze filler metals are generally used for their strength, high temperature properties and resistance to corrosion. 
Some filler metals can be used up to 1800 °F (980 °C) for continuos service and 2200 °F (1205 °C) for short time service. Nickel based filler metals melt in the range of 1630 to 2200 °F (890 to 1205 °C), but can be used at the higher temperature due to diffusion of the melting point depressant elements from the filler metal into the base metal.
Under these conditions, vapour pressure of B2O3 is 10 mm Hg. For this reason, it can be concluded that the reduction of boric oxide with solid carbon tahe place preferebtially in the gaseous phase. 
The affinity of boron for nickel is also higher than its affinity for carbon. Consequently, at a high nickel concentration, the possibility of the formation of nickel boron is higher than the possible formation of boron carbide.
The charcoal and wood chips in selected ratios of H3BO3 and NiO were mixed, and mixture was fed to furnace which open heated arc. After 1-2 hours from start of experimental run, the liquid metal was removed from the tapped holeat the bottom and the arc was stopped. 
When liquid metal was removing the furnace, its temperature was measured with a optic pyrometer. And then the furnace left to coll for inspection. In the experimental, evaluation, the metal boron that remained in the furnace were taken into consideration. 
The energy consumption was also evaluated accordingly. The changes in the electrodes such consumption, erosion, shape and dimension were carefully inspected and quantified.
H3BO3 and NiO ratios were used 1,11 and 1,3. These ratios changed the content of carbon in the furnace. The production conditions of nickel boron were determined, with the charge composition, applied voltage and current, resistance, energy and electrode consumption. 
The boric asid used was % 99,5 pure. The nickel oxide was more than % 99 pure. The particle size of the charcoal and wood chips were 1 to 3 mm and 5 to 20 mm, repectively.
In this study, a source of boron as boric acid and as a source of nickel nikel , charcoal as reductant material, the charge density of the wood shavings are used as constructive reduction and sintering. Nickel boron master alloy prepared by charging different rates in order to produce blends dipped type 270 kVA, single-phase, direct current electric arc furnace melted. 
As a result of experimental studies, the composition of charge, energy and electrode consumption and electrical characteristics of the furnace were investigated. The events also nickel-boron master alloys in the oven in order to explain the mechanism of formation were investigated.
From the study we observed that nickel boron (NiB) alloys is produced with regular grade standarts via carbothermic reduction starting from boric acid (H3BO3) together with high purity nickel oxide (NiO), charcoal and sawdust by using DC arc furnace.
Experiments have been carried out with using different initial mixture ratios (H3BO3/NiO, etc.), with using different ratios of fixed C to initial mixtures. And The analysis showed that the usefull brazing alloy has produced and the alloy had a composition of % 84,12 Ni, % 15,08 B, % 0,11 Al, % 0,005 S, % 0,15 Si, % 0,40 Fe, % 0,18 C by weight.